Dedicated 20 amp lines/should i use a sub panel

noromance
901 posts                                                                     01-04-2018 12:07pm

Jim, Some replies below.

By side by side, do you mean the breakers are installed directly across from one another? Connected to the same main bus breaker tie. (Both are fed from the same leg, Line.) Or, do you mean one is installed above the other, side by side? One fed from leg, Line 1 and the other fed from Leg, Line 2?
>>> Same leg/busbar. One 20A breaker above other.

>>>

Same leg/busbar. One 20A breaker above other.

If the breakers are directly above one another, there in on the same side of the electrical panel, they are not fed from the same leg/bus bar. (For standard size single pole breakers.) One is fed from one leg, Line, and the other is fed from the other Leg, Line.

You can easily verify this with a multimeter.
Insert one test probe in the Hot contact of an outlet fed from one dedicated circuit and the other test probe in the Hot contact of the other dedicated circuit outlet.
~ If both are fed from the same leg, Line, bus bar, the meter will measure zero volts.
~ If the meter reads 240V, nominal, then one circuit is fed from one leg, Line, and the other circuit is fed from the other leg, Line.

Did you use Romex?
>>> Yes. 8/2 NM-B (not 10 as I said before) cable from Lowes.

8-2 with ground? Not 8-3 with ground?

Jim

Besides having built-in noise cancelling features, and surge protection, another advantage to the sub-panel is that you end up with a star grounding scheme that is short, and therefore much less likely to cause differences in ground potential.

The biggest source of noise in my mind is usually other household appliances, and dimmer switches. If you get separate runs, without any noise cancelling, you are literally just making it easier to pick up noise from anywhere in the house. Having a 30 to 60 Amp subpannel that has its own noise and surge protection is the key.

Best,

E

Jim,
8/2 with ground. You are correct about the legs. I also tried it on both legs. So instead of 22, 24, where I originally connected it, I had tried it on 23, 24 but it still hummed. In fact, as it’s a basement space, I just ran in a 12/2 on 15A breaker on the same leg to see if it still hummed with the (2 wire) monos. It did. But it doesn’t when I add my REL sub. So all is not lost! I should say that there is normally no hum from the rig.

How far away is the main panel from your listening room? If it’s more than 50 feet then it pays to put in a subpanel since a branch circuit of that distance will have a high voltage drop (3 volts with #12 and 1.8 volts with #10 at a 15-amp peak draw).

If distance is not an issue, use 10/3 romex because the wires are spiraled and that reduces common mode noise. Cut the bare grounding conductor and use the red wire for ground (tape it green where exposed, of course). Also, use the clamps under the screw of the receptacle for #10 wire instead of looping it around the screw. And use 10/3 from the subpanel to the receptacle also.

@noromance,

From the picture of one of your mono amps you are not using the green safety equipment ground wire. I assume both amps are wired that way.
https://systems.audiogon.com/systems/1593#&gid=1&pid=11

How about the preamp, are you using the safety equipment ground on it?

I also noticed the steel cover plate on the single receptacle outlet.
https://systems.audiogon.com/systems/1593#&gid=1&pid=14
Not that it would cause the hum issue, it could have an effect on the SQ. Just for the heck of it pull the steel cover off the outlet and see if you can hear a difference. If yes just install a nylon plate in its’ place.

By the way, nice looking vintage equipment.


Just an added note.
I ran two 10-2 with ground NM-B cables, (Romex is a Trade Name manufacture of NM-B sheathed cable), around 75ft each in length. Preamp and amp are tube. System is dead quiet. Ear right up next to the drivers of each speaker.


Jim