Megohmeter measurements ?

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Danny89

Member
Location
Indian Land
What is a good guideline basis with using a megohmeter.

Example...

Above this # your good...
Below this # your insulation is compromise d.

Thanks in advance,
Danny

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Tony S

Senior Member
I don’t work to the NEC, BS7671 cites 1MΩ as minimum which I don’t agree with.

I worked to M&Q (Mines and Quarries) regulations where they give “the maximum leakage current is not to exceed 1/10,000th of the circuit FLC”. With older high current circuits you know the acceptable limits.
 

zog

Senior Member
Location
Charlotte, NC
What is a good guideline basis with using a megohmeter.

Example...

Above this # your good...
Below this # your insulation is compromise d.

Thanks in advance,
Danny

Sent from my Moto Z (2) using Tapatalk

All depends on what you are testing, there have been several good threads about this topic here if you use the search function.
 

sameguy

Senior Member
Location
New York
Occupation
Master Elec./JW retired
Per the others, we follow the procedure for the type of wire being tested. Spec. was spelled out.
 

Tony S

Senior Member
Once again it depends, a new circuit with just 1MΩ to earth/ground there is something wrong, an old circuit it may be acceptable.

A point many people get wrong is not allowing enough time for a circuit to charge, at first glance it reads low, wait a while the reading rises.
 

Besoeker

Senior Member
Location
UK
Once again it depends, a new circuit with just 1MΩ to earth/ground there is something wrong, an old circuit it may be acceptable.

A point many people get wrong is not allowing enough time for a circuit to charge, at first glance it reads low, wait a while the reading rises.
Yes. "Circumstances alter cases" as Just William said.

I was at a paper mill where the field on one of the DC motors was under 100 kohm. Not acceptable I thought. The mill engineer said it was OK and would come up once the field had been energised for a while. He was right. It did. Paper mills are very wet places.
 

MasterTheNEC

CEO and President of Electrical Code Academy, Inc.
Location
McKinney, Texas
Occupation
CEO
What is a good guideline basis with using a megohmeter.

Example...

Above this # your good...
Below this # your insulation is compromise d.

Thanks in advance,
Danny

Sent from my Moto Z (2) using Tapatalk
Contact the manufacturer of the wire or cable. They (we) always have specific recommendations and guidelines that can be provided for the customer. Always remember that in MEG testing, if everything is insulated and the raceways are nonmetallic (same for sheathing) then the chances of getting reliable readings are slim. Unless of course there is damage at mutual locations in the raceway or cable assembly. Good Luck.
 
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