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Thread: speaker wiring- class 1 or 3

  1. #1
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    Nov 2003
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    speaker wiring- class 1 or 3

    I am using 10awg 2 conductor wiring with an audio amplifier that has a rated power output of 2500 watts and a 4 ohm speaker that is rated at 2500 watts of input. What class wiring is this? Also I am using 18awg 2 conductor wiring with an audio amplifier that has a rated power output of 1000 watts @ 70 volts to a load of sixteen 60 watt 70 volt speakers paralleled. What wiring is this? Is class 2 or class 3 speaker wiring required to be in conduit? If the 10awg wire is an unlisted type can I put it in conduit to comply? In a permanent installation, if I used 12awg 4 conductor SOW wire for speaker wire for applications that have class 1 requirements, must I put it in conduit?

  2. #2
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    Re: speaker wiring- class 1 or 3

    I belive that the listing info on or with the amplifier will tell you class 1 but look for it on the back of the amp or in the paper work that came with the amp. Most comercial amps are class 1 rated. But heres the kicker nobody make a class 1 speaker cable! I mean nobody. I have looked for this before and even wrote beldin cable with no results.
    Wayne A. From: N.W.Indiana
    Be Fair, Be Safe
    Just don't be fairly safe

  3. #3
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    Re: speaker wiring- class 1 or 3

    The answer has nothing to do with the output wattages, voltage, speaker impedances or most else you listed. The answer to what wiring method to use is listed (or should be) on the rear of the amplifier next to the outputs. It will say Class 1, 2 or 3 wiring may be used. See Article 640.9(C).

    Baring any local restrictions, CL3 and CL2 does not have to be run in conduit regardless of the fact that it is a 70.7 volt output. See 725.25.

    Class 1 is a whole 'nuther can of worms. Class 1 wiring must comply with NEC Chapter 3 just like normal branch circuit wiring. Wiring has to be listed and no, you can't run SOW cord in conduit.

    This is a can of worms because you are pretty much stuck with conduit and TFFN or THHN conductors (725.27(B)) since nobody makes a suitable Class 1 audio wiring product. We have TFFN twisted into a pair and pull it in conduit.
    Another problem is that since this must comply with Chapter 3 you need equipment grounds and appropriate methods to connect to speakers such as standard sized knock outs and enclosed terminals or at least listed connectors. (Don't know if Speakons are listed). Unfortunately many speaker manufacturers do not make a Class 1 compliant product.

    Take heart though because most inspectors will be as much in the dark about this as you were.

  4. #4
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    Re: speaker wiring- class 1 or 3

    Hurk, if you want to split something like 100,000 feet let me know.

    Since this would be MC a problem then is what to do with the green ground at the speakers. All that I have used that have wiring compartments have no ground screw nor can one be fitted. That's why EMT and a greenfield "whip" work out well.

    Incidentally, there is no ryhme or reason to the wiring method required by the amplifier. I've seen 400 watt amps require Class 1 and 600 watt amps require CL2. It's NEVER listed in the amp specs or literature. Only way I've found it (other than actually looking at one) is to look at a photo of the back panel if the literature or web site provides one. It's a conspiracy. I recently saw a photo of a new QSC amp and it said NOTHING about wiring requirements on the back and it was UL listed. Think they photoshopped it out?

  5. #5
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    Re: speaker wiring- class 1 or 3

    I do not work with PAs too much but the ones I have done where not class 1.

    The ones that are class 1, are the speaker terminals on the back enclosed? :confused:

    What I am getting at is if they are UL listed and the speaker terminals on the back are out in the open, wouldn't that mean these are class 2 or 3? :confused:

  6. #6
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    Re: speaker wiring- class 1 or 3

    Bob, kind of. There is really no Class 1 listing for these things so you are really on your own. Some manufacturers like JBL and others make ceiling speakers with a standard size KO and wiring compartment that is enclosed. Only problem is that there is no means to connect an equipment grounding conductor if you used one. These are a totally enclosed metal can and are "cut in" the ceiling. They are UL listed for use in air handling spaces (Article 300.22(C)). They are also listed (UL 1480) for use with fire protective signaling systems. That's it.

    These speakers are becoming extremely popular and many manufacturers are making similar products. Not all will accept standard fittings though and there is really no way to tell which will other than by looking.

    For ceilings you can also use back cans with regular speakers and baffels although the above type sound alot better. The cans have standard size KO's and can be used with Class 1 wiring methods.

    When you get into other than ceiling speakers the issue gets even more cloudy. Here again I've found that some JBL products have enclosed terminals (barrier strip) with a compression connector for cable entrance to the wiring compartment. Other of their products, as well as most other manufacturers, use those crummy push clips that are not enclosed at all.

    With little cooperation from manufacturers and vague direction from the NEC it isn't surprising that there is little compliance in this area.

  7. #7
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    Re: speaker wiring- class 1 or 3

    Thanks very much hbiss for all the info., it does sound difficult to comply.

    We use back boxes on most all ceiling mount speakers that have a 1/2" KO and use a plastic NM connector to enter and exit usually a 16/2 or 18/2 twisted pair cable.

    This would be for 70 volt systems, retail, office PAs.

    I have never seen anyone put it in pipe.

    I thought we did it well because we properly support the cable, as opposed to thrown across the ceiling.

  8. #8
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    Re: speaker wiring- class 1 or 3

    For CL2 and CL3 thats fine.

  9. #9
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    Re: speaker wiring- class 1 or 3

    I'm curious to the 1st amp that you are using. Surely this is 2500wtts bi-amped. he cost of a 2500watt stereo unit would break the bank!
    And if it is biamped, are you sure it is 2500w @4ohm output and not 8ohm. It's possible, I'm just curious.
    And why 10ga. speaker wire? Is this a long run?
    Or did you use ohms law to come up with this size?
    I= sq.rt. of P/R
    I= sq.rt. of 2500/4
    I= sq.rt. of 625
    I= 25
    Do we need to size this wire in this way for this load??
    -Todd-

    -Delawhere?

    Shock Me, Make Me Feel Better.

  10. #10
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    Re: speaker wiring- class 1 or 3

    I can't speak for djmrts, but I'm sure the amp is a 2 channel operated in bridged mono mode. (inputs driven from same source and outputs tied together). Several manufacturers have amps that can deliver 2500 watts into a 4 ohm load and somewhat less into 8 ohms. This is typical for solid state amps.

    As for the wiring, at low impedances like this because of the high current, minimum voltage drop is the primary factor in choosing a wire size otherwise you just waste power due to line loss. I would agree though that for Class 1 wiring the minimum wire size should be per Article 310 and then increased as necessary to minimize voltage drop.

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