dumb question


Old 09-21-04, 04:46 PM
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Join Date: Apr 2004
Location: Los Angeles
Posts: 40
dumb question

I know the only dumb question is the one you don't ask...

What do the numbers 12/3 12/2 mean? I had assumed the first is the wire gauge, and the second is the number of conductors? But then I looked at the romex I've got in my garage and it says 12/2 on the box, but there are three wires, black, white and ground.

Anyone care to enlighten me?

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Old 09-21-04, 04:53 PM
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They are not counting the ground wire (the bare copper one) as the conductor. Most boxes of romex I've seen say either 12/2 or 12/3 and they usually have 'with ground' printed on them.
Old 09-21-04, 05:20 PM
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Join Date: Apr 2004
Location: Los Angeles
Posts: 40
So 12/3 would be for two phases? But don't you want a separate neutral for each phase?
Old 09-21-04, 05:46 PM
Join Date: Sep 2000
Location: United States
Posts: 18,497
There are many different possible applications for the three conductors (not counting ground). Although a shared neutral circuit is possible with 12/3, it is far from the only application of it. If you really want to talk about a shared neutral circuit (officially called a multiwire circuit), we can, but it is a big subject and a lot would need to be written. You can surely find it all simply by searching this forum for "multiwire". It's all been written many times before.

I should note that 12/3 means three conductors plus ground when talking about NM cable. But when referring to other kinds of cable, it can mean two conductors plus ground. Bottom line is that of course, like everything, the devil is in the details and there are very few generalizations you can make without the need to cite exceptions.
Old 09-22-04, 05:34 AM
Join Date: Sep 2003
Location: Central New York State
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As John said, 12/3 could be used for a multiwire circuit, but multiwire circuits are not that common in residences.

More common use of 12/3 in a residence would be for:

Wiring three way and four way switches.
Wiring a ceiling fan where the light and fan are controlled by separate wall switches.
Wiring a switched receptacle where it is also necessary to have unswitched power also available.

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