April 5, 2023 at 3:11 pm #5701
I’ve been diving down the rabbit hole of electrical system design in preparation for the wiring of my new room, which I just finished framing couple of days ago. Any advice that you all may have is greatly appreciated!
Things I’ve learned so far… (and it should go without saying, if any of this is incorrect, please let me know!)
- Twisted pair THHN or similar stranded wire is best for hot and neutral wires
- Size the ground wire up one size and run it along the twisted pair
- Run both inside metal conduit
- Short runs are best, so a subpanel is a good idea
- Running audio and power close, but not too close, is best to minimize ground loop area.
As for my specific situation, this room is kind of going to be the studio before The Studio, and is going to be far from perfect. In fact, it’s nearly worst case scenario. It’s fairly small (10.5′ wide x about 15′ deep x 7′ height) and it’s in the basement. The overall design philosophy is going to be to let as much low frequency energy out of the room as possible. The long term goal is to build an addition to my home, part of which will be a new studio that I can design properly from the ground up. But that’s a project for another day. For now the challenge is to see how much lemonade I can make from this lemon of a house.
So this leaves me with a couple of specific questions…
- Is the performance of romex really significantly poorer than twisted THHN pairs as far as EMI goes? I already have so much romex from existing wiring running near my room, I feel like I might be straying far into diminishing returns to use twisted THHN. Or maybe I can use romex for the 60A run from the main panel, then use twisted pairs for the small runs from the subpanel? I’m not sure what distance this kind of noise can travel.
- What is the main purpose of the metal conduit? Is it to shield the runs from outside EMI or to prevent it’s own field from affecting other external systems? If it’s an effective shield from outside EMI, then this may actually be a worthwhile expense for me given the existing mess of romex I’m working with now.
Also, if I’m allowed to post documents or links to documents, maybe I’ll share them for those who are also interested, I’ve found a few good papers on the subject.
EDIT: Sources so far:
- “An Overview of Audio System Grounding and Interfacing” by Bill Whitlock
- “Grounding, Audio Wiring, and Zero Loop Area Design” by John Brandt
- “Understanding, Finding, and Eliminating Ground Loops in Audio and Video” by Bill Whitlock
- “Noise Susceptibility in Analog and Digital Signal Processing Systems” by Neil Muncy
- “Ground Loops: The Rest of the Story” by Bill Whitlock
- Discussions with Bob Katz about common practices
April 5, 2023 at 4:06 pm #5702
Where did you get the information you posted? Some of it seems highly questionable.
April 7, 2023 at 1:25 pm #5720
Questionable? I can’t speak for Brandt, either positively or negatively. But Whitlock is god and Muncy is supreme god.
April 7, 2023 at 1:29 pm #5722
Bob, I added those sources after he made that comment, so he’d know what I’d been reading. I should have made that clearer.
April 8, 2023 at 8:22 pm #5738
I’ve never designed an electrical distribution system for a pro studio. My experience lies primarily in completely rewiring two houses that I owned in the past, along with a 6 month period where I wired 3-phase motor control boxes for.industrial oil burners.
So, I had not encountered the twisted pair power leads in place of romex. And I had not considered the possible benefit of a local breaker panel. I also, as a home studio guy, found it hard to imagine the need for 60 amp service. So, apparently, I was out of my element here. Feel free to disregard my comments as needed…
April 6, 2023 at 7:34 am #5708
Ok, here are a few items that caught my attention:
– Stranded wire is most useful for cables that will be flexed regularly or are difficult to bend due to large wire gauge (it starts getting difficult to work with at 12 or 10 AWG). But the conductivity will about the same as solid wire with the same gauge. It can exhibit lower losses at RF freqs due to skin effect, but that isn’t really an issue at power line freqs. Speaking of wire gauge, AWG 14 is good for up to 15 amps, AWG 12 is good uo to 20 amps. Unless you are running power-hungry big vintage tape machines, AWG 14 or 12 should be sufficient for a studio.
– The twisted pair thing will indeed reduce loop area, lessening the susceptabilty of the cable to picking up magnetically coupled interference. However, if the cable is insided a grounded metal conduit, it is already shielded. It win’t hurt anything to use twisted pair wire, but is (IMO) a bit of overkill and perhaps unjustified expense.
– Adding a local breaker box won’t help or hurt. A breaker is basically a switch. The load circuit (your studio gear) won’t care whether the switch is in the same room or out in your garage.
But 60 amp service.. that requires three 12 gauge cables fed from three separate 20 amp breakers from the source (the remote breaker box). Or possibly a single AWG #4 romex fed by a single 60 amp breaker in the remote breaker box. 4 gauge wire is extremely difficult to work with, especially if you want to stuff it through metal conduit; each wire has copper of around 0.2″ diameter, not including insulation. (Note: this is one case where stranded wire would be far easier to work with than solid.)
The local breaker box could, un theory, have its own earth ground, but that violates electrical building code. The only legal way to ground the local breaker box is through ground wire(s) going back the to remote breaker.
Unless you plan to do arc-welding in your studio, 60 amp serice seems like overkill.
As far as running audio cables next to power cables: Best practice is to separate them. But balanced and shielded audio cables are pretty immune to nearby power cables.
Magnetic emissions from power cables are limited by loop area of the 2 (very close) AC hot and neutral lines. and amount of AC current. But capacitive coupling from an AC line into a nearby low level audio cable is a possible issue, especially for non-balanced audio cables. The relatively high voltage of the AC power can couple noise (hum) into the shield/ground of a nearby unbalanced audio cable. The capacitive coupling effect is an inverse square reciprocal; doubling the spacing cuts the coupling by 4x.
No criticisms intended here… It looks like you have done extensive research. If you haven’t already, make sure you also look into the local electrical building codes that apply to your area to set up an effective and safe aystem.
April 6, 2023 at 8:55 am #5710
Excellent, thanks for the great reply!
Yeah I’m guessing they recommended stranded simply because they wanted to twist them into a pair. From what I can tell, twisting the hot and neutral together will help prevent inducing any current into the ground wire as well, which seems to be what Whitlock and Muncy are suggesting is the main source of noise. But romex accomplishes that same thing by simply placing the ground in the null area between the two. Might not be quite as perfect cancelation, but I suspect I would be hard pressed to note the difference.
I’m curious, if conduit is a great way to shield from outside EMI/RFI, given that I’m going to be running the main line near an existing mess of romex, do you think it might be worth the expense to run conduit from the main panel to the sub-panel, just to try to eliminate any outside sources of EMI/RFI?
Also, regarding the subpanel, one of the main reasons I wanted to do that was because it’ll use up a little less space in my main breaker box, which is almost full, and will easily allow future expansion. Like you said, 60 amps of service is more than enough for the entirety of my studio.
Thanks again for the replies, I appreciate it!
April 7, 2023 at 1:39 pm #5724
Phil: Putting the sub breaker box in the studio or very near the studio is a big advantage. It’s a central point, all runs are short. All the ground runs, hot and neutral runs are as short as they can, go to the central point and loop area is reduced. The whole room power references to that panel as the “zero reference” for the room. In fact, the run from the breaker subpanel to the main panel is irrelevant. Because all the audio and power (power is part of the audio circuit!) are locally run.
Think of an airplane. How do they keep all the navigation clean without a ground rod? By using the principles of loop area. Everything is in the skin of the plane and follows the central point approach, to my knowledge.
April 6, 2023 at 12:38 pm #5711
Re: using conduit between remote and local breaker box, it depends on the physical layout. If the power cable immediately exits the room from the local breaker box it probably won’t do much. But if it runs around the room through ceiling or wall for an appreciable distance it might be helpful. Cross coupling from other power feeds in the romex nest isn’t really an issue unless there is a poorly designed appliance that dumps high freq noise back to the box. And they are ultimately connected together there anyway.
Note there are likely to be code limits on how much power can be fed through the remote panel. If you have a 100 amp breaker box and there are already 100 amps worth of breakers, you might need to also upgrade the service lines into the panel to make sure it can handle the new additional load.
April 7, 2023 at 1:21 pm #5717
Bill Whitlock’s lecture loves Romex. He also demonstrates that “conduit” is bad. BUT, he is describing BX cable where you can stuff it with lots of parallel hots and neutrals. BAD. I totally agree. But 1/2″ steel conduit with twisted pair hot and neutral and a single isolated oversized ground. That’s delicious and good. Maybe better than Romex. For that distinction I’d have to personally ask my authorities, either Bill Whitlock or John Chester. They would know, authoritatively, the answer to that question.
April 7, 2023 at 1:19 pm #5716
Heya, Ted! You wrote: Run the audio “close” but not too close. Actually, there is no such thing as “not too close” for audio and power. The closer the better. Even if you run a balanced line level cable for fifty feet in close proximity parallel with a twisted pair 20 amp power drawing (typically) no more than a few amps, you’ll get no perceptible induction into the audio and probably no measurable induction either. But the farther away you run the audio from the power, the greater the loop area (difference of potential from external interference) and the greater the potential for external EMI and RFI. In short: The need to keep your audio and your power apart is largely a myth. If you’re drawing oodles of current (say, 50, 100 amps) in a giant power line, and there’s lots of harmonics from nasty power supplies adding power line harmonics, and you coil the audio 100 times around that power line, you MIGHT get some interference.
Try it…. let me know if you EVER get any power interference from proximity of audio runs with power runs.
The reason why it’s good to keep the runs as close as possible is: LOOP AREA. That’s because the audio and the power are part of a circuit. The lower the difference in potential between the two, the lower the loop area for external interference which can cause noise.
HOWEVER, it’s probably a good thing to keep audio cables away from EMI emitters like power transformers. But remember, the inverse square law applies…
P.S. It’s not as if I was always this “enlightened”. Go back 30, 40, 50 years, I, too believed the old myths of “always cross at 90 degrees” (mostly a myth), “don’t run audio and power in parallel next to each other (mostly a myth)” “keep your audio runs away from power lines” (mostly a myth), “heavy duty ground wire back to the ground rod is very important” (definitely a myth: because the longer the cable, the higher the impedance at RF frequencies. When is a ground not a ground? Answer: When it’s more than a few inches long!
April 7, 2023 at 1:24 pm #5718
Haha yep, yesterday I got around to reading an article (I forget if Muncy or Whitlock did it) but they wrapped a power cable and a balanced XLR cable (and mic to record the noise) together multiple times in a large coil and even ran a huge halogen light off the power cable to get a ton of draw, and still the only noise through the microphone was the audible click of the switch for the lights, no noise from the power at all. That greatly simplifies things for my room, especially if I elect to mount the computer outside of the room in a small rack.
April 7, 2023 at 3:20 pm #5725Norman VarneyModerator
You are happily on the right track! I would say that much of this is preventative and conditional to the scenario. I try to get measurements before designing a system to address existing conditions, and/or incorporate a separately derived system, etc. For example is armored conduit a needed expense in your environment? I like to overkill everything electrical to be safe and sanitary.
I do believe in physical isolation. In fact, just last month I installed a Google Nest wifi pod near electronic cables behind my rack. When I fired up the audio system I heard an unfamiliar noise. Turned out the cat6 cable has interfering and injecting noise into the system, until I moved the cable away from other cables. Note, my AC is dedicated, cables, dressing, contacts, etc. are all pretty high-end. With electrical systems I design my goal is for a minimum:
1. Ground Resistance of < 5 Ohm at grounding electrode conductor
2. Peak Current Capability of >1000 amps on each dedicated circuit
3. Voltage Distortion of <5%
4. Common Mode Noise of <10mv
5. Normal Mode Noise of <50mv
6. Harmonic Content of <3% 3rd, with nothing above
7. Electrical isolation throughout.
April 8, 2023 at 1:22 pm #5736Kevin Graf (Sr)Participant
Power and Grounding for Audio and Video Systems
A White Paper for the Real World – International Version
* * * * * * * * * * *
An Overview of Audio System Grounding & Interfacing
* * * * * * * * * *
Grounding and Shielding in Facilities
and other books
* * * * * * * * *
the old Middle Atlantic white paper:
Integrating Electronic Equipment and Power into Rack Enclosures
Optimized Power Distribution and Grounding for Audio, Video and Electronic Systems
now available at:
April 9, 2023 at 8:49 am #5739
Someone posted that for his home studio the idea of a breaker box in the studio seemed like overkill. For most home studio users, one or two dedicated 20 amp circuits should be fine. “Dedicated” means a home run, only the audio studio has use of that circuit. If you install just one dedicated duplex or quad outlet, preferably with isolated ground outlets — and everything in the room terminates at that outlet, then I think you’ve met the minimum requirements to establish minimum loop area.
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