motor branch circuts
- Thread starter newell
- Start date
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Ed MacLaren
Senior Member
Re: motor branch circuts
newell,
Didn't you mean maximum fuse?
Ed
newell,
Didn't you mean maximum fuse?
Ed
pierre
Senior Member
- Location
- Westchester County, New York
Re: motor branch circuts
100 amp fuse, section 430.150, 430.52 table, 430.52(C)exception 1 - 240.6
Pierre
[ January 21, 2004, 07:12 AM: Message edited by: pierre ]
100 amp fuse, section 430.150, 430.52 table, 430.52(C)exception 1 - 240.6
Pierre
[ January 21, 2004, 07:12 AM: Message edited by: pierre ]
- Location
- Illinois
- Occupation
- retired electrician
Re: motor branch circuts
The code only sets the maximum size permitted. The minimum size would be the smallest size that permits the motor to start. In this case I would expect that a 60 amp fuse would be the minimum.
Don
The code only sets the maximum size permitted. The minimum size would be the smallest size that permits the motor to start. In this case I would expect that a 60 amp fuse would be the minimum.
Don
G
Guest
Guest
Re: motor branch circuts
Don I think you would waste a fuse trying to start a 52 amp motor load. Even if unloaded my experiece tells me that a fuse of at least 2.5 times nameplate (NON-DELAY) is needed. A time delay of 60 probably wouldnt work either. Just my opinion but I ran an electric motor shop for 17 years and saw many attempts at skimping on wire size and blown up undersized switchgear and too small a starter etc.
Don I think you would waste a fuse trying to start a 52 amp motor load. Even if unloaded my experiece tells me that a fuse of at least 2.5 times nameplate (NON-DELAY) is needed. A time delay of 60 probably wouldnt work either. Just my opinion but I ran an electric motor shop for 17 years and saw many attempts at skimping on wire size and blown up undersized switchgear and too small a starter etc.
- Location
- Illinois
- Occupation
- retired electrician
Re: motor branch circuts
Joe,
Actually my fuse size of 60 amps is based on information from Buss fuse motor protection "slip-stick". They show the use of a 60 amp dual element fuse to provide both the branch circuit and motor overload protection for a 40 hp 3 phase 480 volt motor.
Don
Joe,
Actually my fuse size of 60 amps is based on information from Buss fuse motor protection "slip-stick". They show the use of a 60 amp dual element fuse to provide both the branch circuit and motor overload protection for a 40 hp 3 phase 480 volt motor.
Don
luke warmwater
Senior Member
Re: motor branch circuts
Don,
My SQ D motor calc. slide rule shows for a 460v. 3phase, 40 H.P. motor (non Design E, 60hz., 1800rpm, squirrel cage) a 80amp dual element time delay fuse or a 90amp breaker.
SQ D shows the 60amp fuse for the same motor at 575v.(600 system).
What a difference.
Todd
Don,
My SQ D motor calc. slide rule shows for a 460v. 3phase, 40 H.P. motor (non Design E, 60hz., 1800rpm, squirrel cage) a 80amp dual element time delay fuse or a 90amp breaker.
SQ D shows the 60amp fuse for the same motor at 575v.(600 system).
What a difference.
Todd
- Location
- Illinois
- Occupation
- retired electrician
Re: motor branch circuts
Luke,
Is that for the branch circuit short circuit and ground fault protection? The Buss calculator shows the same for that purpose. The 60 amp fuse is shown where the fuse is providing both the branch circuit and the motor overload protection.
Don
Luke,
Is that for the branch circuit short circuit and ground fault protection? The Buss calculator shows the same for that purpose. The 60 amp fuse is shown where the fuse is providing both the branch circuit and the motor overload protection.
Don
luke warmwater
Senior Member
Re: motor branch circuts
Don,
Actually, no. The Sq D chart is not for the dual listing.
So, I checked my Littlefuse chart and it shows the same info as your Bussman (with fuse reducers of coarse).
Also, the 60amp listing is for a motor with a service factor of <1.15 according to Littlefuse.
With a SF of >1.15, they list a 70amp.
Todd
Don,
Actually, no. The Sq D chart is not for the dual listing.
So, I checked my Littlefuse chart and it shows the same info as your Bussman (with fuse reducers of coarse).
Also, the 60amp listing is for a motor with a service factor of <1.15 according to Littlefuse.
With a SF of >1.15, they list a 70amp.
Todd
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