# wire size on breaker



## Speedy Petey (Jan 10, 2007)

What is it you want to know?
Have you looked at Art. 440?


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## Speedy Petey (Jan 10, 2007)

The conductors can be sized for the MCA and the breaker for the max breaker/fuse size.


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## paul nunemaker (Dec 13, 2009)

yes, where's the overcurrent protection on the #10? I thought 310.16 * prevented small conductors like 10 from being on larger than 30 amp.


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## Bkessler (Feb 14, 2007)

The breaker is sized for the startup and the wire for the running load Amps. Very common and a very common mistake to run #6 when only #10s are needed.


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## 480sparky (Sep 20, 2007)

paul nunemaker said:


> yes, where's the overcurrent protection on the #10? I thought 310.16 * prevented small conductors like 10 from being on larger than 30 amp.



310.16 does not limit ampacity of 'small conductors'. 240.4(D) does.


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## Dennis Alwon (May 9, 2009)

paul nunemaker said:


> yes, where's the overcurrent protection on the #10? I thought 310.16 * prevented small conductors like 10 from being on larger than 30 amp.


This is because the compressor has overload protection which will protect the conductors from an overload. The breaker, in this case, only protects the wires from short circuit or ground fault.


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## paul nunemaker (Dec 13, 2009)

so, throw out 310.16 * which directs to 240 and says #10 max breaker 30 amp?


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## 480sparky (Sep 20, 2007)

paul nunemaker said:


> so, throw out 310.16 * which directs to 240 and says #10 max breaker 30 amp?


It says nothing of the kind. Try reading 240.4 first. ALL of it.


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## paul nunemaker (Dec 13, 2009)

Thank you Dennis, that makes more sense. Normally have #10 awg on 30 amp breaker for a/c unit.


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## RIVETER (Sep 26, 2009)

Dennis Alwon said:


> This is because the compressor has overload protection which will protect the conductors from an overload. The breaker, in this case, only protects the wires from short circuit or ground fault.


The overloads in the compressor are to protect the compressor...not the building wiring.


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## Wirenuting (Sep 12, 2010)

RIVETER said:


> The overloads in the compressor are to protect the compressor...not the building wiring.


X2, that's right.


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## kbatku (Oct 18, 2011)

Normally, the name plate will spec a minimum and a maximum breaker. So you can size your wire to the LRA and the breaker to the maximum if you feel like it??


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## 480sparky (Sep 20, 2007)

kbatku said:


> Normally, the name plate will spec a minimum and a maximum breaker. So you can size your wire to the LRA and the breaker to the maximum if you feel like it??



I usually look for the minimum conductor ampacity, and the maximum OCD.


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## brian john (Mar 11, 2007)

Paul,

I would suggest this.

http://www.amazon.com/Understanding-Rules-Motors-Motor-Controls/dp/0872886115


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## BBQ (Nov 16, 2010)

RIVETER said:


> The overloads in the compressor are to protect the compressor...not the building wiring.





Wirenuting said:


> X2, that's right.


:no:

No, the compressor OLs provide the overload protection to the building wiring as well.


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## BBQ (Nov 16, 2010)

paul nunemaker said:


> so, throw out 310.16 * which directs to 240 and says #10 max breaker 30 amp?


Not quite, we have to look at the sections in their entirety.




> *240.4
> 
> (D) Small Conductors.* Unless specifically permitted in
> 240.4(E) or (G), the overcurrent protection shall not exceed
> ...



Unless specifically permitted in 240.4(E) or (G), well in the case of a HVAC unit 240.4(G) specifically permits ignoring 240.4(D).

So if you have a unit with a minimum circuit ampacity of 25 amps you find a conductor that has at least that ampcity from Table 310.16

If this same unit has a maximum overcurrent protection of 50 amps you can still use a 50 amp breaker with that 10 AWG.




240.4(E) or (G),


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## chicken steve (Mar 22, 2011)

well it's in 430 too

and perhaps a _simpler_ reminder would be that anything after the first 3 chapters _ammends _the first 3 chapters of the code.....

~CS~


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## captkirk (Nov 21, 2007)

I used to work for a guy that used to size conductors for ACs to the max breaker...... LOL


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## Dennis Alwon (May 9, 2009)

RIVETER said:


> The overloads in the compressor are to protect the compressor...not the building wiring.


 If that were the case then you would not be allowed to use a 50 amp breaker with #10. The OL, as stated, also protects the conductors no matter what its primary purpose is supposed to be.


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## brian john (Mar 11, 2007)

captkirk said:


> I used to work for a guy that used to size conductors for ACs to the max breaker...... LOL


I hope he never had to install circuitry for a 200 HP Fire Pump.


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## brian john (Mar 11, 2007)

BBQ said:


> Not quite, we have to look at the sections in their entirety.
> Unless specifically permitted in 240.4(E) or (G), well in the case of a HVAC unit 240.4(G) specifically permits ignoring 240.4(D).
> 
> So if you have a unit with a minimum circuit ampacity of 25 amps you find a conductor that has at least that ampcity from Table 310.16
> ...


BBQ= MH’s ET Alias?


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