New Electrical Circuit

@puffbojie

The electricians have it scheduled for 15 amp circuit.

My guess, the electrician you are hiring is not an audiophile. He is basing his install of a 15 amp branch circuit on bare minimum electrical code. Electrical code could care less how an audio system sounds. Is it electrically safe? Code is satisfied.

Like others have said have a 20 amp branch circuit installed. Slight difference in cost for the wire. Breaker and labor cost no difference. It’s a no brainer imo.

Bare minimum for a 20 amp circuit is #12awg copper. You can have larger wiring installed if you choose.

If the length of the branch circuit wiring is 50ft or longer from the electrical panel to the wall outlet I would recommend #10awg solid wiring. Breaker in electrical panel will be 20 amp. I would also recommend a minimum of two dedicated 20 amp branch circuits One for digital sources and SMPS 120V power supplies, the other for analog 120V power supplies. Reason, it helps decouple the digital 120Vac power supply(s) from analog 120Vac power supply(s).

A dedicated branch circuit... A circuit with a dedicated Hot, Neutral, and EGC (Equipment Grounding Conductor). A true dedicated branch circuit should never be installed in a common conduit or cable assembly with other branch circuits. Current carrying conductors can/do induce voltage from one branch circuit to the other(s). (See Overview of Audio System Grounding & Interfacing Link below.)

If two or more branch circuits are installed for audio or audio video equipment that is connected together by wire interconnects the branch circuits should be fed from circuit breakers on the same Line, leg, in the electrical panel.

2 conductor NM sheathed cable (Romex) is widely used by audiophiles. I used to recommend it to feed audio equipment. I now recommend 10-2 solid copper MC (Metal Clad) aluminum armor cable.

I consider myself a qualified audiophile Licensed Master Electrician.

Reading material:

Read pages 11 through 13.

Integrating Electronic Equipment and Power

Read page 16. Read pages 31 through 36.

Overview of Audio System Grounding & Interfacing

Jim

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@puffbojie

My electrical box is outside. Can they encase the (Southwire Armorlite 125-ft 10/2 Solid Aluminum MC (Metal Clad) Cable) inside metal conduit for the outside portion for weather proofing?

Not really.

The electrician can use a, (example), EMT to AC/MC/FMC/NM Transition Fitting . He will remove the aluminum armor for the length of the EMT conduit and the wire needed for make up in the electrical panel.

Or he can use a junction box inside to transition from EMT conduit box connector to an MC cable box connector. I think the EMT to MC transition fitting would work better, jmho. Your electrician on the job site will know what will work best for him for his install situation.

If you decide to have MC cable installed make sure the electrician installs 3/8" anti-short bushings on all cut MC armor ends. Anti-short bushings are not required by NEC code. Have him install them anyway... They protect the insulation on the conductors from the sharp edge of the armor.

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@jea48 ​​​​​

Do you normally specify isolated ground and is that why you recommend MC?

@devinplombier

For a residential house I never recommend an isolated ground. It would not serve any purpose what so ever. FYI even in commercial and industrial facilities an IG, Isolated grounding conductor and IG type outlet are seldom used now days. They where big in the 1970s, 80s and 90s. They started fading in the early 2000s.

I recommend 2 wire solid copper aluminum armor MC cable.

Example:

10/2 Solid copper Aluminum armor MC (Metal Clad) Cable

The reason I like MC cable better than Romex is because of the way it is constructed. Hot, neutral, and insulated green equipment grounding conductors are tightly twisted together in a spiral twist and held tightly together by the armor. MC cable NOT AC cable (commonly called BX). AC cable is garbage for feeding audio equipment.

Romex is ok provided care is taken when installing it. Avoid twisting the cable as not to change, distort, the lay of the EGC (Equipment Grounding Conductor) between the Hot and neutral current carrying conductors. That’s next to impossible to do. If you tell the electrician to install the Romex keeping the cable flat without any twists. He will think you are nuts...

Read pages 12 and 13. Note the chart on page 13.

Integrating Electronic Equipment and Power

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Between (a) running 3 separate homeruns to the panel as mentioned above, and (b) a single homerun powering a subpanel in the listening room, which would you recommend?

@devinplombier

Not a simple question to answer. Best answer I can give is, It depends.

How long are the home runs? How many branch circuits will be installed? (You mentioned 3)

Cost of a good sub panel and feeder to feed the panel ain't cheap.

As for where the sub panel will be installed. I read occasionally where the panel is installed in close proximity to the wall outlets being fed. By close I mean less than 25ft of wire. Jmho that defeats one of the reasons for installing multiple dedicated branch circuits. To decouple audio equipment AC power supplies from one another. Not much impedance and inductance in 15 to 25ft length of wiring.

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@puffbojie said:

My understanding is when connecting the amplifier to a 20-amp circuit that the amplifier will draw only the current it requires.

That is correct.

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Regarding the 20 amp circuit, vs a 15 amp circuit, would you not need a 20 amp plug on the amp’s power cord for the unit to utilize the 20 amps?

No, for the reason you stated in the above quote.

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and what if the amplifier only calls for 15?

Usually stated as minimum. Does not imply maximum of 15 amp circuit. (YMMV with your amp.) Food for thought. Why are the majority of consumer power amplifiers sold in the US designed to be plugged into a 120V 15 amp wall outlet circuit? Because the majority of wall outlets circuits found in the home are 120V 15 amp convenience outlet circuits with 15 amp duplex receptacle outlets.

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I guess the question I am getting at is: should I use a 20 amp power cord/ “plug” for the amp to match up with my 20 amp circuit?

No... When looking at aftermarket power cords for power amplifiers seldom is a 20 amp (5-20P) 20 amp plug installed on the power cord. To require a 5-20P 20 amp plug the amplifier would have to have a continuous FLA rating of over 12 amps, not more than 16 amps. In most cases a 5-15P, 15 amp plug is used. What size wire, equivalent wire size, is used for the audiophile power cord? Might be #12 rated for 20 amp. might be bigger than #12awg. 10awg is common, 30 amp rating. Equivalent, #9awg and sometimes even bigger. Well that make no sense... Especially if the in wall branch circuit is a 15 amp circuit.

My guess the electrician that told you a 15 amp circuit is all you need is going to use 14 gauge wire. 14awg is rated for 15 amps. (How long will the branch circuit wiring be? Distance from electrical panel to wall outlet?) Now nothing prohibits the electrician from installing #12awg or even #10awg branch circuit wiring and connecting it to a 15 amp circuit breaker in the panel. The circuit is still a 15 amp circuit. The breaker handle rating determines the size of the circuit. Not the size of the branch circuit wiring.

Why bigger conductors, awg wire? AC mains Line VD, (Voltage Drop) under load conditions. Not just continuous load but for audio amplifiers high dynamic quick peak draws of current caused by the musical source material being played.

Example:

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kijanki

4,428 posts

06-07-2022 at 07:27pm

2x200W amp might take from mains close to 1kW during peaks. The problem is that peak supply current won’t be expected 8A, but rather close to 40A. It is because current is drawn only for very short time (millisecond pulse) at the peak of full wave rectified sinewave. It applies to most of LPS. Power delivered with such short pulses not only creates larger voltage drops in house wiring, but also heat-up amp’s power transformer, that has to be oversized (higher copper losses and higher core losses for eddy currents and hysteresis).

https://electronics.stackexchange.com/questions/329443/current-through-the-smoothing-capacitor-in-bridge-rectifier

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jea48

4,416 posts

06-07-2022 at 08:04pm

 

 

@kijanki

+1

 

Please explain what happens if the power transformer’s secondary winding voltage is lower feeding the rectifier, due to a quick AC mains VD event, and the electrolytic capacitors voltage is higher. Just going from memory the rectifier will not conduct and the caps do not get recharged for that "(millisecond pulse)" in time.

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kijanki

4,428 posts

06-07-2022 at 08:46pm

@jea48 You are right - there will be no current thru rectifiers until capacitor voltage will drop below rectifier supplied peak voltage. Theoretically it is possible to build LPS where capacitors keep average instead of peak voltage, but it requires huge inductor in series (in order of Henries) made with thick wire and AFAIK nobody is doing it. One problem is lower rail voltage (average instead of peak) while the other is dependency on the load current.

http://www.r-type.org/articles/art-144.htm

Does AC mains VD impact the sound of a power amplifier? From my listening experience it does. YMMV.

FYI, a 15 amp circuit breaker will pass quick short draws of current well above its’ 15 amp handle rating all day long without tripping open. The breaker doesn’t see or care about VD on the wiring.

FYI if you have a 15 amp branch circuit installed, per NEC code you cannot install a 5-20R 20 amp duplex outlet on the 15 amp circuit. I believe that most of the audiophile outlets sold today are 5-20R 20 amp outlets. NEC code does allow 2 or more 5-15R 15 amp outlets on a 20 amp branch circuit. A duplex receptacle is two.

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