400HP Frame

[jbouverette]

We recently bought a 4160V 400HP motor. We specified hp, rpm's and frame number. Our system is not sensitive enough as to where small changes in slip and the like do NOT affect this particular system.

When we specified the three stats we assumed that they would be within a certain NEMA tolerance, the same as most of the smaller hp motors we buy. the shaft of the motor is direct coupled (yes, i know) to a fan and the coupler is sweat fit. when the motor came in the shaft was 6/1000 oversized. the manufacturer tells us NEMA has little to do with much less guarantees anything over 250 hp.

is this true? and if it is, is there a standard i should be looking at or should we just be more carefull on these specs.

thank you

 

[motorman]

NEMA protects the user from such manufacturing errors. I suggest that your supplier read it.

Reference:

Section I GENERAL STANDARDS APPLYING TO ALL MACHINES
Part 4—DIMENSIONS, TOLERANCES, AND MOUNTING
…

4.9 TOLERANCES ON SHAFT EXTENSION DIAMETERS AND KEYSEATS
4.9.1 Shaft Extension Diameter
The tolerances on shaft extension diameters shall be:
Tolerances, Inches
Shaft Diameter, Inches Plus Minus
0.1875 to 1.5000, incl. 0.000 0.0005
Over 1.5000 to 6.500, incl. 0.000 0.001

 

[jraef]

They are correct that NEMA frame sizes stop at what equates to 250HP for most types of motors. That just means that motors within these accepted frames will have common dimensions from one manufacturer to another. Beyond those sizes, you are on your own when it comes to minor differences between manufacturers.

That does not excuse sloppiness however, as shown above. They are being technically truthful with regards to fitting a particular industry standard dimension, but they are hiding behind that technicality to avoid responsibility for not meeting their own specified dimensions within a reasonable tolerance IMHO.

And by the way, NEMA does not "guarantee" anything, it is a voluntary standard developed by members for the purpose of allowing customers to expect certain things in the marketplace. What they are saying in that response is that they really don't care about you as a customer, so bug off! If it can be sent back without penalty, I would do it in a heartbeat, NEVER buy their products again and tell everyone I know who they are and how they treated you.

Eng-Tips: Help for your job, not for your homework Read faq731-376

 

[raisinbran]

You have to wonder that if the manufacturer is that "liberal" with his tolerances, what are his tolerances in more critical areas such as bearing and seal fits?
I agree that I would be reluctant to do future business unless this problem is remedied. If it is not, you will have problems with replacement motors fitting up properly.
Raisinbran

 

[jbouverette]

thank you all for your post

jraef, i was just repeating what i was told. i told my managment to go back on the company and try to shame them for the extra plant downtime and the sloppyness. i think it was a little too easy for the supplier to sidestep this.

i am responsible for specs on the electrical side only...the mechanical guys need a little help and i try...knowing a little about nema standards i told them what i knew.

your posts have reinforced what i suspected to be already true....thank you