L&N-E IR Test (and we still haven't fixed the stupid 20 characters)

[hightower]

When you do a L&N-E IR test, is there anything (other than a fault) that could be left plugged in that would produce a low reading?

 

[telectrix]

surge protection?

 

[hightower]

surge protection?

I'm not asking for a particular scenario, like I'm not having issues. Just wondering if there's any predicament that could cause a L&N-E IR test to cause a low reading and stick that knowledge in the back of my head somewhere.

I guess with surge protection, it would show on a 500V test but wouldn't show (or show to the same degree) on a 250V test?

Anything else?

 

[telectrix]

IT equipment. computers are renown for having small earth leakage.typically around 3mA apiece. that's why you never put too many on a circuit with RCD protection.

 

[hightower]

IT equipment. computers are renown for having small earth leakage.typically around 3mA apiece. that's why you never put too many on a circuit with RCD protection.

See what I'm trying to understand is that the regs says it's okay to tie L&N together and test to earth when vulnerable equipment is on the circuit - so what would be the point of that if they give false results

 

[Pat H]

I had a socket outlet RCD in a RFC give me low readings. Likewise a shaver point.

 

[Octopus]

Deffo RCD's, pumps, pretty much anything....

 

[hightower]

So what's the point in doing L&N-E if you're just going to get false results still?

 

[PEG]

Always remember,that the test you describe,is a way round doing the correct,full test

 

[Octopus]

^^ otherwise known as cutting corners

 

[hightower]

Well no, it's not necessarily a way of cutting corners. The regs describe the test, but my question is what benefit does it bring if the results are still going to be influenced by equipment

 

[Octopus]

If somebody does L + N to earth and they fill out the cert as 100 m ohms I begin to doubt the test results

 

[hightower]

OK, the scenario where I'd imagine using this is not for an EIC but maybe to do a quick global IR to make sure an RCD will hold - obviously this will then have a full test but I'm thinking just a quick way to find out if it should generally be OK

 

[Bobster]

Because the results are most likely going to be worse than if you split test with all loads disconnected. Thus if it passes with results that are going to be pulled down by equipment it stands to reason that the circuit is serviceable and without loads, be in better standing.

 

[LankyWill]

Its a handy method for EICRs when you either cant disconnect everything, or are unsure of any loads that are connected without your knowledge.

 

[hightower]

Its a handy method for EICRs when you either cant disconnect everything, or are unsure of any loads that are connected without your knowledge.

But only when there's nothing connected that's going to allow a leakage through the earth?

 

[LankyWill]

Its more of a precaution, most installs have a bit of leakage anyway.

 

[static zap]

( Is it a reason to start splitting ring up ... or is that cheating )
Localise !
Never mind IT equipment plenty of naff IEC cables out there !
(IEC leads may test good at 120V for some reason ...)

 

[PEG]

There is an argument,for "cutting corners",there is also an argument,for including additional sections of an installation,within a test.
We could have that discussion for an eternity...

The actual required tests,are of the installation alone,and not any additional parts,accessible or not. If this is not possible or practical,obvious allowances and measures,are required,to obviate this.

All that is really important,is for all testing,to be relevant and fully understood.

 

[westward10]

( Is it a reason to start splitting ring up ... or is that cheating )
Localise !
Never mind IT equipment plenty of naff IEC cables out there !
(IEC leads may test good at 120V for some reason ...)

IT equipment should not give false readings unless they incorporate filters and this is rare. IEC leads should never give false readings. Testing an office last night nothing unplugged all circuits above 100 meg. Shaver socket is a new one on me and I think you need to ask if such things and IEC leads give false readings then they are faulty.