Insulation Resistance

[TimW]

I need to do a quick check of the insulation resistance of my home wiring.

Am I right in thinking that if I carry out my tests on each circuit using L+N joined together, and earth, I do not need to disconnect any items such as dimmers, neons, lights etc?

 

[Tag]

You need to go between the phase connections and cpc's of each circuit(L to N, L to E, N to E) on the 500v setting of your high reading ohmmeter.

As regards to the disconnection of equipment, put simply, anything electronic like ballasts, transformers for down lights and computers that maybe plugged in

 

[TimW]

Perhaps I didn't express the question very well. Let me put it this way:

Is it acceptable (given that I really just need a quick assessment) to carry out the test as follows:

1. Swich off master
2. Disconnect the L's and N's of one circuit
3. Join them together
4. Test at 500v between CPC and the joined L's and N's.
5. Repeat for the other circuits

The second part of my questions is this: If I carry out my test in the above manner, can I assume that I do not need to remove/disconnect sensitive items from the circuits?

 

[Tag]

Your still sending 500v down each connection, I still recommend disconnecting the equipment

 

[Graeme Harrold]

Linking L&N is a method (not a primary test) for tresting sensitive circuits. You are sending 500V down both lines, therefore technically you should have no PD across components. In the end it is your call on whether the kit you have connected will survive. If in doubt, do the test at 250V, isolate vunerable kit and do as much as you can. Its on your own home. If doing it for real, you would link out the kit or agree limitations with the client before testing

 

[sparks1234]

Your still sending 500v down each connection, I still recommend disconnecting the equipment

It is a recognised way of carrying out an insulation test to connect the L and N together and then test to earth if disconnecting equipment is not an option

 

[Mark.W]

Simply put YES, connecting L-N and testing to Earth is ok but only for periodic testing. If it is a new installation then an initial verification is required!

 

[Graeme Harrold]

Even if you do it for a perodic, Id still cover my back and list it as a test limitation.............

 

[electricAl]

Tim, if you were proposing to do this for one or even a couple of lighting circuits, then okay. But unless i`ve misread your posts, it appears you intend to do your whole house in this manner. Not trying to discourage you from informing yourself & trying to make your home safer, but doing an IR test on only the Live to CPC conductors may give you a very misleading impression on the state of your installation. I applaud you for taking an interest, but i can`t quite see what you`re hoping to achieve by your method.
Have you specific doubt regarding the CPC IR? If so, spit it out - we`re here to help.

 

[TimW]

First, thanks to all for your contributions!

Al, the full story is this: I decided to have my home tested recently. We're about to do some renovations and I figured that if the there are any electrical problems, now is the time to pull the house apart, rather than afterwards.

The tester reported that there was "low insulation resistance" and that further work would be needed to determine which circuit(s) were responsible. I have been given a provisional quote for this and for repairing the circuits that have a problem.

However, it is a complicated period house in which that all mannerof electrical additions have been made over the years. I'm guessing that the work could take quite a bit longer than the tester has allowed for in his provisional quote, so I figured that I could save myself some money by doing some of the investigations myself.

Ideaaly, when the tester ret.urns, we will have a much clearer idea of where the problems lie.

So I've purchased a s/h Fluke 1503 and educated myself as much as I can on the procedures of IR testing.

I have noticed from posts on this forum and elsewhere that one method is to join the L's and N's of a circuit together and test to earth. It seemed to me that this would save time by not having to remove all my light bulbs, dimmers, neons etc etc. Hence my post!

The other factor here is that the Fluke 1503 does not have a 250V setting, so everything will have to be at 500V.

So there you are Al, you asked me to 'spit it out'. There it is!

Tim

 

[mrloy99]

I need to do a quick check of the insulation resistance of my home wiring.

Am I right in thinking that if I carry out my tests on each circuit using L+N joined together, and earth, I do not need to disconnect any items such as dimmers, neons, lights etc?

Yes..but you might also wish to get the condition checked with respect to insulation breakdown occuring
between live and neutral,which WILL require the disconnection of current useing equipment.Its your house thats getting renovated and now is the time to check for potentially looming problems that might give you grief later.

 

[steamboatwilly]

Simply put YES, connecting L-N and testing to Earth is ok but only for periodic testing. If it is a new installation then an initial verification is required!

Folks, FYI....

Added some sockets to an existing RFC last week, Minor Works Cert.....got a very low reading on L-N Insulation Resistance. Empty house (client at work). Figured it was a hidden socket or spur somewhere on the RFC but called the NICEIC Helpline to check the exact process. They advised connecting L/N and testing to earth which tested OK and said to add comments to the Limitations section.

So, I guess L-N, N-C, C-L for new circuit but LN-C OK as a last resort for additions or PIRs?