this one has me thinking

[switch10]

ok guys, answer to this might be simple, sat at home chilling out for a while and thinking of practising some testing, been looking at my house lighting and the ground floor lighting circuit has 14 230v downlighters fitted, all with a 12v transformer fitted . how would this effect my tests? surely insulation resistance readings will be poor?

just a thought really.

 

[switch10]

oh and i cant get to the transformers to diconnect them. never really thought about this before

 

[a1]

Are you asking how to IR test them, as they are ELV and you can't get to them?

How about Live and Neutral connected and test to earth?

 

[Andy™]

IR L-N to E wont be effected by the transformers, unless there is some serious fault (considering there usually class II).

IE L-N would be effected, just the same as if you left a 230v lamp in place somewhere

also, IR testing L-N can damage the electronics in the transformer

 

[SPECIAL LOCATION]

If equipment vulnerable to testing is on the circuit you EITHER

1/ Disconnect it & do your tests

OR

2/ Join L&N together then do an Ins Res test between 'L&N' combined to 'E'

see

Page 83 on-site-guide

10.3.3. Ins Res

i pre-test checks

item b

notes 1 & 2..

Jobs a goodun!

:coffee

Always handy to note some of these sort of references in the back pages of your OSG

So if you are asked on an assessment why you are doing something the way you are..

You can then quote a reference in the book to Mr Inspector...

They like that cuz you need to see you have a working knowledge of the regs as well as you practical skills.

 

[switch10]

ok thanks, was just a general query really, and what to expect in the way of inuslation resistance testing, i think andy has given me the answers at what to expect. in the way that the L-N results would be effected.

so could i do the L-N to E test and note the fact i havent done a L-N test on the certifiate if it was at a actual job?

 

[PC Electrics]

If it was a job you were issuing a cert for, then you'd simply put 'na' in the L-L testing box. L&N to E is perfectly valid testing for an existing installation.

 

[ianmacd]

If it was a new installation, I would expect to see testing L-N as this can be achieved fairly easily. Its not really acceptable to say you can not remove items when you are installing a new circuit.

L-L it always NA on a single phase installation. When testing LN-E for modifications, I put the same value in the L-N L-E and N-E boxes then put that IR tested LN-E as a limitation of testing due to ....whatever reason. I do try and do an L-N at 250V first and isolate anything that is still connected but on mondifications its not always possible.

 

[PC Electrics]

Just to be clear:

In my post #7 above, L-L = live to live

The model form (BRB pg 341) asks for the results of live to live and live to earth.

When testing a new installation you would test line to neutral and put this in the live to live column.

Why? Don't forget that neutral is a live conductor.

 

[Andy™]

L-L it always NA on a single phase installation.

L-L is Live to Live. neutral is a live conductor.

 

[VoltzElectrical]

page 84 of on site guide. reg 612.3.3 states that "where the circuit includes electronic devices which are likely to influence the results or be damaged, only a measurement between the live conductors connected together and earth should be made and the value should not be less than the value stated in table 10.1

 

[batty]

If it was a new installation, I would expect to see testing L-N as this can be achieved fairly easily. Its not really acceptable to say you can not remove items when you are installing a new circuit. L-L it always NA on a single phase installation. When testing LN-E for modifications, I put the same value in the L-N L-E and N-E boxes then put that IR tested LN-E as a limitation of testing due to ....whatever reason. I do try and do an L-N at 250V first and isolate anything that is still connected but on mondifications its not always possible.

Most of the jobs I do have downlights there is no way I will connect all the cables and then do it again to fit the downlights I always test l/n to earth and on most jobs you get readings >500. If it was pendants then I would test live to neutral but I don't get many jobs like that.

 

[VoltzElectrical]

regs allow for the scenario. they don't expect you to reasonably install something, then take it all apart to test it. Do bypass dimmer switches though.

 

[ADS]

Most of the jobs I do have downlights there is no way I will connect all the cables and then do it again to fit the downlights I always test l/n to earth and on most jobs you get readings >500. If it was pendants then I would test live to neutral but I don't get many jobs like that.

This is why they say that 'Initial Verification' (including testing) begins when the 'installing' starts.

Tests can be made at various stages of installation and the results noted.

Nothing wrong with IR testing the fixed 230v wiring before connecting up the transformers and downlights.

It's only the same as taking R1 + R2 readings before connecting earth fly leads etc on a steel conduit installation - and yes, that is the way it should be done. (unless, of course, the conduit is the cpc anyway) ; \