Baseboard heater wire sizing

KUXJ · Oct 11, 2009, 12:51 AM

Hi! Chrisbosco, and welcome to AMHD

Quote:

Originally Posted by chrisbosco

Hey All, Maybe you can help.

I'm installing four 240V baseboard heaters to a room in the back of my house with a total amp rating of 17.7 amps. I intended to use a double pole 20 amp breaker and 12/2 romex, but my brother says I should use a 30 amp breaker and 10/3 wire. The furthest heater is about 30 ft from the main panel. Is the additional sizing necessary or just a nice thing to do?

Quote:

Is the additional sizing necessary or just a nice thing to do

When It comes to electricity, I would rather be right, than dead.

My idea of being "nice" would be sleeping inside while the heaters were humming along, instead of outside watching the fire co. Do it's job.

I'm a DIY'er myself, and I've learned there a reasons why codes are written.

Let's consider:
Code states you have to have 125% of load.....
Your 17.7amps = 22.125

So your plan of 1 D.P. 20amp with 12/2 is already a no go.

Break the job down into two DP 20's, one for each set of two heaters.
You'd even have the option of 15's....50% of 22.125 = 11.0625

Then the 12/2 would be okay, with either the 15 or 20amp breakers.

Make sure you mark the whites with permanent black markers, tape/paint at both terminals.

Check the instructions for the heater, to make sure that
The temperature rating of the insulation, (it will be printed on
The wire in centigrade), is not exceeded.

And make sure the breakers you get will fit the service panel.

That's how I'd do it, but don't take my word, I'm a DIY'er myself

P.s. One of the guys 'll be along to grade me.

K

tkrussell · Oct 11, 2009, 04:45 AM

Kuxj is exactly correct, either one 30 amp circuit with #10-2 with ground cable or two 20 amp circuits with #12 with ground cable.

KUXJ · Oct 12, 2009, 09:04 AM

Tk,
Something that's been buggin' me.

The reason I didn't acknowledge the 30amp DP breaker was, I was also taught that you take 80% of load and add it to the original total. Then you adjust up or down accordingly for the fixtures, I.e. Breakers, and wires.

So 80% of 17.7 = 14.16 + 17.7 = 31.86amps with buffer, and of course 10-2/ground would be underrated also by 1.86amps

And so I suggested two runs of 20amp DP.
It is also to my understanding that you don't want to go too high because if there is a problem the fixtures could/would overheat before the breaker would trip.

Am I incorrect in thinking this way?

K

tkrussell · Oct 13, 2009, 02:32 AM

No, you only add 25% to the load. Just like you stated, 17.7 amps plus 25%=22.12 amps. This one circuit requires a 30 amp circuit with #10 wire.

stanfortyman · Oct 13, 2009, 04:18 AM

Quote:

Originally Posted by KUXJ

The reason I didn't acknowledge the 30amp DP breaker was, I was also taught that you take 80% of load and add it to the original total. Then you adjust up or down accordingly for the fixtures, I.e. Breakers, and wires.

Don't forget, this is only for certain loads as well. Such as electric heaters and continuous loads. Remember, very little in a residence is considered a continuous load.

General lighting and receptacle circuits do NOT use the "125% rule". That is already taken into account in the 3 watts per sq/ft load calculation for dwellings.

KUXJ · Oct 13, 2009, 01:20 PM

Thank You Fellows, for clearing that up for me.

K

chrisbosco · Oct 13, 2009, 09:52 PM

Thank you all for the input. Didn't know about the load calculations.
I guess I should listen to big brother!

Baseboard heater wire sizing

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