Several motors or loads on one branch circuit NEC430.53
Several motors or loads on one branch circuit NEC430.53
(OP)
I am looking for some help.
For HVAC unit I have three Copeland compressors units, which are connected (piped) in tandem. Each compressor rated three phase 460V, 60Hz,load current is 18.6 amp. Each compressor will operate from its own contactor rated for 34 amp equipped with electronic overload relay adjustable range 15-45.
Am I allowed by NEC have only one branch circuit protection circuit breaker for all three compressors? If yes, how to size it? I was reading NEC paragraph 430.53,and got lost.
Thank you,
PaulBr.
For HVAC unit I have three Copeland compressors units, which are connected (piped) in tandem. Each compressor rated three phase 460V, 60Hz,load current is 18.6 amp. Each compressor will operate from its own contactor rated for 34 amp equipped with electronic overload relay adjustable range 15-45.
Am I allowed by NEC have only one branch circuit protection circuit breaker for all three compressors? If yes, how to size it? I was reading NEC paragraph 430.53,and got lost.
Thank you,
PaulBr.





RE: Several motors or loads on one branch circuit NEC430.53
Bill
--------------------
"Why not the best?"
Jimmy Carter
RE: Several motors or loads on one branch circuit NEC430.53
Condenser fans are separate load and on separate branch circuit.
Paulbr
RE: Several motors or loads on one branch circuit NEC430.53
If not, NEC does permit multiple motors on a circuit. Basic rule for the conductors is sum of FLA of all motors plus 25%.
The breaker size typically would be rated for 250% of FLA of the largest motor [i]plus[/1] sum of FLA of the rest of the motors.
Rafiq Bulsara
http://www.srengineersct.com
RE: Several motors or loads on one branch circuit NEC430.53
rbulsara, can you point to paragraph in NEC which is saying:
"The breaker size typically would be rated for 250% of FLA of the largest motor [i]plus[/1] sum of FLA of the rest of the motors. "
Thank you.
Paulbr.
RE: Several motors or loads on one branch circuit NEC430.53
A normal control scheme would let a failed compressor trip off and the system would continue to function on the remaining units.
If you are pushing a penny pinching design out the door and to the end user the consequences, one breaker is fine.
If you are building a quality machine you may want to reconsider the one breaker choice.
An interesting exercise may be to write up a step by step trouble shooting chart with one breaker and again with three breakers.
Bill
--------------------
"Why not the best?"
Jimmy Carter
RE: Several motors or loads on one branch circuit NEC430.53
In NEC 430 there are separate articles for motor circuit conductors, overload protection and short circuit protection.
Each of them has a sub-article on "Several motors" and also "Multiple motor equipment". The breaker would be in the short circuit part.
Please read each one of them. I know they are there, I would leave up to you to browse through the narrow part of the book for a thorough understanding. You still need individual overload protection.
Rafiq Bulsara
http://www.srengineersct.com