Wire size question, 12/2 or 14/2?

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Old 03-01-17, 04:19 PM
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Wire size question, 12/2 or 14/2?

The house was built in 1985 and I think all of the wiring is 12/2. There are 15 amp and 20 amp circuits.

Would there be any issue installing a new bath vent fan where there was not one before with it's own switch, using 14/2 wire on a 15 amp circuit? It's a single pole switch using a jumper off of the 12/2 wire.

How about in another location doing the same thing with 14/2 wire to power a ceiling fan on a different 15 amp circuit?

Thank you.
 
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Old 03-01-17, 04:30 PM
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Welcome to the forums.

It would be very uncommon for a house to be wired completely with 12/2.
Since you have 15A and 20A breakers..... you have 14/2 and 12/2 wiring.

You can not extend a 20A circuit with 15A wiring.
 
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Old 03-01-17, 06:06 PM
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Thanks for the reply. This is a 15 amp circuit with 12/2 wire. Just adding a vent fan onto the circuit with a 14/2 wire.
 
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Old 03-01-17, 06:53 PM
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The experts will correct me if I'm wrong.

You can use 12 gauge wire on a 15 amp circuit, but the circuit will only be rated at 15 amp as if it had 14 gauge wire. Do not attempt to overload the circuit just because the wire used can handle 20 amp service.
 
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Old 03-01-17, 07:23 PM
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The big problem is when #12 appears at the panel. It can be connected to a 15A breaker by the installer but if someone comes in later they'll connect it to a 20A breaker... as it should be based on its size.
 
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Old 03-02-17, 09:55 PM
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At times 12/2 was only slightly more expensive than 14/2, so it would not have been that much of an expense increase to use it in 15A circuits. For circuits with long home runs, you'd see less voltage drop and less wattage loss with 12/2.
 
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