There is a lot of different opinion on how to determine the size for an overcurrent device(3P) for load that is not ballanced. Ex., I need to feed two FTU'S from one breaker, lets say the load for the first one is 7kw/.33hp/208v/4w (phase A=3160, phase B &C=2333), the second load lets assume is the same. Do we determine the overcurrent size base on total VA of 15652va(2*3160+4*2333) or 18960va(6*3160). My understanding we have to do it for the worst case which is phase A, which I'm not sure how would determine the amperage for phase A in our example. Your thought is realy appreciated. Thank you.
overcurrent size!!!
- Thread starter sam34
- Start date
- Status
bphgravity
Senior Member
- Location
- Florida
Re: overcurrent size!!!
You need conductors sized large enough to carry the maximum continuous load. You then need to protect those conductors with appropriate overcurrent protection.
You need conductors sized large enough to carry the maximum continuous load. You then need to protect those conductors with appropriate overcurrent protection.
Re: overcurrent size!!!
Lawrence Lile, P.E.
Project Solutions Engineering
{Moderator's Note: Edited to remove personal contact information. If you wish to contact this person, please send a Private Message.}
[ June 09, 2005, 09:48 AM: Message edited by: charlie b ]
Your wire will need to carry the load, the largest wire would need to carry 2*3160 VA. Most people would size all three wires the same, and you can argue this point forever. The breaker, since it is a 3 phase breaker, would need to have all 3 poles identical, able to handle this current. So you could think of this as 18960VA for the purposes of sizing the breaker and wire. The various phases won't actually see that much current, however.
Lawrence Lile, P.E.
Project Solutions Engineering
{Moderator's Note: Edited to remove personal contact information. If you wish to contact this person, please send a Private Message.}
[ June 09, 2005, 09:48 AM: Message edited by: charlie b ]
- Status