rcd tripping during the night and insulation resistance testing question

[TJ Anderson]

There's no need to link L-N to IR test to earth for fault finding. The linked L-N method of IR testing is for initial verification of a new/altered circuit, or periodic testing. Fault finding does not follow standard test procedures as required for the above, if you link L-N you will not know whether the fault is L-E or N-E

He is testing with loads connected so L&N are connected across the loads.

 

[westward10]

Who is He?

 

[TJ Anderson]

Who is He?

The OP. Have just noticed he has asked two separate questions ... Both have the same answer though lol

 

[westward10]

The OP. Have just noticed he has asked two separate questions ... Both have the same answer though lol

Sorry I have confused you with the OP.

 

[phil lancaster]

if n&e are joined and then tested to earth surely this this would not be poss surely I would need to test the n and e unjoined to get a resistance?

 

[TJ Anderson]

if n&e are joined and then tested to earth surely this this would not be poss surely I would need to test the n and e unjoined to get a resistance?

Yes. He meant test between L&E and then N&E as seperate tests as opposed to L linked to N & tested to E.

 

[TJ Anderson]

.

 

[phil lancaster]

Ok thank you all for your input will let you know what happens

 

[Lucien Nunes]

What a lot of confusingness.

1. Testing IR to find a leakage fault does not require L-N test, which in any case you should not do (and cannot get a meaningful result from) when loads are connected.

2. When testing to earth, the loads will usually link L & N together by a low resistance so the readings of L-E and N-E tests will be the same. Therefore, there is no point doing these two tests separately with loads connected.

3. Just in case the only parts of loads connected between L & N are not of low resistance and cannot stand 500V without damage, you should solidly connect L & N to prevent that any voltage appearing between them. Therefore, only one test can usefully and safely be done, which is from L & N linked, to E. This is how a PAT tester tests insulation.

4. Most devices can withstand 500V on this test, or put another way, if they can't they aren't truly safe. But any appliances or cables with surge protection will give a failure reading, usually something under one megohm, as the surge protection clamps the 500V test voltage. They will usually pass easily at 250V, so that is a good reason to use this voltage when doing a global test to localise a bad load device.

5. Tracing a fault on the installation itself, with all loads disconnected, can and should be done L-E and N-E separately at 500V.

Not all leakage is due to poor IR but it is a good place to start.

 

[Bob Geldoff1234]

If your IR tests are showing good then don't rule out a faulty RCD and/or a loose connection somewhere arcing.This seems to trip RCD's as well but don't know why.Also don't rule out damp and slugs which can come and go which is great fun when your testing the following day with no faults showing

 

[Gavin John Hyde]

Hi I know that insulation resistance testing is normaly carried out with the LN joined but I am always all ways nervous that some damage may sill be done as there is so much sensitive equipment around LEDs Computer eqipiment
phil

If you do the IR test at 250v its not much more than what you get from a good supply anyway, I regularly get 245 to 247v in Bath on some properties. so we are talking a couple of extra volts.

 

[Wilko]

Hi - Don't forget it's a DC voltage during the IR test, vs +/- 400V (peaks) when its energised.

 

[telectrix]

isn't the applied voltage dependent on how fast you crank the handle on a megger IR tester?

 

[Lucien Nunes]

No, provided you crank fast enough there's a governor with a slipping clutch to keep the generator rpm and voltage constant.

 

[PEG]

What a lot of confusingness.

1. Testing IR to find a leakage fault does not require L-N test, which in any case you should not do (and cannot get a meaningful result from) when loads are connected.

2. When testing to earth, the loads will usually link L & N together by a low resistance so the readings of L-E and N-E tests will be the same. Therefore, there is no point doing these two tests separately with loads connected.

3. Just in case the only parts of loads connected between L & N are not of low resistance and cannot stand 500V without damage, you should solidly connect L & N to prevent that any voltage appearing between them. Therefore, only one test can usefully and safely be done, which is from L & N linked, to E. This is how a PAT tester tests insulation.

4. Most devices can withstand 500V on this test, or put another way, if they can't they aren't truly safe. But any appliances or cables with surge protection will give a failure reading, usually something under one megohm, as the surge protection clamps the 500V test voltage. They will usually pass easily at 250V, so that is a good reason to use this voltage when doing a global test to localise a bad load device.

5. Tracing a fault on the installation itself, with all loads disconnected, can and should be done L-E and N-E separately at 500V.

Not all leakage is due to poor IR but it is a good place to start.

Cannot believe you did not get a like,for a concise and useful explanation...

You should have been in the Poseidon Adventure ....could have been an hour shorter