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Conduit, wires, breakers.

 
 
Larryew
 
Reply Sun 4 Aug, 2013 11:07 am
I was reading today on the web that for a 3/4" conduit, 20 amp circuit, 12 gauge wire, you can have a total of six wires, three hot, three separate neutrals. I basically learned that the conduit fill allowance of sixteen wires for 3/4" pipe is just telling you how many wires can fit into the conduit, but after you figure out the derating of the conductors, the safe amount would be six wires.

I get that, but I am confused on why conduit size is not an issue. If you had 1/2" conduit, I would imagine that six conductors would be to many, and if you used 1" conduit, I would imagine that you can put more than six conductors in there safely.

Could some one please tell how many #12 wires a 1/2" conduit can handle safely on a 20mp circuit? Also the same question for 1" conduit

Thank you,

Larry.
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udawg
 
  0  
Reply Sat 10 Aug, 2013 04:20 pm
@Larryew,
Conduit size does not matter when it comes to de-rating. First you must calculate, based on circuit amperage size, what size wire you need. You can have three current carrying conductors in a conduit before you nee to de-rate. When you de-rate for 14,12, and 10 gauge you are allowed to use a higher starting current for your calculations. Example, #12 wire you can use 25 amps for your calculations. ( although you can never put #12 wire on larger than a 20A breaker) When you have up to and including 6 #12 current carrying conductors, you have to de-rate 80%. 80% of 25 amps is 20 amps, so, you can have up to 6 #12 current carrying conductors in a raceway before you have to up-size the wiring accordingly. Once you determine the amount of conductors in the conduit, and, whether they need to be up-sized and to which size, then you base conduit size on conductors contained therein. Whether or not a conductor is considered a current carrying conductor is a whole new topic for debate, but, nowadays with almost everything being electronic, it is wise to consider both ungrounded and grounded conductors as current carrying.
Placid Carcass
 
  2  
Reply Sun 18 Aug, 2013 10:58 am
@udawg,
You have no idea what you are talking about. When determining how many wires can fill a conduit, conduit size absolutely matters, as well as de-rating value.
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