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Old January 3rd, 2018, 05:07 PM   #7
jraef
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Join Date: May 2006
Location: Northern California
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There is a very good explanation of this issue in a White paper issued by (the old pre-ABB) Baldor written by Edward Cowern, a staff PE there. The collection of his works are called "the Cowern papers" and are considered the "gold standard" for describing what motor mfrs do to address issues like this. Here is an on-line copy:
http://www.baldor.com/Shared/manuals/pr2525.pdf

On page 60 of that pdf, he discusses the issue of applying 208V to 230V motors and what most motor mfrs do to accommodate this.

He addresses Service factor in several places and confirms that SF is an increase in HP, not necessarily FLA (although that would likely follow), but the one most relevant to this discussion is on page 14. As I interpret this (and I think most motor suppliers would agree), if the motor is actually showing 208-230/460V on the nameplate, and says a HP value with a 1.15SF, you can operate it into the SF at 208V just as the nameplate implies. But... expect a less than maximum lifespan out of that motor.

I always council end users to not use SF, it is the "fudge factor" you want in order to ensure uninterrupted production. Any money you save on an under rated / over stressed motor goes right out the window the very first time you get unexpected down time.

The only people who regularly use SF are OEMs who want to avoid the cost of a larger motor, knowing that the smaller one run into its SF will out last the warranty, which is all they care about. That decision by the way is at the EXPENSE of that future unexpected down time suffered by the end user.
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