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Topic Title: Earth loop test of a circuit
Topic Summary: Using a supply from a different circuit
Created On: 27 December 2012 11:27 AM
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 27 December 2012 11:27 AM
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leckie

Posts: 1807
Joined: 21 November 2008

Hi all

I've been watching a clip on YouTube showing an earth loop test of a lighting circuit but taking the line from a local socket and connecting a croc clip to a lighting louvre. I can see this would indicate that the louvre has an earth connection, but surely the reading should not be recorded as an earth loop reading? Say the supply was from a radial supply direct to the db, it may be a lot shorter run and of a greater csa than the lighting circuit supply.

Any comments?
 27 December 2012 11:43 AM
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perspicacious

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This practice goes back 30+ years when "loop testers" came hardwired with a 13 A plug and a "plug in" wander earth lead..... The next generation (early 90's) had plug in 13 A leads on a small round 3 pin connector (the name/type eludes me) that you could buy an accessory lead with 3 "split ends" that enabled "same circuit" testing.

Regards

BOD (in recovery mode from "dinner" with Polish friends)
 27 December 2012 12:00 PM
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leckie

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Hope you enjoyed your polish carp for Xmas dinner

But wouldn't the readings be incorrect?
We were talking about doing loop tests from an extention lead on the electricians night out. I must admit I was a bit confused to how the results could be used. Particulary if the results were at the top end of the max acceptable values.
 27 December 2012 12:11 PM
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perspicacious

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"But wouldn't the readings be incorrect?"

Yes, because it wouldn't be the "loop" path that a fault would take.

"Hope you enjoyed your polish carp for Xmas dinner"

It was Christmas Eve and I can see why they drink so much vodka after their food with it being so heavily salted and cooked in what tasted like battery acid..... But, it was the welcome I appreciated

Regards

BOD
 27 December 2012 12:28 PM
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aligarjon

Posts: 2819
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my old Robin loop tester has a seperate earth lead that can be plugged in. basically you plug it into a socket to do a standard loop test . If you plug the earth lead into the tester it disconnects the earth cable in the plugtop internally and you could take an 'earth' reading from any piece of metalwork. I used to use it when testing an earth spike with an extension lead .


Gary

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Specialised Subject. The Bleedin Obvious. John Cleese
 27 December 2012 01:04 PM
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leckie

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If carrying out an EICR, I usually do an R2 test with a wander lead to various points on a circuit and do an earth loop test at the point of the highest R2 reading.

I suppose you could do earth loop tests using an alternative supply line, and do another earth loop test at the point of the highest result but this time using the correct circuit line to get an accurate reading. This might be quicker in some cases
 27 December 2012 02:57 PM
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ebee

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I think it was a way of loop testing at current rather than a continuity test.
ie you`d test at a socket first to get a reading then still using that socket for L & N you could then earth test metalwork near that socket ier not a true EFLI of the circuit you are testing but a handy way of referencing it to earth to see if it had one or not and if it did to get some idea if it is "within the parish" of being possibly reliable

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Regards,
Ebee (M I S P N)

Knotted cables cause Lumpy Lektrik
 29 December 2012 11:46 PM
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AJJewsbury

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If carrying out an EICR, I usually do an R2 test with a wander lead to various points on a circuit and do an earth loop test at the point of the highest R2 reading.

Although bear in mind that the point with highest R2 isn't necessarily the point with highest R1+R2....

- Andy.
 30 December 2012 09:44 AM
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peteTLM

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Originally posted by: perspicacious

This practice goes back 30+ years when "loop testers" came hardwired with a 13 A plug and a "plug in" wander earth lead..... The next generation (early 90's) had plug in 13 A leads on a small round 3 pin connector (the name/type eludes me) that you could buy an accessory lead with 3 "split ends" that enabled "same circuit" testing.

Regards

BOD (in recovery mode from "dinner" with Polish friends)


So whats the regs GN3 opinion of this method?

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 30 December 2012 10:33 AM
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John Peckham

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Are you just looking for a number to write in the box or are you trying to prove something?

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John Peckham

http://www.astutetechnicalservices.co.uk/
 30 December 2012 10:50 AM
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leckie

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Well I suppose a bit of both really. You need, at some point, to fill in the box, and you need to check the overall condition of the installation. From Ebee's previous post I presume the point of this method would be to test under a bit more stress than just carrying out a R2 test with a continuity test. It sounds like an interesting method but I'm a bit unsure how to interpret the result if the line was taken from an extension lead for instance.
 30 December 2012 11:07 AM
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ebee

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BOD, was the name of that plug "Molex" or am I barking mad ?

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Regards,
Ebee (M I S P N)

Knotted cables cause Lumpy Lektrik
 30 December 2012 02:19 PM
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leckie

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I don't think gn3 says anything about this method.

I don't see how it can be used to record or to confirm earth loop impedance readings.

I can only see that it tests r2 under live conditions.

GN3 indicates the wander lead method with a continuity tester for the measurement of r2, so I think I'll stick with that. Unless one of the testing experts can enlighten me?

I think the guy in the youtube video was actually recording the value as the earth loop impedance reading. It would be nice if it was acceptable as it could save a lot of time, but the results would not be accurate.
 30 December 2012 08:58 PM
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alancapon

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I can't see using a phase from an adjacent socket producing any meaningful result really, apart from proof that the light fitting is earthed. As such, I believe that it provides less information than an R2 measurement with a long cable (which does actually produce a relavant reading for the lighting circuit under test). As such, I would find it difficult to justify the use of the loop tester in this scenario against the three requirements of the Electricity at Work Act Regulation 14 (live working).

Regards,

Alan.
 31 December 2012 08:29 AM
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ebee

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I still have a Robin (Model 2111 I think) somewhere with this feature.
I suppose on a twin socket you could plug in an appliance containing an exposed conductive part in one half and the meter in the other then plug the lead in to check the housing has a good Zs rather than just R2 the appliance

-------------------------
Regards,
Ebee (M I S P N)

Knotted cables cause Lumpy Lektrik
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