Testing the SELV

[Engineer54]

In general, the requirement is a thorough inspection to make sure that the source of low voltage (usually a safety isolating transformer) complies in all respects with the British Standard concerned, followed by an insulation test between the extra-low voltage and low voltage systems.

Guidance Note 3 (page 40) reads:

The source of the SELV supply should be inspected for conformity with regulation 414.3 and if necessary the voltage should be measured to confirm that it does not exceed 50 V ac or 120 V dc.

So you would undertake electrical testing on a SELV TX... I was just curious!! I as a matter of course would always check between primary-secondary, and primary - earth/secondary-earth

Had plenty of main contractors complain about testing Distribution TXs in the past, as they always come with a full test report etc, from the factory. They never seem to understand that lot's can happen to a large heavy TX during transportation, often involving sea voyages. Found more than just a couple that needed factory technicians to undertake warranty work at site...

 

[IQ Electrical]

So you would undertake electrical testing on a SELV TX... I was just curious!! I as a matter of course would always check between primary-secondary, and primary - earth/secondary-earth

Had plenty of main contractors complain about testing Distribution TXs in the past, as they always come with a full test report etc, from the factory. They never seem to understand that lot's can happen to a large heavy TX during transportation, often involving sea voyages. Found more than just a couple that needed factory technicians to undertake warranty work at site...

And the forklift or crane for final positioning!

It's competent judgement really, I wouldn't expect anyone to start testing the transformers on a small SELV lighting system but on larger projects I'd find it harder to justify not carrying out the transformer tests.

 

[malcolmsanford]

And the forklift or crane for final positioning!

It's competent judgement really, I wouldn't expect anyone to start testing the transformers on a small SELV lighting system but on larger projects I'd find it harder to justify not carrying out the transformer tests.

11kv/12v get some lights on that baby .........................

 

[Engineer54]

And the forklift or crane for final positioning!

It's competent judgement really, I wouldn't expect anyone to start testing the transformers on a small SELV lighting system but on larger projects I'd find it harder to justify not carrying out the transformer tests.

If you were to see how they treat some of the containers at the docks, and the positioning of them on the decks of those container ships, that forklift for final positioning would be the least of your worries .... lol!!!!

Had at least two TXs with cracked tanks, bad enough to be letting oil pass, bent and/or punctured cooling fins, Welded pipe work for expansion tanks sheared off, Pressure relief valves bent, buckled, and leaking. HV ceramic bushings, cracked/broken, LV bus bars and casing bent an buckled.... Having said all that, the vast majority arrive on site in pretty good condition..:rofl:

 

[La Poste]

Right I have at last got an answer for this question.
As regards the insulation resistance testing of SELV conductors at 250V with minimum allowable value of 0.5MOhms.
Quote:

This test is intended for when you have say a large torrodial transformer feeding dozens of lights with a significant amount of cabling. The transformer and all the lamps would have to be taken out of circuit before the test is done.
It is very rarely used as common practise is to now use pre-leaded transformers which connect directly to the lampholder of a single light fitting.
For a 2391 exam, you need to know how it would be done, but you will never have to do it in this instance. You may however come across some low voltage- selv heating/logic/building controls which are in this category at some time.

 

[Henrimonami]

I am really glad I don't need to investigate testing procedures for SELV,Electrical separation for months on end.
Amongst all the posts,not one post regards multimeter internal resistance in relation to measuring SELV, El circuit output voltages.secondary side as incompatible meter will not indicate correct voltage say these levels
Anytime much ado about nothing measuring toroidal txs resistances,secondary voltages etc load of nonsense
Only time you would consider measuring this type of equipment would be fault finding absolutely nothing to do with EICR,except to say final circuit not working investigation required..
If I buy a kettle I don't measure the element resistance to see if it meets standards indicated on relevant docs standards codes etc I fill it with water switch on and see.
Anyhow the regs for testing in line with your own experience are more than adequate to determine compliance.
Don't try to complicate matters about something you are really not trained/educated to analyse.
Have a safe working day.