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Thread: Portion of 240 Volt Circuit only Delivering 120 Volts to Baseboard Heaters

  1. #1
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    Default Portion of 240 Volt Circuit only Delivering 120 Volts to Baseboard Heaters

    Howdy,

    My family moved into a new (used, actually) house this summer. The gas water heater and gas furnace went kaput soon after. I had a pro install a tankless water heater, but have been working on installing baseboard electrical heat myself (our intent is to install solar panels at a later date to help offset all that power use). They are Cadet "hydronic electric" baseboards, 240 volts.

    Things have mostly been going just fine... with 20-amp and a 30-amp circuits (240v) spanning 6 heaters and 5 zones working beautifully.

    But I have one circuit that's causing trouble. It's a 20 amp/240-volt circuit with a current load of roughly 11.45 amps (one 1,250W baseboard, one 1,000W baseboard, and one 500W baseboard). The 500W baseboard heater is in the upstairs bathroom, and has its own thermostat (all thermostats in the system are Cadet Programmable Double-Pole 16 Amp 208/240 - Model TH110). The other two baseboards (1,250W and 1,000W) are on a separate thermostat (same model) that serves a zone for the living room, dining room, and kitchen. When I originally planned this two-zone circuit, I had hoped to include an additional 1,000W toe-kick heater in the kitchen, but the circuit breaker was tripping under that load (despite being at roughly 15.62 amps--still under 80%). At the time I attributed this to line-loss, and removed the toe-kick with the intent of adding it to another circuit later (or perhaps deciding we didn't need it if the main area stayed warm). The total wire length for the circuit is probably 120 feet, but no one run (from the breaker box, through the line voltage thermostat for that zone, and to the baseboard) is longer than maybe 60 feet. It's wired with copper 12-3 w/ ground (I know the extra neutral is unneeded on a 240-volt circuit, but it's what I had, and I simply used it as an additional ground). The wire's a mixture of NM and MC (for places where I ran it through joist bays or walls and could not attach it to the framing). I confirmed that the two-pole circuit breaker does indeed span the two phases in the panel.

    Here's the problem:

    The living room/dining room/kitchen circuit wasn't "keeping up" in a recent cold snap. I noticed that while all the other similar baseboard heaters throughout the rest of the house get nice and hot while they are cranking... the ones in the living/dining/kitchen zone were only warm. I suspected that these heaters were only getting 120 volts... which would cause them to put out only about 25% of their expected output... and the symptoms seemed to jive with that.

    A voltage meter confirmed that the heaters in this zone are only getting 120 volts. These volts are all coming in through the black "hot" wire. The red "hot" wire is not bringing its 120 volts to the picture. It is NOT a problem that affects the whole circuit... as the bathroom zone works fine and I confirmed that it is receiving all 240 of its volts.

    At first I thought that it was a problem with the thermostat that served the living/dining/kitchen zone, but now I think it is a wiring problem (or possibly a problem with one of the baseboards). I unhooked the (working) thermostat from the bathroom zone and inserted it into the living/dining/kitchen zone, and it didn't work. When I put it back on the bathroom circuit... it no longer functioned properly. I believe it got fried.

    I've checked all connections within the living/dining/kitchen zone... but have turned up nothing.

    My best guess at this point is that the wires somehow got damaged during pulling, and that the red wire is shorting out somewhere.

    My next step was going to be to measure resistance in all the wire runs to see if I could detect a short.

    Any ideas from you guys?

    Thanks!

  2. #2
    DIY Senior Member Reach4's Avatar
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    One possibility that you somehow wired two heaters in series, and maybe the red wire is just a jumper between heaters.

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    Thanks for the reply. The heaters are all at the end of their various runs (which tie back to a junction box downstream of the thermostat). I've checked those connections and everything checks out.

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    Retired Defense Industry Engineer jadnashua's Avatar
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    What are you measuring to get 120vac? That would only be available hot-neutral (well, hot-ground would be close, too). To get the 220, you'd have to measure hot-hot. If one of those hot leads was open or loose, and you measured to the other to ground, then you need to find the open. It could be a contact in the thermostat that is burned, or something similar.
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

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    Hey Jim,

    I was measuring hot-hot. On the functional units elsewhere in the house, measuring hot-hot gives me 240v as expected. But on the "problem" zone, I only get 120v. When I measure to ground (or neutral) from each hot on the "problem" zone, I get 120v on black, and 0v on red.

    Thanks for your reply!

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    Retired Defense Industry Engineer jadnashua's Avatar
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    Well, I think you've isolated the problem...follow the red wire to find out where it is attached at the other end, and it is either open or something it goes through is not making a proper connection.
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

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    DIYer, not in the trades LLigetfa's Avatar
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    Maybe a dumb question, but is the thermostat closed at the time?

    An open on one hot leg would not give you any heat at all. If you get some heat, then either they are wired in series, or wired to a 120V circuit.

  8. #8
    Test, Don't Guess! cacher_chick's Avatar
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    I was thinking the same thing- you would not get 120 across the wires unless one were connected to a neutral or equipment ground. It's time to start tracing the circuit.

  9. #9
    Jack of all trades DonL's Avatar
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    One thing that could give you 120V is if a element is bad and one side is shorted to ground.

    Maybe it was wired wrong from the start ?

    If it worked at one time, then a wiring error should be out of the question.


    Good Luck.
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    Hey LLigetfa, yeah, it was closed. I get minimal heat, 240v going into the thermostat, and 120v coming out. And a portion of this circuit works flawlessly... delivering 240v to the baseboard in the bathroom. It's just one side of the circuit that's having the trouble (so, not a 120v circuit, or a problem at the breaker box, etc.).

    I'm going to trace the circuit. Thanks everyone. I'll let you know what I find!

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