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15 Amp Plug on 20 Amp Outlet

Discussion in 'Lighting and Electrics' started by Andy Haefner, Apr 10, 2018.

  1. Andy Haefner

    Andy Haefner Member

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    Hello, we have some source four lekos fitted with 20 amp twistlock connectors... However we want to use them in a location with 20 Amp Edison outlets. I've always been told "if the circuit is capable of 20A, everything in the circuit need to be rated 20A or higher" but the way I'm thinking right now is that a 575w lamp in our lekos doesn't draw 20A through it's plug... So why can't I use a 15A plug, most 20A Edison plugs I've seen are $10 or more. For 16 fixtures this can be a lot. Is there a good reason for this rule I was told or is that only for the parts of the circuit which will receive 20A?
     
  2. BillConnerFASTC

    BillConnerFASTC Well-Known Member Premium Member

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    There are plenty of instances where not every component on a 20 amp circuit has to be rated for 20 amps but those are for listed assemblies I believe. Like buy a power tool or desk lamp, and it has a plug that is not rated 20 amps, but fine to plug it into a 20 amp receptacle on a 20 amp circuit. But you (not picking on you - even a crusty old licensed electrician) I don't believe is allowed - by code - to make that change if the original listed assembly - which the Source4 was - had a 20 amp plug on it.

    But @STEVETERRY will correct me if I'm wrong.
     
  3. danTt

    danTt Well-Known Member

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    It's in one of those code gray areas. ETC will happily sell you a source 4 with a nema 5-15 plug, and the leads on all? Source 4 units are 16 (I believe) gauge from the connector to the socket. If you use a listed "Med" assembly to convert from stagepin or twistlock to male edison, does this make it safe?

    The theory is that if something goes terribly wrong, all cable needs to be able to handle everything before the OCPD kicks in. The amount of conditionals and associated exceptions when dealing with edison plugs is large enough to make me, personally, not worry if I put a 15 amp connector on a light being plugged into a 20 amp circuit. Your local rules may vary.
     
  4. SteveB

    SteveB Well-Known Member

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    I think the derating of the connector from a 20 amp twist to a 15 amp Edison concern only applies when the device potential current draw could exceed the connector rating. That's not possible on a S4, whose maximum lamp wattage is 750 watts. So I'm thinking that you could correctly install a 5-15 male Edison and be OK. ETC ships the unit with these as note.
     
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  5. BillConnerFASTC

    BillConnerFASTC Well-Known Member Premium Member

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    Yes, but they also had it tested in a NRTL with that connector installed by them. I believe that makes a code difference.
     
  6. soundofsparks

    soundofsparks Member

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  7. danTt

    danTt Well-Known Member

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    Sure. I understand that code will object to the doing of this. I'd respond that in general, it's important to follow rules, and more specifically, it's important to understand why and what rules are before you break them. That being said, I will again ask does connecting an ETC provided source 4 with a nema 5-15 connector to a UL listed female edison->male stagepin adaptor make it any more safe than connecting an ETC cap with a locally provided nema 5-15 adaptor?

    I'll admit that i have trouble generating a scenario in whcih someone was able to pull 19.5 amps on a 5-15 plug using a source 4 cap, but in the world in which someone found a g9.5 base 2000watt lamp (Does this exist? I know an FEL will fit in a source 4 socket) and used it in their source-4, which would work on a 20amp breaker, shouldn't the plug be rated for it? I'll admit ignorance, but does NRTL test these scenarios? Or only a source 4 with an ETC Listed 575/750 lamp?
     
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  8. FMEng

    FMEng Well-Known Member Fight Leukemia

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    The NEC allows a 15 amp plug. Common sense agrees. If we overthink this, then the 18 gauge cord on your TV becomes 12 gauge, which would be absurd. Save your money and sleep well.
     
  9. SteveB

    SteveB Well-Known Member

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    As well if you swapped between 2P&G, L5-20 and 5-15, all being connectors as supplied from the manufacturer, how would anyone know ?
     
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  10. JD

    JD Well-Known Member

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    This is why the cable to your 100 watt ghost light can be 16/3 type S even on stage. Cables are load dependent. This concept grinds to a halt when talking about extension cables. In that application, it is reasonable to assume someone might grab an extension, plug it in and load it down to the dimmers full capacity. As such, most all stage cables are 12/3 type S (or dirv.) and some venues have house rules making 12/3 the minimum standard extension cable.
     
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  11. RickR

    RickR Well-Known Member

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    That "house rule" is backed up by the NEC.

    When you buy a S4 without a connector it comes with a little tag that says to maintain the NRTL listing you must attach a listed connector.
     
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  12. JD

    JD Well-Known Member

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  13. BillConnerFASTC

    BillConnerFASTC Well-Known Member Premium Member

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    I reread that that thread and ST seems to say that the cords - the wire guage - must have an ampacity equal to the over current protection.
    Doesn't that say if you have 20 amp circuits your cables must be 12 guage?
     
  14. danTt

    danTt Well-Known Member

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    The part of the quote you trimmed is highly relevent to this discussion, in full context:
    "Ampacity is determined by the listing requirements for a listed extension cord. Those listing requirements will also determine the largest overcurrent protective devicethat the extension cord can be fed from."

    My interpretation of this is that a listed extension cord will have requirements about what OCPD is necessary for use. The following point in @STEVETERRY 's discussion "4. Ampacity of a "field assembled" extension cord made from listed connectors and cable is determined from NEC table 400.5(A)(1). " Seems to indicate that when not listed, the applicable gauge is determined based on the ampacity table in 400.5(A)(1), with a bare minimum of 16 gauge on a 20-amp branch circuit for field assembled cables.
     
  15. SteveB

    SteveB Well-Known Member

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    My take on that thread was a pre-assembled and listed extension cord must be of the amperage rating of the OCD, but that a field assembled cord non listed but using listed parts) can be a minimum of 16 gauge SO but must be of a size able to handle the load.

    I might be reading this wrong and as I am unable to research the NEC directly.
     
  16. JD

    JD Well-Known Member

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    Yes, the size of the load being the key. For example, a 100 watt ghost lamp with an attached cable. Possibly @STEVETERRY can swing by this thread for additional clarity.
     
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  17. STEVETERRY

    STEVETERRY Well-Known Member

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    OK, to repeat and summarize in one place:

    1. The allowed rating of a connector attached to a luminaire is determined by the Listing of that luminaire. A 5-15P on a Source Four is just fine.
    2. The maximum size overcurrent protective device that may feed a luminaire is determined by the Listing of the luminaire.
    3. An extension cord must be sized to service the load connected to it.
    4. The ampacity of an extension cord is determined by its Listing, if it is Listed as an assembly.
    5. The maximum size overcurrent protective device that may feed an extension cord is determined by its Listing, if it is Listed as an assembly, per section 240.5(B)(3).
    6. For a field-assembled extension cord, assembled from Listed parts, the ampacity of the extension cord is determined by table 400.5(A)(1).
    7. The maximum size overcurrent protective device that may feed a field-assembled extension cord is determined by section 240.5(B) (4). The smallest size field assembled cord that may be fed by a 20A OCPD is #16AWG.

    ST
     
  18. STEVETERRY

    STEVETERRY Well-Known Member

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    You are correct.

    ST
     
  19. danTt

    danTt Well-Known Member

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    Hijacking this post a little... but with the world famous @STEVETERRY present I'm curious now.

    Ran across a rennovation recently that had l5-15 recepticles connected to a patchbay with GPC connectors designed to patch into 20-amp circuits. Leaving aside, for a second, the unfortunate choice of L5-15 as a connector--Is this legally allowed? Are the recepticles rated for 15 amps allowed given that they, theoritecally, limit anything being connected to them draw a maximum of 15 amps of current? Or given that the OCPD protecting this patch is rated for 20 amps, should the recepticle in question also be required to be an L5-20?
     
  20. BillConnerFASTC

    BillConnerFASTC Well-Known Member Premium Member

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    I think if more than one receptacle on the circuit, even a duplex, and it's ok. Probably the component has to be listed for it, like most 15 amp duplexes are listed for being fed by 20 amps.

    I agree, at least currently, that the L5-15R would not be my choice. I currently specify L5-20R for relay controlled receptacles intended for portable stage and studio use. (Though I usually parallel a 5-20RD off one circuit at most plug boxes or a few across a strip just to lessen need for adapters.)
     

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