ECN Forum Forums Code Related Discussion NEC & other Code issues NEC Article 430

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.

ongmark,
do you actually have a 'B'motor?

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

Yes

ongmark,

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.

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.
http://www.bussmann.com/library/docs/Spd.pdf http://www.bussmann.com/apen/pubs/