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testing a motor prior to installation


NWDS

Question

Afternoon all, what two test should I carry out on a replacement motor ???. I have checked DOR and info on the plate all match the existing motor.

1 insulation resistance across L and N ( what range 500v dc/ 250v dc ) ?????

2 continuity of CPC to motor housing ???.

Can some one please advise.

Regards and thanks NWDS

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14 answers to this question

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matt.leung

IR test - bridge over the motor controls..

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Evans Electric

For a 3 Ph motor , megger each pole to earth then megger between ( 500v) then read the resistance between the windings , usually if they are all the same the motor is OK.

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Thanks Evans, its a single phase motor, I was going to do the IR test on the windings ( across brown and blue ), I was then going to test contiuity of the earth connection by testing between the cpc and chasis, I would test these prior to fitting the motor to prove the motor is not faulty, am I on the right track.

NWDS

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Hi,

Before installation test winding resistance, then full IR live/Neutral Live/Earth Neutral/Live. then after installation test back to panel and fully test control and feed circuits, I know this sounds a bit long winded but you could fit a perfectly good motor and find that the control/feed circuit has been played with when the motor failed and someone whilst fault finding has put a wire back incorrectly and motor casing is live. then the big finger of blame gets pointed in your direction, better to spend an extra 30-40mins testing and be sure the motor and circuit is sound.

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Hi,

Before installation test winding resistance, then full IR live/Neutral Live/Earth Neutral/Live. then after installation test back to panel and fully test control and feed circuits, I know this sounds a bit long winded but you could fit a perfectly good motor and find that the control/feed circuit has been played with when the motor failed and someone whilst fault finding has put a wire back incorrectly and motor casing is live. then the big finger of blame gets pointed in your direction, better to spend an extra 30-40mins testing and be sure the motor and circuit is sound.

Sorry to revive an old thread but is this a continuity reading in ohms and what would this normally be for a healthy motor roughly.

Thanks

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mojorebel

single phase motor - would most likley be a spil phase - with a run and start winding- these have to be tested to earth and across winding- on a single phase the windingds will give a different reading (not balanced) should be a difference of about 20%

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seajayess

Why would you insulation resistance test between l/N these are connected together through the windings of the motor it should come back as a short circuit! I would take a continuity reading to make sure there was some form of coil of wire and on a 3 phase would make sure the readings were all about the same. You can do an insulation resistance test on a 3 phase motor between the windings but first you must remove the links that join them either in star or delta connection, You can def do a insulation test between L/E N/E CJS

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Mr Sworld
Phase rotation.

Be careful that it doesn't run backwards.

It's a single phase motor so hence no phase rotation!

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Andy™
Why would you insulation resistance test between l/N these are connected together through the windings of the motor it should come back as a short circuit!

er... if its 3 phase, you will have 3 seperate windings, each isolated from each other (until they are linked either star or delta when installed)

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seajayess
er... if its 3 phase, you will have 3 seperate windings, each isolated from each other (until they are linked either star or delta when installed)

If you read my whole post you will see that I state this CJS

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