Class 2 Circuits on 70V Audio System over 100W

[jaymewright]

I need some help getting clarification on what the NEC states vs what manufactures post on equipment. Code References as follows, 640.9(c), 725.121, 725.139, and Table 11A.
What I'm gathering is that the amplifier output on a 70.7V system can utilize Class 2 wiring (640.9(C)) as long as the amplifier is rated as a Class 2 Output. The issue I'm having in my specific instance is that the total wattage of the amplifier (with a stated class 2 output) is 300 Watts. Per Table 11A, that is over the allowed amperage per the table. I've talked to the manufacture and they weren't able to provide much help as it related to interpreting the table in the NEC. Any input or thoughts are appreciated.

 

[hbiss]

First off, for 725 goes out the window for audio other than requiring you to abide by the label on the back of the amp to determine the type of wiring needed. Doesn't matter what the wattage is, if it says Class 2 wiring may be used you can use CL2. If there is no label or nothing about a wiring requirement you automatically have to assume a Class 1 wiring method.
Whether an amp is Class 2 or not is all determined by the design and the listing. I have seem amps greater than 1000W only requiring CL2. Designers have gotten very good at keeping outputs within limitations that probably have little to do with normal 725 applications. Keep in mind that outputs (and audio) is not continuous so there are duty factors involved as well as sophisticated limiting to protect the amp.

-Hal

 

[jaymewright]

First off, for 725 goes out the window for audio other than requiring you to abide by the label on the back of the amp to determine the type of wiring needed. Doesn't matter what the wattage is, if it says Class 2 wiring may be used you can use CL2. If there is no label or nothing about a wiring requirement you automatically have to assume a Class 1 wiring method.
Whether an amp is Class 2 or not is all determined by the design and the listing. I have seem amps greater than 1000W only requiring CL2. Designers have gotten very good at keeping outputs within limitations that probably have little to do with normal 725 applications. Keep in mind that outputs (and audio) is not continuous so there are duty factors involved as well as sophisticated limiting to protect the amp.

-Hal

Thanks for the input Hal!

 

[don_resqcapt19]

It appears to me that 640.9(C) requires the power output class to be marked on the equipment. You should not need to do any calculations.