Mininmum insulation resistance to earth

What is the minimum value of insulation resistance to earth for a three
phase induction motor.?
Reply to
Skeeter
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For testing quality of the insulation or how low can you go before breakdown ?
Reply to
Rheilly Phoull
0 Ohms.
sQuick..
Reply to
sQuick
As always in this newsgroup "It depends". I'd feel very nervous firing up a 13.8 kV motor with less than 50 megohms to ground on each phase, cold, after 10 minutes - but at other voltages, other criteria apply.
Bill
Reply to
Bill Shymanski
Thanks ,It was a general question really which i had been asked at an interview and felt that it was a "it depends "kinds of answer but wondered if there was a text book value which i should of given.I answered the question with 1meg ohm and the guy seemed happy but i have asked the question to others with varying values.
Reply to
Skeeter
Well, as others have said, "It Depends".
We used 1Mohm as the lower end for 'corrective action required' for 600V and lower. 10Mohm for 4160. I don't do anything higher than 4160 in the way of motors.
But a new one in good condition, I'd expect 50Mohms or higher. In the Navy we used to plot the readings in 'material history' for trending purposes. Any sudden drop meant we should go look things over and see what happened.
But some DC machinery, we would go as low as 50kohms. DC machinery is notorious for having low insulation resistance if they have the brush rigging ventilated with the same fan as the motor. Carbon dust gets into *everything* and is very hard to clean out.
daestrom
Reply to
daestrom

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