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Old 04-15-2009, 11:37 AM   #1
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Mixing 12 and 14 wire in conduit?


Im running a 20 amp circuit in 1/2" thinwall conduit with 12 gague wire down the length of my basement. Is it permissible to use 14 wire to drop down to each outlet and/or light fixture? Or must a 20 amp circuit maintain #12 wire throughout?

Another question:
Im also running a seperate 20amp #12 wire to the bathroom circuit breaker outlet. Am I permitted to run a 270 watt heat mat off this same cuircuit?

Thank you.


Last edited by Quickdraw; 04-15-2009 at 11:40 AM.
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Old 04-15-2009, 11:42 AM   #2
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Mixing 12 and 14 wire in conduit?


Quote:
Originally Posted by Quickdraw View Post
Im running a 20 amp circuit in 1/2" thinwall conduit with 12 gague wire down the length of my basement. Is it permissible to use 14 wire to drop down to each outlet and/or light fixture? Or must a 20 amp circuit maintain #12 wire throughout? Thank you.
You must maintain 12 gauge wire for the entire circuit to keep it protected at 20 amps. 14 gauge wire gets a 15 amp breaker, 12 gets a 20 amp breaker.

You could run 10 gauge in the conduit and drop down to 12 gauge for the outlets and protect the circuit at 20 amps, that is of course if you are concerned about voltage drop. This is done quite commonly in commercial applications with long runs to the circuit panel, 10 gauge wire to get to the location it serves, then 12 gauge in between recepticals

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Old 04-15-2009, 12:25 PM   #3
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Mixing 12 and 14 wire in conduit?


Quote:
Originally Posted by Quickdraw View Post
Im running a 20 amp circuit in 1/2" thinwall conduit with 12 gague wire down the length of my basement. Is it permissible to use 14 wire to drop down to each outlet and/or light fixture? Or must a 20 amp circuit maintain #12 wire throughout?

Another question:
Im also running a seperate 20amp #12 wire to the bathroom circuit breaker outlet. Am I permitted to run a 270 watt heat mat off this same cuircuit?

Thank you.
270 watts = 2.25a, not a big load
I see no problem with that
Is this going under tile?
What does the Mfg installation instructions indicate?
Does it need to be GFCI or is that built in?

Mine was almost 7a, so I used another circuit
My GFCI was built into the thermostat
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Old 04-15-2009, 12:34 PM   #4
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Mixing 12 and 14 wire in conduit?


Quote:
Originally Posted by Quickdraw View Post
Another question:
Im also running a seperate 20amp #12 wire to the bathroom circuit breaker outlet. Am I permitted to run a 270 watt heat mat off this same cuircuit?

Thank you.
Is this being installed in the bathroom or outside the bathroom? Are there any other circuits feeding the bathroom? You mention this circuit is for the outlet, is there another circuit feeding the lights or is this one circuit feeding the entire bathroom?
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Old 04-15-2009, 01:10 PM   #5
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Mixing 12 and 14 wire in conduit?


My reason for using the 20amp circuit was to allow more lights and outlets than a 15amp circuit would permit. I don't really need it "protected" to 20amps. It doesn't seem to me a problem to run a main #12 wire and branch off to lights & outlets using #14 wire. No single outlet or light would use more than a minimal amout of current. My concern was if CODE prohibited this?

On the heated floor, yes, it is in the same bathroom as the 20amp GFCI outlet and will be under tile. Since its a concrete basement floor I plan to lay 1/4" cork down before the mat. I plan to run the lights and exhaust fan off a different circuit than the required-mandated 20amp GFCI outlet.

Thank you everyone for your responses.
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Old 04-15-2009, 01:42 PM   #6
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Mixing 12 and 14 wire in conduit?


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Originally Posted by Quickdraw View Post
My reason for using the 20amp circuit was to allow more lights and outlets than a 15amp circuit would permit. I don't really need it "protected" to 20amps. It doesn't seem to me a problem to run a main #12 wire and branch off to lights & outlets using #14 wire. No single outlet or light would use more than a minimal amout of current. My concern was if CODE prohibited this?
If you run a 20A breaker, then yes CODE prohibits this.
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Old 04-15-2009, 02:05 PM   #7
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Mixing 12 and 14 wire in conduit?


Yes Code prohibits it
But you will notice that almots every lighting fixture you install has 14g wiring. In some cases even smaller

There is "something" - possibly only in commercial installations?
that allows you to use 14g feeder wire
But the distance I think is very short & it was very specific as to the installation

You can have #12 & #14 on a 15a circuit
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Old 04-15-2009, 05:08 PM   #8
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Mixing 12 and 14 wire in conduit?


Can I assume it's OK to run #12 and #14 wire in the same run of conduit as long as they connect to different breakers in the box?

I have a Square D Homeline breaker box with 30 breakers, 15 on the left & 15 on the right. I understand I only need one neutral wire for each two hot wires as long as each of the hot wires comes from a different buss. Does that mean one hot wire should come from the left side of the box and one from the right side? OR that they should come from breakers one just above of the other? Due to only having two blank spaces left in the breaker box I'm going to use half size tandem breakers to get four circuits.
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Old 04-15-2009, 05:13 PM   #9
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Mixing 12 and 14 wire in conduit?


Quote:
Originally Posted by Quickdraw View Post
Can I assume it's OK to run #12 and #14 wire in the same run of conduit as long as they connect to different breakers in the box?

I have a Square D Homeline breaker box with 30 breakers, 15 on the left & 15 on the right. I understand I only need one neutral wire for each two hot wires as long as each of the hot wires comes from a different buss. Does that mean one hot wire should come from the left side of the box and one from the right side? OR that they should come from breakers one just above of the other? Due to only having two blank spaces left in the breaker box I'm going to use half size tandem breakers to get four circuits.
You only need (1) neutral wire for 2 hots ONLY when you are running a multi-wire branch circuit, under NEC 2008 you need a double pole breaker to run a MWBC. This double pole breaker will automatically pull power from opposite "sides/phases" of the buss
You can't use a tandem breaker to run a MWBC, it pulls all power from the same buss

You need 1 neutral for every other circuit
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Old 04-15-2009, 09:40 PM   #10
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Mixing 12 and 14 wire in conduit?


Quote:
Originally Posted by Scuba_Dave View Post
Yes Code prohibits it
But you will notice that almots every lighting fixture you install has 14g wiring. In some cases even smaller

There is "something" - possibly only in commercial installations?
that allows you to use 14g feeder wire
But the distance I think is very short & it was very specific as to the installation

You can have #12 & #14 on a 15a circuit

I found it - Table 210.24 lists 14g OK for "taps" on a 20a circuit

So...define "taps"

mmmmm.....see 240.5

Last edited by Scuba_Dave; 04-15-2009 at 09:45 PM.
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Old 04-15-2009, 11:02 PM   #11
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Mixing 12 and 14 wire in conduit?


Quote:
Originally Posted by Scuba_Dave View Post
I found it - Table 210.24 lists 14g OK for "taps" on a 20a circuit

So...define "taps"

mmmmm.....see 240.5
Oh, you've done it now. There is no reason to have mentioned that. Now every hack that is lurking will take it to mean they can do it all day long. It only applies to a very narrow range of circumstances, and DOES NOT apply to receptacle and lighting circuits.
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Old 04-15-2009, 11:08 PM   #12
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Mixing 12 and 14 wire in conduit?


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Originally Posted by InPhase277 View Post
Oh, you've done it now. There is no reason to have mentioned that. Now every hack that is lurking will take it to mean they can do it all day long. It only applies to a very narrow range of circumstances, and DOES NOT apply to receptacle and lighting circuits.
You might want to check 210.24 before saying it doesn't apply to receptacle and lighting circuits.

It does apply, in general, but there are limitations.
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Old 04-15-2009, 11:14 PM   #13
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Mixing 12 and 14 wire in conduit?


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You might want to check 210.24 before saying it doesn't apply to receptacle and lighting circuits.

It does apply, in general, but there are limitations.
That's just it. 210.24 says we must defer to 210.19, 210.20, and 210.21. 210.19(A)(2) says it all, at least for the purpose that I made my statement.
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Old 04-15-2009, 11:30 PM   #14
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Mixing 12 and 14 wire in conduit?


yes, but it does apply to power and lighting circuits

you said:
Quote:
and DOES NOT apply to receptacle and lighting circuits.
and not to be argumentative, but the limitations are not all that restrictive, in my opinion.

look at your 219A2 for an example. It simply states the conductors must have an ampacity not less than the branch circuit rating. 14 is rated for 20 amps so it is acceptable per 210.24 for a 20 amp branch circuit.
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Old 04-15-2009, 11:39 PM   #15
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Mixing 12 and 14 wire in conduit?


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Originally Posted by nap View Post
yes, but it does apply to power and lighting circuits

you said:
and not to be argumentative, but the limitations are not all that restrictive, in my opinion.

look at your 219A2 for an example. It simply states the conductors must have an ampacity not less than the branch circuit rating. 14 is rated for 20 amps so it is acceptable per 210.24 for a 20 amp branch circuit.
OK, maybe I'm just thick in the head (and I am), but where, outside of the conductors built into a light fixture itself, can #14 be used on a 20 A lighting circuit?

And I see where the word play could be manipulated in that article, but I really don't think that is the intent of the Code. In my opinion, 240.4(D) sets the ampacity for #14, #12, and #10, for use in branch circuits of the nature described by 210.19 et al. I'm not being argumentative either, but inquisitive. In a residence, and not including cooking equipment or HVAC equipment, or welders, or fixture wires and cords, or any other special device, where can #14 be used on a 20 A circuit?

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