Another 2391 question

[bigbob1]

I think if this was installed properly each individual light would be on a greg, so you can unplug all of the lights because you must remove any sensitive equipment.
You must test at 500v dc if a single phase circuit up to and including 500V.
This is a new installation not a fuseboard change and you are 100% sure of where everything is.
The SWA should be earthed so you need to disconnect any fly leads so you are just testing between the cpc and live then neutral, then neutral and live. 612.3.1 says you can connect line and neutral together, but this is not good practice and also states when appropriate (new circuit).
The linking out of the photocell is a must as this is sensitive equipment, and you would not test the switch live if not linked to the feed.
**You must notify the owner of the property that you are about to do an insulation resistance test**.

This is a classic 2391 question because you have to understand how to use SWA and install it to be able to answer it.

 

[IQ Electrical]

The question is referring to an IR test on 1 lighting circuit and I still believe the C&G answer would be L+N together to earth at 500 Volts dc.

Why risk marks by using a contentious answer?

Like I said, in the real world, I'd probably advocate the 250 Volt test as a 'toe in the water' but not as a 2391-10 answer.

 

[Chr!s]

The question is referring to an IR test on 1 lighting circuit and I still believe the C&G answer would be L+N together to earth at 500 Volts dc.

Why risk marks by using a contentious answer?

Like I said, in the real world, I'd probably advocate the 250 Volt test as a 'toe in the water' but not as a 2391-10 answer.

I see nothing contentious about it myself, 612.3.2 and 612.3.3 are clear.

The only contentious area is GN3. Test 2 - insulation resistance to earth, GN3 mentions
no voltage, so we refer to the paragraphs on the previous page, the second paragraph is relevent to Test 2.
Further precautions in my opinion leads us to the 250v test voltage.

I don't believe you would be marked down for this, i suppose the best answer would to
state the added option to also reduce the test voltage if vulnerable equipment required this.

Chris

 

[Deleted member 26818]

There are two methods of conducting an IR test where there is voltage sensitive equipment.
One is to link live conductors together and test to earth at 500V d.c.
The other is to test between individual conductors at 250V d.c.
Both tests will require the minimum resistance to be 1MΩ.
SELV and PELV circuits should be tested at 250V d.c. and the minimum resistance is 500Ω.

 

[La Poste]

So with this motion detector in the bathroom a 250V dc test between Line and Neutral and a 500V test between L+N to earth.
Motion detectors, do they have a Line and Neutral supply and then a switched Line to operate any equipment or just a Line and switched Line.
I am not sure exactly how they work.
I'm not sure if they need their own power supply to function or if they are just passive devices with a Line and switched Line the only two cables supplying them.

Edit:
http://webcache.googleusercontent.c...en&ct=clnk&client=opera&source=www.google.com

 

[Chr!s]

There are two methods of conducting an IR test where there is voltage sensitive equipment.
One is to link live conductors together and test to earth at 500V d.c.
The other is to test between individual conductors at 250V d.c.
Both tests will require the minimum resistance to be 1MΩ.
SELV and PELV circuits should be tested at 250V d.c. and the minimum resistance is 500Ω.

The way i read it is this.

You apply either 612.3.1 "Between live conductors and between live conductors and the protective earth"

or

612.3.3. "Live conductors connected together and protective earth"

Along with the above we also use 612.3.2. The test voltages are as in table 61 or if the equipment is vulnerable we may reduce to 250 v dc.

So if we have vulnerable equipment, we shall use 612.3.3 as our test method.
The voltage in table 61 states 500 V d.c though we may use 250v d.c.

Chris

 

[bigbob1]

A photocell has a neutral going to it, a feed and a switch wire.

If i was doing my 2391 again i would do what i did last time and give the correct answer according to the reg and guidance note 3.

500v dc, testing the insulation resistance of all the cores in the cable, disconnect all sensitive equipment and notify the owner of the property what you are about do.

250v dc is for people that are not certain of what they are about to test as there might be something they have missed, or are to lazy to make sure 500v will fry something.

connecting the live and neutral together is another lazy way of doing this, as you can also check that there is no cross connection between live and neutral, so the correct way of doing this is by testing the live and neutral at 500v to make sure they are 2 distinctly diffrent cables. linking them together means you will never know if there is a leakage between them both, untill you switch on and start fault finding which takes longer than just testing them in the first place.

And according to the NIC
"Exceptionally, for periodic testing, if it is impracticable to disconnect electronic devices from a circuit, a measurement to protective earth only should be made, with line and neutral conductor connected together"

Obviously at 250v DC 1mA

" It is therefore important that insulation resistances are tested either to verify the satisfactory condition of new installation work BEFORE the supply is connected, or to check the condition of an existsing installation"

Do it once do it right eh

 

[Deleted member 26818]

The way i read it is this.

You apply either 612.3.1 "Between live conductors and between live conductors and the protective earth"

or

612.3.3. "Live conductors connected together and protective earth"

Along with the above we also use 612.3.2. The test voltages are as in table 61 or if the equipment is vulnerable we may reduce to 250 v dc.

So if we have vulnerable equipment, we shall use 612.3.3 as our test method.
The voltage in table 61 states 500 V d.c though we may use 250v d.c.

Chris

Whilst it may be that there is nothing in the Regulations preventing the use of a 250V d.c. test voltage when the live conductors are connected together and tested to earth, there is little point in doing so.
ESQCR sets a maximum distributed voltage at 253V, as such all 230V electrical equipment should be capable of withstanding a 250V d.c. test voltage.
The point of linking live conductors together and testing to earth, is to prevent excessive voltage flowing through the equipment.
250V d.c. would not be an excessive voltage.

 

[La Poste]

This is good because there does seem to be some ambiguity.
Just another small point to help clear things up.
With surge protective devices.
If we are unable to remove them GN3 states we can test between Line and Neutral at 250V.
The only thing I am not sure about is after this test do we then link Line and Neutral together and test between them and earth at 500V or do we keep our 250V test voltage and test between line and earth and neutral and earth?