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Thread: steam generator - wiring 8kw on 30amp break

  1. #1

    Default steam generator - wiring 8kw on 30amp break

    I have a Thermasol 140 series steam generator installed 25 years ago in a residentional bath southern california. In the process of a bath remodel and wanting to change to the curent 25yr old steam generator with the same model from the same manufacuture. (the old one has gotten corroded but still works).

    Looking at the wiring and breaker, it is on a 30 amp double breaker with 10AWG wire type THHN flexible conduit. The specs for the new generator and the old specify for the SSM-140 series Thermasol:

    37 amp @240VAC, 8 Wire, 40 breaker, 1 ph, 8.0 KW

    I see I have two options:

    option 1. For the last 25 yrs, have been running a dangerous and illegal fire hazard. Need to call a licensed electrician immediately. Change the breaker to a 40 amp, pull 8 AWG wire in...and pay him $300 to $800.

    option 2. Have never had a breaker trip in 25 years, if there was any fire hazard the breaker offers protection. Only use the steam about 5 minutes at time , 3 times a week. Not a long draw. Don't worry. Code allows one step up anyway on wire size.

    What option do you recommend or what additional should i know?

    Thanks

    Malcom

  2. #2
    Retired Defense Industry Engineer jadnashua's Avatar
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    In the funny, non-logical wire gauge sizing, up means smaller number (larger diameter wire, not up as in bigger number. If it actually pulls the stated 37A, then it's a surprise that the breaker didn't trip. Plus, if the thing actually was left on for awhile, it could burn up the wiring. It depends on how it was run how easy it is for the wire to dissapate the heat. Run it tight in a wall with lots of insulation verses stapled to the joist, sitting in the open will make a difference in how hot the wires actually get. if this was ever inspected, it would fail...you should follow the manufacturer's instructions.

    Is the data plate for the old one state exactly the same values as the new one? The same model doesn't necessarily mean the same thing after 25-years.
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

  3. #3

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    Hello Jim,
    thanks your quick reply.
    The new is certainly not the same as the old. The old model is a simple heater with an on/off switch. The old is stainless boiler and aluminum plates. The new has a printed circuit board, thermostat, and all Stainless steel..
    I'll pull the plate tomorrow.

    Third option that I should consider is to to scale down to a less powerful model that draws 28amps.

    thanks,
    Malcom

  4. #4

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    Your #10 wire is protected by your 30A breaker. There is no fire hazard unless for some reason the breaker is bad.

    You should really follow the ratings on the nameplate. If you choose not to the wire should still be protected. However if the breaker trips you will obviously have to upsize both the wiring and the breaker.

    -rick

  5. #5
    Plumber jimbo's Avatar
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    Quote Originally Posted by Poisson Cru View Post
    . Don't worry. Code allows one step up anyway on wire size.

    What does that mean??

    And consider the possibility that the old one, for reasons of "old age" or it was modified by original installer, might not be really operating on 8 KW. Apparently not if you don't have breaker trips. But the new one might start up at 8KW right out of the box!

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    Moderator & Master Plumber hj's Avatar
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    Circuit breakers are sized to protect THE WIRE first, and the device connected to it second. IF the breaker is correct for the wire, there is no fire hazard. ANY attempted overload, regardless of the reason will trip the breaker before the wire can be damaged.

  7. #7
    Retired Defense Industry Engineer jadnashua's Avatar
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    My point was, things may not have been working right...if the old one was actually pulling the 37A, and the CB wasn't tripping, things could have gotten hot. He originally indicated it was the same model, which implied it was drawing 37A, which is not good on 10g wires, and SHOULD have tripped the CB, but if it was working, and didn't, create problems.
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

  8. #8

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    In my experience, electrical things are "happier" when they are run on the correct size wire or larger.

    I don't know if you have ever tried using a long small extension cord for something way out in your yard - like an electric lawn mower or air compressor. But these things will not work very good if the wire is too small. Sometimes they will just "humm" and that is it!

    If the wire is the correct size or larger, they sound "robust" and seem to be saying "Let's get to work!"

    So I say correct size wire or larger gauge and proper associated breaker.

  9. #9

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    Excellent and very good.
    Found the original data plate as Jim recommended and lo and behold the previous older model 140 Thermasol is wire 2, 230 volts, 30 amps, 60 cyc, phase 1. So the manufacturer did change things after 25 years.

    The new model is 40 amp. So I'm going to downsize to their smaller model, SS-84, that specs at 28 amps. The shower size is 78 cubic feet and I hope will be ok.

    Pulling new wire, is too much of a gamble. Don't know what I might run into.

    Malcom

  10. #10
    Retired Defense Industry Engineer jadnashua's Avatar
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    It's my understanding, and I"m not a pro, even the old one should have had a larger circuit as it's generally not recommended to load the thing beyond 85% of rated load continuously. That may apply for other types of loads. Anyway, as you indicated, going with a smaller unit and leaving the wiring alone is certainly easier and cheaper assuming it performs to your needs.
    Jim DeBruycker
    Important note - I'm not a pro
    Retired Defense Industry Engineer; Schluter 2.5-day Workshop Completed 2013, 2014

  11. #11

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    Option 1) Pull new wire. Might be easy, might not.

    Option 2) Get a small unit. Will be easy.

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