Another 2391 question

[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?