sizing a three phase breaker for a single phase transformer
sizing a three phase breaker for a single phase transformer
(OP)
I have a single phase 10kVA transformer that is fed from two phases of a 480V 3 phase supply. If I want to protect the transformer with a 3 phase circuit breaker, how should I size it? The full load amps of the single phase 10kVA transformer is 20. So do I use 20A as my basis for choosing the 3 phase circuit breaker? Or do I size the 3 phase circuit breaker as if it were feeding a balanced load of 30kVA (10kVA on each phase)?






RE: sizing a three phase breaker for a single phase transformer
RE: sizing a three phase breaker for a single phase transformer
RE: sizing a three phase breaker for a single phase transformer
xnuke
"Live and act within the limit of your knowledge and keep expanding it to the limit of your life." Ayn Rand, Atlas Shrugged.
Please see FAQ731-376: Eng-Tips.com Forum Policies for tips on how to make the best use of Eng-Tips.
RE: sizing a three phase breaker for a single phase transformer
So you use the actual current that will be flowing through the poles of the breaker.
You can generally use only one or two poles of a 3-pole breaker - this is fairly common. In the US, the UL listing for the breaker must indicate suitability for this use. Simplest thing is to check with the breaker manufacturer and get a copy of the instruction sheet for the breaker being considered. It should be covered there.
David Castor
www.cvoes.com
RE: sizing a three phase breaker for a single phase transformer
Keith Cress
kcress - http://www.flaminsystems.com
RE: sizing a three phase breaker for a single phase transformer
Rafiq Bulsara
http://www.srengineersct.com
RE: sizing a three phase breaker for a single phase transformer
RE: sizing a three phase breaker for a single phase transformer
Rafiq Bulsara
http://www.srengineersct.com
RE: sizing a three phase breaker for a single phase transformer
If you are not in North America however, the safest bet is to wire 2 poles in series or just do it so as to not have to think about it.
"If I had eight hours to chop down a tree, I'd spend six sharpening my axe." -- Abraham Lincoln
For the best use of Eng-Tips, please click here -> FAQ731-376: Eng-Tips.com Forum Policies