george (dicegeorge) wrote:
Andy Dingley wrote:

Use a high voltage resistance meter to check this, not just an average
multimeter. Don't complete electrical installation work without one.
If you don't have one, eBay's your friend.


I want one...
like this one?

http://cgi.ebay.co.uk/Digital-Insula...71410002r29602


Item number: 360165628074

Digital Insulation Meter Volt Resistance Tester 1000V £50.90

[g]


Yes, like that, but if you're going to buy one, you should consider
getting one that is compliant with the wiring regulations (introduced in
the 16th Edition). This requires (among other things) that the short
circuit current is a nominal/minimum of 1mA. You will note that all
major branded product will either state "16th/17th edition compliant" in
the general features or state this explicitly in the specification:

e.g. from Megger website:

"Test Current on Load = 1 mA at min. pass values of insulation (as
specified in BS7671, HD 384 and IEC 364)."

The unbranded Chinese model you have seen does not explicitly state
this, which *may* mean that the 500V generator circuit is not capable of
delivering a nominal 1mA into a short circuit, which may in turn mean
that under certain circumstances it's readings may not be trustworthy.