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Author Topic: What does it take to run AC and signal in the same box?  (Read 3285 times)

Art Welter

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Re: What does it take to run AC and signal in the same box?
« Reply #10 on: March 29, 2018, 05:50:32 pm »

Code doesn't allow mixing of "services" in the same box, but IIRC the box can have a divider so long as each service remains on its respective side.  The idea is the divider makes each side its own "box" for the purpose of splicing or terminating.  The sides cannot share a common cable entry or exit, I think.
I'm no code expert, but I  have rarely seen any audio device with interior dividers, and they are still UL listed, presumably code compliant.

That said, I've also never had an electrical inspector look close enough at audio gear to determine if it has a UL listing...
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Jonathan Johnson

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Re: What does it take to run AC and signal in the same box?
« Reply #11 on: March 29, 2018, 06:15:46 pm »

Which means there can be no voltage inside the common jacket higher than the derated voltage?

Dang, that's what I've been trying to get someone to say in that other thread.

Also posted this in that other thread:

Here's what seems to be the relevant section of the National Electrical Code, from Chapter 3, Wiring Methods and Materials:

Quote
300.3 (C) (1) 1000 Volts, Nominal, or Less. Conductors of ac and dc circuits, rated 1000 volts, nominal, or less, shall be permitted to occupy the same equipment wiring enclosure, cable, or raceway. All conductors shall have an insulation rating equal to at least the maximum circuit voltage applied to any conductor within the enclosure, cable, or raceway.

And here's a related article based on a different section of the code.
« Last Edit: March 29, 2018, 06:22:24 pm by Jonathan Johnson »
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Stop confusing the issue with facts and logic!

brian maddox

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Re: What does it take to run AC and signal in the same box?
« Reply #12 on: March 29, 2018, 06:16:33 pm »

There's a saying that kind of applies: the dose makes the poison. In other words, running power next to signal lines can be a problem when very low-level signal lines (i.e., microphone) are run adjacent to high-current power lines (hundreds of amps) over very long distances (hundreds of feet) AND the signal is then amplified. Running a few amps of power next to shielded signal line for a few tens of feet will result in unnoticeable effects.
...

This^^

I have this conversation often with less experienced A/V types on show sites whenever there is any kind of buzz or other audio issue.  "Well the Audio is like super close to the Power backstage.  That's what causing it..."

Uh, no....

I've chased several [tens of... ] thousand [s of] buzzes and it's been induced buzz from a power cable maybe twice.  maybe...
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brian maddox
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Tim McCulloch

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Re: What does it take to run AC and signal in the same box?
« Reply #13 on: March 29, 2018, 06:44:18 pm »

No myth here.

Near-mythical.

Statistically very low chance... until it happens to you, then it's 100%.

It takes a fair bit of induction but it *can* happen.  I'm with Brian Maddox, I'm not sure I can count such incidents on more than 2 fingers in over 35 years, though.

More often where there are hum/buzz issues I find ground/neutral swaps or inappropriate ground/neutral bonds.
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John Ferreira

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Re: What does it take to run AC and signal in the same box?
« Reply #14 on: March 29, 2018, 10:40:37 pm »

I just avoid Henrys all together.
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John Ferreira

Tim McCulloch

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Re: What does it take to run AC and signal in the same box?
« Reply #16 on: March 29, 2018, 11:01:22 pm »

I just avoid Henrys all together.

Yeah, but then a whole bunch of milliHenrys gang up on you!  ;)
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"Practicing an art, no matter how well or badly, is a way to make your soul grow, for heaven's sake. Sing in the shower. Dance to the radio. Tell stories. Write a poem to a friend, even a lousy poem. Do it as well as you possible can. You will get an enormous reward. You will have created something."  - Kurt Vonnegut

Kevin Graf

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Re: What does it take to run AC and signal in the same box?
« Reply #17 on: March 30, 2018, 10:16:35 am »

Interestingly the Bill Whitlock and the Dale Shirk papers have somewhat different view-points on Romex. I suspect that Bill Whitlock tested real SouthWire brand Romex® and Dale Shirk tested generic Non-Metallic (NM) cables.
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Andrew Broughton

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Re: What does it take to run AC and signal in the same box?
« Reply #18 on: March 31, 2018, 12:28:13 pm »

I've chased several [tens of... ] thousand [s of] buzzes and it's been induced buzz from a power cable maybe twice.  maybe...

I've experienced it many times, when people not watching have excess mic cable coiled on or near soca running to self-powered speakers or laying on feeder. It's low-level hum induced into the mic lines, and only in mic-level signals.
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Jean-Pierre Coetzee

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Re: What does it take to run AC and signal in the same box?
« Reply #19 on: April 06, 2018, 05:06:45 am »

I've stuck sensitive clamp on meters around both our temporary and permanent power lines here and have never measured any current from them, doubt that it will cause an issue but then again we are at 240v and thus significantly less current...
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