EICR Limitation - no L to N IR Test

[smity]

Alrite lads,

i am am currently buying a house and as part of the valuation report they wanted a EICR doing as the electrics are clearly old.

So the owner employed a company to do the report and I have been passed on a copy. Now i I don't do EICR's but one of the limitations sounded strange to me and they haven't given a reason.

The limitation is - no L to N IR test

Why are your thoughts on this? Seems abit of a cop out to me, is this an acceptable limitation especially with no reason on the document? Iam not too bothered as I will be rewiring at some stage and putting a split board in straight away so will end up having it tested but seemed strange.

cheers

 

[telectrix]

it's fairly common for 2 reasons.

1. all loads need to be dissed in order to IR test L-N.

2. any sensitive equipment left in circuit may be destroyed by IR test.

 

[smity]

I presumed this would be the case but surely that's the whole idea of testing an installation? So can you put a limitation of not testing sockets as my back hurts and can't neel down?

 

[OhmElectrical]

it's fairly common for 2 reasons.

1. all loads need to be dissed in order to IR test L-N.

2. any sensitive equipment left in circuit may be destroyed by IR test.

A lot of our clients stipulate this as they won't pay for us or anyone else to disconnect every single load etc, in a house though I personally would go the extra as it should not be that hard to disconnect most things.

Some clients have requested we test at 250v too as they have sensitive (dimmer packs) etc connected at high level and will not take them down.

So there are a range of reasons people request things and ultimately it's normally down to price. Time = money

 

[telectrix]

a L-N IR test would always be done on a new install, but on a EICR, unless there was a concern about the circuit, it's not usually done.

 

[alanl]

Agreed, a quite legitimate Limitation, which is described in GN3 thus ".. the most practical test is .. between live conductors (joined together) and earth. In practice, time does not usually allow for a line to neutral test."

The same goes for the Zs live test. Why bother if you have already done the R1 + R2 testing. No need at all, it just takes you mor etime, and tells you nothing more than you already knew.

 

[davesparks]

Some clients have requested we test at 250v too as they have sensitive (dimmer packs) etc connected at high level and will not take them down.

Which is completely pointless as this is less than the peak voltage of the AC supply that you are testing the insulation' suitability for.

What kind of dimmer is going to suffer from a L+N to E IR test at 500V?

 

[davesparks]

The same goes for the Zs live test. Why bother if you have already done the R1 + R2 testing. No need at all, it just takes you mor etime, and tells you nothing more than you already knew.

Are you on a wind up?
Circuits with good continuity of the CPC can still have unacceptable EFLI!

 

[cliffed]

There is no reason why this test should be omitted ,especially in a house,where I would of thought it would be no problem isolating all equipment plugged in etc,cheers

 

[alanl]

Have a read of GN3.
Zs may be calculated. Reg. 612.9, with a bit more on p.52 of GN3.

 

[alanl]

Are you on a wind up?
Circuits with good continuity of the CPC can still have unacceptable EFLI!

How so?
Continuity of R2 is not enough to calculate Zs, you do a R1+R2, then it can be seen pretty quickly if it is likely to comply.
You know the R1+R2, you know the maximum size of the permitted Zs, you know the Ze of the installation, so before you do a live Zs test, you should know whether it is likely to pass or fail.
Doing a live Zs test adds further time and inconsistency into the results.
Try a Megger or Metrel tester through a MK CB and RCD on a no-trip setting, and you will not get an accurate result due to the internal windings of the RCD adding extra resistance to the reading.
This is due to the meter not being accurate at these low settings, so to do an accurate result, a high current test should be done, which is not possible without bypassing the RCD, which adds more complications, so, overall, it is far better to do a proper R1+R2 test, then adding on the Ze (which is tested at high current, so gives a more accurate result).

 

[Engineer54]

Have a read of GN3.
Zs may be calculated. Reg. 612.9, with a bit more on p.52 of GN3.

Why calculate Zs when it is far easier to test and gain actual values as opposed to maybe values??

If there is no power available at time of test, fine that's when you calculate....

 

[alanl]

How accurate are loop testers when using the no-trip test?
They are not accurate at all.
See above, try a Metrel, Dilog or Megger through a new MK RCD, and your measured results will be far higher than the calculated result.
This is a known fault, as the tetsers calculate the result internally, by using a very low current to take the reading. This is acknowledged in GN3, with the line " these instruments are not as accurate at low resolutions.... some maufacturers state results should be treated with caution below a half or one ohms...calculations may be necessary to cross-check test results"

So why bother at all? Yes, easy to do at socket outlets. What about fused spurs? Far harder to do safely, with the added chance of adding a fault to the installation - trapping a wire behind a screw etc.
If you've done the R1+R2, and a Ze, then there is little need to do a live Zs test, and the Regs and guidance notes specifically stating this.

 

[Engineer54]

How accurate are loop testers when using the no-trip test?
They are not accurate at all.
See above, try a Metrel, Dilog or Megger through a new MK RCD, and your measured results will be far higher than the calculated result.
This is a known fault, as the tetsers calculate the result internally, by using a very low current to take the reading. This is acknowledged in GN3, with the line " these instruments are not as accurate at low resolutions.... some maufacturers state results should be treated with caution below a half or one ohms...calculations may be necessary to cross-check test results"

So why bother at all? Yes, easy to do at socket outlets. What about fused spurs? Far harder to do safely, with the added chance of adding a fault to the installation - trapping a wire behind a screw etc.
If you've done the R1+R2, and a Ze, then there is little need to do a live Zs test, and the Regs and guidance notes specifically stating this.

Unlike many here we rarely conduct Zs tests using the 15mA no trip test function, and if we do we use our high resolution ELI test kits. Testing in my book is an integral and important part of being an electrician, who should know how to obtain meaningful values, not just relying on lazy no trip settings.... As for the Reg's and guidance notes on this topic, ...your welcome to them, when it comes to ''testing'' i prefer to see things done correctly....

 

[alanl]

Could you please explain how to do a live Zs test 'correctly' when there is an RCD present?

The only accurate test is an high current test, which would have to bypass the RCD. With terminals and CUs so small in domestic environments, it is not practical, or advisable, to bypass the RCD during a Periodic I&T.

Again, I come back to the UK Regs. They clearly state that a live Zs is not mandatory, so long as other tests have been done beforehand.