Another 2391 teaser.

[La Poste]

The toilet lights are controlled via a motion detector which cannot be removed during an insulation resistance test. State TWO alternative methods of preparing this circuit for the insulation resistance test.

The thing that is confusing me is the question asks specifically for methods of preparation not for test voltages to be used.


1) Isolate circuit from rest of installation and test between line + neutral to earth at 500V.
The preparation being I would isolate the circuit from the rest of the installation.

If the Motion sensors cannot be removed I am stuck on thinking of another way of preparing the circuit.

Any thoughts on this one?
Thanks.

 

[Deleted member 26818]

I thought this had been explained.
SELV is tested at 250V, LV is tested at 500V and for circuits with voltages above 500V, 1000V is used.
As the circuit is LV, the voltage used for testing is obviously 500V.
The two methods would be to link line and neutral together and test to earth, or link out each motion detector, bridging between the line and neutral terminals and then test between each individual conductor.
Both methods would involve isolating the circuit from the rest of the installation.

 

[La Poste]

It's the link out method that is new to me.
Bridging between the line and neutral terminals.
Could you explain a bit more how this is done.
Cheers.

 

[Deleted member 26818]

You want to prevent the test voltage flowing through the item of equipment, so you create a short between the line and neutral at the item, use a short lead with two croc clips and attach each clip to the terminals.
Another method would be to remove the conductors from the detector, and test the circuit each side of the detector, although that would probably be considered as removing the detector.
I suppose you could cover the detector so that it won't operate, and then test each side without removing the conductors from the detector.

 

[La Poste]

You want to prevent the test voltage flowing through the item of equipment, so you create a short between the line and neutral at the item, use a short lead with two croc clips and attach each clip to the terminals.

So I would link line and neutral at the sensor, then go back to the DB and test between L+N and earth.
The test between line and neutral would be pointless because line and neutral are linked at the sensor.
Is this correct?

Also we have a line and a switched line at the sensor, we would need to be sure the switched line was included in the test. The switched line would have to be linked to the supply line to include it in the test otherwise that part of the circuit would not be tested in much the same way as if we had not switched a light switch on to test a lighting circuit.

Let's say we were to test the circuit at 250V DC from the DB and test between all conductors. So we put 250V DC down the line and neutral of the circuit.
The motion sensor is in the bathroom.

My question is if we were to test a motion sensor at 250v DC would we need to link line and switched line?

Perhaps this is a good second answer.

So I could write down maybe these two answers.

1) Isolate circuit and link line and neutral together at DB and also at sensor (you say to link line and neutral at sensor although if we were to connect line and neutral at the DB I am not sure if we would also have to link line and neutral at the sensor, still not sure about this) then test at 500V DC.
Also not sure if this would include the switch line at the sensor, I don't think it would.

2)Isolate circuit and link line and switched line at motion sensor (to ensure switched line is included in the test) and then test between all conductors at 250V DC.

Another method would be to remove the conductors from the detector, and test the circuit each side of the detector, although that would probably be considered as removing the detector.

Agreed.

I suppose you could cover the detector so that it won't operate, and then test each side without removing the conductors from the detector.

At a voltage of 250V?
This sounds like a good answer also.

I know it's a long winded post but you really have to be careful of the wording in these questions and linking out is a relatively new expression for me to get my head around.

 

[Deleted member 26818]

Sorry yes not between line and neutral, don't know what I was thinking there. The detector probably doesn't have a neutral anyway.
I should have said between line in and line out, or between feed and load sides.
Your methods are:e
Test between L&N linked together, to earth at 500V. As you say no point in linking L&N at the sensor.
Link out the feed and load sides of the detector and test between each individual conductor at 500V.
Disconnect the detector and link out using a connector block and then test between individual conductors at 500V.
Disconnect the detector, and test the conductors on either side again at 500V.
If none of the above is practicable, then test between individual conductors at 250V, remembering that the minimum resistance allowed is still 1MΩ.