Installation of new AC lines......best way to ground to avoid loops and noise

It absolutely does not matter is all your circuits come from the same leg or not. That is factually and electrically false.

While I don’t doubt that in some and perhaps many setups it won’t matter whether the components in a system are all powered from a single leg or from both legs, I would respectfully disagree with a contention that claiming it may matter in some or many systems "is factually and electrically false."

Following are excerpts from posts I had made in a couple of past threads which dealt with this question. (I’ve edited the excerpts slightly to remove wording that is not relevant here, as well as to remove links that no longer work):

Regarding the issue of splitting the load between two AC phases ... I looked through the ExactPower paper Jim (Jea48) referenced, the relevance of which is captured in its subtitle, "A practical guide for AV designers, installers, and electricians."

As an EE with extensive background designing analog and digital circuits (not for audio) I find the paper to be authoritative and credible. Which is to be expected, considering its authors. Among them, Henry Ott is a world renowned authority on numerous aspects of electrical and electronic design. Bill Whitlock (of Jensen Transformers) is certainly no slouch either. Some excerpts from their paper:

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.

Also, regarding ground loops ... it seems to me [Almarg] that if leakage current finding its way to the chassis (and safety ground) of a given component, via stray capacitance in the power transformer, EMI/RFI filters, etc., is out of phase with leakage current in another component that it is interconnected with, inter-chassis current flow between the two components, and therefore susceptibility to ground loop-related hum and noise, will have been maximized.

Again, I don’t doubt that in some and perhaps many setups it won’t matter whether the components in a system are all powered from a single leg or from both legs. But unless the system draws unusually large amounts of current and therefore might significantly unbalance the two legs if it is powered by a single leg (and keep in mind that most systems draw considerably less current than most hairdryers), it seems to me that what Henry Ott and Bill Whitlock have to say on the matter should be considered to be definitive as to what is best practice. And certainly not alleged to be "factually and electrically false."

Regards,
-- Al

My two 20 amp dedicated circuits were installed by a licensed electrician, then checked by the City's Code Inspector. 
Why? Homeowners Insurance, City requirements, Warranty for the work, and Peace of Mind. 

I'm a very senior (Old Fud) retired electrical engineer. I could have done the work, but understood my current knowledge of the Codes was not up to snuff. Inadvertent mistakes can be costly.

brayeagle211 posts

03-20-2019 10:56pm

My two 20 amp dedicated circuits were installed by a licensed electrician, then checked by the City’s Code Inspector.
Why? Homeowners Insurance, City requirements, Warranty for the work, and Peace of Mind.

I’m a very senior (Old Fud) retired electrical engineer. I could have done the work, but understood my current knowledge of the Codes was not up to snuff. Inadvertent mistakes can be costly.

Agree 100%


But in case you didn’t know the NEC (National Electrical Code) is bare minimum electrical safety code. You can exceed the bare minimum requirements of the NEC, you just can’t go below the minimum safety electrical standards, requirements, of the NEC.

National Electrical Code 90.1 Purpose:

(A) Practical Safeguarding. The purpose of this Code is the practical safeguarding of persons and property from hazards arising from the use of electricity.

B) Adequacy. This Code contains provisions considered necessary for safety. Compliance therewith and proper maintenance results in an installation that is essentially free from hazard but not necessarily efficient, convenient, or adequate for good service or future expansion of electrical use.

FPN: Hazards often occur because of overloading of wiring systems by methods or usage not in conformity with this Code. This occurs because initial wiring did not provide for increases in the use of electricity. An initial adequate installation and reasonable provisions for system changes provide for increase in the use of electricity.

(C) Intention. This Code is not intended as a design specification or instruction manual for untrained persons.

(D) Relation to Other international standards . The requirements in this Code address the fundamental principles of protection for safety contained in Section 131 of International Electrotechnical Commission Standard 60364-1, Electrical Installation of Buildings.

FPN: IEC 60364-, Section 131, contains fundamental principles of protection for safety that encompass protection against electric shock, protection against thermal effects, protection against overcurrent, protection against fault currents, and protection against overvoltage. All of these potential hazards are addressed by the requirements in this Code.

Look Closely at Section (B) Adequacy it reads as follows: "Compliance therewith and proper maintenance results in an installation that is essentially free from hazard but not necessarily efficient, convenient, or adequate for good service or future expansion of electric use."

 

B) Adequacy. This Code contains provisions considered necessary for safety. Compliance therewith and proper maintenance results in an installation that is essentially free from hazard but not necessarily efficient, convenient, or adequate for good service or future expansion of electrical use.



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@minorl

First you have a mighty fine 2ch audio system there.

As for your statement stating that dedicated circuits installed to feed an audio system installed in a home must be fed from both 120V Lines, Legs, is not accurate, imo. Would you please cite in the NEC where it says it.

In probably the majority of audio systems in the US and Canada the total combined load of the audio system equipment at best would add up to 8 to 12 amps continuous load at best. One 120V 15 amp branch circuit would be more than enough. Not to mention it would meet or exceed the bare minimum NEC standards. (#14awg copper wire fed from a 15 amp branch circuit breaker.)
If the home owner wanted the electrician to install two 120V 20 amp dedicated circuits fed from the same Line, Leg, I see nothing in the NEC that says it would violate the the NEC.

In your case with your audio equipment I can see and would agree the ARC mono amps should be be fed from both AC Lines, Legs. Yes, to balance the two loads across both Lines of the electrical service panel.
Jim