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#89645 10/12/04 04:32 PM
Joined: Feb 2004
Posts: 494
M
Member
Is it not required to limit the load on a 15A breaker? I have a 11A load on a Condensing Unit that is being fed by a 15A brkr...I am thinking this is too small.

Any replies will be greatly appreciated.

regards

mustang

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#89646 10/12/04 04:37 PM
Joined: Jan 2003
Posts: 4,391
I
Moderator
A 15 amp breaker is allowed to be loaded 100% up to 3 hours, longer than 3 hours the load may only be 80% which is 12 amps.

11 amps on a 15 amp breaker is fine.

However you said this is a condensing unit, the label should say what size overcurrent protection to use.



[This message has been edited by iwire (edited 10-12-2004).]


Bob Badger
Construction & Maintenance Electrician
Massachusetts
#89647 10/15/04 07:42 PM
Joined: Feb 2001
Posts: 308
S
Member
The breaker for a condenser is only short-circuit protection which can be 175% of the rated load current or branch circuit selection current, whichever is greater. If that's not enough to allow the compressor to start then you can go up to 225%. 11x1.75=19.25 an 11X2.25=24.75.

#89648 10/16/04 01:28 PM
Joined: Aug 2003
Posts: 1,374
R
Moderator
Steve: I agree with Bob on this. I typically just apply
Quote
440.22(C) Protective Device Rating Not to Exceed the Manufacturer’s Values. Where maximum protective device ratings shown on a manufacturer’s overload relay table for use with a motor controller are less than the rating or setting selected in accordance with 440.22(A) and (B), the protective device rating shall not exceed the manufacturer’s values marked on the equipment.

Not that the math is that difficult, but in my opinion, why go through it?


Ryan Jackson,
Salt Lake City
#89649 10/16/04 01:37 PM
Joined: Jan 2003
Posts: 4,391
I
Moderator
You can not "do the math" you must use the Manufacturer’s Values.

Anything higher than that and you have tossed out the UL listing. [Linked Image]


Bob Badger
Construction & Maintenance Electrician
Massachusetts
#89650 10/16/04 01:52 PM
Joined: Aug 2003
Posts: 1,374
R
Moderator
That too [Linked Image]


Ryan Jackson,
Salt Lake City
#89651 10/16/04 05:04 PM
Joined: Feb 2004
Posts: 62
S
Member
#14 awg wire ok?

#89652 10/17/04 01:11 PM
Joined: Aug 2003
Posts: 1,374
R
Moderator
Absolutley #14 is OK. If the load is 11 amps, all you need is a conductor that satisfies the load. You can then put on the highest fuse or breaker allowed by the manufacturer and still be OK. For example, if the load was 11 amps and the nameplate says maximum OCPD is 40 amps, you may install a 40 amp breaker and run #14 for the circuit.

See 240.4(D) which points you to 240.4(G), then go to part IIIof article 440 for A/C units.

Quote
III. Branch-Circuit Short-Circuit and Ground-Fault Protection
440.21 General.
The provisions of Part III specify devices intended to protect the branch-circuit conductors, control apparatus, and motors in circuits supplying hermetic refrigerant motor-compressors against overcurrent due to short circuits and grounds. They are in addition to or amendatory of the provisions of Article 240.


Ryan Jackson,
Salt Lake City

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