insulation testing

[spanner51]

when I do an insulation test I use my Megger MIT200 on the 500v setting. It has a red lead and a black lead, so I assume the red lead is live, and the black is neutral, at DC current

SO
When I test a machine from the plug between the earth and the current carrying pins, does it matter which way round the leads go?

Thanks.

Graham

[stratfordgirl]

Re: insulation testing

Makes no difference as far as I know. Mains votage alternates between positive and negative anyway.

[leavemetogetonwithit]

Re: insulation testing

From memory I think Martin’s PDF recommended attaching the red lead to the earth pin. This puzzled me a bit as my instinct was to put it the other way around. After thinking about it for a spell, I decided the reason must be to minimise the possibility of damage to electronics due to accidental connection of clip to one current pin only. With the DC going the other way (in via the earth pin) it would only reach the live/neutral parts via any earth leakage. Hope that makes sense.
Mike.

[squadman]

Re: insulation testing

where can I find Martins PDF that you refer to on this subject ?

[Phidom]

Re: insulation testing

I wonder how it’s done in a PAT tester? My megger is faulty so I tend to do insulation tests using the PAT tester. The worry with that is that I have to carry a cable with a 13 amp plug one end and individual spades for connecting to elements, motors etc. If my back was turned, a small child could pick up said cable and plug it into an ordinary socket :zap:

[Martin]

Re: insulation testing

leavemetogetonwithit wrote:From memory I think Martin’s PDF recommended attaching the red lead to the earth pin.

Not really Mike, red or black lead, makes no never mind either way!

squadman wrote:where can I find Martins PDF that you refer to on this subject ?

Just click HERE 😀

[spanner51]

Re: insulation testing

Thanks for the replies

The reason I posted the question is that I went to a Hotpoint washer dryer and the dryer element was down to earth. But when I connected my megger one way the meter bleeped, as if there was a voltage present, when connected the other way it behaved as normal.

[Martin]

Re: insulation testing

spanner51 wrote:But when I connected my megger one way the meter bleeped, as if there was a voltage present, when connected the other way it behaved as normal.

Errrr eh, run that by us again? 😕

Assuming of course that the dryer element terminals were fully isolated, then what happened???

[spanner51]

Re: insulation testing

Machine unplugged. Dryer element disconnected. When I first connected my megger, 1 lead to earth and the other to one of the element terminals, my meter was bleeping (as it should if a voltage is present) and the display showed Vr.

When I reversed the meter leads, it was normal. This has happened a couple of times this year

I was puzzled as well

Graham

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