Ampacities

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Old 09-15-02, 08:14 PM
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J A Boggan
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Ampacities

Could someone tell me what are the ampacities of #14 thru #4 copper wire under 'normal' conditions?
 
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Old 09-15-02, 08:46 PM
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texsparky
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Post ampacities of type nm

for type nm cable(romex)
14-15 amps
12-20 ''
10-30 ''
8-40 ''
6-55 ''
4-70 ''

Hope this is what your looking for,You didn't specify a type of wire.
 
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Old 09-15-02, 09:29 PM
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J A Boggan
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Tex,
Thanks so much for the information.
Jack
 
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Old 09-15-02, 09:35 PM
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texsparky
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Your Welcome
 
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Old 09-16-02, 06:31 AM
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There are quite a lot of exceptions to "normal", some not very obvious. So before using these numbers, make sure you know what "normal" really means.
 
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Old 09-16-02, 05:21 PM
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J A Boggan
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John,
Would you mind explaining some of the "not so obvious conditions". I certainly don't want to get into trouble. Thanks for your concern.
 
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Old 09-16-02, 05:42 PM
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There are lots of times you will need to derate or increase the basic conductors ampacity. Just a few include more than 3 current carring conductors in a raceway, the termination temperature rating of what you are connecting to, motor loads relative to breaker/fuse size, etc.
 
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Old 09-16-02, 06:56 PM
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Be sure to consider these factors when deciding whether your situation is normal: (1) number of conductors running in the same raceway or cable, (2) type of insulation or the wire, (3) type of sheathing on the cable, (4) type of cable -- there are special ampacity rules for NM, SE, UF, etc., (5) whether the installation is wet or dry, (6) whether the installation is above ground or underground (7) ambient temperature through which the wires run, (8) material from which the wires are made, (9) purpose of the conductors, e.g., whether they are used as feeders, branch circuits, or services.

All of these factors can affect the ampacity. Maybe others can think of more factors.

Once the ampacity of the wire is determined, then you need to determine the proper breaker size to protect that wire. They are not always the same number.
 
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