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NEC 210.21

Discussion in 'Electrical Engineering' started by Matthew Beasley, Oct 27, 2006.

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  1. Am I reading Article 210.21 (B) (1) properly?

    If an receptacle is the only one on the circuit, the branch circuit rating
    may be less than the receptacle? For example, according to this article, it
    would be allowable to put a NEMA 14-50R on a circuit with a 30A double pole
    breaker and wired with 10-3 wire? Or to place a NEMA 5-20R on a circuit
    with a 15A single pole breaker and wired with 14-2 wire?

    I'm surprised with this - I always figured that the receptacle rating must
    match the circuit, with the exception of multiple 5-15R on 20A circuits and
    14-50R on a 40A circuit when feeding a range.

  2. Ben Miller

    Ben Miller Guest

    The point is to protect the receptacle by insuring that it can safely carry
    as much current as the rest of the circuit, determined by the rating of the
    OCPD. If you put a 15A receptacle on a 50A circuit, it could burn up under
    overload conditions without ever opening the circuit. If you put a 50A
    receptacle on a 15A circuit and you plug in too big an appliance the OCPD
    opens. Of course, if you do that then you haven't sized the branch circuit
    for the connected load (see 210.23)

    Ben Miller
  3. Bud--

    Bud-- Guest

    But if there are 2 outlets on the 15A circuit, one of them can't be 50A
    (or anything but a 15A receptacle).
    I don't understand the logic for this section except for relatively
    obscure configurations like twist-lock. Replacing a 15A single outlet
    for an air conditioner with a 20A one (15 ckt) doesn't make sense to me.

    A code proposal to require equal rating was rejected with the comment:
    "The recommendation would be overly restrictive in the case of some
    larger receptacle applications that do not directly correspond to the
    standard ratings of overcurrent protective devices. The panel notes that
    a 20-ampere receptacle installed on a 15-ampere branch cirrcuit is
    protected within it’s rating."

    A duplex 20A receptacle on a 15A branch ckt is also protected within
    it's rating but is a code violation.

  4. Guest

    | A duplex 20A receptacle on a 15A branch ckt is also protected within
    | it's rating but is a code violation.

    However, the reverse (20A protection on a circuit of #12 or larger wire
    with 2 or more 15A configuation outlets) is OK. That's they way I plan
    to go in my kitchen ... mostly NEMA 5-15R on the required 20A circuit.
    Additionally, there will be 2 or 3 dedicated 5-20R and 6-20R on their
    own circuits at 20A. The idea is heavier load appliances plug into the
    single outlet circuits, and smaller appliances into the others. Here
    are some possible arrangements:
  5. But to take the example of a 50A receptacle on a 15A circuit. What if there
    isn't a defined load? A receptacle implies a degree of portability,
    anything could come along. It seems like the way it's currently written, it
    leaves out a degree of flexibility.
  6. daestrom

    daestrom Guest


    With only one receptacle on the circuit, they are somewhat considering it a
    dedicated circuit, not a generic 'branch' circuit. Then the OCPD rating may
    be limited by the specific load, and be lower than the other components in
    the circuit (wiring, receptacle).

    Sort of a waste to use a large receptacle and wiring, then limit its use by
    a smaller OCPD. Unless the OCPD needs to be smaller for some reason *other*
    than protection of the wiring and receptacle (perhap a dedicated motor

    Just a 'shot in the dark'...

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