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Thread: Low Voltage Cable Used For 120v Signal horn/strobe

  1. #1
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    Low Voltage Cable Used For 120v Signal horn/strobe

    Have a project in a high rise apartment parking garage trouble shooting the exhaust fan control that evaluates the fumes from cars.

    In doing so it was found that the siren circuit which is powered by the 120 volt breaker that feeds the fan motors. Furthermore the 120 volt siren is wired with Cl2 -Cl3 low voltage wire. Then to top it off it was run in the same conduit as the Gas sensors. The siren only operates in a event. It is my understanding this is Class 2 wiring. The sensors are DC.

    I believe the code at the time was either 1996 or 1999 NEC.
    I don't seem to find anything in the book that allows this.
    SECTION 725?

    Any knowledge would certainly be appreciated.

  2. #2
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    Anyone?

  3. #3
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    Not quite following what you are asking. Let's take what I see to be relevant:

    ...the 120 volt siren is wired with Cl2 -Cl3 low voltage wire.
    No!

    ... it was run in the same conduit as the Gas sensors. It is my understanding this is Class 2 wiring.
    The gas sensors may be but not the 120v siren. Even if the siren used THHN it couldn't be run in the same conduit.

    -Hal

  4. #4
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    Yes. I think you have it .
    What. I can't find is the exact code reference. It would need to apply to construction under 1996 or 1999 NEC.

    I thought that if all the wiring insulation was the highest necessary voltage rating then you could share conduit ,providing that all conductors served the same system.

    Is there something I can clarify?

  5. #5
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    Quote Originally Posted by flatlander View Post
    Y
    I thought that if all the wiring insulation was the highest necessary voltage rating then you could share conduit ,providing that all conductors served the same system.
    See 725.130 exception No. 2

    Exception No. 2: Class 2 and Class 3 circuits shall be permitted to be reclassified and installed as Class 1 circuits if the Class 2 and Class 3 markings required in 725.124 are eliminated and the entire circuit is installed using the wiring methods and materials in accordance with Part II, Class 1 circuits.

    Informational Note: Class 2 and Class 3 circuits reclassi-

    fied and installed as Class 1 circuits are no longer Class 2 or
    Class 3 circuits, regardless of the continued connection to a
    Class 2 or Class 3 power source
    So not only will you have to change the fan conductors to THHN, you will have to change the sensor wiring also to THHN (or TFFN if you want 18ga conductors).

    It used to be that you could only reclassify the CL2 conductors and run it with the power conductors if it was functionally necessary for the operation of the device. Strict interpretation of that statement made reclassification almost impossible so at some point it was changed to the above. I think that's where you get the "same system" from.

    -Hal
    Last edited by hbiss; 09-17-18 at 12:18 AM.

  6. #6
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    Quote Originally Posted by hbiss View Post
    See 725.130 exception No. 2



    So not only will you have to change the fan conductors to THHN, you will have to change the sensor wiring also to THHN (or TFFN if you want 18ga conductors).

    -Hal
    And more importantly perhaps, the sensors and the panel circuits they connect to must be approved for use in a Class 1 system. If the sensors are limited to Class 2 operation you cannot reclassify the circuit feeding them to Class 1.
    The common reclassification of remote switching or dimmer control circuits to allow them to be run with luminaire power or generator control circuits to allow them to be run with the generator output depends on all of the control components being rated for *either* Class 1 or Class 2 or 3 operation.

    Sent from my XT1585 using Tapatalk

  7. #7
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    I agree except the Article makes it seem that you can just take a sharpie and cross out any reference to CL2 on the devices.

    -Hal

  8. #8
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    Quote Originally Posted by hbiss View Post
    I agree except the Article makes it seem that you can just take a sharpie and cross out any reference to CL2 on the devices.

    -Hal
    Which is indeed misleading. I think the intention is to remove any reference to CL2 on power sources. What is not stressed is that once you have done that you have to worry about whether the other devices in the circuit can be supplied by a non-CL2 power source.

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