IR Testing DOL Motor

[Mark213]

When testing a DOL motor is the best method to disconnect the cables from MCB to DOL and connector block them.
Then disconnect cables from DOL to Motor and connector block them and then IR both set of cables.

Or would switching the isolator off and test from MCB to DOL then DOL to Motor without disconnecting any cables.

N.B motor will not be connected.

Thanks

 

[brianmoooore]

No problem with testing all together if it all passes. It's when you get a low IR you have to start disconnecting things. I would test at the in and out terminals of the contactor.

 

[Mark213]

Its for the AM2 exam.

Yeah so your saying if the whole circuit was IR tested including the DOL and the reading was good it would be acceptable ?

I think I will split into two for exam I am just trying to find out if it was the best method

 

[Lucien Nunes]

It's always preferable to test with all connections completed and equipment in situ if possible. Otherwise, new faults could be created when reconnecting after the test that would then be missed. Any deterioration in the insulation of the switchgear would also be missed, which in some cases is more important than the insulation of the cables. The exception is where electronic equipment is involved that cannot be subjected to the IR test or would spoil the test results, e.g. due to built-in SPD. A basic electromechanical starter can be tested to the same voltage as the circuit so there is no need to disconnect it.

BTW FWIW IMO it's not a 'DOL.'
It's a starter, a DOL starter if you need to be specific, but in real life I would only call it a starter. Just as I would not call a star-delta starter a 'star-delta' or a soft-starter a 'soft.' People preparing for the AM2 often seem to call it a 'DOL.' IDKY, YMMV.

 

[ewandingwall]

When testing a DOL motor is the best method to disconnect the cables from MCB to DOL and connector block them.
Then disconnect cables from DOL to Motor and connector block them and then IR both set of cables.

Or would switching the isolator off and test from MCB to DOL then DOL to Motor without disconnecting any cables.

N.B motor will not be connected.

Thanks

The normal practice would be to IR test at the motor thermals. Make sure you remove the terminal links first before IR testing. You can either IR test from phase to ground or phase to phase to check winding insulation condition. A low reading below 1 M Ohm for a 440V motor would indicate either phase to ground fault or phase to phase depending on which IR test was carried out and what reading was measured on the IR tester.

The trouble will IR testing at the MCB is that if there is either a phase to phase or phase to ground fault on any motor winding, you won’t know where the fault is located, only that the motor has insulation issues. Then you would have to remove the links and carry out the tests until you found the fault.

The benefits to IR testing at the MCB is that if you get a high IR reading, it tells you that from the MCB cabling to the motor and the winding phase coils of the motor are both good. Therefore you don’t have to go to the motor locally, remove links and then connect everything back.

 

[Lucien Nunes]

The benefits to IR testing at the MCB is that if you get a high IR reading, it tells you that from the MCB cabling to the motor and the winding phase coils of the motor are both good. Therefore you don’t have to go to the motor locally, remove links and then connect everything back.

But if you are testing at the MCB the starter will be de-energised so the motor and its wiring will not be in the test circuit. A separate test is needed downstream of the starter.

 

[ewandingwall]

But if you are testing at the MCB the starter will be de-energised so the motor and its wiring will not be in the test circuit. A separate test is needed downstream of the starter.

Sorry I meant after the contractor not MCB

 

[James]

Sorry I meant after the contractor not MCB

IR testing contractors is not advisable, they could get really grumpy!!
got to watch that autocorrect ?

 

[David Prosser]

IR testing contractors is not advisable, they could get really grumpy!!
got to watch that autocorrect ?

I find sometimes IR testing contractors is the only way of getting them up and moving, especially on a Monday morning.

 

[Aaron b]

I find sometimes IR testing contractors is the only way of getting them up and moving, especially on a Monday morning.

What is the recommended setting? Just 50V for those born after 2000 perhaps.

 

[James]

Always 1kv, if a jobs worth doing, it’s worth doing properly ?