# Circuit breakers and wire size



## stan 41943 (Feb 27, 2008)

I know that the breaker amps/wire size for 120v is: 15amp=14g & 20amp=12g. What about 240v ratios? Also in my panel there are 2- 240 circuits - one is in a double breaker & the other is a single (or is it called 1/2 ) breaker (50amp). What's the difference. Both are 10/3 wire one orange wrapped the other black.


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## CowboyAndy (Feb 19, 2008)

stan 41943 said:


> I know that the breaker amps/wire size for 120v is: 15amp=14g & 20amp=12g. What about 240v ratios? Also in my panel there are 2- 240 circuits - one is in a double breaker & the other is a single (or is it called 1/2 ) breaker (50amp). What's the difference. Both are 10/3 wire one orange wrapped the other black.


10AWG should be protected by a max of 30AMPS, unless there are special rules , but I do not know what those rules are. Maybe someone else can fill in the blanks for that.

Technically speaking, most cable has a higher rating that it is used for, but breakers that size are not avalible...

14AWG=17AMP
12AWG=23AMP
10AWG=33AMP
8AWG=46AMP
6AWG=60AMP

But, because a 17A breaker is not avalible, 15AMP is used, etc.


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## 220/221 (Oct 9, 2007)

> What about 240v ratios?


 
No difference. Each leg is protected individually. Your #10 wires should be on 30 amp breakers, not 50's




And.....there was nothing wrong with Andy's post.


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## CowboyAndy (Feb 19, 2008)

Just wanted to clarify something in my post about breaker ratings where I said it was because (example) a 17 amp breaker wasn't avalible so 15 was to be used. I should have said a 15 has to be used because thats what the NEC says has to be used.

Overcurrent protection as stated in table 210.24

conductor size 14------12------10------8------6
breaker size 15------20------30------40-----50


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## hpp58 (Feb 28, 2008)

210.24 is only used for "Branch Circuits". Dedicated circuits is a different animal.


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## CowboyAndy (Feb 19, 2008)

hpp58 said:


> 210.24 is only used for "Branch Circuits". Dedicated circuits is a different animal.


Well, it depends on what the circuits are for. Like I said in an earlier post, things like motors, fixed electric heat and welders have their own special rules.

A range, dryer, etc are still branch circuits.


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## Joba Fett (Aug 14, 2007)

That was not insulting at all .... it was totally deserved.


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## jrclen (Feb 20, 2008)

The ampacity of a wire depends on the wire type, the conditions, and the application.

Check this out:
Table 310.19 Ampacity of single insulated conductors. Wire type PFAH, TFE.

14 - 59 amps
12 - 78 amps
10 - 107 amps

Now don't anyone try this at home. This is not DIY stuff. :yes:


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## CowboyAndy (Feb 19, 2008)

JGarth said:


> That was not insulting at all .... it was totally deserved.


Then please cite specific examples about what was wrong with my post and why you feel it should be deleted. If you can prove that I gave out FALSE info, then I will delete it.


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## InPhase277 (Feb 9, 2008)

Andy, just for the record, motors, refrigeration equipment, welders and some feeders are allowed to have a larger overcurrent device that the wire size would normally allow. Fixed electric space heating IS NOT allowed to be protected by an OCPD larger than the branch circuit conductors.

In fact, electric heating equipment is considered a continuous load and as such must have conductors rated 125% larger than the load.

InPhase277


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## CowboyAndy (Feb 19, 2008)

InPhase277 said:


> Andy, just for the record, motors, refrigeration equipment, welders and some feeders are allowed to have a larger overcurrent device that the wire size would normally allow. Fixed electric space heating IS NOT allowed to be protected by an OCPD larger than the branch circuit conductors.
> 
> In fact, electric heating equipment is considered a continuous load and as such must have conductors rated 125% larger than the load.
> 
> InPhase277


 
Ok, thanks for that correction (and I DID mention in my origional post that I wasn't 100% on that and maybe someone else would help).


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## HouseHelper (Mar 20, 2007)

CowboyAndy, I believe you are citing the ratings of fixture wires, not branch circuit wiring. Article 240.4(D) limits the ampacity of 14, 12, and 10 gauge wire to 15, 20, and 30A, respectively. Motors, HVAC, and welders are treated differently.


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## Speedy Petey (Feb 1, 2004)

CowboyAndy said:


> Technically speaking, most cable has a higher rating that it is used for, but breakers that size are not avalible...
> 
> 14AWG=17AMP
> 12AWG=23AMP
> ...


Andy, don't take this the wrong way. 
While I generally don't agree with Garth's approach to posting, in this case he does have a point. 
You CANNOT post a blanket chart like that for ampacity. There are several factors that determine ampacity; insulating type and temp rating, AL or CU, cable or conduit, and more.

T310.16 has many columns, and there are several articles that apply adjustment factors to that table with respect to breaker size. 

Also, that is NOT the reason that #14 is generally "limited" to a 15A breaker. 240.4(D) is.


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## Silk (Feb 8, 2008)

I think you guys are getting confused between conductor ratings and overcurrent protection. Conductor ampacity ratings for a specific AWG are varied dependent upon insulation type, ambient temperature, number of conductors in a raceway, ect. (Article 310.15). You need to be concerned about overcurrent protection. Article 210.20(B)-Branch Circuit Overcurrent Protection states "_Conductors shall be protected in accordance with 240.4."_

Article 240.4(D) states the following:

*Small Conductors*. Unless specifically permitted in 240.4(E) or (G), the overcurrent protection shall not exceed that required by (D)(1) through (D)(7) after any correction factors for ambient temperature and number of conductors have been applied.
*(1) 18 AWG Copper. 7 amperes*, provided all the following conditions are met: 
(1) Continuous loads do not exceed 5.6 amperes. 
(2) Overcurrent protection is provided by one of the following: 
a. Branch-circuit-rated circuit breakers listed and marked for use with 18 AWG copper wire 
b. Branch-circuit-rated fuses listed and marked for use with 18 AWG copper wire 
c. Class CC, Class J, or Class T fuses 
*(2) 16 AWG Copper. 10 amperes*, provided all the following conditions are met: 
(1) Continuous loads do not exceed 8 amperes. 
(2) Overcurrent protection is provided by one of the following: 
a. Branch-circuit-rated circuit breakers listed and marked for use with 16 AWG copper wire 
b. Branch-circuit-rated fuses listed and marked for use with 16 AWG copper wire 
c. Class CC, Class J, or Class T fuses
*(3) 14 AWG Copper. 15 amperes
(4) 12 AWG Aluminum and Copper-Clad Aluminum. 15 amperes
(5) 12 AWG Copper. 20 amperes
(6) 10 AWG Aluminum and Copper-Clad Aluminum. 25 amperes
(7) 10 AWG Copper. 30 amperes*
​In general, remember the NEC has countless exceptions to every rule, when you have larger conductors they shall be protected against overcurrent in accordance with their ampacities specified in 310.15


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## Silk (Feb 8, 2008)

I guess Petey beat me to it.


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## darren (Nov 25, 2005)

InPhase277 said:


> Fixed electric space heating IS NOT allowed to be protected by an OCPD larger than the branch circuit conductors.


Unless your in Canada then you can wire to the load of the heater, so if you have 3200W of heat(amp draw of 13.3A) you could use #14 but then you have to derate(125%) when you size your breaker so this would mean you would be allowed to put a #14 on a 20A breaker. 

To the OP, wire size is based on amp load not voltage, at least for a house it is.

Darren


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## CowboyAndy (Feb 19, 2008)

Speedy Petey said:


> Andy, don't take this the wrong way.
> While I generally don't agree with Garth's approach to posting, in this case he does have a point.
> You CANNOT post a blanket chart like that for ampacity. There are several factors that determine ampacity; insulating type and temp rating, AL or CU, cable or conduit, and more.
> 
> ...


I agree that it probably wasn't the best thing for me to post a table like that considering there are so many factors and exceptions to the issue.

That being said, I did not deserve to be attacked like a dog. I still take the stance that I did not post anything dangerous. My first post made it clear that 10AWG has to be protected at 30AMPs. And I realized I didn;t express myself the right way as to WHY they had to be protected at the ratings they are, which I later edited my post and corrected it.

I appriciate you guys taking the time to explain it all in detail.


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## jrclen (Feb 20, 2008)

Speedy Petey said:


> Also, that is NOT the reason that #14 is generally "limited" to a 15A breaker. 240.4(D) is.





CowboyAndy said:


> I appreciate you guys taking the time to explain it all in detail.


Don't worry about it Andy. Some people seem to be wound a little tight. Just take a look at what Petey and Silk told you about 240.4(D). That is what you look at for protecting your house circuits. That is the reference to the asterisks in the ampacity tables for "small conductors." "Unless specifically permitted in (E) or (G)." Do you have an NEC Handbook? If not, I recommend you pick one up. :thumbsup:


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## CowboyAndy (Feb 19, 2008)

jrclen said:


> Don't worry about it Andy. Some people seem to be wound a little tight. Just take a look at what Petey told you about 240.4(D). That is what you look at for protecting your house circuits. That is the reference to the asterisks in the ampacity tables for "small conductors." "Unless specifically permitted in (E) or (G)." Do you have an NEC Handbook? If not, I recommend you pick one up. :thumbsup:


I don't have the actual book, but I do access it online...
http://www.nfpa.org/freecodes/free_access_agreement.asp?id=7008SB



I was thinking about getting the actual book though.

I totally understand what the difference between what conductors are RATED for and waht they must be PROTECTED at. I was just so surprised at the posts that followed by certain people.

I guess what bothered me the most about it was that just last week the same thing was said (by you, actually) and no one jumped all over it like stink on... well you know.

http://www.diychatroom.com/showpost.php?p=101204&postcount=7
(granted, it was in a little different context)

But, it's all good.


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## jrclen (Feb 20, 2008)

CowboyAndy said:


> I guess what bothered me the most about it was that just last week the same thing was said (by you, actually) and no one jumped all over it like stink on... well you know.
> http://www.diychatroom.com/showpost.php?p=101204&postcount=7
> (granted, it was in a little different context)
> But, it's all good.


Yeah, that's a problem with a DIY forum. And with the code. Electricians would know what I was referring to, but a home owner/handyman might think if 14 THHN could handle 20 amps in that particular case, why couldn't it handle 20 amps on his constantly tripping 15 amp whatever circuit. And I would hate to think I was responsible for someone swapping his 15 amp breaker for a 20 on number 14 wire.

When you buy your NEC book, think about the handbook. The handbook has pictures and explanations that you would find very helpful. It's well worth the extra money. I ordered mine from Mike Holt, along with the indexing tabs.
http://www.mikeholt.com/index.php?id=homegeneral


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