# 210.3 - branch circuit rating



## 360max (Jun 10, 2011)

owl said:


> This question is about 210.3. It basically says that branch circuits are rated according to the rating of the OCPD. It then says that if conductors of a higher ampacity rating are used, you still go by the OCPD. in what situation would you use bigger wire than the OCPD rating?


voltage drop concerns


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## bkmichael65 (Mar 25, 2013)

owl said:


> This question is about 210.3. It basically says that branch circuits are rated according to the rating of the OCPD. It then says that if conductors of a higher ampacity rating are used, you still go by the OCPD. in what situation would you use bigger wire than the OCPD rating?


Derating


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## owl (Oct 31, 2012)

Of course. Thanks.


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## Dennis Alwon (May 9, 2009)

I never liked that rule because you could have a 40 amp overcurrent protective device on a 12 or 10 gauge wire and the cir. would be consider 40 amps when the wire is not rated 40 amps.


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## Rockyd (Apr 22, 2007)

Dennis Alwon said:


> I never liked that rule because you could have a 40 amp overcurrent protective device on a 12 or 10 gauge wire and the cir. would be consider 40 amps when the wire is not rated 40 amps.


 Is this the part that is irritating to you Dennis?

(G) Overcurrent Protection for Specific Conductor Applications.
Overcurrent protection for the specific conductors
shall be permitted to be provided as referenced in Table
240.4(G).


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## Dennis Alwon (May 9, 2009)

Rockyd said:


> Is this the part that is irritating to you Dennis?
> 
> (G) Overcurrent Protection for Specific Conductor Applications.
> Overcurrent protection for the specific conductors
> ...


No I understand that part and that is the case I was talking about. It is 210.3 I have problems with. In general it seems appropriate but in the case of a/c units etc as stated above it does not seem to be true.


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## BBQ (Nov 16, 2010)

Dennis Alwon said:


> No I understand that part and that is the case I was talking about. It is 210.3 I have problems with. In general it seems appropriate but in the case of a/c units etc as stated above it does not seem to be true.


If the circuit size was not based on just the OCPD we would not be able to wire AC units with smaller wire than the OCPD.


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## Dennis Alwon (May 9, 2009)

BBQ said:


> If the circuit size was not based on just the OCPD we would not be able to wire AC units with smaller wire than the OCPD.


Sure we could it is a matter of semantics or rewording. art. 240 allows us to use a larger overcurrent protective device but imo a 12 awg wire on a 40 amp breaker does not really make that a 40 amp cir. The circuit is not intended to ever see 40 amps except on startup. There is overload protection which allows us use the 40 amp overcurrent protective device.


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## SteveBayshore (Apr 7, 2013)

You guys need to hook up some welders. Say #8s on a 100 amp breaker or #2s on a 200 all per article 630.


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## buddhakii (Jan 13, 2011)

SteveBayshore said:


> You guys need to hook up some welders. Say #8s on a 100 amp breaker or #2s on a 200 all per article 630.


This is exactly what Dennis is getting at. #8's on a 100 amp breaker does not make that a 100 amp circuit. But according to 210.3 it is a 100 amp circuit.


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## BBQ (Nov 16, 2010)

Dennis Alwon said:


> Sure we could it is a matter of semantics or rewording. art. 240 allows us to use a larger overcurrent protective device but imo a 12 awg wire on a 40 amp breaker does not really make that a 40 amp cir. The circuit is not intended to ever see 40 amps except on startup. There is overload protection which allows us use the 40 amp overcurrent protective device.


Actully it does make it a 40 amp circuit regardless of the 12 AWG. The circuit could supply 40 amps for quite some time. 

I guess I don't understand why you want to reword 210.3 only to have reword other sections to get us back to where we are now.

As it is now it works fine.


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## BBQ (Nov 16, 2010)

buddhakii said:


> This is exactly what Dennis is getting at. #8's on a 100 amp breaker does not make that a 100 amp circuit. But according to 210.3 it is a 100 amp circuit.


Reread what you typed, I find it funny. 


You know the code says it is 100 amp circuit but you claim it is not.

Can the circuit supply 100 amps to the welder?

Yes.


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## Dennis Alwon (May 9, 2009)

BBQ said:


> Actully it does make it a 40 amp circuit regardless of the 12 AWG. The circuit could supply 40 amps for quite some time.
> 
> I guess I don't understand why you want to reword 210.3 only to have reword other sections to get us back to where we are now.
> 
> As it is now it works fine.


I wouldn't know how to re word it other than to say the wire and the overcurrent protective device determines the ampacity of the circuit. Personally I don't think it is important enough to waste the time with. It just seems odd to me.


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## papaotis (Jun 8, 2013)

glad we are on this very subject! why is it that we now have a 50a welder that needs to be on a 50a circuit (according the label) but it only has a #12 cord on it? and electric baseboard heaters are 4000 watts but only draw 7.2 amps?:001_huh:


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## Dennis Alwon (May 9, 2009)

papaotis said:


> glad we are on this very subject! why is it that we now have a 50a welder that needs to be on a 50a circuit (according the label) but it only has a #12 cord on it? and electric baseboard heaters are 4000 watts but only draw 7.2 amps?:001_huh:


4000/240 = ???? it is not 7.2 amps. I don't understand the comparison


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## papaotis (Jun 8, 2013)

sorry, dennis, i think i had two different heaters in mind. let me check on that!:whistling2:


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## BBQ (Nov 16, 2010)

papaotis said:


> glad we are on this very subject! why is it that we now have a 50a welder that needs to be on a 50a circuit (according the label) but it only has a #12 cord on it?


It has to do with the welders duty cycle and the fact that smaller conductors can carry much more current than we normally use them at.

Duty cycle is how long the welder can be used, a welder with a duty cycle of 50% can only be used 30 minutes out of every hour and may be restricted to 5 minutes welding and 5 minutes of rest. Because of this the conductors suppling it will not overheat even though they may be supplying much more current than they normally would. 

This is the key, the 50 amp circuit with number 12s will still supply the unit with up to 50 amps. That is why it makes sense to call it a 50 amp circuit. 




> and electric baseboard heaters are 4000 watts but only draw 7.2 amps?:001_huh:


I have no clue what you mean.


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## owl (Oct 31, 2012)

Branch circuit rating is determined by the OCPD rating, not the wire size.


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## Rockyd (Apr 22, 2007)

240.4(G) could be considered the exception(s) to the standard branch circuit rating. It's one of those instances where the code is quite a ways behind where reality is. When you look at motors (430's) the average protection is at 250% because of the 5 to 8 times hit from start-up. Overcurrent in the long term is addressed by heaters (solder pots or electronic) - same for compressors. Duty cycles and balance by capacitors, welders, and the like.

It's one of those times you just have to accept "Charlie's Rule".


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