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240V Baseboard heater wiring questions

Post in 'DIY and General non-hearth advice' started by SolarAndWood, Dec 16, 2012.

  1. SolarAndWood

    SolarAndWood Minister of Fire

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    I am trying to resurrect an old baseboard system I pulled out 5 years ago to replace exterior walls...http://www.hearth.com/talk/threads/backup-heat.101152/

    All of the heater loops were powered by 4 adjacent 20 amp single breakers. One of the cables went through a Honeywell box that the thermostat goes to and then to one end of the string of heaters. The second cable went directly to the other end of the string of heaters. A few ?s:

    1. I would like to string 10 of the units together. They are 240V single phase 600 watt 2.5 amps. Do my 4 20 amp breakers effectively give me a 40 amp circuit? i.e. 25 amps is ok?

    2. All of the cabling is 12 wire. Does this mean I can't string 10 units together safely?

    3. It looks like half the strings of heaters are wired parrallel on the two white wires and the other half on the two black wires. Does this make sense?

    4. Should both cables come out of the wall with 240 across the black and white when the tstat is calling for heat and only one when the tstat is not calling for heat?

    I think I need to wire these as two separate circuits because of the total current on 12 wire? Thanks for the help.

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  2. Highbeam

    Highbeam Minister of Fire

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    You've got a mess there. I suspect you actually only have 2, 20 amp, 240 volt circuits but the original installer used four of the cheaper single breakers and skipped the grounds for some reason or you just haven't found how he did it yet. For example, with metal conduit some folks use the metal conduit for a ground. The heaters should have a ground but will function without. Daisy chaining is fairly normal so long as the sum of the amperage draw does not exceed 16 amps which is 80% of the breaker.

    I would not wing it. This doesn't sound to be set up legally or properly.
  3. SolarAndWood

    SolarAndWood Minister of Fire

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    I figured out the ground and took care of it. They definitely went over 16 amps on the original runs. There were two strings in the space controlled by one tstat. One string was 22.5 amps and the other 20. I want to run 25 amps total. So, I think I will run 2 sets of 12.5. Just need to run the other tstat controlled feed over for the other bank. This should keep the wiring simple and safe other than the 4 breaker thing. That will go away with the new service/panel next year.
  4. Highbeam

    Highbeam Minister of Fire

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    To fix the 4 breaker thing, you just replace them with the appropriate double breakers which are cheap for common panels. You can also tie the breakers with a bar somehow, a sparky will know, to guarantee that both breakers will trip together.
  5. woodgeek

    woodgeek Minister of Fire

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    I'm no tradesman....but I know that you should use a double breaker for 240V, not wire a 20A breaker into anything smaller than 12 ga, and ground your appliances.

    You might look into getting new baseboard/tstats as they should be pretty cheap...and maybe you can get something that fits the bill a little better. IMO, of you end up running 2 or 3 circuits each with their own stat, that's ok too. Zoned heating is one of the advantages of baseboard.

    If OTOH you don't have enough slots in your existing panel, put in a higher amperage (double) breaker, and run a new heavier gauge line.
  6. SolarAndWood

    SolarAndWood Minister of Fire

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    12 wire is already run...just need to not have it hooked up to 40 amp of breaker. I'll have to see if I can still get breakers for this thing or find some kind of a bar to connect the singles. I have a bunch of doubles for that box but they are all at least 30 amp.
  7. brian89gp

    brian89gp Feeling the Heat

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    Sounds like ring circuit like what is found in the UK. I don't think they are legal here.

    1. No. 80% rule says no more then 16A of constant load on a 20A double pole breaker
    2. No. Get rid of the ring (break it in the middle) which will split it into two separate 20A strings that have 12.5A constant load with 5 heaters each
    3. Sounds half-assed
    4. You need a 240v double pole thermostat. The thermostat needs to be inline on both hot conductors.

    If it were my house I would rip it all out. Whoever installed it didn't do it right. Same way everybody on here advocates for proper installation for stoves for safety reasons, electrical is no less important.

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