THHN/THWN for loudspeakers?

[willisrb]

Hi Folks, I need a little Code interpretation.
I'm an A/V design engineer and regularly spec individual THHN/THWN conductors for loudspeaker lines in larger facilities as a cost saving measure both in conduit size and cable cost.
For the first time in 40 yrs , I've been questioned as to whether this practice is Code compliant. The EC's position is "Per NFPA 70, Article 725 THHN and THHW are considered a Class 1 wiring method and is not an acceptable wiring method for Class 2 or 3 circuits." They are wanting to charge to upsize the conduit to accommodate PVC jacketed CMR cabling.
My question is does Code article hold for loudspeaker circuits or are these exempt per Chapter 800 Communications Circuits?

 

[infinity]

The EC's position is "Per NFPA 70, Article 725 THHN and THHW are considered a Class 1 wiring method and is not an acceptable wiring method for Class 2 or 3 circuits."

What specific code section would they cite in Article 725?

 

[LarryFine]

I've never heard of wire being too good for a certain use.

 

[hbiss]

THHN/THWN has always been used , pulled through conduit, for speaker wiring. One example would be movie theaters. Normally I would recommend to have it twisted into pairs but that's not always necessary. I have had reels of 18GA TFFN red and black twisted up and then I pulled it through conduit for Class 1 70.7V speaker wiring.

The EC's position is "Per NFPA 70, Article 725 THHN and THHW are considered a Class 1 wiring method and is not an acceptable wiring method for Class 2 or 3 circuits."

That's just flat out wrong. Look at the hierarchy tables in any of the Chapter 7 and 8 articles. Yes, THHN is a Chapter 3 wiring method suitable for Class 1. But it's at the top of "wire pyramid" and can substitute for any other lesser classes (CL3 and CL2) below it no problem.

Indeed, it may be correct that if you were to use jacketed cables, depending on the number, that you may have to upsize the conduit to maintain fill and pulling tension requirements. So, you are correct that pulling THHN/THWN conductors (weather or not twisted) would keep the conduit diameter to a minimum.

-Hal

 

[Todd0x1]

Nothing to do with OPs issue but I had a funny (well funny all these years later) issue with thwn speaker wire. Entertainment venue had thwn speaker wire, conduits stubbed out on a wall behind amp racks and the wires in free air between the conduits and amplifiers. Big fire which eventually involved this room but the origin was elsewhere. Insurance co tried to deny the claim (millions) by saying there was 'exposed electrical wiring' in an area involved with the fire, based on the observation of a bunch of burned up exposed thwn. Insurance co lost that battle and had to pay something like a million more because they were on the hook for business interruption during the delay they caused.

 

[Speedskater]

This is one of my favorite topics.

Random thoughts on loudspeaker cable:

1] Twisted pair is good. Because there is a slight possibility that cable could act as an interference antenna. The interference follows thru the feedback loop and is detected by the sensitive input stage. Back in the olden days this often happened with CB, taxi cab and police radio transmissions. Twisting reduces the antenna effect.
2] the cable AWG is not so much about the audio power, but more about the length (end-to-end resistance) in relationship to the loudspeaker's impedance curve. More so in multi-driver loudspeakers.
3] 14AWG/3+gnd Romex® is a great in-wall loudspeaker cable. It can be wired as an 11AWG StarQuad or to 2 loudspeakers.
an old blog on the subject.

http://www.hps4000.com/pages/spksamps/speaker_wire.pdf

 

[LarryFine]

In my home-theater system, I use inexpensive 12ga copper speaker wire. My main left and right speakers are bi-wired, so they have two pairs of wire. The tweeters and woofers have separate terminals, and the amp has separate output terminals. Total audio power is 2,100w RMS over seven channels plus powered sub-woofers.

(I have made a few equipment changes since taking this pic)

 

[Speedskater]

If you turn the amps on one at a time and only listen to music or movies, the entire audio system can operate on one 15 Amp circuit.

 

[willisrb]

Thank you all for your insights.
I believe I found the passage which specifically authorizes our design practice. NEC 2023 - 725.130(A) States:
Use of Class 1 wiring methods for Class 2 and Class 3 circuits shall be permitted.
This would seem to permit the use of THHN/THWN for use in this application.

 

[LarryFine]

If you turn the amps on one at a time and only listen to music or movies, the entire audio system can operate on one 15 Amp circuit.

One circuit.

I ran a 50a feeder to a sub-panel:



The yellow cable feeds a reed relay that controls a 10a cube relay that controls a 4p contactor that switches four of the eight 15a circuits for the power amps, sub-woofer amps, and other components.

The top two breakers are reserved for future use, maybe lighting. The other two non-switched circuits supply the preamp/processor and the CRT projector, both of which should have power all the time.

 

[Todd0x1]

2] the cable AWG is not so much about the audio power, but more about the length (end-to-end resistance) in relationship to the loudspeaker's impedance curve. More so in multi-driver loudspeakers.

Too small of wire can wreck the amplifiers damping factor and result in not good sound. I've had to explain to more than one A/V installer that their 300ft run of 14ga speaker wire isn't going to cut it...