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05-25-2012, 03:44 PM
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#16
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It was a dark and stormy
Join Date: Jul 2008
Location: NW of D.C.
Posts: 5,954
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220v in garage help.
Quote:
Originally Posted by Missouri Bound
Oddly enough, you can maintain the 12 ga. with a 30 amp breaker in this instance. The NEC has allowances / specifications for this type of situation....and this type only.
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While we're on the subject,
if this is true,
why does the NEC force us to buy #12 AWG worth of copper for "only" 20A?
You have a code cite for this 30A case?
TIA.
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05-25-2012, 04:35 PM
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#17
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Licensed electrician
Join Date: Sep 2007
Location: Maryland
Posts: 6,007
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220v in garage help.
Conductor sizing for motors is different than for general purpose branch circuits.
The breaker is sized to allow the startup current while the conductor is sized for the run current.
__________________
Answers based on the National Electrical Code. Local amendments may apply. Check with your local building officials.
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05-26-2012, 08:17 AM
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#18
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It was a dark and stormy
Join Date: Jul 2008
Location: NW of D.C.
Posts: 5,954
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220v in garage help.
Does anyone agree with this?
A 30A breaker on #12 does not seem to adequately protect the wire if other applications call for a 20A breaker.
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05-26-2012, 09:51 AM
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#19
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A "Handy Husband"
Join Date: Feb 2007
Location: South Carolina Low Country
Posts: 2,940
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220v in garage help.
Quote:
Originally Posted by Yoyizit
Does anyone agree with this?
A 30A breaker on #12 does not seem to adequately protect the wire if other applications call for a 20A breaker.
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Yes I agree with Jim Port.
here is a good reference from another poster (Electures)
Sizing Motor Branch Circuit Conductors and OCPD's
__________________
Location:
Coastal South Carolina
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05-26-2012, 11:50 AM
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#20
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E2 Electrician
Join Date: Apr 2012
Location: Litchfield, CT
Posts: 3,098
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220v in garage help.
Quote:
Originally Posted by Yoyizit
Does anyone agree with this?
A 30A breaker on #12 does not seem to adequately protect the wire if other applications call for a 20A breaker.
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Because, the breaker is only providing ground fault and short circuit protection, the motor contains the overload protection... and you can only do this when the motor is hard wired, not cord and plug connected.
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05-26-2012, 11:54 AM
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#21
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Licensed Electrician
Join Date: Mar 2012
Location: SE Wisconsin
Posts: 3,228
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220v in garage help.
Quote:
Originally Posted by stickboy1375
Because, the breaker is only providing ground fault and short circuit protection, the motor contains the overload protection... and you can only do this when the motor is hard wired, not cord and plug connected.
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I see no indication of internal overload protection.
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05-26-2012, 12:07 PM
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#22
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E2 Electrician
Join Date: Apr 2012
Location: Litchfield, CT
Posts: 3,098
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220v in garage help.
Quote:
Originally Posted by k_buz
I see no indication of internal overload protection.
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Only a picture of the actual nameplate on the motor would tell us that...
But Im betting it's already in place. With that said, most compressors that are bought are inflated with an unrealistic HP rating.... as a sales gimmick.
Last edited by stickboy1375; 05-26-2012 at 12:19 PM.
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05-26-2012, 12:32 PM
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#23
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Licensed Electrician
Join Date: Mar 2012
Location: SE Wisconsin
Posts: 3,228
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220v in garage help.
Quote:
Originally Posted by stickboy1375
Only a picture of the actual nameplate on the motor would tell us that...
But Im betting it's already in place. With that said, most compressors that are bought are inflated with an unrealistic HP rating.... as a sales gimmick.
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I wholeheartedly agree that if there is internal overload protection (protection at 25A or less) it would be compliant to run 12's on a 30A breaker. BUT, I would not tell someone to put 12's on a 30 without proof there actually is protection built into the motor.
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05-26-2012, 02:08 PM
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#24
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It was a dark and stormy
Join Date: Jul 2008
Location: NW of D.C.
Posts: 5,954
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220v in garage help.
Quote:
Originally Posted by rjniles
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Thanks for the link. 
I'll have to chew on this rule for a while.
Quote:
Originally Posted by stickboy1375
Because, the breaker is only providing ground fault and short circuit protection
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I was under the impression that to give long life to wire insulation and to prevent igniting nearby combustible materials, breakers provided protection for all levels of overload, bolted shorts and otherwise. Is this incorrect?
Maybe mild overloads (2x rated current, 3x rated current) are so infrequent compared to dead shorts that the NEC doesn't worry about this?
Last edited by Yoyizit; 05-26-2012 at 02:13 PM.
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05-26-2012, 03:10 PM
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#25
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E2 Electrician
Join Date: Apr 2012
Location: Litchfield, CT
Posts: 3,098
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220v in garage help.
Quote:
Originally Posted by Yoyizit
Thanks for the link.
I'll have to chew on this rule for a while.
I was under the impression that to give long life to wire insulation and to prevent igniting nearby combustible materials, breakers provided protection for all levels of overload, bolted shorts and otherwise. Is this incorrect? |
In certain applications, yes, you are incorrect. 
For motors, Breakers only supply ground fault and short circuit protection.... generally, anything over 10 HP will have external overload protection, but anything smaller will generally have overload protection built into the motor.... So, as long we follow article 430 in the NEC, everything is okay.
Another great pic....
Last edited by stickboy1375; 05-26-2012 at 03:22 PM.
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The Following User Says Thank You to stickboy1375 For This Useful Post:
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06-05-2012, 04:45 PM
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#26
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Newbie
Join Date: May 2012
Posts: 13
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220v in garage help.
haven't done anything yet.... but i figure i would ask.
Can i "borrow" some 220 from the AC? would that be easier? it is right next to my garage and we never use the AC (compressor will also be used a handful of times) would that work?
or would a "rv temporary outdoor" box at the panel work as well?
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