circuit testing

hmiddity · Mar 23, 2011

Hello,
Is there a problem testing a circuit if there is a SELV spur off the circuit?

eg, doorbell, power shower..

Thanks
hmiddity

malcolmsanford · Mar 23, 2011

Yes certainly on an IR test as it would give you a dead short if you do not disconnect the appliance. If you can not disconnect the appliance you can test as per regulation 612.3.2 as L/N joined to Earth.

On a R1 + R2 then no, as the system will be isolated and you will be testing before the load side of the appliance. If it was a live Zs test the same it would be done on the supply side of the system.

Deleted member 26818 · Mar 23, 2011

Not really a problem.
The feed circuit would be tested as normal at 500V DC, and the SELV spur at 250V. You would then need to test the separation between the live conductors of the SELV spur and the feed circuit at 500V.

hmiddity · Apr 5, 2011

malcolmsanford said:
Yes certainly on an IR test as it would give you a dead short if you do not disconnect the appliance. If you can not disconnect the appliance you can test as per regulation 612.3.2 as L/N joined to Earth.

On a R1 + R2 then no, as the system will be isolated and you will be testing before the load side of the appliance. If it was a live Zs test the same it would be done on the supply side of the system.

Thanks Malcolm. when you say disconnect would it be ok just to remove the fuse from the fused spur or should the cables to the transformer be totally removed?
I was reading the User guide (probably 612) which mentioned the L/N join.
I had an electrician in to check the wiring (35 years + and part P) but he didn't seem to think that it would be a problem.
regards HMIDDITY

malcolmsanford · Apr 5, 2011

Is your spur a double pole switch type?

Unfortunately just removing the fuse would not isolate the neutral so you would get a false reading back through that, you have to isolate both LINE and NEUTRAL from the load.

What did he not thing would be a problem mate ?

SimpleSimon · Apr 5, 2011

Certainly false reading would be given on an IR test. Pull the fuse and disconnect the neutral.
Hmm no problem eh? Wonder if he'd be saying that when he gets a 0 reading he can't figure out.

hmiddity · Apr 8, 2011

Hello Malcolm,
The spur is a double pole fused switch with the feed taken from the lighting circuit.
So if the switch is off will it be ok to run the tests on the lighting circuit?
One other silly question, if a lighting circuit is said to be 'open' does that mean the light is on?
Regards and thanks for your time.