EICR - RFC higher than calculated end to end on cpc (code advice required please)

[Ash]

I'm now genuinely intrigued why the on site guide is different to other science references.

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The Ze is measured at 0.21 ohms. It's a real job and i repeated the end to end test twice at another socket outlet on the circuit with the same results. From the calculated length of the ring that has been stated, something has got to be wrong as the circuit supplies s/o in two rooms with an estimated distance much greater. Not sure what to do now.

did you do the R1-Rn test for interconnections?

 

[freedomrun]

No, did'nt do that, only as stated previously, L-L & N-N & cpc-cpc. This is the first time i've had a cpc-cpc reading so much higher than calculated.

 

[SPECIAL LOCATION]

No, did'nt do that, only as stated previously, L-L & N-N & cpc-cpc. This is the first time i've had a cpc-cpc reading so much higher than calculated.

:Cheadbang

This bloke here had similar problem in November....

http://www.talk.electricianforum.co.uk/electrical-inspection-testing-forum/17774-high-zs-rfc-domestic-periodic-inspection-report.html

Post #1....

Hi all, just completed a PIR on a domestic install. The Zs on the RFC is a bit high for a B32 MCB, i'm getting several readings between & around 1.16 ohms (some just below and a few higher), up to the worst being 1.43 ohms. The cct is RCD protected with 30mA protection. The readings were taken with the circuit energised. Also, my reading of the end to end readings of the RFC gave a higher than calculated value for the cpc - could this be the reason for my high Zs maybe? I'm going to give a CODE 3 to investigate the high cpc value further. I seem to remember reading that Zs figures can be higher when taken live, should i repeat the Zs as a dead test? Cheers.

oh...

hang on...

that was you as well... :_|

:C

Friendly forum -vs- factual forum...

option (1) your doing a great job... keep it up...

option (2).........

In all honesty I think you need to work along side someone if you are trying to do PIR's ...

As its looks like you are out of your depth with basic continuity checks amongst other things......

http://www.talk.electricianforum.co.uk/search.php?searchid=980067

Guidance note 3 does say the inspector must have sound knowledge and experience of the type of installation to be inspected..

Sound knowledge and experience??????

You are asking some very basic questions here...

Its not just getting numbers to fit the boxes to comply with regs...

They must also match the physical circuit...

e.g.

you could have a cooker circuit within its max Zs.....

but if the R1+R2 implies the lengths are way out with the actual circuit length...

then either it has been tested wrong..

or there is a defect on the circuit...

even if it is within Zs!!!!

No doubt some other members will moan that we are not been helpful enough....

BUT..

we are talking about verifying the safety of an electrical installation that could kill an unskilled person (the customer) in a few seconds!

:C

 

[Doc Hudson]

I'm now genuinely intrigued why the on site guide is different to other science references.

Adjustments for ambient temperature when taking readings? I assumed most electricians would use the quick reference tables for resistance/metre or (R1+R2)/metre, for copper and aluminium conductors up to 50mm2 C.S.A. as given in the on site guide, as it is a quick and easy calculation, clearly not.

Doc H.

 

[Ash]

Both values are on the assumption of 20 degrees.

about the on site guide, I prefer doing it properly, the on site guide is a guide, and not because I want to be pretentious but because I like to keep my theoretical knowledge up. I'd like to think when my back goes or I get too fat I can become a college tutor.

 

[sparkytim]

In the REAL world actual readings very often vary from the calculated ones, especially at those small values, just how tight your crock clips are nipped can alter the value measured and on an existing install varing tightness of connections and/or worn contacts on sockets will greatly effect things.

You are expecting to much to see perfect readings

 

[freedomrun]

Well, i may not have the experience of you guys, and i would dearly love to be able to do some work along side another that has had all of these problems before......... but this is the real world and i'm on my own, trying to do my best - at least i'm trying to resolve an issue and get to grips with these errors when they arise, i have been reading other posts on this site where PIR's / EICR's are just being made up and the money taken - nobody is shooting these guys down, just having a laugh about it happening all the time. Also this problem has been found as part of an EICR, i am simply inspecting and recording my test results, if the customer wants further investigation to take place due to faults / errors found - then this is extra to just generating a report.

 

[ProDave]

Just my thoughts.

That's a LOW reading for a ring, it's either a short ring, or it's bridged somewhere. Do the figure of 8 test and measure R1+R2 at each socket to confirm.

Also, you say most of the CPC's are twisted and sleeved together then into the same earth terminal. Pull the sleeving off to have a look. Could one CPC be a bit short, or snapped, so it's not reaching the terminal, and the circuit is only being completed by virtue of them twisted together in the sleeving?

 

[freedomrun]

Yes, i will do that - sounds like a good bit of advice there. I will let you know how i get on.

 

[PC Electrics]

How are you measuring? It's vital to get good contact - I use my crocs and apply finger pressure to ensure they are tight on the cable ends.

Are your leads in good order? esp where they plug into the tester.

Can you answer the previously posted question about the rfc length?

 

[Maplasterelec]

Agree with Dave. Always do figure of eight to make sure all sockets on the ring and not spurs from spurs etc.....

Matt

 

[Maplasterelec]

Dodgy results from certain sockets will highlight which sockets to look at. Obvious though I suppose!!

Matt

 

[Doc Hudson]

How many rooms and outlets does the circuit supply. The L & N readings are excessively low for a ring in the average domestic property.

Doc H.

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I am simply inspecting and recording my test results, if the customer wants further investigation to take place due to faults / errors found - then this is extra to just generating a report.

Yes, i will do that - sounds like a good bit of advice there. I will let you know how i get on.

It is actually quite concerning that this is not a college question. An average PIR would be half to one days work on a typical domestic property, you appear to suggest you are now going to do repeat visit as you were unable to establish the results on the first visit. Have you passed 2391, as these sort of anomalies are just common understanding of actual test results compared with expected and permitted test results. They should be a skill already acquired by every practicing electrician capable of doing PIR's. If you haven't done 2391 you would be wise to get enrolled ASAP if you intend doing further PIR's or if you have already done 2391, it sounds like you may need to recap on some of the course work. Brian Scaddan also has some very good books that would probably help.

Doc H.

 

[freedomrun]

I put the croc leads on the ends of each conductor and applied even pressure, my leads are in very good order throughout and leads nulled before testing. I can estimate the RFC length at about 30M or so, install is a small cottage - not a large dwelling.

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The property is vacant whilst renovations take place, i've been asked to report on the condition of the property and make good any possible defects, problem is the flooring is already in and i have no access under floors.

 

[green-hornet]

Far be it from me to try and teach people how to suck eggs but here goes.

When testing any installation of any age, and indeed initial verification you need to know what results you are more likely to get unfortunately this is a skill that is often learned over time and experience gained from years of testing. The actual testing procedures are always the same and can be learned from reading a book in reality; it

 

[freedomrun]

Many thanks, very much appreciated for taking the time to respond with such excellent advice.