How To check a motor to ground
How To check a motor to ground
(OP)
I am new to building engineering and we have a motor on our air handler 3 phase 15 horse motor and we need to check it for ground how do i do that. thanks for the help.
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How To check a motor to ground
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RE: How To check a motor to ground
Gunnar Englund
www.gke.org
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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...
RE: How To check a motor to ground
Insulation resistance to Ground: Tie together making electric connection between all motor terminals. Connect a"Megger Tester" hot terminal to the common connection and the return to the motor frame. Aply 500 Volts DC test and allow for 1 minute, record the megohm reading and the winding temperature. For accurete evaluation you could refer the insulation resistance to 40 °C. Check IEEE Std 43.
RE: How To check a motor to ground
RE: How To check a motor to ground
IEEE Std43-2000 part 5.3 Table 1 states the guidelines for DC voltages to be applied during insulation resistance test.
Winding Rated Voltage Voltage Test
<1000 500
1000-2500 500-1000
2501-5000 1000-2500
5001-12000 2500-5000
>12000 5000-10000
I prefer to follow a recognized standard rather than popular rules of thumb.
RE: How To check a motor to ground
RE: How To check a motor to ground
And since you mention EASA, EASA AR100 (specification for rewind/repair) section 4 also specifies 500vdc.
1000 vdc on a 460vac motor would be considered a hi-pot in my book. Most likely would pass... but I'd hate to be the test guy that failed a motor applying more than standards specify, when owner of the motor simply asked to check for ground... didn't ask for hi-pot.
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RE: How To check a motor to ground
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RE: How To check a motor to ground
For lv motors (< 600 V) rewound at my shop, I use 1 KV megger.
*Why a man thinks he outrun a chasing dog when it has twice as many legs?*
RE: How To check a motor to ground
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Sometimes I only open my mouth to swap feet...
RE: How To check a motor to ground
Scotty - I hadn't heard of the higher phase-to-phase test voltage.. But since the subject is checking for grounds... 500vdc matches the IEEE43.
To go back to the beginning of my comment. The subject here is insulation resistance check ("checking for grounds").
There are opinions and there are standards. As a tester, if you go above the standard or specification test voltage when a hi-pot was not requested, and the motor fails, you are not in a good position. You might say that in your opinion the the motor was bad anyway, but you don't have a standard to fall back on. Why would anyone put themselves in that position intentionally?
dickdv said he was speaking for thousands of EASA repair shops. In fact the document I cited is an EASA document:
http://www.easa.com/indus/ar100-2001.pdf
4.2.2 - Insulation Resistance Test
Winding rated < 1000 v => Insulation Resistance test voltage 500 vdc
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RE: How To check a motor to ground
I did mention that I "upgrade to applicable higher voltage" which depends on the motor/generator voltage. So, if it is a LV machine with someone else's winding (that has come in for a overahul and check), I would keep it at 500 V.
(In any case I wouldn't call a 1000 V megger test on a LV AC machine as a hipot. If the winding fails at 1 KV DC, it is unfit for service anyway. That is why I do 1 KV megger test before and after a 2 KV AC hipot and 2 KV surge on the machines rewound in my shop. For overhauled LV machines, I use 1.5 KV AC and 1.5 HV surge. If they fail these tests, then it is better that they fail in my shop than during service )
BTW, I do not know whether our replies satisfy reefbum11's requirement.
*Why a man thinks he outrun a chasing dog when it has twice as many legs?*
RE: How To check a motor to ground
As usual, the guys that actually do the work often have to add a little judgement to what they do for their customers.
RE: How To check a motor to ground
I've just got back into working with motors, after spending to much time in digital world.
I need to check out motors periodically, and have been doing the following:
1) Check winding continuity
2) Check winding continuity to ground. Redundant but easy, if I'm going to Megger the motor
3) Check winding w/ insulation tester. I've got access to a Fluke 1587.
Proceedurally with a 3phase motor, can I test the motor leads seperately or should I gang them?
Should I expect different results for Delta and Y motors based testing?
Thanks in advance.
RE: How To check a motor to ground
I am with aolalde and EP, you should follow a recognized standard.
RE: How To check a motor to ground
Listed below that statement, IEEE. So I wonder if that book references the IEEE 43?