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Motors #98049
05/01/06 01:01 PM
05/01/06 01:01 PM
kyelectric  Offline OP
Joined: Aug 2005
Posts: 64
When installing a motor...Shouldn't you rate the fuses at 125% of FLA and the overloads should be set to run at FLA? Thanks

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Re: Motors #98050
05/01/06 02:20 PM
05/01/06 02:20 PM
gfretwell  Offline

Joined: Jul 2004
Posts: 9,186
Fuses have to handle LRA for a significant part of a second and higher than FLA for another second or so depending on load.
430.52 says you can use 300% of FLA for a single element fuse and 175% of FLA for a time delay fuse.

Greg Fretwell
Re: Motors #98051
05/01/06 05:14 PM
05/01/06 05:14 PM
Redsy  Offline
Joined: Mar 2001
Posts: 2,056
Bucks County PA
OL heater selection depends on Service Factor. See 430.32(A)(1)

[This message has been edited by Redsy (edited 05-01-2006).]

Re: Motors #98052
05/02/06 05:27 AM
05/02/06 05:27 AM
iwire  Offline
Joined: Jan 2003
Posts: 4,391
North Attleboro, MA USA
I agree with the other responses and will add that the OLs are based directly off the motors name plate rating.

The conductors, fuses or breakers are based on the HP and the info in Article 430 tables.

The conductors must be at least 125% of the table values

I do not recall an NEC minimum size for the fuses or breakers but common sense would say at least 125% and perhaps much higher for hard starting loads.

Bob Badger
Construction & Maintenance Electrician


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