Metal conduit as earth conductor.

[tim.cooper5]

I have just had a niceic electric test done on a maisonette I rent out.

It failed on "no earth conductor on downstairs ring" and "no earth conductor on downstairs lights".

I got a very well known firm to come and quote me on a price.

They said that it was'nt a failure as the wireing was in a metal conduit which acts as a earth.

I then rang up three firms to come and do a test. Two said it was a failure and one did'nt!
If I remember correctly the one that said it would pass was very busy so could'nt come for three weeks.

So basicly can anyone put me right on what is a failure and what is'nt.

Thanks

 

[pdcelec]

There is no reason why metal conduit cannot be used as a cpc, as long the earth is continued to all accessories and the earth loop readings and continuity tests prove ok. Did they issue certificates and if so what did they put on them regarding this?

 

[breezer]

that is all vey well but just suppose its a plastic consumers unit, it would fail then

 

[pdcelec]

that is all vey well but just suppose its a plastic consumers unit, it would fail then

As I said the cpc should be connected to all accessories. Maybe I should have mentioned that it should be connected to the cu as well (sorry but I thought this bit was obvious), but I suppose this is the DIY forum.

 

[ban-all-sheds]

that is all vey well but just suppose its a plastic consumers unit, it would fail then

There are all sorts of reasons it could fail, from bits of plastic in the way to poor quality joins, to breaks in the conduit - doesn't do much good to list "what ifs".

It should be tested (AFAIK using a proper tester that puts several amps through the conduit infrastructure?)

 

[pdcelec]

It should be tested (AFAIK using a proper tester that puts several amps through the conduit infrastructure?)

I think that this test (flash test) has now been dropped since it used to cause problems with connected equipment and could injure people. GN3 says to use a low reading ohmmeter and test as you would R1+R2. If any one knows different I would sap up the info.

 

[ban-all-sheds]

I looked in GN3 for the info, and put down the fact that I couldn't find it to me not looking properly........

 

[mapj1]

There is still an argument for doing a full current test, after the low voltage test, namely that you could pass as being connected at 200mA, but have a CPC just hanging on by a whisker that could blow to clear in a real fault when hundreds of amps could flow until a fuse melts or MCB trips. However, the risk is small, and must be offset against the risk raising of the metalwork to a high voltage if the earthing does blow open during test.
Favoured method is to use low current only on PIRs and so on, where the circuit is in use, and delicate things may be connected.
It is worth noting, that as part of a normal PAT test, anything with a 13A fuse, needs to carry 25A down the cable and connecter. It seems a little odd that the circuits it plugs into should be exempt from such a test. another example of not entirely joined up thinking.

 

[kai]

A bit like when I installed an economy seven immersion heater - no supply available during working hours - so did all the usual earth continuity tests etc, and the applied a 1000 volt megger to the circuit, instead of the usual 500 volts - anything that passes at 1000 volts with an 120M reading between Red and Black and Red and Earth lines on meggering, will certainly satisfy the Regs!

 

[kendor]

It should be tested (AFAIK using a proper tester that puts several amps through the conduit infrastructure?)

I think that this test (flash test) has now been dropped since it used to cause problems with connected equipment and could injure people. GN3 says to use a low reading ohmmeter and test as you would R1+R2. If any one knows different I would sap up the info.

Flash tests are higher voltage not current.

 

[securespark]

You still get a nasty belt if you're touching the conduit when the guy hits the test button.....

Come on, Ban, time for your frazzled spark graphic once again!!

 

[ban-all-sheds]

 

[securespark]

Hurray!!

I didn't know Kingfisher had opened B & Q's in the States??

 

[tim_h]

NICEIC state on there website that conduits can be used for CPC.
http://www.niceic.org.uk/approved/quest7.html

To test this properly you need to use a high current ohmmeter. These test at upto 25A but at a low voltage. They are also known as Clare testers or ducters, but not many sparks have these, or even heard of them.

 

[ban-all-sheds]

Hurray!!

I didn't know Kingfisher had opened B & Q's in the States??

OK - I've changed it.

I'm sure the new one will meet with everyone's approval....

(PS - it's the other way round, possibly. It is rumoured that Home Depot are in talks about taking over Kingfisher..)