Problem with 240V Elect Baseboard Heater

JRHP · 10-03-2010, 11:10 AM

I have two 240V Elect Baseboard heaters wired to a wall mounted SP line voltage Tstat and a 240V DP breaker. Everything seems to be wired properly - it all worked OK last year. The black wire runs through the Tstat to the 1st baseboard, and the second baseboard is wired in parallel at this point (so both baseboards are controlled by the single tstat). The white wires are connected together at the junction box on the 1st baseboard. Nothing unusual here.

My problem is that the 1st baseboard seems to always be on, even when the tstat is off. It appears to be running only off of the 120V white wire. Do I have a bad baseboard heater?

Why doesn't the other one run only off of the white wire (120V) when the black wire is "broke" at the tstat when it is off? Is there something in the baseboard that prevents it from turning on unless it sees only 240V mol? If so, can this be repaired without purchasing a new baseboard heater?

Thanks in advance for any explanation!

McSteve · 10-03-2010, 01:16 PM

Assuming the wiring is correct, it is possible that the first heater may have fault to ground. Since the thermostat only opens one leg, current can still flow from the other leg, through the fault, and to ground. The amount of heating element between the incoming power connection and the fault has enough resistance to keep from tripping the breaker like a direct short would.

You can confirm this by disconnecting the wires at the heater, and measuring with a multimeter set on resistance. I'm not sure what the resistance between the two line terminals should be, but the resistance between line and ground should be infinite. If it is not, than the heater is shorting to ground and should probably be replaced.

joed · 10-03-2010, 07:25 PM

I agree. It sounds like a fault to ground in the first heater.

Kirky · 10-03-2010, 08:46 PM

ucan check the resistance of the heater by looking at the unit itself and seeing what its rated at and dividing 240v into the wattage and getting the current, and then divide that into the voltage of 240v that will give you the resistance of the heater. With that you can determine if its bad. And by the previous threads, fault is at hand. And sometimes the resistance is marked on the element itself (sometimes).

JRHP · 10-04-2010, 10:30 AM

You are right! Found one wire on the first baseboard had a short to ground. Thanks for the help! This site is great!
Jim