I have installed a receptacle for a portable heater that runs on 240. I used 10/2 wire and a 30 amp breaker. It seems that I am only getting 120 off the breaker.

I used the black and white wires to the breaker and the ground to the ground bar.
The receptacle is grounded.

Any ideas what I have done wrong.

Are the poles of the breaker tied together by a bar?

Yes it is a double breaker

I did try the breaker in the main panel and it worked fine. I have moved it to a pony panel but I didn't think it would matter.

How big is the heater? Did the instructions recommend a certain SIZE circuit?

What made you arbitrarily pick #10 and 30 amps??

What brand panels are they?

The heater is industrial. I was advised that it required 30 amp and 10/2 wiring.

The panel and breakers are stab lock. When I test the breaker with a volt meter I get 120 on each side.

For some reason it appears that the breaker is spit.

Sound like a "tandem" circuit breaker, two separate poles or circuits in one full size breaker.

Placement of this type of breaker is critical in a panelboard.

Sounds like you have it in one standard breaker slot, in which case, only one leg of the two inside a panel has been connected to. The result will be 120 vol output on both poles, fine for two 120 volt circuits, but impossible to get 240 volts.

A tandem breaker is intended to connect to both hot legs in a panel, so the result will be 240 volts.

Or you have a half size two pole 240 volt breaker, same case, must connect to both legs in panel, not just one.

If it is a Stabloc panel then I bet you are not installing it across the two busses. It is quite easy to install it wrong.

WHO told you to use #10 and 30A?? What does the heater draw? How many watts is it?

The heater is 4800 watts 240 volts.

I notice that there is another 30 amp breaker in the box for the dryer that seems to be working well.

I did try the breaker in the main panel and it worked fine. My problem seems to be with the pony panel.

Are you saying that I need to replace my 30 amp breaker for a 30 amp tandem breaker.
Would this be what they are using for the dryer.

Is there a way for me to connect the one breaker to both legs in the panel.

Thanks everyone. The problem is fixed. I had the breaker in a single slot. Of course, once I crossed both bars everything was fine.