Loop Impedance Testing

Methods of testing external loop impedance and prospective fault current. Part of a series on electrical installation testing, other videos here: • Electrical Installatio...
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[@fattoamanowoodwork3638]

Thank you again mr Ward. Really appreciate all your videos

[@wezzabryant7284]

I really love your videos John !! You have taught me so much, the way you lay it out and explain everything properly really fills me with confidence for my next job. I've been a sparky since I left school. I'm 42 now. I wish I had you as a lecturer at college when I was sixteen. It would of sunk in so much quicker. You're a legend mate, keep it up!!

[@bartom309]

So you are a qualified sparky with 20+ experience and you don't know the standard tests that are required to be done ? 😲

[@Ryan-nh8ef]

Hi JW, id just like to say thank you for these electrical videos, I'm just coming up to the end of my apprenticeship and preparing for my testing and trade test and your videos have been more of a help thank anything else, including lecturers. So thank you, my understanding from testing to earthing systems. Keep up the good work it doesn't go unnoticed!

[@tristanfareel7184]

Thanks so much for the detail you go into in these videos. You’ve bin a lot of help with my defined scope course. Legend. 👍🏼

[@fairisfairfairisfair9788]

Good one jw...I've watched your videos repeatedly. Thanks

[@donjude9585]

In the US most regions I have worked in have the TT / ground rod install. The maximum allowed impedance is 25Ω on a single ground rod. If it is greater than 25Ω than a 2nd ground rod at least 10' (3 meters) away is required.

[@stevebollinger3463]

Don Jude i don’t think the US is truly TT because in the US the neutral and ground are joined at the main breaker box. Thus it’s more like TN-C-S with an additional bonded earthed rod. So your primary ground in the US comes in on the service neutral and the bonding mostly keeps a potential from developing between the ground wire and the actual ground you may be standing on.

[@bobhatcher5505]

Brings back memories of my working life! Good vid, thanks!

[@Xxxcappie23]

Wonderful video, best on the Internet for sure. Keep it up John, keep them comming.

[@SeanBZA]

Prospective fault current determines the class of breaker you van install. PFc of 5kA you cannot use a regular cheap domestic breaker, but must use one rated for 5kA breaking, otherwise a fault can destroy the breaker without it actually opening safely. Mostly in domestic you never see this, unless you live right next to the substation, have brand new cabling that comes direct from there and there is around 20m of cable total between you and the transformer. Then you need much higher rated breakers. Of course on the supply side the supplier always puts a much higher rated breaker, as there a shorted cable will have very high fault current, and upstream on that cable at the main line connector there will be a fuse link as well, capable of massive fault clearance. Fuse is single use, but in general it is always rated to protect the cable to the house, not the house, so is generally 100A or so, while the breaker downstream to protect the house is 63 or 80A instead. If the fuse blows and the cable is fine they will always replace the house breaker as well with it, as it then is likely to have been faulty, if it did not clear a fault before the fuse did.

[@chrisbenjamin8843]

Total rubbish you two are talking!

[@craigspacie7048]

Great video John , really helpful your videos as I'm trying to pass 2394/95 exams👍

[@terrysteel6706]

Excellent description very easy to follow.

[@francisexperience]

Really like these presentations this presenter is excellent!!

[@gurdialtoora2143]

John; Thanks for the information.

[@mattappleyard92]

Another great video, thanks John

[@christianfletcher1976]

Hello john love watching your videos always informative. Could you explain sometime about how the PFC and earth loop impedance effect how quickly a circuit breaker or fuse will trip and what is allowable. Best regards Chris

[@ImranKhan-cf8gs]

Well explained this explanation and video stays in my head

[@onefortheroad1]

Hi john I've been told that if we now run power to a shed , garage etc then the dno will not allow the house earth to be used in the shed, so we now have to make the shed a TT system, is this correct and would a Ze test suffice or do we need to carry out the earth electrode test with the correct tester and test the ground around it etc?

[@warrengray610]

Thanks John!

[@train4905]

Superb john.brilliant.

[@johanburger6109]

Great video mate.

[@shilks8773]

I've got one of the TN-S / TN-C-S hybrids where there is both a braided earth strap on the incoming metal outer and also a 10mm earth going into the Cutout via a block marked PME. My ECI is recorded as 0.27ohms. Would this indicate that it is indeed a TN-C-S or could it still be a TN-S. I've had no reply from Western Power about what they have it recorded as. The Electrician who installed the CU ticked both the TN-S and TN-C-S boxes. His recording for the PFC was recorded as 0.85kA. Nominal voltage of 245v.

[@danieleuboldi996]

Hi John DO you have any videos fro a refresher on 3 phase PFC and E Loop testing..Many thanks for all your hard work..regards

[@alfieg4106]

did he?

[@joemcuac]

Hi John, great video! What about IT systems, how could we measure some kind of loop? We would actually want to measure earth rod resistance without having access to the actual rod. I've seen in some occasions that the earth rod has been covered by a concrete slab once the building was modified and there isn't any physical contact to the rod but from the main earth bar at the main electrical board. However on IT systems (three phase) the loop path from L-E on a good installation should be very big (as the insulation resistance of the cables?). What are your thoughts on this situation? Thanks!

[@train4905]

Thankyou kindly helped loads.

[@mtmotemekoane9652]

thanks for the info

[@harrycallaghan2531]

Top Man John!

[@shaunbeard593]

Hi jw great video again. I am about to embark on an electrician course to become part p registered. I hope u don't mind fielding questions as I find your videos a great source of information

[@jwflame]

That's ok but do remember that part p registration is only useful for people who intend to do significant amounts of notifiable electrical work regularly, and that most electrical work is not notifiable.

[@mohammedkhan5344]

John you are better than my tutor, but I am not going to tell him that

[@mefed1760]

👏👏👏👏 thanks JW

[@mark90229]

Thanks very helpful

[@acikgozerkay]

Can you also explain how to test for system loop impedance Zs. Thanks a lot

[@seandempsey9396]

Hi John can you please do a video on loop and psc testing using the kewtech kt62 or the ROBIN kts 1620 MFT'S Many thanks. Your videos are great and a big help keep them coming

[@gurbindersidhu6697]

Hi jw can you explain how is installed rcd thanks

[@Khanjan-si8me]

Thank you

[@nrg-5003]

Hi john, I'm sorry if this is very basic but does the loop impedance vary from time to time for a specific circuit? or should it be pretty stable? the reason I ask is because installed a spur double socket from the ring final in my house and the reading at the spur was originally 0.65 ohms, then all of a sudden it went as high 0.95 ohms, i checked it again today and it was back down 0.68 ohms. Is this normal or could it something more sinister? thanks

[@jwflame]

The circuit wiring should not change. The external impedance can change sometimes, as the supply network may have alterations and repairs. However if it's changing often, it suggests a loose connection or some other fault. Another possibility is something connected to the system causing interference, so the high reading may not be accurate.

[@nrg-5003]

@@jwflame Thanks👍

[@stevecocker3491]

Hi John, on the generic schedule of test results, what is Zs at DB referring to? is it a test like for Ze but with the earthing conductor in place?

[@jwflame]

Same as Ze, but applies where there are multiple distribution boards in an installation - Ze at the origin, Zdb at the incoming supply at other distribution boards. If there is only one DB / consumer unit, then Ze and Zdb are the same.

[@stevecocker3491]

@@jwflame Thank you for clarifying

[@shahzadhussain1908]

just wondering did you test the earth with the live wire coming from the main meter. to test the earth loop impedance ?

[@TommysToesandHeels]

I spotted that as well.

[@kamuts7]

John, how is then gonna trip the fuse with 6KA breaking capacity if the PFC is well below 6KA during a direct fault between Line and Earth or Line and Neutral? I know breaking capacity is different from Tripping capacity but what happens during a direct fault, how is it gonna clear the fault?

[@jwflame]

The breaking capacity 6kA is the maximum allowed fault current. To trip the circuit breaker reliably the fault current needs to be 5x the rated value for a B type, so 160A for a B32 circuit breaker. If the fault current is between those values, the circuit breaker will disconnect.

[@EwanMarshall]

In principle, is the loop impedance tester just an ampmeter, voltmeter and known load, applying ohms law and negating said load?

[@ernstpeterlegrand]

If you have a ground electrode, then you only need to do Loop Impedance Testing or Earth testing?

[@jwflame]

Both. Electrode tested separately to confirm that is installed properly, and loop impedance once it is connected to confirm the rest of the loop including the earthing arrangement at the supply transformer.

[@lurkzie]

My jaw dropped when I saw the impedence on a TT compared to a TNS and TNC-S

[@jodylomax8067]

Thanks JW Great Videos fantastic help with my collage homework MORE PLEASE JODY

[@Khanjan-si8me]

Your the best

[@petelownie4270]

Does your Sharpie seep through to the paper on the other side?

[@brianalexander7625]

do you have a video on the following I bought a ceiling light but the live and neutral wires are not coloured. how can I identify??

[@jwflame]

If both are the fairly common transparent plastic, one usually has a very fine thread inside of either blue or brown. If not, it probably doesn't matter as many lampholders can have the lamp inserted either way. Only really of significance with screw thread holders where the inner contact should be line and the thread neutral. If it does matter then use a multimeter in continuity mode to determine which wire is connected where.

[@brianalexander7625]

Appreciate your time thanks

[@azajakal9614]

Thx

[@154electrician]

Can you explain reg 434.5.1 ? Thanks

[@vhsable]

for anybody studying 2365 the values for TT is anything in between 21 ohms and 200. however is reality 100ohms is max . what I've learned anyway

[@cumberland1234]

21 ohms is the maximum value for the means of earthing, i.e. the connection between the star point of the distribution transformer and mother earth (via electrode etc). If this is less then you can have lower readings.

[@vhsable]

On site guide, Page 47. Section 4.9 note 2

[@mikeZL3XD7029]

JW, One thing I don't understand about America, they don't test their installations before livening, like the rest of the world. I was speaking with an "electrician" from the US, and he asked me why he should even do these tests. Weird.

[@samsword3210]

thank you for the video , what is the loop impedance test device name ?

[@jwflame]

Loop impedance tester. Can be a separate device, or combined with other test functions. A selection: www.tester.co.uk/electrical-electronic/electrical-test-equipment/earth-loop-testers

[@jackychua3323]

how to connetion wiring by hager mz915?

[@emmanuelsang213]

Why disconnect then later connect? Suppose I connect directly to the earth bar and incoming supply?

[@jwflame]

Disconnecting ensures you are only testing the earth connection. If testing to the earth bar with everything connected, there will be other paths through the bonding connections to metallic services and other parts.

[@emmanuelsang213]

@@jwflame thanks alot, your explanations are so well articulated..

[@peterdkay]

I assume "Loop Impedance Tester" sources current from active wire and voltage is measured at ground pin, but where is the reference. Is there a third ground wire that system uses as a reference ground?

[@cumberland1234]

The loop tester is measuring the impedance of the line (active) path from the supply transformer, distribution cables to the house, back via the earth (ground) to the supply transformer. The loop tester is using voltage and voltage under load on that path to do the calculation hence only the 2 probes are needed.

[@peterdkay]

Thanks cumberland1234. I assume actual ground impedance is difference between GROUND and NEUTRAL measurements.

[@TheEulerID]

I suspect the meter measures the potential from line to earth with no load then allows a current to flow, measures the potential again and from that change and a known current it's possible to work out the impedance. Of course, mains voltages aren't completely stable, so it probably has to do lots of tests and average the results. For example, if the test current is (say) 10 amps, if the potential drops by 2 volts, that would indicate a loop impedance of 0.2 ohms. It might even be that the meter can monitor the actual voltage waveforms and measure instantaneous voltage changes at a number of points during the AC cycle.

[@Tommyinoz1971]

Testing like this is important. I wish the electrician that installed my bathroom light/heat/exhaust fan did some testing besides just turning it on to see if it works. Some months later, I was testing with my multi meter the continuity between earth and neutral from my fluoro light in my garage and found that there was no continuity! I went hunting for the problem and found this - drive.google.com/open?id=0B5Wm-dWZjGIpdXhhM1JUV3VmSGc (Sorry I've shown this pic before). Also notice the red wire connected to the top terminal on the fan? That is actually a neutral connection, I'm not sure what the regulations are for re-purposing the wire that is normally used for active connection without using a sleeve or heat shrink to indicate it being used for neutral connection. Anyway, I cleaned up the mess of wires and added a junction box, so it looks like this now - drive.google.com/open?id=0B5Wm-dWZjGIpQTBtYkZHRHNNdGM

[@cumberland1234]

There should be a cover over the terminal block on the side of the fan. Also a fan venting a bathroom to a loft space is a bad idea, I doubt will pass building regs.

[@Tommyinoz1971]

G'day, I was already thinking about the cover for the terminal block on the fan myself and I was wondering if it came with one but was then thrown out by the electrician when he installed it. I will have to think about making one myself. I'm not sure what to do, maybe modify a plastic JB to fit? As for the venting into the roof space, I checked the regs here (Sydney Australia) and it's ok to do it if you have a tiled roof, which I do, because the roof space is already well ventilated. Besides it is hot has hell in roof space at the moment, check out this pic I took the other day - drive.google.com/open?id=0B5Wm-dWZjGIpa1VuUkpCTFRxTlE (FLIR image of roof tiles from inside the roof space).

[@thomasneallthorn9076]

Tommy Oz I

[@Power52]

Thomas Neall Thorn Good job ✌Your all good that fan never had a cover for the terminals

[@willdatsun]

hi its not clear whether you are testing it to the L or N they are not marked on your diagram or mentioned.

[@johnburns4017]

Is a loop impedance test one of tests on a new installation? There is continuity, polarity and insulation resistance. Is this one?

[@jwflame]

Yes, the complete list of tests is in this video: kzbin.info/www/bejne/iZSTpX19oZmCl9U

[@AllenGoldsmith]

what would be the next step if a circuit didn't meet max zs for example tns or tncs

[@jwflame]

Either use larger wires, or a smaller rating of MCB/fuse.

[@rafalotreba6824]

Hold a minute. Most of testing devices requires connection between L+N+E to determine Ze and Zs. How I can understand that?

[@geoffspar]

Your incoming Ze is resistance between L and E, on TN-s on TN-CS the neutral and earth are connected, your Zs is Ze + R1+R2

[@aleferrardo]

I really appreciate this videos, not this one but, some of them. Thanks for sharing these info. Dear John, I am from Brazil and I am looking for a equipment that can measure a line impedance. Can you indicate something to me?Thank you!Alexandre

[@wolfiestein7641]

You could have been a great airline pilot

[@MagnetechSolidSolutions]

Good evening ladies and gentlemen welcome to this Ryanair flight from Dublin to anywhere. Before we depart Id just like to say that we will be cruzing at 55,000 ohms with a voltage of 230, if we exceeded the maximum permissible value for earth fault loop impedance well then just keep calm a multimeter will drop from the overhead compartment.

[@afripowerengineeringcoltd6837]

someone send me the photo of a loop impedence machine that tests loop

[@milesbancroft]

Interesting video. The audio looks slightly out of synch to me

[@jayway6823]

Miles Bancroft Yeah just a bit.

[@jamanemaraashollington8760]

I hope sharpie send you free pens

[@user_i.d]

Why is this not a dead test

[@moufidjazouli1778]

Talking quickly and monotone!!!!!!!!!!!!!!!!!!!!!!!!!!!!!