More questions about dedicated lines

@ orthomead

+1 almarg post on 12-15-2019

almarg9,244 posts

12-15-2019
8:14pm


Regarding keeping the two AC legs from becoming significantly unbalanced, I would infer from the literature on your VAC amps that they operate primarily in class AB, since only the input and driver stages are described as operating in class A. And given their 200 watt rating in mono mode I suspect that aside from occasional very brief dynamic peaks in the music each amp will probably be supplying well under 100 watts to the speakers, with the two amps together consequently drawing no more than about 500 watts of AC. With the system as a whole probably drawing no more than 800 watts or so most of the time, including the sub amp. Which seems to me to be sufficiently low that keeping the legs in balance is a non-issue, regardless of which of the three approaches is chosen.

Using Al’s (almarg) calculations for total average energy usage of 800 watts would not be a problem, imo, putting the four 20 amp dedicated branch circuits on the same Line , leg.


One 120V 20 amp (2400 watts) branch circuit would easily handle a 800 watt load. Spreading, separating, the loads of your audio equipment across 4 branch circuits will not change the total connected load.

800 watts / 120 volts = 6.7 amps. 6.7 amps will not cause a significant imbalance load on the electrical service of your home.
The average portable vacuum cleaner has an FLA of 12 amps. A portable electric space heater 1500 watt @ 125V, 12 amps. An average microwave oven 1200 watts, 10 amps @ 120V.

Using 10-2 with ground Romex (NM sheathed cable) where the total length is 45ft should rule out the chance of ground loop hum..... Should..... I can’t count all the threads I have read over the years where monoblocks were/are used where the user is fighting ground loop hum problems.

Here is just one running now.
https://forum.audiogon.com/discussions/krell-kas-amplifier-hum

@Atmasphere explains most ground loop hum is caused by the audio equipment itself. Poor design in the way the designer connected the circuit ground/signal ground to the AC mains safety equipment grounded chassis of the equipment.

Jim

@ orthomead

1 gang new work plastic boxes have more internal space/area than 1 gang new work steel switch boxes. Home Depot carries good quality plastic boxes.

+ 1 on using deep boxes when using #10 Romex. Your electrician will/should already know that.

@ orthomead


Just curious,


Where is the main electrical panel located? Example, garage, laundry room, mechanical room, on the outside of the house. Manufacturer of panel? Electrical panel main breaker size?

Where is the sub panel located?
How big is the sub panel, ampere rating? What is the handle ampere rating of the 2 pole breaker in the main electrical panel that feeds the sub panel? (Number is on the breaker handle) How many empty spaces are left in the sub panel? Number of empty spaces on each side? Panel manufacture?

Any idea how big, horse power rating, the pool pump motor is? Voltage rating? 120V or 240V? Is the motor controlled by a VFD (Variable Frequency Drive) controller?

Use three wire Romex just in case you ever want to run a 220 volt amp.

You don’t need a 3 wire with ground Romex cable for 240V. A 2 wire with ground Romex is all that is needed.


Problem with using a 3 wire with ground Romex cable for a 2 wire circuit is what do you do with the unused conductor? Ground it? Leave it floating, taping both ends?
Floating the unused wire will act as an antenna and will introduce RF noise onto the circuit conductors.

If the unused wire is grounded because of the lay, position, of the conductor in the Romex cable, the hot and neutral current carrying conductor’s magnetic fields will induce a voltage on the grounded wire. Result is a ground loop and hum.

Worth mentioning again, as I have mentioned before in other posts, two conductor with ground NM sheathed cable (Romex) is not the best branch circuit wiring for controlling induced voltage from the magnetic fields of the hot and neutral current carrying conductors. The reason is because the paper filler that surrounds the bare ground wire does not rigidly hold the ground wire centered between the hot and neutral conductors. Twisting the Romex cable, imo, would make it even worse, not better.

A better Branch circuit wiring is 3 wire MC (Metal Clad) armored cable. (Hot, neutral, and green insulated ground) The 3 wires are tightly held together in a spiral twist housed inside a metallic armor. MC cable is manufactured with a steel armor or aluminum armor. Also manufactured with solid or stranded conductors. (Solid wire is recommended for audio branch circuit wiring.)
Example of MC armored cable.
http://www.afcweb.com/mc-metal-clad-cables/mc-lite-aluminum-armored-cable/

Best branch circuit wiring is to twist the hot and neutral conductors together and install the equipment ground along side the twisted pair in a conduit.

Jim
.

audiozenology96 posts

12-20-2019
9:28am

jea48,

This is why I would never recommend multiple runs from the breaker panel unless the grounds are tied at your stereo system. This is why I ran a single heavy gauge to a mini panel and then put the outlets right next to it.

@ audiozenology

Why do audiophiles have multiple 20 amp branch circuits installed when in most cases one 20 amp branch circuit would be plenty big. The OP audio system has a total average continuous connected load of around 7 amps? (Music playing at a moderate to load listening level.)

It has been a while, and I no longer have the posts in my favorites, from two well respected EEs that posted on the Audio Asylum audio forum. When I get a chance this weekend I will check the archives to see if I can find them.

Just going from memory though it has something to do with decoupling the power supplies of audio equipment from one another. Especially digital equipment from analog. Distance, length, of the branch circuit wiring has something to do with it.

Jim

@ millercarbon


read pages 11 thru 13.
https://www.anixter.com/content/dam/Images/Logos/Supplier-Logos/Middle-Atlantic/PowerPaper.pdf


read pages 31 thru 35
https://centralindianaaes.files.wordpress.com/2012/09/indy-aes-2012-seminar-w-notes-v1-0.pdf

FWIW, I used 10-2 w/grd NM sheathed cable for the two 20 amp dedicated branch circuits for my 2ch audio system. Each cable is 75ft long......
My system is dead quiet...

Job layout and the wiring method used makes the difference.
.

orthomead OP28 posts

12-21-2019
2:36pm

I think I’m getting somewhere here thanks to y’all. Jim, the PowerPaper you referenced indicated that there were two sheathing options-aluminum or steel and the article further references the aluminum sheathed hospital grade cable. Of these 3 options, what would you currently choose? Are all your components plugged directly into the wall or do you use a power strip and/or conditioner/regenerator?

@ orthomead

MC aluminum armored cable is more widely used than steel. Aluminum will help shield from RF noise but not AC magnetic fields. The steel armor helps reduce AC magnetic fields. Though the twisting of the current carrying conductor does most of that. The steel armor will help protect the conductors of the MC cable from close near by parallel running NM cables from induing an AC voltage, AC noise, onto the conductors of the MC cable.


If aluminum armor MC cable is used it should be kept, spaced, from other branch circuit wiring probably a safe distance would be 8" to 12" or so. 8" would be enough but 12" would be safer. (Within reason after getting out of the electrical panel and starting the parallel runs, of the dedicated branch circuits, as well as any existing parallel running NM (Romex) branch circuits, as they are being installed to the audio room and down the wall to the outlets.) (With Romex you need to pay more attention to cable separation.)

FWIW.
(I am not a fan of 4plexs, 2 duplex outlets (for two dedicated branch circuits), sharing the same outlet box. Kind of defeats the purpose of dedicated circuits separation. Also worth mentioning if wall warts are used, depending on the physical size of the wall wart, it blocks part of the outlet on either side of it.

If you want to use the steel armored MC cable I wouldn’t be surprised if the electrical contractor will have to special order it. I suppose it depends on amount of usage of steel armored MC cable in your State, area, though.

As for hospital grade MC armored cable it has two equipment ground wires. One bare ground that runs along side the spiraled twisted circuit conductors, (to bond, connect, the equipment grounding conductor to the steel outlet box). The other grounding conductor is a green color insulated wire for an IG, (Isolated Ground) type outlet). (This insulated green wire is tightly held in place and twisted in a spiral together with the black and white current carrying conductors.)

You don’t need to use IG outlets in a single family dwelling house structure. IG outlets aren’t used that much anymore and when they were used they were used in commercial and industrial facilities where branch circuit steel conduits are fastened to other steel objects. The theory is AC noise is traveling all over the place through the interconnecting steel and other electrical steel conduits.

Of these 3 options, what would you currently choose?

This is a question you really need to have with the electrical contractor you are working with. He has been on site and is better qualified to assess your situation. For one thing can he keep the 4 dedicated MC armor cables separated from one another after he gets out of the electrical panel, as well as other parallel running branch circuit wiring. As for me, I would go with the aluminum armor MC cable.

ONE THING FOR SURE! Make sure you tell the contractor you want #10awg SOLID wire. Not Stranded wire...... Make sure he understands you want solid.... Don’t let him try to talk you out of it. He will tell you the ampacity rating is exactly the same, and yes it is. Your audio system won’t sound the same though. Solid wire only.

Are all your components plugged directly into the wall or do you use a power strip and/or conditioner/regenerator?

Yes directly plugged into the wall outlet. No power conditioner.
And again, I used NM (Romex) cable. Your situation may be different than mine though. I didn’t feel the need to spend the extra money for the MC armored cable.

If you don’t mind having a sub panel installed in your audio room you may want to go that route. One factor to consider though is resale of the home.


Best place to Install it is in the new wall you will be building. Speaking of the new wall you may want to consider building a double wall with staggered studs. Leave a slight space between the two framed walls. A 1/2 inch to an inch would probably be plenty.


Per the NEC, and I’m pretty sure the AHJ (Authority Having Jurisdiction) in your city, the electrical panel must be readily accessible and have a clear working space in front of the panel. Your electrical contractor can tell you what the minimum front and side distance measurements are.


If you decide to have a sub panel installed, because of the cost of the installation, (material and labor), you should add plenty of a fudge factor for future. It’s a lot cheaper now than later if you decide to buy bigger amplifiers.


I would wire sub panel for 120/240V. With your present audio equipment you can still feed all the 4 dedicated circuits from one Line, leg. With both Lines, Legs, available you have the option to easily move the dedicated branch circuits to the Line, leg, for what ever reason if you so choose.

Sub Panel Feeder:
If it were me I would feed the sub panel with at least #4awg copper or #2awg aluminum conductors. I would oversize the equipment grounding conductor as well.
If the electrician used #4 copper, (or #2 aluminum), he could use a 2 pole 70 amp, or a 2 pole 80 amp, breaker at the main electrical panel. Code only requires a #8 copper for the equipment grounding conductor. I would probably bump it up to a #6 copper wire.

Overkill? Yeah, probably...... But consider you want four 120V 20 amp dedicated circuits, using #10 wire, to feed an audio system that draws around 7 amps.


Combined wire gauge calculator.
https://www.wirebarn.com/Combined-Wire-Gauge-Calculator_ep_42.html

Enter 4 for the number of wires.
Enter #10awg for wire gauge.4 #10s = #4awg.

Jim

EDIT:

jea483,227 posts

12-22-2019
1:57pm


Sub Panel Feeder:
If it were me I would feed the sub panel with at least #4awg copper or #2awg aluminum conductors. I would oversize the equipment grounding conductor as well.
If the electrician used #4 copper, (or #2 aluminum), he could use a 2 pole 70 amp, or a 2 pole 80 amp, breaker at the main electrical panel.

I just used the NEC ampacity rating of the wire to size the 2 pole breaker for the feeder. Going back this AM and rereading what I posted yesterday I should have posted a 2 pole 60 amp or a 2 pole 70 amp breaker. It could even be a 2 pole 50 providing the wire lug size is big enough for #4 copper or #2 Al (aluminum) wire.

Example Square D is listed at,

35A - 70A

• 1 wire per lug: (1) #8 - #2 AWG Aluminum or Copper

https://www.se.com/us/en/faqs/FA237923/




@ audiozenology

If you are in a major city, I don’t think you will have too much trouble finding steel armoured cable. Most of the major electrical distributors will stock it, though maybe not in their branch outlets, so you may have to order today, deliver tomorrow.

You would think so. But unless there is a demand for steel armor MC cable, Electrical Wholesale Houses, today anyway, don’t stock items that just take up self space.
I called 4 large wholesale houses this morning and none of them stocked the steel armor MC cable.

My brain is starting to go into Christmas shutdown mode, so I am not sure I am 100% accurate when stating that using 120/240 will create unbalanced current which could cause ground injection. Assume I am wrong, but please check my work.

Not sure I follow, please explain.
Remember in the OP’s case his average load is around 7 amps. #4awg copper is rated for 70 amps (60 degree C, 140 F) and 85 amps (75 degree C, 167 F, THHN/THWN)
(There are factors that may apply for the adjusted ampacity rating of the wire.)


The circuit is through one of the feeder’s two hot legs and the feeder’s neutral conductor, a 7 amp load is insignificant in the scheme of things in my opinion.

Jim