ToddFun.com: Isolation Transformer - Tripp Lite IS1000

[@HackersbenchPage]

Hi Todd, Great video! FYI, the green dot is a UL required indication of a hospital grade wiring device per UL-498. The requirements all have to do with the physical ruggedness of the outlet. There is no electrical distinction at all. For the technically curious ... an orange dot means the outlet is connected to a UPS of some sort, and a red dot mean the outlet is connected to a generator or other "life safety" rated power source. JohnS_AZ

[@EEVblog]

I recognise that T-Shirt...

[@Moonbase59]

After 7 years, still one of the best explanations for the hobbyist (and maybe semi-pro) on KZbin. Here in Germany we have some differing regulations (VDE) that would prohibit using one of the mentioned transformers, but nevertheless, you explained it very well. Many thanks for taking the time to explain and actually demonstrate all the possible dangerous caveats that could easily cost a layman his life!

[@ToddFun]

You're welcom Moonbase59

[@trekgeek1]

P.S. My comment was really intended to clarify the concept for anyone who may have caught what you said and did not know you were simplifying it. I didn't think someone of your technical expertise would have that misconception and I did figure you were trying to convey the idea of how quickly you'll get hit with a shock. I look forward to more videos, as before I saw this one, I would have lit up like a light bulb since I did not realize the danger of ground loops through oscilloscopes. Thanks!

[@queuerious]

Thanks for this impassioned and responsible video on the safety and dangers of working with these isolation transformers. The demonstrations and your clear commentary have helped me undertand more the situation a burgeoning tech finds themselves in

[@djfrank59]

Hi Todd! I came across your video by accident; it was a recommended video on the YT home page when I opened it tonight...I watched it in it's entirety and I must say, this is a good reminder for techs that are not just newcomers, but veterans like myself. I specialize in the repair of vacuum tube amplifiers both vintage and modern-day tube gear, as well as vintage radios and tube TV sets. A good handful of equipment I work on has internal power transformers...however, some of the cheaper tube amplifiers, and vintage 5 tube-series heater string radios have one side of the AC line connected to the chassis which creates an even more dangerous situation! If the DUT doesn't have a polarized plug, and it is inserted opposite where the hot goes directly to the chassis, you have what's known as a hot chassis and if you come in contact with a ground point, ZAP! After about 100 shocks, and going through 3 boxes of fuses for my scope, I started to use an old RCA Iso-Tap IT. I have 2 scopes, one vintage EICO 460, and a Tektronics dual trace-triggered sweep scope...My old Eico survived many incidents, but I know my Tektronics won't...I strongly recommend that the new kids on the block (and even old-school techs) watch this video. I would hope to see that this video got many hits on YT...Keep 'em coming. Frank Ferraro--Audio Craft Electronics.

[@ToddFun]

Thanks Frank, And I couldn't agree more. Share the vid on FB, Twitter and email with anybody in your circles and that would help distribute the link. It only takes a few shares for a 10's of 1,000's to become aware of the video. Thanks.

[@9laral9]

Thanks Todd for this detailed explanation and demonstration of the need for an isolation transformer for safety reasons. I am getting the non-HG version of this for my personal safety and not for noise isolation. I read one review on Amazon that tipped me off to the need to modify this transformer to be used as a safety isolation transformer: "This is a nice unit, but be aware that it does not provide full isolation from the mains. The hot side is isolated, but the load neutral and load ground are bonded to the lines ground. It is not possible to float a device-under-test with this transformer in its stock configuration. If you only need hum bucking this device will work fine. If you intend to do electronics work with floating power you will need to modify the internal wiring, which I am sure voids the warranty. It's not hard to do - if you need it, you should have the knowledge of how to do it. Be aware that the load receptacles are electrically bonded to the case, which means the case must be moved to the load ground." www.amazon.com/review/R3NYMSG0S1X2CP/ref=cm_cr_rdp_perm?ie=UTF8&ASIN=B00006HPFI Unfortunately, it doesn't mention just what needs to be done to do this so I did a Google search and hit upon your video. I like to know in advance just what I am getting into if I buy an expensive piece of equipment like this BEFORE plopping down all that money. Your video showed me most of what I need to know but not all. You didn't show the removal of the ground strap lug and what you covered it with. The video had a glitch at that point and jumped directly to the point after which you modded it. This is the only part of the video that is of interest to me at this point as I intend to use the transformer for antique radio restoration, heater control circuits, and motor control circuits. My first question is, is that common wire attached to a spade lug which is simply attached with a screw? Then, did you crimp the spade lug into a crimp coupler or tape it or what? The sound glitched at exactly the point where you say what you covered it with. Also, did you use a philips head screwdriver or a proprietary one like a torx, etc. to remove the cover? I'd like to know what I need to gather before my unit arrives. Another point I'd like to make is that you really scared me when you picked up that live aligator clip attached to the lightbulb powered by the unmodified unit. Your fingers were millimeters away from the live metal clip, making you a potential path to ground! BTW I visited your blog and wanted to make these comments there, where it would perhaps be more appropriate, but I could find no way to register. Are you accepting registrations at this time? If so where is the link?

[@stephanc7192]

Im just checking. Even through a isolation transformer, not grounded, you cannot connect the ground clips to points at different potentials. The ground clips are still connected internally. Your demonstration at the end makes it clear! Thank you

[@edgoswick1271]

Todd, this by far the best explanation how to isolate at the bench; and I have searched for days. I have built 3 guitar amps from kits, but now I am about to start building a Vox AC10 from scratch. I need to learn much about safety. I look forward to checking out your other videos.

[@ToddFun]

Great to have you aboard! Glad you liked the video,

[@edgoswick1271]

If I work only on tube amps with transformers, do I need to plug the amp into an isolation transformer? Would this type of amp be safer to work on just plugged straight into a GFCI outlet? Most of the discussion I have read about concerning isolation deals with working on old radios and transformless amplifiers.

[@ToddFun]

If everything in the AMP is after the built in transformer than you don't need an IS as everything is already isolated from ground referenced power in your home. A GFCI doesn't even add anything for the same reason after the transformer, but for the wiring before the transformer the GFCI does help and it helps for anything other equipment plugged in that uses direct house mains power.

[@ToddFun]

@sivaraj, With a tech isolation transformer the earth point is not connected anywhere on the secondary. It is only there as a safety, in case some metal becomes energized with high voltage that can reference to ground. Lightening or other source could cause this condition. If you connect your probes across the established neutral and hot leg of the secondary and you are using a 10x probe your scope should read the voltage. No current will flow through the probe because of its 1 Meg input.

[@ToddFun]

@sivaraj, Water example: If you tip a class of water, the water will flow out onto the floor (ground) because of gravity. Yet if you put a piece of paper over the glass and flip it upside-down real fast and then let go of the paper the paper stays in place and the water does not poor out on the floor (ground). Gravity is still there and is trying to pull the water down but it can't. It is a closed system, no open loop for air to replace the water in the glass so the water does not flow.

[@gchenley]

Thanks you so much for this video, I have a non tech version of a Tripp Lite ordered for my bench. Your demonstration saved me from a serious mistake. I will modify my isolation transformer when it arrives. Thanks again for a very informative video.

[@ToddFun]

Glad to help Gary.

[@RicRic-bg8sn]

Hello I would like to thank you for this video ! I needed to watch it several times to understand (well) process, before doing it by myself...without a big bang in the cellar In France, 230 v, and 30 ma security on the line...But with a maximum care i tried to connect my scope Rigol 1102, behind my 600 W transformer. So, no fire, no explosion, and i have always the cellar too Many many thanks cause it was difficult for me to prevent misunderstanding around ground, secondary line, and scope. That's ok now and very happy to do this in real life, after many tests to control all connections on the transformer and to verify all separations between them, i decided to run experiment, and i could see (with happyness) the same result on my rigol and the beautiful waveform for the secondary 230v AC So this test makes me understand some rules and gives me basis for the future GREAT ! rgds Eric.

[@ToddFun]

Glad to help Eric.

[@ronbercan1000]

If I understand I get my self a new insolation transformer. Then I plug in a old tube radio. The metal chassis of that radio cant kill me anymore. GREAT. Now I connect the ground of my oscilloscope to that metal chassis and I'm no longer protected. WOW Thanks for the wakeup. Great video.

[@ToddFun]

Sure. Glad to have helped. I was just as shocked ;) to learn the same.

[@Jo-lw2df]

thank you V much for an excellent video covering all the safety aspects and explaining that an isolation transformer does not offer 100% protection (touching Line + neutral is still V dangerous). BR Jo

[@sivucit]

Thanks a million. Awesome and sorry for not asking questions clearly. I appreciate your super fast response. I still cant believe u reply immediately. Even if i pay some one to guide me, they would not have responded this fast.. Thanks again.

[@rotlerin]

Thanks for the informative response Todd. Time to get the thinking cap on and go over and over your stuff till it finally sinks in.

[@youpattube1]

I have watched this video a couple of times. Here is what I came away with. If you make the IT the tech version, and plug your circuit under test to its output, you protect yourself from shock thru the ground. Also, you can connect your oscope ground strap to either side of the secondary and you won't accidentally short it to ground thru the oscope. However, once you connect the scope strap to circuit under test, that connection is now the ground and if you touch anywhere else on the circuit under test, current will flow thru your body to anywhere you are connected to ground. It is a catch-22. You can protect youself from some shocks in the CUT by using a tech IT, but as soon as you get a scope strap connected, you are back in the getting shocked game again.

[@drdomestos]

Yes, that is why avoiding using standard probes and using differential probes instead is a better option. With a differential probe the isolation remains in place. Things have moved on since this video was made; differential probes are now available much more cheaply. Siglent make some that are quite well regarded. It's also worth mentioning that if you attach a signal/function generator to the circuit, you again will create a ground reference. This is because most signal generators have one side of their outputs grounded. There are isolated signal generators available, but these do tend to be more expensive. Another alternative which is more pertinenent today rather than at the time of the video, is that battery-powered scopes and signal generators are now more readily available. These float so will not create a ground reference when connected. You do have to be aware however that the 'ground' clips even on a battery scope may be connected together so you should avoid connecting them to different parts of the circuit otherwise you risk a short.

[@ToddFun]

@sivaraj, You assume correctly. You can touch the same point as the ground clip all day long, even if you are grounded during the positive as well as negative cycle at that point. You, the ground clip and physical ground will always be at the same potential throughout the AC cycle.

[@seamusg8911]

Thanks Todd for making this video. I am in the UK and have an isolation transformer by Carroll & Meynell. The earth is different in that it is a fully potted transformer and the earth is strapped to the core/frame and common to both input and output and would appear to work as yours when you modified it. I am glad I watched this again since I missed the point that you raise the chassis of the scope to the potential of the secondary. I haven't noticed this mentioned by other videos here - but maybe I missed it. I don't intend doing any mains work but it is good to know the pitfalls. Thanks again

[@kentvandervelden]

That low-Z meter comparison is interesting. I found this video at a perfect time. I was planning to buy the same isolation transformer (non-HG model) and assumed this modification would not be required. Thanks for posting the video.

[@ToddFun]

Sure, glad to help. I should shoot this video again as this was one of my first videos when I was still using video tape recorder. My newer digital storage handycam is tones better.

[@kentvandervelden]

A VHS style recorder? That's fantastic. Unless the information is being refreshed, it's just my opinion, but I'd work on new content. Recording, editing, etc. takes so long and the information is more important than production details. Just my opinion. I'm just curious, are tech-style isolation transformers available, without the need for the modification? It's fascinating that this is one of those rare cases where safety regulations create less safe conditions. Best wishes, Kent

[@ToddFun]

Yes. see the first isolation transformer link on my beginner page: www.toddfun.com/category/beginners/

[@bailamosmundolatino]

thanks for your answer. I've already seen Mr Carlson video. I stay tuned to hear some more tips. Have a happy New Year

[@SalettaRocks]

Great reminder on the receptacle screw going to ground.

[@michaelhawthorne8696]

Just the ticket this video..... I just bought a DSO, Siglent 1102CML but I have been using a portable Tek for years. I was a tad worried of using my scope on anything other than battery or PSU based circuits. My DSO is far more capable than the old Tek (THS720A from mid 90's) and want to start using it, I feel as though I can now with more confidence.... thanks Todd.

[@ToddFun]

+Michael Hawthorne Glad to help. The video has lots of tips on all the things that can go horribly wrong and I watch it once in a while myself just as a refresher.

[@rotlerin]

I'm getting there Todd. I already bought an IT but would like to know why you can't just plug the oscilloscope into the IT rather than into your house mains supply. Todd I watch every episode of Dave Jones' but as a newbie to repair electronics I'm going to be watching you just as much. Thanks for the great vid. Well explained and very professional.

[@williammorris7571]

Hi Todd, Thanks for your excellent video. I’m newly interested in electronics because I became interested in repairing AA5 tube radios. I quickly learned that I needed an isolation transformer for safety working on a potentially live chassis and, after reading different sources and watching your video, got a Tripp-Lite IS-500 IT. As someone noted below, the wiring isn’t exactly like your IS-1000 in the video. Five ground wires connected to the IT’s grounding point. One from the mains; one accompanying the neutral from the secondary side; one from the primary (?) side; and two from the IT’s outlets. I disconnected the one that accompanied the neutral from the secondary as you described in your video. After reading some other information I also disconnected the two ground wires from the outlets. I tested the outlet voltage with a Fluke 117, and got results similar to yours using both V-AC and the Auto Volts/LoZ settings. Checking continuity and ohms, there’s no continuity from the IT’s line cord plug’s ground prong to any of the IT’s neutral or hot outlet slots; those read OL. There is continuity from the plug’s ground prong to the IT outlets’ ground slots, depending on where the probe makes contact. It can read OL, but sometimes reads around 0.3 ohms depending on probe placement in the ground outlet. I’m uncertain exactly why there would be any continuity there with the outlet ground wires disconnected, but... After reading some of the comments on your video it appears that it might be safer if I reconnected the outlet ground wires to the chassis ground, leaving only the secondary neutral ground disconnected. Do I have that right? If I understand correctly, there would still be no reference to ground on the secondary side for the DUT even if those outlet grounds were re-connected, so I’d still be protected from completing that circuit. Sorry if I didn’t explain this clearly or used incorrect terminology. I’m definitely just learning. Thanks!

[@ToddFun]

You are correct. You want the secondary not wired to ground. You do want the IT outlet's ground connecting to earth mains through the IT chassis or you can drop the outlet's ground connecting to earth mains through the IT chassis which is save too "maybe even safer" but if your DUT becomes mains energized by some other lab equipment or wiring then having the grounds connected through the IT chassis gives an alternate path to ground through the IT chassis. Hardly an issues either way so if you don't connect those IT outlet's ground wires to the IT chassis that's fine too.

[@williammorris7571]

Thanks very much, Todd! I may reconnect those outlet grounds, then, to provide that “alternate path” should the DUT become energized by test equipment, etc., as you say. Along those lines, if I understand correctly, if I put a Variac betweeen the Modified IT and the DUT, I should still be isolated because the power from the IT through the Variac is still not referenced to the mains ground, even if the Variac has a 3-prong grounded line cord. Thanks again!

[@ToddFun]

@@williammorris7571 yes, you would still be isolated.

[@williammorris7571]

Perfect. Thanks, again, Todd!

[@windward2818]

For a bench isolated AC supply I think the approach is to both isolate the power and the grounds, for personal, equipment and soldering iron (ESD tip grounded type) safety. Meaning if the DUT has a hot chassis then connected a grounded scope, or other earth grounded equipment, would not cause a short or electrical overstress. If you want to keep the AC isolation supply chassis at earth ground for electrical safety reasons, but float the receptacle ground, you would need to install a hospital grade isolated ground orange receptacle (green dot and green triangle), or you could just float the chassis which is probably not ideal. Most receptacles are internally straped to connect the body (and metal faceplate if used) to the grounding screw for ground fault. With the result being that the ground screw and chassis connection are shorted, or non-isolated. The Green dot hospital grade receptacles on the AC supply output of the unit as shipped do not have ground isolation.

[@ToddFun]

@sivaraj It will not cause a problem because with the ground clip of the scope connected to the neutral point on the secondary, the only path back to the circuit would be through the probe tip which should have a 1 Meg impedance. Far to large of a return resistance for a 110 V or even 220 V mains. Your body however is a much lower resistance and it would conduct just fine, that is why you can't touch the circuit once the ground clip is connected and you are grounded to the floor or other point.

[@swvincent]

Thank you, this was very helpful! I picked up a used power conditioner today for $5 that's rated for 1 amp and your video helped me to make the same conversion. It's not very big but it's enough for working on LED projects and Christmas light strings.

[@reefgeorge1]

Best tutorial on the inter web about this subject. Thanks.

[@garydailey809]

I just purchased a Tripp-Lite IS500HG isolation transformer which I intended to modify by removing the ground connection to neutral , similar as in your video, then discovered it comes with full floating secondary. There is no ground to neutral connection on this model. This is also stated in the manual and printed on the panel face. I just wanted people to be aware that modification might not be necessary.

[@ToddFun]

WOW! I wonder why? maybe that one was wrong by mistake as all HG should be strapped. Or maybe they decided being they where trying to use them to isolate medical equipment from a ground reference that using a strapped neutral wasn't such a good ide as the current, or maybe now old, design was only really added power conditioning and not isolation and finally somebody caught on. Or seen my video and said "WTF" HA. Never know.

[@garydailey809]

I have some additional information. The Tripp-Lite IS500HG model used to have the the output neutral bonded to ground but it was changed. I compared a 2015 to a newer 2019 data sheet and the older data sheet states "Secondary neutral-to-ground bonding eliminates common mode noise, providing an isolated ground reference for sensitive equipment". This was removed from the data sheet and replaced with "Floating AC output prevents noise coupling from noisy hospital ground circuits". I don't know about the other models. I guess this means whatever isolation transformer you buy, it's probably best if you carefully examine it yourself and modify if necessary in order to be sure and to be safe. When you buy one, it's hard knowing what you'll get or what revision level.

[@ToddFun]

@sivara, Close. You only need to touch any part of the circuit that is at a different potential than the state at the ground clip of the scope. You do not have to touch another bit of metal, the fact that your feet are on the ground puts your whole body in the loop (in the USA). I say in the USA because some countries don't put physical earth in the loop like the USA does. In such a case you would have to touch something that links back to the neutral of your house wiring, not necessarily metal.

[@call5sam]

Why did you not show the voltage between ground and neutral; ground and hot; and ground and chassis on the modified transformer?

[@richardshort4587]

Is fair to assume that the ISO trans output outlet ground pins, have zero connection to ground also. I didn’t see you remove the outlet socket ground pin connections. You only disconnected the neutral side of the sockets that went to ground. I want to make a power system for bench work. I’m going to run the bench equipment through an isolation transformer with three outlet hospital grade outputs. One for the scope, one for my Variac and keep a spare outlet should I need it.

[@pah3523143]

Thank you for your video. It is just what I was looking for. I am a beginner at working on antique radios and your explanation was very helpful. Thanks again.

[@ToddFun]

@sivaraj, Correct, no short circuit. Because there is no path back to the circuit. It is like the two AA example not having a closed loop. The potentials maybe + and - but there is no complete path back to the secondary of the transformer so no short circuit unless you provide that 2nd path with another wire or your body. If you proved that 2nd conductive path, at low resistance, then POW! you or your gear is died.

[@ToddFun]

@sivaraj, That last statement wasn't quite 100% but I do now understand your dilemma. You are thinking that if something is positive it MUST flow to something that is negative. That is not the case. Example: If you put the positive end of a AA in contact with the negative end of a AA no current will flow. The reason is because you have not loop. The ground clip on the scope connected to some point on the secondary is just like my 2 battery example. No loop. I will continue with water example....

[@mjlorton]

Great video Todd....thanks very much for posting it...and your support! Cheers, Martin.

[@guslionel9360]

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[@laynecristian7702]

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[@guslionel9360]

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[@guslionel9360]

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[@laynecristian7702]

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[@SS-pi2yi]

Thanks for the great vid - - one clarification I not sure I totally understood.... GENERALLY , do we usually power: A) the SYSTEM UNDER TEST via the ISOLATION Transformer, & the AC TEST EQUIPMENT (such as oscilloscope) is powered as usual via regular home 3-prong AC outlet ? OR B) BOTH SYSTEM UNDER TEST and AC TEST EQUIPMENT (such as oscilloscope etc) is powered via ISOLATION TRANSFORMER ? Which is the correct guideline to follow A or B ? thanks.

[@teechui2401]

Regarding the remarks at the 24 to 25 minute mark - I believe there is a way to utilize a GFI with the scenario depicted, but it involves placing the DUT (for example, a 'hot chassis' radio, etc) *after* the GFI but the scope ground clip *before* the GFI, on one of the ports of the isolation transformer. That allows for the opportunity to have two current loops, one through the load (DUT) as intended, and another unintended (and otherwise potentially fatal ) loop through your body and back to the ground which is *before* the GFI. Any current returning to the point prior to the GFI bypasses its return port, and it sees a current differential, which would cause it to trip. The key is having more than one current loop path back to source, which is how GFI works in the home as well.

[@ToddFun]

Sure. That would work. Great point. Thanks.

[@ToddFun]

@Sean, Plus floating a scope can damage it. Sounds strange but that is what it says in the documentations.

[@jamesbullock8722]

If you've converted your medical grade to tech grade, meaning the secondary is truly isolated, then you plug your DUT into the isolation transformer, your DUT is now floating, right? Now you connect your oscilloscopes ground lead to a point then your probe to another point. How does that impact the signal when you have two different reference points?

[@THEDOGBOYS3]

Tod, This unit has three (3) wires connected to chassis ground. I left the ground wire from outlet to chassis. The secoundary side had two wires going to ground? I disconnected the ground on the white wire from the secoundary, but the other ground wire is connected to chassis ground-not carried through to outlet 3 rd prong. Just the phantom load I told you about. I think I did the same thing as gvahe did. I am just courious about the other secoundary ground wire connected to the chassis. TY TDB

[@Automotive-Velocity]

Let's say you are looking for output scope patterns on a stereo system. Question: You hook the scope probes to the left and right channels (Left red+ black- and Right red+ black-). Even though the scope probe clips are on different points they are still a common chassis ground reference and do not pose an issue? Is any common chassis ground a safe hookup when using a two-channel scope to compare patterns?

[@whiskeyify]

My understanding is it protects your scope and the tv etc. you're working on from damage, I forgot to use it one day and boom I thought I had blown up my scope. I just blew a fuse however. It also makes it safer for you but you can still get a shock.

[@michaelcostello6991]

Great video except at 49 minutes where the circuit was not clear. Are you scoping between a live and earth wire supplying the bulb resulting in referencing the secondary winding to earth. A wiring sketch would have been helpful to clarify. Thanks for great video. Michael

[@jeffkosowsky67]

You mentioned in the video that adding a GFCI after the isolation transformer won't help... and that makes sense since if you complete the following circuit for example secondary hot -> scope ground -> earth ground -> "human" -> secondary neutral you have mains current flowing through the human but no current imbalance between the secondary hot and neutrals to trip the GFCI. However, how about if instead you are plugging the scope into a GFCI. I believe that GFCI's (at least in the US), in addition to sensing hot-neutral current imbalance, they also check for ground currents. In that case in the circuit above, the current flowing "scope ground -> earth ground" would trip the scope GFCI, saving your life and likely also the scope. Am I understanding this correctly?

[@ToddFun]

@sivaraj, You would be a good conductor causing a short through your body if you did that. Once you connect the ground clip of your scope to any point on the secondary that point becomes the earth reference on the secondary and then any other voltage point on the secondary becomes dangerous to you and your gear. With a tech isolation transformer If you don't connect your ground clip then mains earth and neutral are not connected in any way.

[@SeaJay_Oceans]

Tripp Lite, saving lives & equipment worldwide !Thank you Tripp Lite for making the world a better and safer place ! :-)

[@ToddFun]

True, only this IT needs to be modified or it isn't to safe for a tech bench.

[@ToddFun]

@sivaray, No, there is no loop. However, if you touch some part of the circuit at that point and complete the circuit through your body back to ground then you will close the loop with your body and die. You could do the same with some test gear and then it would die.

[@aerofart]

Great video, Todd. Demystified the whole isolation transformer thing for me.

[@_droid]

Shouldn't you remove the ground completely from the output side? You also need a non-conducting faceplate to mount the sockets because the socket screws connect ground to the faceplate and the flaceplate is connected to Earth via the chassis. If a DUT connected ground to its neutral (accidentally or otherwise) then you're not isolated any more.

[@chestman6511]

Great video, man! I've been thinking about making an isolation transformer by myself since it's simple.

[@MrOlliegab]

Does this mod remove the line cleaning capabilities of the isolator? I bought this to help fix a ground loop issue in my studio but it didn't help. Then I heard of this mod.

[@mjlorton]

I watched and enjoyed ALL of it!

[@jeanjacques9462]

Thank you. Very clear explanation

[@Electric_Hambone]

I always like reading the comments from the people that know it all...

[@LouisWilen]

After making the modification described in the video to a Tripp Lite IS-250HG (same as the unit in the video except lower current capabilty), I made the following observations: 1. There is 80 VAC RMS between the outlet neutral (wide hole of the outlet) and the ground connector on the output. This was not expected and indicates incomplete isolation. 2. There is 16 VAC RMS between the outlet hot (narrow hole of the outlet) and the ground connector on the output. This was not expected and indicates incomplete isolation. 3. With the unit unplugged and the power switch on, resistance between outlet neutral (wide hole on the outlet) and neutral on the input is infinite, as expected. 4. With the unit unplugged and the power switch on, resistance between outlet hot (narrow hole of the outlet) and hot on the input is infinite, as expected. 5. With the unit unplugged and the power switch on, resistance between outlet neutral (wide hole on the outlet) and the ground connector is infinite, as expected. This confirms that the modification was made as instructed. 6. With the unit unplugged and with the power switch on, and with the neutral prong of the input power cord shorted to the ground terminal of the input power cord, resistance between outlet neutral and ground is infinite, as expected. (This was done to simulate the ground to neutral connection that is provided at the circuit breaker box.) The measurements were made with a calibrated Fluke 179 DVM, which is a high impedence DVM. Observations #1 and #2 indicate that isolation will be complete only if a 2-wire to 3-wire "cheater plug" is used between the IS-250-HG output and the DUT. However, observation #6 tends to indicate that the voltages detected in #1 and #2 are actually phantom voltages. If the voltages in #1 and #2 are phantom voltages, a cheater plug would not be required to provide full isolation. Any comments?

[@ToddFun]

Louis Wilen The word you need to look up is "Ghost Voltages" Kind of what you hint to with "phantom" voltages. I did cover this in the video and it is normal when using a high impedance DVM, As you will note in the video, I used a Fluke 117 set to Auto-V LoZ which is a low impedance test setting the Fluke 117 has to eliminate ghost voltage readings. Ghost voltage readings are harmless. A cheater plug will float whatever is plugged in but will not help with isolation, cause as you said, the common leg is tied to the ground rail at the fuse panel and many things around you are grounded including "the ground". Your modified isolation transformer will help with protection but take careful note that you can still get hurt or killed in may ways, as I noted in the video, even when using a Tech Isolation Transformer. Be safe and I hope that helps.

[@LouisWilen]

***** "Ghost Voltages" -- yes, that's a better term for this. Thanks so much for your explanation. As you suggested, I looked up "Ghost Voltages". Seems that putting a moderate load across the output will eliminate the ghost voltage reading if it's truly a ghost voltage. If the voltage reading is still present with a moderate load, then the voltage is very real and isolation is not complete. An excellent explanation of Ghost Voltages is in this Fluke document: support.fluke.com/find-sales/Download/Asset/2105317_A_w.pdf And yes, you do mention Ghost Voltages in the video. I missed the explanation the first time that I watched.

[@mmortal03]

It's interesting that you mention a cheater plug, because, a few years ago, I bought a Tripp Lite IS-250 as a last shot at trying to solve a hum that I was experiencing through a subwoofer, but it didn't solve that problem. I see that Todd states in the video that these Tripp Lite isolation transformers strap the secondary coil winding to the chassis for common mode noise rejection (acting as a secondary neutral). Is that done only to solve noise issues on the AC line, but not the ground? Since I wasn't going to pay to ship the transformer back, I've just had the Tripp Lite in a closet until today. Today, I was reminded of all this when I noticed that whenever my laptop, which uses a three prong power supply, was plugged into the wall along with its headphone out plugged into some of my powered audio equipment, that this would cause some major ground loop noise. Plugging the laptop power cord into the isolation transformer did not solve this problem. Unplugging the power cord, or plugging it into a non-grounded cheater plug *did* solve the problem (though, it's my understanding that I shouldn't do the latter for safety reasons). Is it possible that one of these Tripp Lite isolation transformers could still solve my problem, with or without the above modification, but mine just happens to be a dud, or is it the wrong tool for the job? Would doing the above modification to it make it capable of solving my ground loop problem without having to resort to a cheater plug, or is the above modification *also* not the solution to my problem? I know they make 3.5mm ground loop isolator filters, but I'm curious if there's a way to create a safe, isolated circuit to plug offending devices into that would stop the problem at the source.

[@cmj20002]

Sounds like bleed over to me. When I kill outlets in my home at the breaker they still can show as much as 60 volts, however it wouldn't light a bulb. Really no current behind it.

[@diocorissosa4448]

Thank you so much for this video. Hey... your'e actually saving lives by this video.

[@ToddFun]

Diocoris Sosa I think so too. Thanks!

[@waynegram8907]

TODDFUN, I think you can use a dual 2 channel oscope used in the ADD mode instead of using an isolation transformer?

[@drumrboynoid]

Thanks for this great video. What if you also plugged the scope into the iso transformer? Would that provide any extra protection?

[@Sonny_Eclipse]

OK, I did this but found I still had ground continuity through the metal screw holding the outlet to the chassis, so I need to either disconnect the chassis ground or insulate the screw holding the outlet to the chassis. I could still use a 2-to-3 prong adapter, please correct me if I'm wrong. Also, I would isolate the equipment under test and ground the scope.

[@batvladi1]

Very useful and perfectly explained lecture. Congratulations.

[@guitarman430]

Rubber bench Mats and rubber floor Mats are also recommended.

[@patrikprekop8975]

Hi Todd! A very nice video and could get exact answers to my questions about what I had. Nice demonstration. I got also a differential probe. I like your videos! Don't stop. Thank you

[@REVERSE_BIAS]

Hi. Thanks for posting this, I've found it very helpful. However I wondered if you could help me with one last point of confusion I have please? I understand that the whole point of isolation transformers is to eliminate the connection you device under test has to "earth ground" to stop a return path should you clip your scope probe alligator clip to the wrong place. However my question is...if your circuit under test is an AC circuit, and no longer has a "ground"...where do you connect the probe alligator clip to?????

[@ToddFun]

Well when your DUT is on an IT you could hook that ground clip to whatever point of the circuit you want. However if your scope is grounded to Mains power in your house, that is your scope is not floating too, you are then strapping your circuit at that point to your mains ground which will cause all the AC voltages in reference to that point of the ground clip to be dangerous to you again. You can float a scope but it’s not recommended, to float your scope you just use a three prong to two prong adapter. But doing so can also cause your signals not to look or be correct, or look noisy. So be careful is the big thing to always keep in mind and keep one hand behind your back and Don’t touch the DUT circuit

[@joelaffey7838]

This is a great video, and I have shared it with many people. I am setting up my IT now, and actually adding a clearly marked switch to enable or disable the "tech" isolation. This way I can use the IT either way as needed (being careful to check the switch for each mode). Just to be clear, you have left the chassis of the IT, as well as the output outlet ground pins, connected to the incoming earth ground wire, correct? Thus, any device you plug in which has a three prong plug will still be earth grounded, but its neutral leg will not be earth referenced... Right? Thanks.

[@ToddFun]

+Joe Laffey The switch is a nice idea. Yes, your statement about earth ground is correct.

[@carraror]

Great video, Todd, thanks a lot. So if I use a portable battery-powered DSO to test a live circuit and I am under an isolation trasformer I shouldn't have the same risk (being lit as a light bulb!) that I could have with a 'normal' grounded DSO, right?

[@ToddFun]

+Roberto Carraro Correct. But also remember you can get yourself between a high and low potential with the isolation transformer itself so keep one hand in your back pocket. ;) and if you use 2 probes from your DSO they can short if the ground clips are not at the same potential in the circuit.

[@howardtaylor2405]

I recently purchased the same Tripp-Lite model you have but upon opening the cover I see it is wired a little different. I do not have the extra green wire you have that you disconnected. I have a green wire coming from the Output side that is attached to the unit’s grounding post. From the grounding post I have two green wires that go up to the backside of each outlet connected on the top to a green screw. I disconnected only the green wire coming from the Output side and completed your lightbulb tests and it seems to be working. Then I got a surprise. I had read a comment on a video that said Tripp-Lite now ships the unit OPEN GROUND. I connected the green ground back as it was and plugged in a outlet tester and it signaled OPEN GROUND. With no modification the unit is OPEN GROUND. What do you think?

[@ToddFun]

They must’ve figured out they were shipping these things as non-isolation, transformers, and advertising them as isolation transformers. They really should’ve been advertising them as signal conditioning filters. Well, if they’re going to sell them as isolation transformers, it’s best they make the change.

[@tangolima4148]

Negatieve feedback: Earth ground symbol is not the triangle, triangle is chassis.

[@dembydish]

Perhaps a stupid question, but if you plug the oscilloscope into the isolation transformer, does that prevent the circuit to ground?

[@jamesbullock8722]

An additional question to my last question, will you create a ground loop?

[@InsurgentX]

Hi Todd, Thanks for the great video. On the last demonstration "you are the light bulb", what would the result be of hooking the green wire to the mains ground if the o-scope itself was also plugged in to the isolation transformer?

[@celtichongy]

Todd, thanks for this good information on grounding risks and Isolation Transformers (I/T). Understood about connecting DUT to the tech-safe Isolation output but what if we also connect the DSO /Freq Gen to the I/T output? So both the DUT and any Test Instrument are all on isolated side connection. Has this got additional safety merits or are new risks (unforeseen to me) introduced? Appreciate all thoughts on this aspect.

[@ToddFun]

Not really helpful. You are not going to be inside your other test equipment. If you want to float your equipment just use a 3 prong to 2 prong adapter. Doing so with your gear can lead to damage so floating gear isn't a good idea, however it is safer. Your call at this point. I do float gear on a 2 prong adapter for safety once in a great while but only for a quick test and even then I cross my fingers I don't damage or throw my gear out of calibration.

[@vintageceilingfans]

Those things will last forever.. I have an insolation transformer that I have since 1993 and has been plugged in pretty much ever since..

[@Texacate]

Thank you for the excellent tutorial. One thing I don't understand is when you illuminated the bulb, pre-modificaiton, by connecting on lead of the bulb to the isolation transformer hot, and the other lead of the bulb to the surface of the bench outlet box, (time=32:10 in the video) did you not create ALSO ground fault? Your GFIC did not trip. Has the "isolation" aspect of the transformer rendered the GFIC's protection useless?

[@ToddFun]

+Steve Cozart Yes, that is exactly correct. All transformers with separated secondary / primary windings, whether they are 1:1 isolation or not, render CFIC useless. This is not true for auto transformers like variacs which don't have separated secondary / primary windings. Keep your head in the game at all times and be save when working with high voltages. Thanks for joining.

[@jacek7178]

Great video. But why they call Tripp Lite Transformer an Isolation Transformer with secondary earth connected to the ground? There is no galvanic isolation.

[@diregremo]

Hey Todd, I just found your channel, and I'm enjoying your vids. I have a question about this transformer. I'm not planning to do any circuit testing. I'm actually just trying to do away with some line noise in my music equipment. I have a recording console with an old power supply. The outlet plug, for the power supply, doesn't have a ground. You have to ground to the power supply box itself, then to something else. Anyway, my question is.. Do I need to do the ground loop modification, that you demonstrated here, if I'm just looking to eliminate some noise in my scenario? Thanks for the info.

[@ToddFun]

+diregremo No. This mode in this video would make for more noise on the line to your recording equipment. I would spend money on a line conditioner for your needs. Such as: www.furmansound.com/product.php?div=01&id=P-1800PF

[@christiandietachmair334]

Today i got a Statron 5315-4 Isolation Transformer- hope this is a good choice - very good video indeed - Greeting from Austria !

[@Neilrrc37]

Hey!! I built a Variable AC Power Supply, with ISO transformer installed inline before Variac, and I use 6 ohms(60 watts) in series with the secondary windings on the Variac in case of short.

[@ToddFun]

+Neilrrc37 I too will connect my IT to my variac when working on old gear and want to bring up the power slowly. However I connect a Kill-o-Watt meter to my variac's output to monitor current and if I see a spike I know something is wrong. I guess a 6 ohm 60 watt would be a good safety option too, like having an inline light bulb in the old days of working on tube radios.

[@nickk3765]

Hi, great video! I just got one of these isolators and curious if there's any benefit to use it in my RV? It has 30 amp shore power and generator with inverter/charger to house batteries... There's an auto transfer switch between them. I'm wondering if there's any use for the isolator off the inverter or anywhere else. Thank you!

[@nickk3765]

My thought is, if I understand how they operate, I could plug it in to my invertor and have newer electronics plugged in to the isolator. Would it "clean" the signal from my generator in case there's a spike in voltage from turning off or on other appliances?

[@ToddFun]

@svivaraj, 2) yes. But don't float such a scope, you could damage it and it wouldn't give correct reading anyway. Floating scope and touching BNC is bad because most people do this because they don't have an isolation transformer to plug the device under test (DUT) into. If your DUT is on a IT transformer and you float your scope you can touch the BNC, however if you are also touching the circuit at some other high voltage potential while you switch probes or touch a BNC you will get hurt.

[@jsc3417]

the take away is, ditch the earth ground from the scope, measure it with differential probes, or use two probes and set to math function, probe 1 - probe 2.

[@ToddFun]

Yes, that is a very good short summary. Thanks.

[@skunkydonkey3897]

I live in a country where we use 220V and no ground slot in the outlet, would I still need an isolation transformer? Also, isn't removing that ground wire inside the transformer the same as removing the third prong from the power plug of whatever equipment you're plugging into the transformer or maybe using a cheater plug? Thanks, just subscribed to learn more.

[@ToddFun]

Skunky Donkey If your country uses "earth" grounded domestic power delivery scheme then, yes, you still need an isolation transformer with or without a ground slot. Some countries and industry buildings don't use an "earth" grounded scheme in which case "earth" is not in the electrical loop, but other plugged in objects would be in the loop so an isolation transformer is still recommended when working on mains powered electronics. Removing the ground wire inside the transformer would be the same as removing the third prong or using a cheater plug. However, that leaves no safety ground to the metal transformer chassis which is not a big deal other than it would be a bit less safe than if it had a safety ground. Does that help?

[@skunkydonkey3897]

***** Thanks for the response. Your video and your answers helped me understand what I need to do to protect myself and my equipments.

[@repairfreak]

Good video for a somewhat difficult to understand subject. Bravo

[@ToddFun]

Glad you think so!

[@repairfreak]

This is my setup: My Trippe Lite modified tester has no continuity between its output socket grounds or the neutral slot and the transformers input cords power plug ground pin or “wider”common blade. The input power cords ground pin is no longer connected to the iso’s transformers metal chassis either. I feel safer as a human tester knowing the metal chassis of a guitar amp can never pose a shock hazard to me the tester to earth ground or short out my scope probe or probes ground connected to exact same chassis ground point ever be an issue for the scope. Can this paragraph just above be achieved with either a 3 prong guitar amp “chassis grounded” under test and as well as with a 2 prong unpolarized powered plug on amp plugged in any direction, as long as the death cap is still un-shorted? Thank you

[@rogergrossenbacher4979]

Thanks for the excellent presentation on isolation transformers. Really clear and easy to understand. Just a stupid question from a greenhorn: what would happen if you connected the test object AS WELL AS the oscilloscope into the "tech-version" of the isolation transformer?

[@ToddFun]

+Roger Grossenbacher You could do that but then you are floating your scope which isn't a good idea. If you just wanted to float your scope then it would be just as easy to put a 3 prong to 2 prong adapter on your scope. Not good for the scope, it could damage it from what I have read, however I have done it myself as a fast way to isolate my scope from ground. I didn't have any damage but it is a risk and your scope might not read correctly however mine seem to read fine.

[@DavidBerlind]

My understanding is that the best of both worlds is to have an isolation probe.

[@ToddFun]

Yes it is. They are very expensive. I have seen some DIY isolation probe hacks but making them to also work with high frequency can be tricky hence the high price of such probes.

[@warplanner8852]

Todd, thank you for the informative video. A quick question: basically, after modifying an isolation transformer, the resistance ground plug on the input versus the outplugs should be infinite, true?

[@warplanner8852]

..er..disregard, Todd. I read other coments. Thanks again for the video.

[@Okie-Tom]

Ok, so since you removed the ground connection from the output neutral connection, and therefore the transformer has disconnected the neutral/ground connection that is at the Mains power panel. You should be able to have the ground, that goes all the way through the isolation transformer, hooked to the chassis of the piece of equipment your working on. Am I correct on this? I just ordered a Tripp Lite IS1000 isolation transformer and will need to modify it like you did yours. Great video. Thanks.

[@ToddFun]

Yes that is correct.

[@IanMcLeish]

I am completely new to this, but recently bought an oscilloscope, and attempted to repair my 5.1 surround sound amp, though it ( the amp) failed after I decided to become interested in electronics. I have never dared to use the scope on the "test equipment/ repair equipment" - I know either me or my new scope would die. But still, I have a few questions, which may seem real dumb. BTW everything where I live is really expensive - €168 minimum for the cheapest isolation safety transformer I can find. But it is a reputable brand I believe. Carroll & Meynell, 750VA CM7501 Single Phase Isolation Transformer, 230V ac Are we always going to be safe if we connect the probe ground to GROUND? I am a complete newby, but even I can find a ground - usually the metal case of the "test gear". But why is that bit so difficult? I am NOT being sarcastic here, but why is that so hard, unless it is one of those mental american radios? I do not intend to ever touch an old product with a "live/hot" chassis. Next question is, what if we used the oscilloscope and the test equipment isolated? Either on the same "isolator" or even on two different isolators? Would 2 different and separate isolators protect person and scope, at least in a one probe scenario? Obviously a 2 probe scenario on the one oscilloscope might/would not work, but going on... What about 3 isolation transformers and 2 oscilloscopes, all running on separate isolation transformers- would that be "safe"??? I do not know this answer, which is why I am asking - I watch a fair bit of EEvBlog, but am still trying to understand what will cause me to have a BANG and a really bad day.! I think I may just stick to low voltage stuff, - does anyone want to buy an unused used Rigol 1054Z pirated to the last? I only started, but already feel wayyyyy over my head. I think this stuff has to be learned by "osmosis" over decades, or the hard way.

[@boblou6270]

I forgot to use the isolation transformer one day at work and Pow the scope went dead, it was a brand new $3500 Oscilloscope. Lucky for me it just blew a fuse, so be careful always plug the item you're working on into a isolation transformer.

[@guitarman430]

Isolating a scope and floating also causes excess noise since the ground shielding in the scope is now removed.

[@sbreheny]

You should not "float" your scope because you would then be touching parts of it which are not grounded and could, depending on the way you connect it, be at a high voltage with respect to ground. You should get either a differential probe or a scope with isolated inputs OR, what I think would be even better in your case, make a device which high-pass-filters the AC line and then passes the result through a broadband, tiny isolation transformer which then allows you to connect your scope to it.

[@tonysfun]

I have couple oscilloscopes that have batteries - if I unplug the charging cord, It will not have reference to ground, right? So using the battery operated scopes are safer to use with high voltage equipment or am I not seining this right? Also, why aren't you making more videos? Thanks for all your videos!

[@ToddFun]

Right if you use one prob. if you use two or more probs just make sure the ground clips are all on at the same point. Just busy with my day job and working on a small farm in ND now. Might make more videos someday but it is a ton of work to make good videos.

[@fbw47]

Excellent explanations. I really wanted to see how you identified the neutral ground strap, but you didn't really cover how exactly to identify that. I wish you would have spent a bit more time on the actual modification. Isn't that what this video was supposed to illustrate? Do you have any further illustrations to show the modification?

[@ToddFun]

It is easy to find. It will be a wire connecting one side of the output outlet to a grounding stud on the chassis. Just remove it and you're good. Your 220v AC power does have a neutral. It will be a 8 to 10 food copper clad rod in the ground near your breaker box. The two 110v AC in legs will have a good path through the ground rod, through ground back to the transformer'r center tap near your house. They only do this in places that have good soil conditions and the distance to the sub transformer isn't too far. It save on copper wire to all the homes in your area. And yes, current is flowing through the earth back to the sub transformer center tap for everything running on 110 in your house. Quit common really. Hope that helps some.

[@fbw47]

Todd Harrison : There are systems in the Philippines like you describe, but I have been told that ours isn't like that. It certainly makes more sense. I will investigate further. I have driven my own grounding rod - copper clad, 3 meters long - and either of my "hot" wires, when measured to that ground reads 110v. I'll call our electric company for an explanation. I hope you are right. It's very difficult to get accurate explanations here... Thanks much!

[@sivucit]

I appreciate all your comments. In your example what i understand is, when i connect positive end of AA to negative end of another AA battery that current will not flow. am i right.. if so i agree because the 2nd AA battery negative have no relation to 1st AA battery negative.. so there is no path to complete the cirucit. In our case, we are connecting secondary end of one wire to Mains earth. Since AC is alternating that secondary will have negative potentinal for some time ..continued

[@fbw47]

I actually plan on building my own isolation unit. Here in my town in the Philippines our mains consists of 2 - 110vac legs coming in from the meter to give us 220vac. No neutral; no ground. Yeah, weird. I will just treat it as one hot and one neutral for the transformer, giving a 220v output. So I don't have to worry about a ground. I haven't found anyone here who has even heard of an isolation transformer. My 220v variac was hard to find - finally did from Amazon, and AVRs are definitely required here because of the power fluctuating so much, and the very common power outages. Instead of burning up my PCs, I burn up UPS units. That's where I'll get my 2 transformers for the isolation transformer.

[@SkyWire88]

Hellooo. So, what is "AVRs" ?? And, what is "UPS units" ?? Thanks, in advance.

[@davido.hamilton3254]

Bless Your Bunions!...Todd. Thanx for your effort.

[@sivucit]

I cant believe that you are replying even at this time. i pressed subscribe button immediately. One last Q, we agreed that secondary is connected to the earth. Now the question i had is(may be stupid) the seconday wire is alternating(can be + or -). when that secondary wire is negative i dont see a problem, but when that secondary wire connected to earth alternating to positive at the 2nd half of cycle, will not it cause short to earth. Please advise if u have paypal ac i like to donate ..

[@trekgeek1]

Fair point, though I believe their are few occasions where misinformation should be spread for the sake of simplicity. I think "quickly" or "really fast" would have sufficed to explain the speed of electricity. There is so much misinformation in this world with science already, I shutter whenever the potential for more occurs. I don't think the speed of electricity in this video was the key point conveyed and as such unlikely to add confusion. Great video otherwise! Always a fan, Trekgeek1

[@JohnAdams-hd5mw]

I have a Viz Isotap WP-26A 400 VA. Would you happen to know if that is a tech version. This is a older model but I like it. By the way. I have learned a few things. You are a good teacher.

[@ToddFun]

Hard to tell. Do the test I did in the video with a light bulb and you'll know.