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#81248 - 07/29/02 01:48 PM NEC Article 430
ongmark Offline
Junior Member

Registered: 07/29/02
Posts: 2
Loc: Salem, OR, USA
Minimum size branch circuit for (1) 15HP, 208v, 3phase, design letter "B", operating at 80% power factor.
I know the process, however the design letter and PF are throwing me?

Any help would be greatly appreciated.

2014 / 2011 NEC & Related Books and Study Guides
#81249 - 07/29/02 02:03 PM Re: NEC Article 430
sparky Offline

Registered: 10/18/00
Posts: 5545
do you actually have a 'B'motor?

[This message has been edited by sparky (edited 07-29-2002).]

#81250 - 07/29/02 03:02 PM Re: NEC Article 430
ongmark Offline
Junior Member

Registered: 07/29/02
Posts: 2
Loc: Salem, OR, USA

#81251 - 07/29/02 03:59 PM Re: NEC Article 430
3 Way Offline
Junior Member

Registered: 07/29/02
Posts: 6
Loc: TX

for one motor on the branch...
size branch circuit @ 125% of motor full load amps as listed in NEC 430.150.
15HP @ 208V 3ph ==> 46.2 amps
125% ==> 57.8 amps
select wire (after derations) for 57.8 amps

the design letter "B" is used for selecting overload protection
PF=80% is typical for induction motors but has no bearing on wire size. NEC table 430.150 has PF allowances "built-in" for induction motors.

hope this helps.

#81252 - 08/08/02 01:26 PM Re: NEC Article 430
Dan Neeser Offline

Registered: 03/12/02
Posts: 29
Loc: St. Louis, MO, USA
I think your question has been answered, but just an fyi.

A good reference tool that we provide is in the Bussmann SPD. See 84-99 for the Motor Circuit Table that shows the sizing required. The link for the SPD is below, below that is the link for other pubs and articles.


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