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Old 03-05-2008, 08:59 AM   #1
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Circuit breakers and wire size


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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Old 03-05-2008, 09:16 AM   #2
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Circuit breakers and wire size


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Originally Posted by stan 41943 View Post
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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Old 03-05-2008, 11:12 AM   #3
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Circuit breakers and wire size


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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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Old 03-05-2008, 11:20 AM   #4
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Circuit breakers and wire size


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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Old 03-05-2008, 11:43 AM   #5
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Circuit breakers and wire size


210.24 is only used for "Branch Circuits". Dedicated circuits is a different animal.
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Old 03-05-2008, 11:45 AM   #6
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Originally Posted by hpp58 View Post
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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Old 03-05-2008, 12:34 PM   #7
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That was not insulting at all .... it was totally deserved.
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Old 03-05-2008, 12:42 PM   #8
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Circuit breakers and wire size


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.
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Old 03-05-2008, 12:44 PM   #9
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Circuit breakers and wire size


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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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Old 03-05-2008, 01:00 PM   #10
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Circuit breakers and wire size


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.

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Old 03-05-2008, 01:03 PM   #11
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Originally Posted by InPhase277 View Post
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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Old 03-05-2008, 01:39 PM   #12
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Circuit breakers and wire size


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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Old 03-05-2008, 03:02 PM   #13
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Circuit breakers and wire size


Quote:
Originally Posted by CowboyAndy View Post
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.
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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Answers based on the 2008 & 2011 NEC. If you're on the '14 already I feel sorry for you.
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Old 03-05-2008, 03:36 PM   #14
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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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Old 03-05-2008, 03:37 PM   #15
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Circuit breakers and wire size


I guess Petey beat me to it.

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