I am about to add electric baseboard heat to a finished attic space in a
house that I own.
The wiring diagrams in a book that I have and on the Internet show to create
a 220/240-volt system using a 12/2 feed up to the heater(s), with 12/3 going
from the heater to the thermostat. I assume that means that at the panel
box there would be a double breaker to create the 220/240-volt, and that the
white wire would be coded at the panel and at the heater to be black. But,
that seems a little strange to me.
Is that how it is supposed to be done, or is it better or more correct to
run 12/3 as the feed and use the black and red wires as the hot wires?
No, because there is no need for a neutral for a 240V heater. Just
extra expense and more wires in your boxes.
I'm curious why you'd need 12/3 from the heater to the thermostat?
Are you using electronic thermostats? Typically the 240 just goes
from the panel to the thermostat and then from the thermostat to the
There is a special 12/2 made for 220v heaters, the outer jacket is red and
the wires inside are colored red and black with a ground. It is acceptable
to run regular 12/2 cable but the white wire must be recolored with most any
color except white, gray or green.
I'll have to check the wiring diagram again to be sure I read it correctly.
It's in a Black and Decker wiring book that I have at the house (page 171, I
think), and I thought I remembered seeing 12/3 going to the thermostat which
was between two heater units. Maybe it's because the diagram I was looking
at showed the thermostat between the two heater units, or maybe I just plain
read it wrong, or I am not correctly rembering what I saw. I'll post back
later today when I look at the book again.
Assuming your thermostats are 230 volt 'line voltage type' ?????
Also don't know why you need 3 conductor; either from panel to
thermostat or thermostat to heater!
More normal (and exactly how this house 1970 is wired) is 12-2 red/
black (with a bare ground conductor of course).
Black/white can be used provided the white is colored or taped (red
nail polish will do) to identify that it is hot (not neutral!).
You are correct, the red and black are connected through a double-pole
circuit breaker for #12 AWG that's a 20 amp DP breaker. Don't forget
the ground connection at each point also. For 230 there is no neutral.
Use standard wiring practice; insurance companies (both for property
and life insurance) can be picky!!!!!!!
With some (double pole thermostats) both red and black connect
'through' the thermostat. Most of my original ones do so.
But I have one or two that are single pole; in that case the black
goes through the thermostat and the red is connected straight through.
Make sure you thoroughly understand how the thermostat must be wired
also that they are the correct type. There have been cases where
people have hooked up low voltage thermostats to 230 volt line voltage
and blown the sh** out of them. In one case starting a small fire!
Low voltage thermostats are commonly used to control the low voltage
controls of furnaces etc. Or they can, using extra hardware (control
relays) control line voltage heaters. That then becomes a matter of
why use relays, where to mount them and how to get low voltage wire
from them to the 'low voltage thermostats'! Different discussion
BTW we have found electric baseboard heaters and line voltage
thermostats very reliable. Since 1970 we have less than $100 in
maintenance. Two thermostats and one circuit breaker.
Any doubts get advice/help. In this area we have had three fatalities
(all children!) and a total of 3 fires all blamed on electrical
problems prior to Feb 15th, this year of 2009!
No matter what heating is used do not let people sleep in areas
without escape routes; whether that is basements or attics etc. Equip
(for only a few dollars) any new areas with smoke detectors.
Thanks. My mistake. I checked the wiring diagram again and what I thought
I remembered seeing was not correct. It does show all 2-wire and no 3-wire.
I had briefly noticed red and black wires in the circuit and I was thinking
that meant 3-wire. But, upon looking more carefully, I see now that the red
and black wires were just the thermostat wire colors.