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#98049 - 05/01/06 10:01 AM Motors
kyelectric Offline
Member

Registered: 08/30/05
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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#98050 - 05/01/06 11:20 AM Re: Motors
gfretwell Offline

Member

Registered: 07/20/04
Posts: 9045
Loc: Estero,Fl,usa
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

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#98051 - 05/01/06 02:14 PM Re: Motors
Redsy Offline
Member

Registered: 03/28/01
Posts: 2138
Loc: 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).]

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#98052 - 05/02/06 02:27 AM Re: Motors
iwire Offline
Moderator

Registered: 01/05/03
Posts: 4343
Loc: 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
Massachusetts

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