Commerical Sound Systems

[WirenutGP]

Hi all, I been lurking for a while but now need some help.

Some basic info, I'm installing a 70volt sound system in a doctors office with a speaker and volume control in each exam room. The drop ceiling is acting as a plenum. The amp is listed as a Class 3. Ran 16/2 CL2P through out, no wireways or conduit.

My inspector tells me that all wires must terminate in boxes since it's over 50 volts. I used deep metal old works for the volume controls and have commerical grade ceiling speakers which are completely enclosed.

Now I'm starting to second guess myself. First, where does the code say I need boxes? Second, should I be grounding the boxes and speaker housing and if so how?

Thanks

 

[LarryFine]

The last 70v system I installed, I used shielded 18ga wire, which provided me with a ground wire and prevented any noise from fluorescents and the like, although induced noise is unlikely.

Handy-boxes are probably the easiest way to house the junctions, and you should be able to bond the boxes to nearby building steel or electrical grounds. Talk to the inspector about this.

 

[hbiss]

The amp is listed as a Class 3. Ran 16/2 CL2P through out...

You should have used 16/2 CL3P. The hierarchy is Class 1, Class 3 then Class 2. Check the charts in Art. 725. CL2 is not a substitute for CL3 so apparently you got it backwards.

As for boxes, there is nothing in the Code that requires them for Class 3 or Class 2 wiring. However, a few jurisdictions that have not kept up with the times take the 70 volt designation literally. They have a limit of 50 volts for low voltage wiring and since 70 volts exceeds that they require all wiring to comply with chapter 3 Class 1 requirements and yes, that includes the grounding. That's where the conduit and box requirement comes from and that's also the reason 25 volt systems exist.

In your case, unless the jurisdiction is one of those that has amended the NEC to require Class 1 wiring for this I would ask the inspector to cite a code section that requires boxes with CL2 and CL3 wiring and devices. Voltage and current cannot be considered because that has already been taken into account when the amplifier was tested and listed for use with Class 3 wiring. You need only to follow the NEC requirements for the class of wiring printed on the amplifer next to the output to ensure a safe installation.

Larry, actually shielded wire is frowned upon since it is of no benefit and increases costs. Even a 70 volt system has a low enough impedance as not to be susceptable to noise from lighting, etc. As for boxes and ground bonds, I covered that above.

-Hal

 

[WirenutGP]

I'm back, sorry for the delay but I had to go out of town.

Thanks for the replys, I wanting to hear from the inspector now.

Hal, I had one of those "Oh, Shoot" moments after reading about needing CL3P wire instead of CL2P. I had my fingers crossed when I went back and checked the amp hoping I misspoke and didn't just wire the whole suite wrong. Luckly I told you guys wrong. It is rated as a class 2.

Will let ya know how I make out.

 

[WirenutGP]

As a follow up I wanted to let you all know every passed with no problems.

I'll be really happy if the customer in the other office signs on the dotted line.

 

[iwire]

WirenutGP, thanks for the follow up, it's always nice to hear the outcome.