Why is it necessary to have gear on the same phase from electrical panel?

The only thing I can think of that would improve things is to keep all the noisy stuff on one side of the panel, like refrigerator, and the cleaner stuff on the other side.

Its a myth... No such thing. IF the electrician did his job right and followed NEC as well as AHJ he balanced the 120V loads, within reason, as evenly as possibly on both Lines, legs, to the common neutral.

Also, FYI, Line 1 (L1), leg, and Line 2 (L2), leg, feed both sides of the circuit breakers in the electrical panel.

Example:

(L1) - - BRK 1 - - - - - - BRK 2 - - (L1)

(L2) - - BRK 3 - - - - - - BRK 4 - - (L2)

(L1) - - BRK 5 - - - - - - BRK 6 - - (L1)

(L2) - - BRK 7 - - - - - - BRK 8 - - (L2)

And so on down each side of the panel.

The source of power from any circuit is 120 V - therefore having some circuits on a different phase Side from the panel would seem OK.

When audio equipment is connected together by wire interconnects it is best practice to feed all 120V audio equipment, as well as video equipment, from the same Line, leg. Either from (L1) to neutral or (L2) to neutral, but not from both Lines. Example say a 120V preamp is fed from (L1) and a 120V power amp is fed from (L2) there is a 240V potential, voltage, between the two HOT conductors feeding the two pieces of equipment. With this wiring configuration there is a greater chance of noise, hum, from the system through the speakers.

When both pieces of equipment are feed from the same Line there is not any nominal difference of potential, voltage, between the Hot conductors feeding the two.

That’s the basics....

"Less than 300 microamps of ground loop current can cause hum as it flows in an unbalanced audio interconnect cable. However, harmonics of 60Hz that are generated from lighting dimmers or switch-mode power supplies sound like Buzzz mixed with a bit of Hummm and are more easily coupled by even smaller currents. Harmonics can add together when equipment is powered from different phases, so clearly there is an advantage to specifying same-phase electrical service to power the electronics systems in most cases....

Any leakage currents on the safety ground wires of split single phase load circuits fed by different phase legs will add together due to the 240V potential difference....

Power conditioners do not solve any of these common problems: Cross phase coupling (doubles hums & buzzes) .... What actually does solve them: Same phase power.
http://www.exactpower.com/elite/assets/pdfs/theTRUTH.pdf
 

(With big Monster mono Power amps the user may not have a choice and may have to feed them from both Lines. OR if money is no object a large VA rated single phase 240V to 120V isolation transformer can be used. Result one 120V Line... I worked with a member that has a single phase 240V to 120V 15KVA outdoor Pad Mount transformer that feeds a 120V only sub panel for his dedicated audio room.)

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Correction.

I worked with a member that has a single phase 240V to 120V 15KVA outdoor Pad Mount transformer that feeds a 120V only sub panel for his dedicated audio room.)

That should read:

I worked with a member that has a single phase 240V to 120V 15KVA outdoor Pad Mount transformer that feeds a 120V only panel for his dedicated audio room.)

It is not a sub panel.

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I ran two circuits to my system, one on each leg. I do keep my system all on the same leg and plug other things into the other leg but that is really just a local thing.

@carlsbad

What type of wiring method did you use?

Did you install a 3 wire 120/240V multi wire branch circuit consisting of two Hot conductors, one common shared neutral conductor, and one EGC (Equipment Grounding Conductor)?

If yes, only the unbalanced load current of (L1) to neutral and (L2) to neutral will return on the neutral conductor back to the source. The balanced load of (L1) to neutral and (L2) to neutral are in series with one another and are fed by 240V, nominal.

Here is a good example of how a 3 wire multi wire circuit works.

(Imagine the transformer’s split phase secondary winding is 120/240V)

@carlsbad said:

are you suggesting that the common neutral allows noise from one leg to affect the other leg?

No I am not suggesting that at all. What I am saying is the balanced load(s) "noise" on one leg is in series with the other leg and is fed by 240V.

Example: Say you have a total of 2 amps on (L1) leg and 4 amps on (L2) leg. That means only 2 amps, (the unbalanced load), will return to the source on the common neutral conductor of the multi wire 3 wire branch circuit. The other 2 amps, (the balanced load), of each leg is in series with one another and is fed by 240V. So say in the "other leg" there are devices that create "noise" that goes back out on the mains. Say this leg has the total of 2 amps. None of this "noisy" combined loads will will return on the common neutral conductor to the source. All of the 2 amp load will be in series with the AC line side of all the audio equipment on (L2) leg and return to the source.

The Circuit:

Hot (L1) leg conductor connected to >> (2 amp "noisy" loads) connected to, >> common neutral connection joint connected to >> ( 2 amp balanced load of the 4 amp total load(s) on (L2) leg), connected to the Hot (L2) leg conductor back to the source .

Worth noting both the Hot and Neutral conductors are current carrying conductors when a load is connected to both of them. In a normal 2 wire circuit the current in both conductors will be the same.

I hope you took the time and watched the video in my last post.

This also may help.

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