Thanks for the fast response.
I have one more question: Is it possible to wire 120V IR heaters on a 240V circuit? �When I run my heater with a 120V hot and a neutral, it works fine (it draws around 2.8 A), but when I run it with two 120V opposite phase leads (without a neutral), it doesn't heat up. �What is different about the 240V heaters? �Should I exchange my 120V heaters if I want to run them on a 240V circuit?
Thanks,
Ed

To run 120 volt heaters off 240 volts you need a 240 volt supply with a neutral wire.  One lead of all heaters is connected to neutral.  1/2 of the other leads are connected to L1 and the other 1/2 to L2. Figure 2 and 3 give you an idea how to do it.

IR heaters once installed are not returnable.

Dieter

To run 120 volt heaters off 240 volts you need a 240 volt supply with a neutral wire.  One lead of all heaters is connected to neutral.  1/2 of the other leads are connected to L1 and the other 1/2 to L2. Figure 2 and 3 give you an idea how to do it.

IR heaters once installed are not returnable.

Dieter

If you run either leg of a 240 volt supply with a neutral wire then you are supplying 120 volts to the heater. �I understand that. �
However, if you supply both legs of a 240 volt supply, then one wire is negative and the other positive and�the two hot wires complete the circuit together because they are "out of phase". �In practice, this does not happen and the IR heater does not draw any current in this configuration. �Since a heater is just a big resistor, there's nothing that should prevent this from working, is there? �Is there some kind of diode in the heater? �Is it because there is an inverter doing something to the electricity supply? � �Figures 4, 5 and 6 show a configuration without a neutral, so I guess the 240 volt IR heaters don't have the "diode" or inverter? �Is that what the black plastic rectangle on the back corner of the heater is?
Kind regards,
Ed

I don't understand your question.  Nor do I know how you are controlling the heaters.  In all cases when using 120 volt heaters with a 240 volt service, the service cable must have a neutral.  The controller (what ever type it is), supplies contacts to switch both hot lines (L1 and L2).  When closed there will be 120 volts present from each contact output to neutral.  It is true the two voltages are 180 degrees out of phase from each other and that is why you have 240 volts from Line to line.  But the heaters are not wired Line-Line, but Line -Neutral.  Half of the heaters attach to Line 1 and half to Line 2.  If all IR heaters had exactly the same resistance, the current in the neutral conductor would be zero.  There are no diodes, rectifiers or anything else in the circuit.  The IR panels, electrically are a resistor that ave voltage on across them switched on and off by a switch or relay contact.

Figure 4, 5, 6, show the use of 240 volt IR heaters and these are thus wired L1 -L2 which produces the 240 volts.  Neutral is not used by these heaters. 

Dieter

Hi Dieter,
Sorry about the confusion! �I'll try to be clearer and let me know if I'm missing something. �
If I wire up 120 volt heaters as shown in figures 4,5,6, with L1-L2, they will not heat up. �Therefore, there is something different between the 120 volt heaters and the 240 volt heaters. �
My questions is: �What is different about the 240 volt heaters compared with the 120 volt heaters? �

A 120 volt heater heats up when connected to Line 1-Neutral, but why doesn't it heat up when connected to Line 1-Line2? �What prevents it from heating up?
Does that help you understand what I'd like to know? �I don't have the heaters connected one way or the other, but I would like to know why one way works and the other does not.
Kind regards,
Ed

Incorrect, If you substitute 120 volt heaters, in a circuit meant for a 240 volts, each 120 volt heater will produce 4 x its rated power, thus 1200W instead of 300W.  If it does not heat up (as you say) then you either burned them out or the high temperature safety device opened up.  Try putting a 6 volt bulb on a 12 volt battery and see what happens to the light.  Same situation here.

The difference between a 300W heater designed for 120 volt and one meant for 240 volt, is in its resistance. P=Voltage squared dived by R.  So 48 ohms vs 192 ohms.

Dieter

Ok, that makes sense. �There is probably some kind of limiter/safety device on the 120 volt heater because it draws very little current (0.05 amperes) when connected to 240 volts, but it works just find when connected to 120 volts, drawing around 2.8 amperes.
One final question: �what difference would there be in the performance of a group of 240 volt heaters connected to a 20 amp circuit with two hot wires (like in Figure 4) and a group of 120 volt heaters connected to a 20 amp circuit with two hot wires and a neutral (like in Figure 3)? �Since the heaters all have the same wattage, they would draw the same amount of power. �Would the 240 volt heaters heat up faster because they have both phases going through each heater?
Kind regards,
Ed