How to hook up 240 V Heater?

[craignlisa]

Good morning all,

My project is going well (takin long but advancing). I am now doing the electrical. I have no problem doing the 120V wiring. I think I understand the concept of AC at 120V. Correct me if I'm wrong: The black, being the hot wire, brings the power to the outlet, and the white, being the neutral, returns to the CB panel, thereby completing the circuit (almost like DC?).

However, with 240V, we use a double pole breaker (both breakers activate at once by means of a mechanical joint (clip) on the breaker handle. The red is hot, the black is hot but what brings the power back to the panel to complete the circuit? Surely not the ground! Hell even with the stove or dryer circuit there's a white or neutral wire completing the circuit at the breaker panel.
So how come heaters only use 2 hot wires?

I need the explanation from an electrician, but more urgently I need someone to show me on the accompanying diagram how to wire my particular heating circuit. It involves 2 blower heaters in the kitchen and one in the bathroom. Each heater must be controlled by its own thermostat. These are simple 2 wire t-stats (digital) that I've used before. I just do not know how to run the wires to utilize only 1 breaker spot (or circuit) in the panel. The situation in the apartment I've renovated has all the heaters on this 1 breaker. I want to use 1 breaker for my new kitchen/bathroom reno, and reconnect the other heaters using the original breaker. I do not think the total wattage of my new blower heaters will exceed the maximum allowable for the breaker but I will check on that.

Help!

Thanks,

Craig

http://www.homerepairforum.com/images/uploads/2005-5-19_Electrical_heating_w550.JPG

[SSN596]

Usinf your DC analogy, current flows "out" the black and "in" the red, or vice versa. If you picture your supply as a large transformer, there is 240 volts between the two "ends" of the transformer. If a load, such as a heater, is connected to these two points, current flows.

Now, the neutral wire is connected at the center of the transformer, so 120 volts would be measured between the white lead and either red or black. On a time diagram, the two voltages are 180º out of phase, but this is not important in house wiring. Every load is considered a single phase load.

In house wiring, the neutral wire is connected to ground at the panel. In a 120 volt circuit, current flows in the neutral wire, so it cannot be part of the safety ground. In a device like a wall heater, all that is needed is the red and black. A ground (bare) wire should also be provided to ground any metal junction boxes or cabinets.

In a stove or dryer, the main loads are 240 ( heaters ) but there may also be some 120 volt components such as timer clocks, drive motors. So the white wire is needed.

In older codes, the white wire was allowed to serve as the safety ground, on the theory that the load was so balanced that little or no current actually flows in the white. Today, most codes do require a 4-wire plug to stove or dryer.

[HayZee518]

Your concept of the 120 volt to neutral is correct. 240 isn't any different other than the two phases are out of sync with each other that means at any given time interval 120 is going out a black and returns via the red and upon the other time interval current is flowing out the red and back along the black,

[craignlisa]

Okay

So if I understand this, I can interrupt either the red or the black using a thermostat and the heater won't be energized.

So in my diagram, since the t-stat is at the end of the run, I should, for example, run red and black to the heater first connecting the red to the heater terminal and joining the black with a new black wire using a wire nut then running it to the t-stat wire. The red of the new wire is attached to the other terminal on the heater and runs to the other wire on the t-stat thereby completing the circuit.
Clear enough? Ha Ha

By the way, since I'll be connecting more than 1 heater on a circuit, how many parallel wires can I attach to the terminal screws on the heaters if I follow code? I know that presently there are 2 wires on each screw terminal.

If you see anything wrong with this please write and comment because this is how I'll be running the wires Monday.

Thanks,

Craig

[HayZee518]

For a 240 heater with an integral "stat" or a remote "stat" normally both sides of the line are disconnected. Don't use a single pole stat. The thermostat will have two blacks and two reds (pigtails) The line side goes on one black/red pair, the output on the other red/black pair. You can use two wire for the feed and output just tape the white with a red tape or black tape to distinguish it from a regular 120 volt circuit for the next person that might open up the junction box. Black or red tape on a white is an electricians universal language that the wire is something other than a neutral.
For instance in a 480 three phase circuit you'll find the conductors wrapped with a yellow tape, brown tape and a orange tape on their outermost points where they connect to breakers, starters etc.
A 120 volt heater uses a single pole "stat." In this case you'll be breaking the black wire "hot." with the "stat."

[SSN596]

It is true that breaking either the red or black stops current flow. However, the other lead will still be hot ( 120 volts to neutral or ground. This is not a safe situation for anyone who might work inside the heater.

[Rewired]

Just a note on some of these electric heaters and how they are wired... I am not sure about other parts of Canada, but here in Ontario, I know and have seen many MANY times where electric heater circuits were wired with a single pole thermostat breaking ONE leg of the 240V feed!!! (except in bathrooms they do require a 2-pole thermostat)
Yes I know it doesn't sound correct and I agree it can be unsafe if you go poking around in the heater but technically the thermostat isn't really deemed a " disconnecting means" and really, you should be pulling the fuses or turning off the breaker before you mess with anything, especially if you are messing about with "Canadian" electric heating circuits!

A.D

[craignlisa]

Whoops, now I'm confused.

The fact of the matter is I do not understand why to use a 4 wire t-stat in the [u]bathroom</u>? Is it because of the possibility of someone adjusting the t-stat while running a faucet? Is the 4 wire t-stat better grounded? What are the advantages and/or disadvantages of a 2 wire as opposed to 4 wire?

I learned long ago that you do not touch anything in the switch box unless the breaker has been switched off! So there wouldn't be any danger of electrocution if someone else followed that simple rule whether it was 2 wire or 4 wire. I'm hoping people follow that rule.

So if I was to use a 2-pole t-stat, how could I wire it so that it is at the end of the run? Do I need 1 wire in and 1 wire out in this case? I see that Hayzee has shown it schematically this way, but would I do that in practice?

Thanks again,

Craig

[HayZee518]

While it's true a thermostat is not a disconnecting means it is a controlling device. A disconnecting means SHALL open all current carrying conductors. A disconnecting means shall have a visible break in the case of a disconnecting switch. A circuit breaker cannot be seen to be open so one just assumes that with the handle in the off position it is open.
Maybe this diagram will help you with those heaters.

[Rewired]

Sorry if I confused anyone about the "one pole two pole" thing.. I was just mentioning how they wired some things up here and they like 2-pole thermostats in bathrooms ( I assume) so there is NO chance of a shock or a tingle by having a heater thats "energized" and in a damp location.. No worries though.. Use the 2-pole thermostat ( I would myself) and everything will be fine.


Oh ya, HayZee.... Your diagram with the 3 strip heaters... You show them wired in SERIES , not PARALELL..[:0]

Sorry, just had to point that out!!

[HayZee518]

Oops - I boo booed.

[craignlisa]

Guys,

I've got it!

It's cool Hayzee, I understood the series/parallel thing.

Re-Wired: Thanks too, I live in Quebec and our codes pretty much resemble those of Ontario and in the US as well. I am wiring it all with 2 pole stats.

Thanks though Hayzee to have explained the definition of "disconnecting means". I now think I can make a knowledgeable decision on this topic.

Thanks to the forum (Jeez it sounds like an acceptance speech at the awards- ha ha!)

Craig[8D]

[HayZee518]

I have a suggestion - if you have multiple heaters in the same room and would like them thermostatically controlled but the current draw for all heaters is too much for thethermostat, consider a contactor for the total current draw and use a single pole thermostat wired into the coil of the contactor. Use 120 volts for the control circuit or at best a 24 volt coil for the contactor through a step down transformer. (high tech!)
Parallel wire all heaters and bring the loads to the contactor - feed the line (240) to the line side of the contactor.
Use part of the 240 to feed a 240 volt to 24 or 120 volt step down transformer. One side of the transformer would go to one side of the coil of the contactor. the other goes through the thermostat then back to the other side of the coil of the contactor. Now the contactor coil is operated off the thermostat and the contactor will handle the higher currents presented by the heaters. Add the total amps together and use this for sizing the breaker which will feed the heaters through the contactor.

[HayZee518]

AC contactor for heaters