Using an Oscilloscope to Understand 120 VAC Split phase Household Power Supplies

[@tempviduse]

This guys very comfortable sticking his hands in the main panel

[@gsegallis]

An important safety note: relying on the the thin insulation of a mini alligator clip to protect you from a mains feed is EXTREMELY UNSAFE. Also, using a DMM in resistance mode to measure for a short on a circuit that might possibly be energized can be dangerous and unreliable. Even the potential of a ground loop can cause an erroneous reading. Measure voltage first - a short circuit will have 0 V, and open will likely have a drifting reading. If the potential is 0V, then you can measure ohms. Ideally, you trip the main breaker so no potential can exist, even between non-shorted wires.

[@Zonfeair]

Oh God thank you for this explanation as I struggled with the concept of floating ground vs earth direct ground for years until I saw this video. It clearly explains the difference by your explanation of neutral vs L1 and L2 how neutral IS earth ground and not just L2 which is the negative reverse phase of L1. Thank you. I am a subscriber now.

[@octoarts3617]

You clarified for me a lot of misinformation and confusion about 120 vac and 240 vac. The oscilloscope demonstrated the truth of what you said. Thank you.

[@johnjacobs6234]

The meter reads RMS voltage. It's the equivalent voltage to get the same power if it were DC. 120V RMS AC = 120V DC (power wise).

[@kydkop]

This was a fantastic video, perfectly answered my question. It makes so much more sense to realize that neutral is simply a center tap on the secondary of the transformer. thank you sir

[@Zonfeair]

Where the center tap is Earth grounded and L1 and L2 are not ground but two legs of power 120v each but in opposite phase.

[@voxpathfinder15r]

If you are confident that your scope doesn’t have any internal shorts to the chassis- you could put a ground lift on it and measure anywhere you like. But the second you do - you give a ‘ground’ reference to the scope- and if you use the second channel, it’s ground lead has to clip exactly to the ground lead of the the first channel or you can get a short that way as well

[@sto2779]

Extremely helpful video, Thanks! - Note: It is possible to measure the phase difference between L1 + L2 with L1 and N or L2 and N. You would need a true Isolation power supply to power the oscilloscope, so that the oscilloscope does not have a common ground with respect to L1 or L2. - I just tested this process with my own Mains Panel power.

[@wbfaulk]

There are other ways to isolate your oscilloscope's ground from the mains ground, too, but the best way to do this is to use a differential probe.

[@sto2779]

@@Jnglfvr that’s makes no difference. Same thing. And yes, you do want to isolate the ground if you are probing mains voltage, you’re gunna electrocute and damage yourself and the oscilloscope if the ground is not isolated when probing mains voltage. It’s literally shorting the mains voltage. You can use a battery or an isolation transformer, both does the same goal, isolating the ground.

[@sto2779]

​@@Jnglfvr what are you trying to say here? you have no idea what you are talking about. I'm talking about when we need to probe the ground/earth conductor, many of the mains voltage uses different power delivery scheme and it is vital to probe the ground conductor. For instance, my home mains voltage is directly delivered to the mains panel in the delta-wye configuration. I needed to probe the main's 120V ground/earth conductor, what is the most safest way to probe it using the rigol oscilloscope? Best method to use is a 12 volt DC battery hooked to a 120 AC inverter, then have it power the Rigol oscilloscope, this will be the most safest way when probing on the mains voltage of it's ground and live conductors since the oscilloscope is 100% isolated, this is what professionals do, they use a battery powered oscilloscope. Another method is to use a proper isolated transformer which you are talking about, and then probe the ground/earth terminal. The isolated transformer method and battery method are the exact same conflagration and makes no difference with ground fault in the Rigol oscilloscope. I agree a high voltage differential probe is the way to go.

[@sto2779]

​@@Jnglfvr I agree, defeating the ground is not a good idea, however this is a different scenario, the mains neutral conductor line needs to be probed and we are absolutely not defeating the ground or earthing for couple of reasons here. I'm not sure why you think this way. One of the reasons is that here in USA, most of the modern cities, the legal electrical code states that the neutral bus line must be directly connected to earth. It is extremely highly unlikely that the Rigol scope will have a serious internal ground fault in which the 120 AC mains volt will cause a shock hazard to the user, this is a serious bad design on the Rigol and blame has nothing to do about using an isolated powering scheme. It's more likely that the fault will come externally from the AC mains voltage source, like some kid sticking a fork at the power outlet or a thunder hit one of the mains voltage conductors, in this scene, theres not much anyone can do, simply call it bad luck, no matter how safe the power scheme is used, there is always a risk. Using the proper scheme will reduce the severity and chance of the risk greatly. Not to mention, here in USA, we do not need to worry about internal ground fault from the Rigol, because the AC neutral conductor is also attached to the earth at the panel, so lets say a ground fault did occurred in the Rigol, it is precisely engineered that the fault in the Rigol must sink to the neutral line and also to the ground line, eventually the fault will want to go to the least path of resistance which is earth. Since we are using 100% isolated powering scheme, we do not have a common ground, this is an issue, however if a fault occurred in the rigol, the fault must travel in the Rigol to the ground bus which are all common, this fault will want to travel to the least resistance path which is the neutral line being probed, now if the user is not stupid, he must connect the ground probe to the AC main's neutral line since it is connected to earth and this limits the shock hazard sinking to the user. The fault will travel to the ground probe, to the neutral line and sinking to earth. Therefore the user is safe from deadly shock hazard. Now you could also say that the ground probe doesn't have enough amperage to sink since the wires are thin, well thats even better, the user is safe from high amperage shock hazard since high amperage can't travel via the wires and the fault will reside in the rigol, possibly destroying a capacitor or some component. Better yet, the rigol also have a dedicated ground terminal at the front far right, a thicker wire probe can be used for probing the ground, now it's even more safer to probe mains voltage since high amperage fault in rigol can simply sink the fault easily to the thick gauged ground probe to the neutral line. This is why the ground probes have an alligator clip, to make sure the ground/neutral is always attached at all times. The issue is that when using a lab oscilloscope, for probing at the mains panel, AC voltage usually have the neutral and earth connected together, this is what gives us the trouble in probing and cause the shock hazard and it is not safe to detach the earth bus to the neutral mains bus at the panel. The logic also applies when using battery powered multi-meter or devices to probe the 120 AC voltage, there could also be a fault in the multi meter or device, shock hazard introduced to the user. Therefore you can't be too paranoid when probing on the AC mains voltage, you need to use proper professional industry products like Rigol and use safe powering schemes like to make sure that the Rigol is 100% isolated powered and also to make sure that the AC main's voltage neutral bus is directly connected to ground. This is the safest way to probe AC mains voltage. It is also much safer to use a high voltage differential probe, I completely agree on that, so long the differential probe is also used in conjunction with an isolated powered oscilloscope. Would also like to say that all risks of internal fault at the rigol is omitted if using high impedance settings on the probe.

[@JoeSmith-cy9wj]

Most municipalities, in order to deliver three phase power to commercial industry most efficiently, will send those three phases out onto power lines 120° out of sync with each other, not 180°. Any pole mounted transformer for residential supply will tap two of these. Therefore, a home service panel will have two lines at 120° phase angle, not 180°.

[@williamthomas2063]

Excellent info. Love the direct information without a bunch of "ummm" and "ahh" and other time wasting noises.

[@davidleblanc1812]

Thank you! I've been trying to wrap my brain around how the neutral works in a split phase system and this video finally made it click for me.

[@mtraven23]

same for me and its weird, I have a decent grasp on more complicated electrical concepts (3phase for example), but this one has alluded me. Seeing it on a scope brought it all into focus. Thanks!

[@itsnotfar]

Thanks for posting. I'm new to the oscilloscope thing. I always check info before doing stupid stuff. That's why I'm here !!!!

[@sisseeboy]

the analogy about the goldfish earned you my subscription

[@ceilingwalker1]

You're a funny guy! Looking at your scope still has me wrapped around the axel of this being a 2-phase system though, instead of split or single phase.

[@fredsalter1915]

Absolutely one of the best videos showing how USA residential power works. Too many of us are scared of examining our electricity! 240v is still fairly low voltage. Be smart, and don't be afraid. PS- I'm rocking an older DS1052E......

[@shieldcracker]

This is a very good video! It is a pity we did not see the 240V ocillograph. To get this just use the A-B function on the scope.

[@paulpowell4871]

LOL our Safety Coordinator screamed ARC Flash and ran out of the room

[@stevenadeau3807]

Yes those grounds swinging around in there is just a really BAD idea. Using an active differential probe would be MUCH safer.

[@toneysunny9283]

Sounds like the Fed

[@stevenadeau3807]

The reason the Fluke meter can go from L1 to L2 is because it’s floating, it has no reference to ground, it is run by a battery, unlike the scope which is NOT floating and DOES have a reference to ground. You could measure from L1 to L2 using the scope IF you use an isolation transformer.

[@pbl57lsu]

Or a handheld battery powered oscilloscope?

[@stevenadeau3807]

Or a floating (battery powered) oscilloscope RUNNING ON BATTERY. If it’s plugged in via a power source MAKE SURE ITS ISOLATED FROM GROUND. Some USB power supplies might have a reference to ground. Another option is to use a (rather expensive) active differential probe on the scope.

[@ousmanesarr7287]

This is an excellent video .one of the best. On the subject

[@jkk5us]

On your scope you can tie two ground leads together and then put the two leads (blue & yellow) to L1 and L2 and then add and invert to get your 240 VAC RMS 340 VAC peak to peak wave form on the scope.

[@walterbrown8694]

If one is not bright enough to understand something as simple as single phase split power, how likely is it that they would be able to use an oscilloscope ? When I was still in grade school in 1948, I was building full wave rectifier 250 v power supplies for homemade vacuum tube radios and other electronic equipment. Never owned an oscilloscope in those days, but the concept of opposite instantaneous voltage polarities at both ends of a center-tapped transformer winding was no mystery.

[@AppliantologyOrg]

Thanks for your commoners, @walterbrown8694. I’ve had appliance techs and electricians argue with me that the two split phases are not 180 degrees out of phase. I’ve had appliance techs tell me that that two ‘in-phase” voltages ADD to make 240 VAC. And you can’t tell them the actual physics of what’s really happening because they know it all. This is the sad state of the trades today.

[@toneysunny9283]

thank for explaining RMS!!!

[@СтаниславКарамов-й9щ]

Omg. Cool. Never thought that in North America such electrical distribution system

[@Glockperfection666]

If you power up the scope from a battery power station, then you can measure it either directions. The reason is by powering the scope from a battery pack, you've completely isolated the scope ground from the neutral of the household panel. This is the reason why your Fluke DMM would never blow up when you reverse the measurement because it runs with a 9V battery, which is completely isolated.

[@petertyrrell6690]

An excellent overview, thank you.

[@AppliantologyOrg]

Glad it was helpful!

[@equinixjohn1056]

"I've got my HAND ON IT! "

[@igfoobar]

"I'm grabbing it! I've got my hand on it!" Love the delivery :)

[@zone07]

Put a battery on that scope and your ground will be isolated so that you can measure between both hot leads.

[@tjmonks]

Thanks for visually proving what I knew all along...lol. I need your help with a question: Ok have a 4500 watt INVERTER generator for when power dies. It's single phase, but that's the trade-off to get nice clean power. Yes, I split it and backfeed the dryer plug AFTER TURNING OFF ALL 220V breakers, especially the main. Ok, I'm thinking about doing a power transfer switch with a proper-safe generator inlet for others who are not clever. For sure, I need 4 legs...2 (125A) Mains, and 2 (20A) Solar system... I want the solar panels disabled when generator is running. QUESTION, must I also disable the following 220V appliances with the transfer switch ? Central A/C, Electric Oven/Stove, Electric Dryer, etc... ? I would think it doesn't matter to do this as anything wired for 220V needs a reverse phase to operate. Since it will be the same 120V phase applied to both A and B legs of the house, it simply will not operate with no damage. Example: If you hook a 120V hot wire to one side of a light bulb, motor, or whatever... then hook the same exact 120V wire to the other side of the device... nothing will happen and nothing will be destroyed. AM I CORRECT and can just ignore other 220V devices (except solar panels) with regard to me transfer switch ?

[@justin128584]

Did you ever figure this out?

[@youpattube1]

Very informative, thanks. But I wish that you would have also connected the Oscope across L1 & L2. I think it would show 240v rms SINGLE Phase, not 2 phase as my brother contends.

[@AppliantologyOrg]

Takes a special adapter to put the other end of the o-scope probe on a live line for the reasons I explain in the video. L1 to N and L2 to N are two different phases, 180 degrees out of phase, split from the a single phase by the center-tapped transformer. Keep in mind that voltage isn't actually a sine wave-- it is merely *represented* as one. I explain this in detail in this article: appliantology.org/blogs/entry/919-whats-your-sine-how-sine-waves-are-used-on-oscilloscopes-to-represent-the-real-world/

[@youpattube1]

yes, I think I get why you see 240v from L1 to L2. I mean your analysis seems to make sense, and I did carefully read the link article. But still, it seems that... wait a minute, I think I see where I have been confused for many years. The transformer at the pole is a step down with a center tap and takes the single phase 14Kv line and steps it down to two 120v lines, one from the top and one from the bottom of the secondary winding, with the center being the ground/neutral. And following on from your reasoning, each of the two lines into the house are 120v relative to the neutral, and they are 180 out of phase with each other. Now being that current flow requires a difference in potential, let's consider one of the 120v lines. it is 120v rms relative to neutral. That means that, at any given time, to find the difference in voltage (potential) , we just take that voltage and subtract the neutral voltage from it (0v), thus we see a difference in potential, and current can flow. Now how do we explain 240v ? At any given moment of time, take the second voltage (L2) and subtract it from L1. At a given point in time, say L1 is positive, then L2 is negative. Our point of reference is not the neutral, it is each other. So subtracting L2 from L1 and that time, we have a negative being subtracted from a positive, so that means subtracting a negative, which yields a positive. this then adds L2 to L1. If they are both at say 170v (considering peak voltages), we take a +170v peak (L1) and subtract the -170v peak L2 from it, which gives 170 - (-170) = 340. So when L1 is at a positive peak voltage of 170v, the net voltage between L1 and L2 is +340v. Now when L1 is at a -170v, then L2 is at a positive 170v. L1 - L2 yields -170 - (+170) = -340v. So relative to each other, we see a single phase sine wave of 340v peak to peak. Which is 340v x 0.707 (the value to get rms) = 240v. A lot of difference of potential. As I was writing this, every time I realized something more, a little voice told me, damn it, that's not your own brilliance, that's what he said in the video, and even more clearly in the link article. Would you say I have got it ? One other thing. When you said you could not put one o'scope probe to each line (L1 & L2) for the reasons in your video, you lost me. I am not talking about swapping leads for an o'scope channel (which I can see would be a short), I mean one channel on L1, and the second channel on L2. Wouldn't that show a 370v p to p single phase waveform ? Can't o'scopes combine two channels ? Thanks for responding to my reply. I look forward to your next comments. I think my brother was right.

[@AppliantologyOrg]

+youpattube1 1) your voltage difference explanation is exactly what I showed in the linked article. 2) if I put the grounding lead of the scope (note the name, grounding lead) I will have a dead short from Line to Neutral. Rewatch the video where I explain this. Google around for using a scope to measure line to line. Takes an expensive adapter.

[@youpattube1]

This is aggravating. I wrote another reply, but it didn't show up.

[@AppliantologyOrg]

+youpattube1 Yes, KZbin comments are a cumbersome medium for technical discussions. Join Appliantology and post your comments in my blog post there: appliantology.org/blogs/entry/926-using-an-oscilloscope-to-understand-120-vac-split-phase-household-power-supplies/

[@gsegallis]

Actually, most breaker boxes will have the left and right sides of a particular breaker row on the SAME phase. In other words the right column is also ABABAB... just like the left side (not BABABA... as you have shown. The buss bar for a given row is accessible to both left and right breakers.

[@Cougdit]

The left and right side of a breaker row are opposite phases in America. Can't speak for other parts of the world. You can actually see the bussing alternate when the breakers are removed.

[@carlossantini]

Can you do a video explaining a USA split system that comes out of 2 legs of a 3 phase system?

[@mikhail_h]

Excellent. Thank you. Subscribed. To add to your points, watching 'EEVblog #279 - How NOT To Blow Up Your Oscilloscope!' (youtube search for link) he is also excellent in something you reference, namely the dead short and how to avoid in Oscope use. My question is ' Will removing your scope from the main ground protect it for the measurement between L1 and L2.' I operate my scope from battery supply not mains when doing measurements where the test circuit is powered from mains.

[@richardcranium5839]

depends on if your scopes power supply nuetral is connected to the grounds most likely is. safest way is to hook the scope to an isolation transformer. but be carefull i've seen these with a three prong plug that the ground is hooked up. and that ties to the nuetral in the service box

[@Infinitesap]

Thanks for clearing that up for me :) great video 👍

[@jeremyli2871]

Please don't put your fingers in the panel samurai man, especially when you're not looking at what you're pointing at. Thanks for sharing.

[@techsguild]

lol... the whole time he was doing that I figured the panel was dead. nope LIVE! LOL.. Great video tho. Thank You!

[@hughleyton693]

Good to use an Oscilloscope on Household 2-phase 120/240V power. . . . Just remember to keep the Oscilloscope "Common" connection on the Zero volts Neutral connection.. . . . Thank you, so you correctly say L1 is 180° from L2 Good, correct, so that makes it a 2-phase supply, even if Americans have a problem admitting that.. . . Correct, and good you stress that Neutral is the Reference point, because it is Neutral and tied to Ground... . Thank you.

[@jma8352]

the same way way to check the gas generator 220 output?

[@Do_the_Dishes]

If you had an isolated oscilloscope instead of that dinosaur, you could put that “ground lead” on L1 or L2 without fireworks. 😊

[@Engineer9736]

I was curious if those 2 signals actually both with from -60 to +60 volts, or that one was -120 to 0 and the other 0 to +120. This video answered it perfectly. They are on the same voltage range indeed. Thanks. By the way, you can measure between phases with a scope. But for that you have to use a transformer. But that's a bit more effort. I have exactly the same scope by the way, DS1054 :-) I'm from Europe.. Nothing like split phase here, only single or 3-phase, so got to satisfy the curiosity via the internet.

[@chrisbauer1925]

Actually, since 120v RMS corresponds to 170 volt peaks, they both alternate between -170 and +170 (peak) in the form of a 60 HZ sine wave. Since the 2 legs are of opposite polarity (180 degrees phase shift), you get 240 RMS between them, or 340 volts peak between them.

[@ryanevans7253]

I have a 240v mini split can I use 120 L1 and 120 L2, NOT 180 degrees out of phase? I want to use a solar generator on L1 and L2 this being inverted to DC does phase matter to the board. I will be using two 120-volt outlets on the same inverter.

[@mrflamewars]

Watching this because I replaced the AC Condenser unit shutoff box and I don't get the two hots, no neutral, and a ground connection. I still don't get it but at least I halfway understand why it's connected that way. Hurts my head.

[@TnTBLACK95]

Neutral and the ground are 2 different reference points. Neutral is a current carrying conductor, thus must have a voltage. The ground should never carry current except in a fault.

[@cyberwasp461]

I've watched many videos on measuring ac iwth a scope and I'm still don't feel confident enough to do it due to several videos I've watched. They stated that connecting a scope to a shared ac ground would blow the scope and or the device. Glad I only work with dc! still want to learn thoughh but not at the cost of my scope or me;)

[@wiltanschannel82]

can i use stock probe on main AC or a special probe is require?

[@arthurvin2937]

Can you hook up probes over L1 and L2 if you run scope off battery? Dead short problem is gone.

[@BATTERY73]

Well, you know maybe I like to call my dog goldfish... you sir are winning and got another subscriber.

[@DracoXul]

Great video! It should be called "Dead Short" ... haha

[@ilovecops6255]

EXCLENNETE! THANS Y OU VERY MUCVH!

[@IsaacOLEG]

Thank you, that is interesting. May be in Europ the ground is not plug similarly (I am unsure) I see you do not need a differential probe when using ground as reference. I have a question, if I use a differential proble for ground to L1 (We have neutral, phase and ground so it is different probably) may I usze the probe on the other wire without grounding it, and obtain a valuable reading ? Thanks

[@snaprollinpitts]

excellent explanation!!!!!! thanks

[@Okie-Tom]

So, with an old Tektronics four channel oscilloscope, if I want to check the three phase lines coming into the shop, would I need three differential probes or could one hook all three ground pigtales to the ground pin and the three probe ends to the three different phases, if I have 10 to 1 ratio probes? Thanks, Tom

[@skyboy98046]

All that pointing close to L1 and L2 had me on my toes. lol Have you ever accidently touch either one? lol

[@AppliantologyOrg]

Oh yeah. I think I've made every mistake there is to make. That's called "experience." 🤪

[@jeffmclowry]

Well maybe I have a dog, and I like to refer to him as a goldfish.... Hahaha.... awesome!

[@Anappa11]

“I like to call my dog a goldfish” 😂

[@corydavey3026]

What happens if the neutral connection is broken and you grab the neutral

[@AppliantologyOrg]

None of the 120VAC circuits in the house would work. This would clue me in that I have an open Neutral in the power supply. You can also check for an open Neutral with a simple voltage check between Line and Neutral with a LoZ meter.

[@Marr_SC]

Excellent video!

[@henmich]

My anxiety level was through the roof watching you poke your finger at the incoming mains. Is that panel disconnected? That's extremely dangerous. You are too cavalier showing that to people with probably no experience.

[@ShannonHHicks]

Thank you!

[@mostlikelywedoitservices6926]

Question. Your scope is plugged in? So your ground is to the chassis which is to the BNC exterior. What if you're running a battery-operated scope. Could you then read L1 and L2 because you are not grounded? Yes, I know nothing about oscilloscopes that is why I am here trying to learn about them.

[@NMranchhand]

Doggone! That was well presented! Only ONE question left to be answered for electrical bliss. Is the canceling of the split waves from L1&2 the reason that there is a current cancellation/reduction on the neutral, or the shared neutral in a multi wire branch circuit?

[@danielb5081]

I'm going to blow a fuse (mentally) if I hear one more person stating that you can't measure peak to peak voltage directly across L1 and L2 while connecting the ground lead of your probe to either L1 or L2 without blowing up your scope. DUH . . . To measure across L1 - L2 simply use an isolation transformer to run power through to your (AC powered) scope . . . OR . . . us a battery powered scope. DUH!

[@trangofast9692]

so one 120 v wave form is 120 v. so two 120 v wave forms is 240 volts? three 120 v wave forms is 480? i dont understand how the magnitude of two 120 v wave forms makes 240. i also dont understand where 480 comes from.

[@AppliantologyOrg]

It’s the difference between the two phases that gives the 240 volts. Since they are 180 degrees out of phase, you can simply subtract them. In a 3 phase system, you’re no longer dealing with a simple 180 degree phase shift. Each phase is shifted by 120 degrees and this phase angle has to be accounted for in the math. This is done with polar notation or with vectors. Bing AC voltage phase angle for more info. Here’s an example: resources.pcb.cadence.com/blog/2020-use-the-phase-angle-formula-to-understand-power-delivery

[@BATTERY73]

See... I’m GRaBBIN it! I got my hand on it. Hahaha 🤣 Love it

[@patri0t1776]

I've got a question if you can answer it. Why is 220v N.A. always represented as a full sine wave if they are anti phasor? And if you isolated neutral from earth, could you use L1 or L2 as reference (ie: would it be similar to the primary side of the pole transformer, with one side of the coil relative to ground as shown in your diagram?) Would that then represent the 220v as a full complete phase?

[@GlennMartinez]

Aloha from Hawaii, thanks for the effort. But I must point out that your drawing of the panel is not correct, Condor and GBrew caught it right. In 40 yeats of being an electrician is USA all residential panels I hav seen.the breakers are A toA Next row B to B Or put another way breakers opposite each other are the same phase and breakers side by side are opposite phase. As an electrician I do not understand what difference the phases being 180 out makes a difference. They are what the utility provides.

[@AppliantologyOrg]

Voltage is always the DIFFERENCE in potential between two points. The 180 degree phase difference is what allows for your 240 VAC phase to phase. So +120 - (-120) = 240 VAC.

[@bernardocisneros4402]

@@AppliantologyOrg You still didn't address how your illustration of the electrical panel misrepresents how circuit breakers that are across from each other draw current from different hot leg. From my experience, circuit breakers directly across from each other (on the same row) draw current from same hot leg and circuit breakers next to each other in the same column draw current from opposite hot leg.

[@leroydalton173]

So appliance repair techs supposed to be inside boxes like this?

[@G-Tech10]

Thanks

[@rapunzeleh546]

you used single phase and split-phase as the same thing. there is so much confusion about this.... countries like NZ use 'single phase' - they don't use 120v just 220, so it's single phase 220. we use splitphase 240, each 120v half out of phase with the other - the reason we don't need a neutral with 240v. i've heard NA called single-phase three wire, and split-phase... it's maddening! also, i have an inverter that has two symbols for 'neutral' and ground.... one is the standard ground symbol we're used to, like an upside down xmas tree, and i also have the symbol you used, looks like a rake...

[@Azam94856]

the phase shift here is 180 degrees. what about when the phase shift is 90 or 0 degrees, or even 270 degrees ? do we still get the 240 V line-to-line ?

[@AppliantologyOrg]

No. You have to take into account the phase angle using either vectors (phasors) or polar-rectangular notation. In 3-phase power, for example, each phase is 120 degrees out of phase with each other so you cannot simply take the arithmetic difference between each phase to get your phase-to-phase voltage difference.

[@michaeljordan1053]

Are you using special oscilloscope probes?

[@Hermiel]

Fun video. I don't know that I'd let a blind person wire my electrical panel but to each their own. ;)

[@jpl57210]

this guy makes me nervous

[@mikeeiben3430]

I have seen maintenance men use 2 phases of 3 phase power to plug in a welder. Would the phases being 120 degrees apart instead of 180 cause any issues with a welder or 240 volt single phase motor?

[@TigerUNC52]

It depends on how sensitive to voltage the piece of equipment is and if the equipment is designed to operate on either voltage. When you go between 2 legs of 3 phase power the voltage difference is 208 volts instead of 240 volts. 2legs X (120v - (120v X sin(120)) = 208v [sin(120) = 0.866] 2legs X (120v - (120v X sin(180)) = 240v [sin(180) = 0.0] This situation would have the equipment designed for 240V operating in a "brown out" situation which might cause damage. The equipment is pulling the same power at a lover voltage so the current goes up which could cause small smaller conductors to overheat and fail.

[@arcsnsparks76]

how do line 1 and line 2 become 180 degrees out of phase?

[@jeffmclowry]

Good question. The power station, just like the alternator on your car, is producing 3 phase power. If I understand correctly, l1 and l2 are two of the phases There are two types of production winding, Delta. Which is shaped like a triangle and the other looks like the Flux Capacitor from Back to the future. Both configurations have a neutral tap and a tap for each of the three phases. One cycle is 360 degrees. So... Rack phase, or tap, is 120 degrees apart. Or as is commonly known. 120 volts in our home.

[@anupamvipul233]

Electro boom did a video where he shows 220v 2 phase which is 120 degrees out of phase .In case of this video I think combination of Delta & star transformer which shifts the phase by 30 degrees and center tap which add 30 degree resulting 120 + 30 + 30 =180 degrees or something like that

[@billelkins994]

A pole transformer is a single phase device. It doesn't care what is hooked to the input it will see it as single phase. The secondary winding is center tapped. The ends of the secondary are 180 degrees out of phase because that is what transformers do. Measured to the center tap the ends will be two phases 180 degrees apart.

[@MuddFlappRanch]

@@billelkins994 You are correct, this video errs in the assumption that we get 240 by adding 120V+120V out of phase. That statement defies logic and physics for several reasons, (1) it assumes that a 240V circuit uses a neutral, it doesn't. A neutral is only used for 120V circuits. (2) incorrectly applies phasor addition. We don't get 240V by adding 120V and 120V, we start with 240V and get 120V by dividing 240V in half with a center tap transformer. There is no phase shift in a 240V circuit. Up until recent history, 240V appliances were fed with 2 legs and a ground. It wasn't until the 1990s that we saw a neutral added to 240V outlets (for theoretical safety reasons and it made 120V available for control circuits and clocks). Many older homes still have a 3 prong plug for the dryer and range.

[@johnjacobs6234]

Neutral in split phase will always be a straight line 0V due to Faraday's Law. It's just how transformers work. If you know this as an electrician, you'll wow people in interviews.

[@pashkamerica]

L1 + L2 is it 120 hertz between phase ?

[@AppliantologyOrg]

The frequency is 60 Hz meaning 60 cycles per second. That means 120 polarity reversals per second. Each phase, L1 and L2, is 180 degrees out of phase with each other.

[@pashkamerica]

@@AppliantologyOrg I still don't get it. If measure only two phases L1 and L2, what frequency of the AC will be between L1 and L2, 60Hz or 120Hz? Thank you for your time .

[@AppliantologyOrg]

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[@kevingu7503]

Is that suitable to install 240V inverter with L1 and L2? We are Chinese ESS developer, is trying to expand to Caribbean countries.

[@jimcarson9656]

And the question to the million dollar answer is, If L1 and L2 are 180° out of phase with each other, why is it call single phase? -enjoyed the video, just stimulating thought

[@AppliantologyOrg]

I actually show why that is in the video. It’s a split phase system that is *derived* from a single phase on one winding of the transformer. In other words, a single phase is “split” into two phases by the center tap on the transformer secondary. And, to be precise, these are called “split phase systems.” It is imprecise to call them “single phase systems.”

[@jimcarson9656]

L1 and L2 are single phase current. Maybe we should call L1 or L2 to common 1/2 phase? -In the interest of phrasing

[@AppliantologyOrg]

“Single phase current”? On any given conductor, the current will always be a single phase. You can’t have polyphase current on a single conductor. Technical vocabulary needs to be precise.

[@Rkroe24]

@@jimcarson9656 you need to read electric machines of Dwayne Cal you're gonna find those answers on it

[@panon5292]

So you have a panel after a transfer switch fed with SEU?? I hope this is not your own panel.

[@davedave6650]

I wholeheartedly agree. Let us not be dumb-asses.

[@diydantex6150]

Connecting clip leads to the main lug terminals is a very bad example. I guess you don't do any arc flash safety training. It is good to understand center tapped transformers but if someone misunderstands your lesson and goes poking around in a live panel they could easily be killed or suffer permanent burn injury or blindness.

[@hfe1833]

I thought Einstein is alive

[@IllumTheMessage]

nice

[@voxelmaniam]

You killed it! Wonderfil presentation but I would like to see you wearing insulating gloves when you go poking around in the box.

[@dextertech6570]

I put 1000-th like

[@michaeldose2041]

Hey my dog's name is goldfish.

[@skyboy98046]

You know I looked all around the internet for advice about testing my home powers sine wave but everyone is says it would ruin the oscilloscope if you hooked the probe directly to the power line. But you do and no explosions. Is everyone else wrong? Seeing is believing but maybe you’re using a little magic??!??!

[@AppliantologyOrg]

No magic. It is as you saw. Just make sure you understand everything I’m explaining in the video.