Adding a Bath Electrical Circuit

Discussion in 'Electrical Forum discussion & Blog' started by diydude, Jul 30, 2012.

  1. jwelectric

    jwelectric Electrical Contractor/Instructor

    Messages:
    2,529
    Location:
    North Carolina
    The maximum circuit that can supply the mat regardless of the square feet being covered is 20 amp. The largest load the circuit of the mat can carry is 15 amps. All this is directed to the mat itself and has nothing to do with the controller that you posted.
    Should one to decide to use a larger mat then they would choose a larger controller that would match the square footage being installed.
    http://www.warmwire.com/products/co...or-larger-areas-controlled-by-thermostat.html

    The controller which is the weakest link in this circuit is what will mandate what is to be installed. It requires a 15 amp circuit and recommends a dictated circuit.

    As an electrical inspector I would not pass the installation should it not be as the controller states in its installation instructions.

    As to your cable installations question, I can’t address Washington but the here in NC we are not requiring anything special in the crawl space or any hole drilling.

    Each node of a parallel circuit will add current to the entire circuit. In the node for the heating mat the mat and its controller will be a series circuit of a predetermined resistance. This node will add to the other nodes of the circuits for a total amperage draw that the conductor must be capable of carrying.

    The total resistance of a parallel circuit will always be less than the lowest resistance of any single node. Should one of those nodes lose all resistance then the amperage draw will increase to the point that damage would occur to the insulation on the conductor. This is the job of the fuse or the circuit breaker. It will open in the event of a high current draw and protect the conductor.

    A GFCI device does not open in the event of an overcurrent event. All the GFCI device is looking for is a difference between two current carrying conductors of 4 to 6 milliamps.
    What the manufacturer of the GFCI device is saying is if more than 15 amps is allowed to flow through this device it could damage the integral wiring of the circuit board and render the device useless.
  2. diydude

    diydude New Member

    Messages:
    62
    Location:
    Seattle,WA
    Ugh, ok. jwelectric, I'll take your suggestion. Please confirm this is what you stated:

    Circuit 1 (20 amps): GFCIs only
    Circuit 2 (15 amps): Floor thermostat and mat
    Circuit 3 (Existing 15-amp branch circuit): Add recessed light and sconces that are substituting for existing vanity lights

    Edit: My concern is overloading the 15-amp branch circuit. When I add up the wattage, including the new recessed light, I'm at 1575W. This would most likely not pass an inspection, correct?:

    Lights fixtures:
    - kitchen (2): 240W (4 - 60W bulbs)
    - chandelier (1): 360W (6 - 60W bulbs)
    - downstairs bathroom (1): 315W (Recessed light (75W), Sconces (4 - 60W bulbs))
    - deck (1): 180W (2 - 90W bulbs)
    - downstairs bedroom (2): 120W (2 - 60W bulbs)

    Outlets:
    - downstairs bathroom GFCI (1)
    - downstairs bedroom (1)
    - upstairs bathroom GFCI (1) - probably not necessary that it be GFCI, since it feeds off the downstairs GFCI. Anyway.
    - living room (1)

    Other:
    - downstairs bathroom fan (180W?)
    - kitchen range hood (180W?)
    Last edited: Aug 4, 2012
  3. jwelectric

    jwelectric Electrical Contractor/Instructor

    Messages:
    2,529
    Location:
    North Carolina
    Are you planning on having all these light on at the same time?

    If it is a concern while the walls are open then install an addtional circuit
  4. diydude

    diydude New Member

    Messages:
    62
    Location:
    Seattle,WA
    No, I wouldn't have all the lights on at the same time; there are only two of us in the house :D I remember reading something about a 3-hour continuous load, and only the deck light would be on continuously for 3+ hours. I believe I have 5 open slots in the panel (although, it's only a 60-amp panel - that's another issue I'll have to deal with later), so I could run three new circuits.

    I'd have to amend my electrical permit. Oh, boy. And yes, I was supposed to meet with an electrician this past Thursday before applying for a permit, but they never showed. So, I decided to move forward with getting permits before the weekend.
    Last edited: Aug 5, 2012
  5. jwelectric

    jwelectric Electrical Contractor/Instructor

    Messages:
    2,529
    Location:
    North Carolina
    There is a difference between calculating a load for commercial and industrial than doing a dwelling unit calculation.

    In industrial and commercial we do a continuous calculation but for a dwelling we do the 3 watts per square foot and no continuous load for these circuits.

    Although it is a good idea to do the wattage per light fixture for branch circuits there is no need to do the continuous factor to the circuit. It is very unlikely that one would have 1400 watts of lights burning for a very long period of time let alone for three hours at a time. Should someone do this repeatedly the power company would invite them to the board of directors meeting as a stock holder.
  6. diydude

    diydude New Member

    Messages:
    62
    Location:
    Seattle,WA
    LOL. Ok, thanks. So, I'll just add the recessed light to the existing 15-amp circuit and call it good. Thanks for the advice.
  7. diydude

    diydude New Member

    Messages:
    62
    Location:
    Seattle,WA
    Ok, I have another question. I'm investigating another floor warming system by Warming Systems, Inc. The instructions mention that only a certified electrician can connect the floor heating mat (I'm actually going to be using the warming wire instead of the mat - don't think it matters). Do I need to worry about this mandate with regard to an inspection?

    http://www.warmingsystems.com/Cable Set Install Instructions.pdf

    Only a certified electrician who is familiar
    with electrical installation codes and
    practices can connect the floor heating mat.
    All wiring must comply with the
    specifications in the US National Electric
    Code and all local electrical regulations
    and standards.
    Last edited: Aug 7, 2012
  8. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

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    Location:
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    You may lose any warranty claim if not installed by a licensed electrician.
  9. diydude

    diydude New Member

    Messages:
    62
    Location:
    Seattle,WA
    I can live with that. I'm just concerned about legal issues.
  10. diydude

    diydude New Member

    Messages:
    62
    Location:
    Seattle,WA
    I'm replacing the existing two-gang box with a three-gang, and I'd like to use an adjustable box. However, I'd have to make a small notch in the jack stud to install it. Is there a reason why I shouldn't make a notch? I didn't think so, but I thought I'd ask.

    Attached Files:

    Last edited: Mar 8, 2014
  11. jwelectric

    jwelectric Electrical Contractor/Instructor

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    Location:
    North Carolina
    Only if you are not worried about your roof swagging
  12. ActionDave

    ActionDave Electrician

    Messages:
    345
    Location:
    Colorado
    How big of a notch? Load bearing wall?

    If it is a small notch or a non-bearing wall then the wood is nothing but in the way.
  13. diydude

    diydude New Member

    Messages:
    62
    Location:
    Seattle,WA
    I decided to just use a different box. The wall is load-bearing, and it's not worth the risk just for an electrical box. It would have been nice to have the flexibility to adjust the depth, though.
    Last edited: Mar 9, 2014
  14. Reach4

    Reach4 Active Member

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  15. houptee

    houptee Member

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    Last edited by a moderator: Mar 9, 2014
  16. diydude

    diydude New Member

    Messages:
    62
    Location:
    Seattle,WA
    Hmm. I ended up using the Carlon BH353A Super Blue box. I followed someone else's lead and installed a piece of 1/2" drywall on the stud next to the box so I could line it up flush. It appears to be perfect. Switches installed are temporary basic single-pole switches. Once I get closer to finishing the bathroom, I'll install the real switches.

    Attached Files:

    Last edited: Mar 9, 2014
  17. diydude

    diydude New Member

    Messages:
    62
    Location:
    Seattle,WA
    The manual for the Suntouch floor mat mentions needing a dedicated circuit, and it also mentions the possibility of installing the mat and thermostat on an existing circuit. I've installed a dedicated 15-amp circuit for the floor heat in the downstairs bathroom, but I was wondering if I can run the upstairs bathroom's mat on the same 15-amp circuit I'm using for the downstairs floor mat. Each mat will only consume about 2 amps. The reason I ask is that my panel's neutral bus bar is full, and I'll be working on the upstairs bathroom later.
    Last edited: Mar 20, 2014
  18. diydude

    diydude New Member

    Messages:
    62
    Location:
    Seattle,WA
    I got in touch with Suntouch this morning, and I was told that the two thermostats have to be on different circuits.
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