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Thread: Multiple Space Heaters - Article 424

  1. #1
    Join Date
    Apr 2017
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    Richmond, VA
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    Multiple Space Heaters - Article 424

    In preparing drawings for commercial buildings, how big of a circuit can we have for things like heat pumps, VAVs with heating coils, etc. (dedicated pieces of equipment that provide heat)?

    I've found section 424.22(B) that says 60 A OCP is the biggest I can have.

    (B) Resistance Elements. Resistance-type heating elements in electric space-heating equipment shall be protected at not more than 60 amperes. Equipment rated more than 48 amperes and employing such elements shall have the heating elements subdivided, and each subdivided load shall not exceed 48 amperes. Where a subdivided load is less than 48 amperes, the rating of the supplementary overcurrent protective device shall comply with 424.3(B). A boiler employing resistance-type immersion heating elements contained in an ASME-rated and stamped vessel shall be permitted to comply with 424.72(A).
    However, 424.3 gives me this:
    424.3 Branch Circuits.(A) Branch-Circuit Requirements. Individual branch circuits shall be permitted to supply any volt-ampere or wattage rating of fixed electric space-heating equipment for which they are rated.
    Branch circuits supplying two or more outlets for fixed electric space-heating equipment shall be rated 15, 20, 25, or 30 amperes. In other than a dwelling unit, fixed infrared heating equipment shall be permitted to be supplied from branch circuits rated not over 50 amperes.
    (B) Branch-Circuit Sizing. Fixed electric space-heating equipment and motors shall be considered continuous load.
    which makes me think that I can only provide 60 A OCP if I'm only feeding one piece of equipment. If I'm feeding 2 or more heaters I can only go up to a 30 A branch circuit. Does that sound right to everyone? If that's the case, why would it be? What's the difference between feeding two 24 A heaters from one breaker rather than a single 48 A heater?

    If I'm trying to squeeze down the number of circuits on the panel, could I provide each heater with a fused disconnect and then feed those disconnects with a bigger breaker? If the disconnect is fused, that would make it the final overcurrent device, correct? Therefore I would be feeding each branch circuit with OCP that it's rated for, since the branch circuit would begin after the disconnect, correct?

    I tried searching around for this, but I either couldn't figure out the right words to search for, or it must be something strange we want to do. I'd be grateful for any insight anyone has. Thank you.

  2. #2
    Join Date
    Jul 2003
    Location
    New Jersey
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    23,295
    Can you run a feeder and then tap to individual disconnects with overcurrent protection?
    Rob

    Moderator

    All responses based on the 2014 NEC unless otherwise noted

  3. #3
    Join Date
    Apr 2017
    Location
    Richmond, VA
    Posts
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    Quote Originally Posted by infinity View Post
    Can you run a feeder and then tap to individual disconnects with overcurrent protection?
    That's what I'm thinking of doing. I just wanted to get some feedback on the language of the NEC and whether that's what I'd be doing within the language of the NEC. I just don't want to submit drawings for permit and have the code reviewer come back and say the OCP on my branch circuit is too large because he considers the branch circuit to start at the panel, when I'm considering it to start downstream of the fuse on the disconnect.

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