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#79433 12/21/01 08:12 PM
Joined: Aug 2001
Posts: 545
A
aldav53 Offline OP
Member
Is it legal to use a 25 amp breaker with # 12 wire? if not, why do they make them?


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#79434 12/21/01 09:56 PM
Joined: Jan 2001
Posts: 1,044
Tom Offline
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Yes, and it is also possible to use a 25 amp breaker on #14 wire. I am currently doing an installation with #12 wire on a 40 amp breaker.

The usual reason for this is that motor loads may have a breaker that does not correspond to the normal wire size/breaker combination. The breaker in this instance supplies short circuit & ground fault protection while the motor overload element provides the overcurrent protection. See all of 240.4

Tom


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#79435 12/22/01 10:50 AM
Joined: Aug 2001
Posts: 545
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aldav53 Offline OP
Member
Tom,
Thanks for replying-
What do you mean when you say the motor leads have a breaker? Are you talking about the auto overload shut-off built into the motor? How can it be legal with a new installation to put a 40 amp breaker using #12 wire, even though the motor leads are smaller. Am I wrong here?


The Golden Rule - "The man with the gold makes the rule"
#79436 12/22/01 11:16 AM
Joined: Oct 2000
Posts: 4,116
Likes: 4
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Al,

Motor loads can have a very high inrush current when first turned on. A motor that only uses say, 10 amps can draw 60 or 100 for a short time when first turned on. So, it is sometimes necessary to use a larger breaker to allow the Motor to start, and the wire is basically sized to the running load of the motor.

Take a look at 430-52 and Table 430-152 in the 1999 NEC

Bill


Bill
#79437 12/22/01 11:30 AM
Joined: Dec 2000
Posts: 4,294
Member
Please note that if not a motor or A/C load, the #12 is not legal. You would need to use #10

#79438 12/22/01 11:41 AM
Joined: Jan 2001
Posts: 1,044
Tom Offline
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Al,

Again, take a look at 240.4 and table 240.4(G). There are quite a few instances where the standard wire to breaker size relationship is not what you would normally expect.

Tom


Few things are harder to put up with than the annoyance of a good example.
#79439 12/22/01 02:51 PM
Joined: Nov 2001
Posts: 280
M
Member
One thing I have found a use for a 25 amp breaker is A/C, and for those units the Breakers are suppose to be HACR RATED, a lot of service revamps I do, that have air conditioning is to check the name-plate on the unit and it will tell you what size breaker to use and have found a lot of units that call for a 25 amp breaker.
When doing the revamp I find a lot of 30 amp breakers used inplace of the 25 amp breakers, thats about the only place I have ever used them.
The only people that have them on the shelf is the big Orange place, and they are usually Murray or basically a Siemens. I am sure every breaker manufactureer makes them just not a big demand for them.


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