I have heard in general, airgap measurements should be within 10% of the average for 2-pole machines and 20% for slower machines.

Does anyone have a reference for this?

(I have found some references that apply 10% to all machines but can't find the one that allows 20% for slower machines)>

Hey Pete just did a quick search and found this on the web hope it helps http://www.findarticles.com look in hear for an article on air gap and how it is arrived at

Pete,
I don't have any documentation on it but have always heard 10% on everything. I will check with our test guy next week and see if he has anything on it.

Ronnie

Pete,
I went to the website Lee posted and did a search and came up with this site http://www.findarticles.com/p/articles/mi_qa3726/is_200509/ai_n15349943/pg_2

It is a good article but specifically paragraph twelve of page two states + or - 10% average air gap.

Hope that helps,
Ronnie

Pete:

The EASA published standards, as well as several other industry standards, including the NEMA MG-1, show the 20% max. Personally, I would shoot for the 10%, it is not un-doable, and can be included in your own spec to a repair shop.

I am traveling, but will be happy to post a reference when I return next week.

Howard

Thanks. I have been unable to find anything about 20% in NEMA MG1 or EASA AR100.

I agree 10% should be achievable. We have a unique situation of motor already being reassembled, will be run in the near future (no uncoupled run yet) and I am asked to evaluate whether the airgap readings (somewhere around 13% deviation from average) should be accepted. It seems to me if 10% is acceptable for 2-pole than 13% should be no problem for a 4-pole. I just wish I had some solid backup (reference) to prove it.

Pete:

Part 14 of the attached medium voltage repair specification. I had developed this for customers of the repair shop I worked for in the early 1990's.

I will let you know if I find other references.

Howard

Form_Wound_Repair_Specification.pdf (165 Kb, 41 downloads)

Thanks Doc. Looks like a good spec. Also another reference for 10%.

14.2 - "No feeler gauge reading shall deviate from the average of all readings at that end of the motor by more than 10% of the average. If the deviation is greater, the cause shall be determined and corrected."