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NEC Code Applicability

Discussion in 'Lighting and Electrics' started by Charc, Aug 29, 2008.

  1. Charc

    Charc Well-Known Member

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    Heya guys, I've got a bit of question dealing with the NEC. I am in working with an architect for this community theatre, and we have been trading e-mails with management level personnel, and he as brought up the NEC in regards to our lighting.

    Anyone heard of this in the NEC? Do we, in theatre, using dimmers fall under different applicability? Bonus points if you can write a detailed explanation, siting codes. If the professional architect stresses his point, we will not be able to use two 500W Fresnels on one circuit/dimmer, let alone 575W Shakespeares, or an assorted wattage of track-lights.

    I'd really appreciate the help guys.

    Thanks.
     
  2. TimMiller

    TimMiller Well-Known Member

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    this is why i always go with 2.4k dimming. Dimmers do fall under a different animal than the normal NEC ratings. Theaters are a whole different ball game in the NEC. You go by the dimmer rating of 1.2k. You do not want to exceeed 1.2k or you will end up tripping the breaker. 1.2K dimmers have only 10A breakers installed. You do not want to exceed the 80% margin, just due to they breaker will hold the load but only for so long before it gets hot and trips. Now there are some 1.2k dimmers that use 15A breakers (usually the guts inside of the dimmer are actually rated for 20+ amps). So you can attach a true 1000 watt load.

    Just as a little reference table
    20 Amps x 120 Volts = 2400 Watts
    15 Amps x 120 Volts = 1800 Watts
    10 Amps x 120 Volts = 1200 Watts
     
  3. SteveB

    SteveB Well-Known Member

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    I thought the NEC 80% loading factor was only for circuits connected/wired directly to a dimmer - I.E. permanent house lights. I believe that dimmed circuits that have circuits on receptacles are allowed full loading, not that this is advisable or good practice.

    Steve B.
     
  4. STEVETERRY

    STEVETERRY Well-Known Member

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    Most theatrical dimmers like ETC Sensor are UL listed for 100% duty cycle, 100% loading. I am attaching an article I wrote on this subject.

    ST
     

    Attached Files:

    fredthe and (deleted member) like this.
  5. JD

    JD Well-Known Member

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    I thought that applied to distribution panels. For example, If there was a hallway and the lights were on a 20 amp circuit, then the load for all the lamps in the hallway should not exceed 16 amps. As "built in" dimmer systems may be considered to be a type of distribution panel, this ~may~ apply. The real question comes in the fact that a UL approved dimmer pack will list "1200 watts load." The literal interpretation is that they are rating the maximum "load wattage" not load current. If it is the load current, then there are about 4000 touring systems out there that are out of code! One would think that the UL rating would require them to list dimmers with 10 amp breakers as "960 watts load." Of course, there may yet be a different standard for portable equipment. Steveterry would probably be able to answer that. What I do know is that every DPC system I have seen in the last 35 years has been based on 1.2k dimmers, usually loaded with 1k pars.

    EDIT: Oops! He beat me to it !! ;)
     
  6. len

    len Well-Known Member

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    Since most of what I do is temporary install/event work, I just use the 100 rule, i.e., that one ampere equals 100 watts. It gives a buffer for loads on a circuit, and is way easier to calculate total draw than using the actual formula.

    So if I have a 600 watt per circuit tree dimmer, I can put one HPL 575 lamp on it. Period. And as an extra safety, never run the master up beyond 90%.

    Keep it simple.
     
  7. zac850

    zac850 Well-Known Member

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    Theater dimmers actually take this into account. If you look at a 20 amp Sensor dimmer, its really a 25 amp dimmer, 80% later you have your 20 amp dimmer. (which is why we're allowed to use them as 20 amp dimmers). Your 10 amp dimmer is really a 12.5 amp dimmer, which is why everyone calls it a 10 amp dimmer.

    Note: It is still a good idea to have a little headroom, since as breakers get old they start to trip earlier and earlier, but your legally allowed to load it up with the full 10 amps, as long as you don't load it up with the full 12.5 amps.

    Explain this to him, to begin with. Then have a look in the back part of the book. NEC 520 (I believe its 520, don't have my code book next to me) goes over theatrical work, (including some different cable ratings).
     
  8. JD

    JD Well-Known Member

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    Or, just print out the page Steveterry has linked above. Kind of covers it all.
     
  9. derekleffew

    derekleffew Resident Curmudgeon Senior Team Premium Member

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    Last edited: Aug 29, 2008
  10. cdub260

    cdub260 CBMod CB Mods

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    Yes, it is article 520 of the NEC that specifically addresses theatres.
     
  11. STEVETERRY

    STEVETERRY Well-Known Member

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    Err--not exactly. Sensor 20A dimmers have 20A breakers. Sometimes they are marked with FLA (full load amps)=20. Others are marked with the "must trip" rating of 25A. Both are UL listed for 20A. See my article attached to an earlier post.

    ST
     
  12. STEVETERRY

    STEVETERRY Well-Known Member

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    And here's another article that deals with the same issue on lower power distributed dimmers fed from normal branch circuit breakers in a facility.

    ST
     

    Attached Files:

  13. STEVETERRY

    STEVETERRY Well-Known Member

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    Generally, fuses are 80% continuous devices. I do not see a fuse ampacity listed, but if it is 10A, your likely continuous rating is 960W. Continuous = 3 hours or longer.

    It is not clear to me that this unit is Listed. Data sheet says "complies with UL508", but I see no reference to a third-party listing from UL, ETL or any other NRTL.

    ST
     
  14. STEVETERRY

    STEVETERRY Well-Known Member

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    Surprisingly, yes.

    However--you might be surprised by a blackout before 2:59 if the fuse blows.

    ST
     
  15. FMEng

    FMEng Well-Known Member Fight Leukemia

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    Not knowing the scope of this project, I have to wonder if it should involve an electrical engineer. There's more to an installed system than just dimmer rating, breaker rating and load size. Other factors to consider include ampacity of the conductors, conduit sizes and the number of wires in them, neutral conductor sizing for harmonic currents, main breaker sizing for the dimmer rack, capacity of the electrical service, and on and on.

    You could be doing things that won't get passed by an electrical inspector without drawings with an EE's PE stamp on them, especially since it isn't stuff that is common and familiar to the inspector. That's why an architect will often hire an EE to work on a project, rather than just have the electrical contractor do a design/bid/build.

    As a lighting designer, you can provide a lot of input to the EE on the kind of lighting equipment you want to employ, but then he/she needs to design how it gets installed in the facility in order to work safely and meet the NEC.
     
    Last edited: Aug 30, 2008
  16. FMEng

    FMEng Well-Known Member Fight Leukemia

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    Well then, never mind. When you said architect, I assumed you were designing a theater, not hooking up a few lights.
     
  17. TimMiller

    TimMiller Well-Known Member

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    hell there is the old failure test. All you do is connect up a wall clock set on 12 o clock and two 500w par cans to the dimmer. Come back when the fuse finally blows and you will know how long it will hold the load. After 6 hours you know it will be ok. Also you can do the same with two 575's. You cannot hurt anything, and fuses are cheap.
     
  18. MNicolai

    MNicolai Well-Known Member Fight Leukemia

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    Lamp your Shakes with HX401's, 375W/120V. You can fit two on a circuit comfortably.
     
  19. SteveB

    SteveB Well-Known Member

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    Good luck finding a wall clock that runs on AC. These days, most use a AA batteries.

    SB
     
  20. TimMiller

    TimMiller Well-Known Member

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    Then you can use one of those cheap plug in timers, like those you use to turn on christmas lights on and off. Just dont plug anything into it.
     

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