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  #1  
Old 2/7/08, 3:46 PM
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Mark Nicholet Mark Nicholet is offline
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Default 20 amp outlet on 15 amp circuit

Can anyone tell me why a 20 amp receptacle (t-shaped neutral) can't be used on a 15 amp service (14AWG)?

I can understand why a 15 amp receptacle shouldnt be used on a 20 amp (12AWG) service but a 20 amp receptacle should be able to handle the load safely.

Is this just a misleading issue for a 20 amp appliance that may lead to a nuisance trip?
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Old 2/7/08, 4:05 PM
Speedy Petey Speedy Petey is offline
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Default Re: 20 amp outlet on 15 amp circuit

Quote:
Originally Posted by Mark Nicholet
Is this just a misleading issue for a 20 amp appliance that may lead to a nuisance trip?
Not just misleading. An applaince with a 20A plug has the potential of drawing up to 20 amps. More likely it is under 20, like 14-18. So having an applaince or tool that draws 15 or 16 amps will load a 15a circuit to or just over capacity for who knows how long. No, a 15A breaker will not trip at 16 amps, at least not for a long time.




Quote:
Originally Posted by Mark Nicholet
I can understand why a 15 amp receptacle shouldnt be used on a 20 amp (12AWG) service but a 20 amp receptacle should be able to handle the load safely.
But a 15A receptacle CAN be used on a 20A circuit, IF there is more than one.
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Old 2/7/08, 4:33 PM
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Default Re: 20 amp outlet on 15 amp circuit

Quote:
Originally Posted by Speedy Petey
Not just misleading. An applaince with a 20A plug has the potential of drawing up to 20 amps. More likely it is under 20, like 14-18. So having an applaince or tool that draws 15 or 16 amps will load a 15a circuit to or just over capacity for who knows how long. No, a 15A breaker will not trip at 16 amps, at least not for a long time.
I thought breakers were overrated? ie 20 amp breaker trips at 18 amps?

Quote:
Originally Posted by Speedy Petey
But a 15A receptacle CAN be used on a 20A circuit, IF there is more than one.
Only in multi-wire branch circuits with 12 AWG?
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Old 2/7/08, 5:34 PM
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Default Re: 20 amp outlet on 15 amp circuit

Quote:
Originally Posted by Mark Nicholet
I thought breakers were overrated? ie 20 amp breaker trips at 18 amps?
Oh, my goodness no. Breakers trip on a time-current curve. The greater the magnitude of the overcurrent, the quicker the breaker will trip. For instance, a hard short will trip pretty much instantly. A 22 amp overcurrent on a 20 amp breaker will go on for hours and hours. A 40 amp overcurrent may last for a couple minutes. Every breaker has an associated "trip curve" published by the manufacturer. Here's a one-page .PDF of a Square D QO breaker trip curve:

http://ecatalog.squared.com/pubs/Cir...ers/910-04.pdf
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Old 2/7/08, 8:29 PM
Speedy Petey Speedy Petey is offline
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Default Re: 20 amp outlet on 15 amp circuit

Quote:
Originally Posted by Mark Nicholet
Only in multi-wire branch circuits with 12 AWG?
Huh? Who said anything about a MWBC?
If there is more than one "receptacle" on a circuit, and a duplex receptacle is considered two in this case, then you CAN use 15A receptacles on a 20A circuit. Simple as that.
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Old 2/11/08, 4:54 PM
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Default Re: 20 amp outlet on 15 amp circuit

Attached is a copy of the NEC table on receptacle ratings. Note that as previously mentioned for a 20A circuit you can install either 20A receptacles, or 15A receptacles as long as there is more than one. But for a 15A circuit, only 15A receptacles should be installed ...
Attached Thumbnails
20-amp-outlet-15-amp-circuit-receptacle-rating-table.jpg  



Robert O'Connor, PE
Consulting Engineer & Inspector
LIU CW Post Adjunct Professor
NACHI Education Committee
www.reporthost.com/-rjo

I am absolutely amazed sometimes by how much thought goes into doing things wrong ...
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  #7  
Old 2/11/08, 5:20 PM
Doug Edwards Doug Edwards is offline
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Default Re: 20 amp outlet on 15 amp circuit

Hey Robert,
Haven't seen you in a while. Always appreciate you inputs.
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