Got big amp-help with 20A line and receptacle


So, I just purchased a Krell FPB 400cx, which I'm told requires a dedicated 20 amp line. Yes, I have read some Agon threads on running dedicated lines, as well as 20 amp receptacles. But they are mostly several years old and I am interested in some current basic recommendations.

I am not looking for the most expensive or esoteric setup, but do want to do it as best I can. The receptacle location is in the family room, which I estimate will require about 50-60 feet of cable from the breaker box in the garage.

So, at first all I knew was that I would be running a new line from the breaker box and that it would be grounded there. But some posters here and elsewhere stated that I should have an isolated ground installed outside the house and at least 6 feet from the existing ground. There were also suggestions around exactly which location IN the breaker box to place the new line and breaker.

We do have three refrigerators here, one in the kitchen, one in the utility room, and another in the garage. Of course, we we have all the other typical appliances in the house. One good thing is that, in my current setup with no dedicated lines, I don't hear any noise through the speakers unless I use the dimmer in the family room. So, maybe the power in the house is pretty decent.

With regard to receptacles, I've read various comments about the different brands, as well as the various effects of gold, rhodium, or other plating. To start with, I would like to try the most neutral sound I can get.

I did speak with two electricians today, and neither seemed to have much familiarity with the considerations for audio quality that I mentioned to them. Therefore, I would like some input on what to ask of them. If I am making this too complicated and harder than it needs to be, I'd like to know that as well. I would really appreciate any tips and input!
mtrot

Showing 4 responses by jea48

But some posters here and elsewhere stated that I should have an isolated ground installed outside the house and at least 6 feet from the existing ground.
Bad advice, forget the dedicated earth ground. The earth does not possess some magical mystical power that sucks nasties from our audio gear. The safety equipment ground main purpose is to provide a low impedance, resistive, path for ground fault current to return to the source, the electrical panel.

I did speak with two electricians today, and neither seemed to have much familiarity with the considerations for audio quality that I mentioned to them. Therefore, I would like some input on what to ask of them.

First off it depends on the local electrical code in your state and city what type of electrical installation can be used in your area. The electricians in your area will know what is allowed.

Because you are using an existing convenience receptacle outlet circuit to power your audio equipment I would suggest installing at least two new dedicated branch circuits. One dedicated circuit for the new power amp and one for the other equipment. With two dedicated circuit there is a less chance of a ground loop hum problem. This will lessen the chance of a difference of potential, voltage, existing between the two equipment grounding conductors of the two dedicated circuits.
If it were me I would feed my preamp and power amp from the same dedicated circuit. Use the other dedicated circuit for the other associated equipment.

You said the length of the run is around 50 to 60 feet. Did you figure up and down over and around in your calculation? If not that can add another 20 feet to the length.

IF you decide to plug the preamp into the same receptacle as the power amp I would install #10 AWG wire for this 20 amp dedicated circuit. With #10 AWG wire you won't have to worry about any dynamic power demand fluctuations from the power amp effecting the power being fed to the preamp.

For the other dedicated circuit use #12 Awg wire.

Type of wiring and wiring method used.

Probably the worst type of wiring method is to install conduit then pull the wires loosely randomly into the conduit. This method will assure you ground loop hum problems. Worse yet is to install more than one dedicated branch circuit in the same conduit.

If conduit is used, or must be used to meet local code, use aluminum armor MC Cable. One cable for each dedicated branch circuit. I would recommend solid core wire over stranded wire. MC is made both ways.

If code in your area allows NM-B cable,( Romex is a trade name of NM-B cable), works well providing long parallel runs are kept separated by at least 6 inches to reduce induced magnetic fields of the current carrying conductors from inducing a voltage onto the one another most importantly onto the equipment grounding conductors of the NM-B cable.

Make sure all the dedicated branch circuits are fed from the same Line, leg, of the electrical panel for all audio / video equipment that is connected together by interconnects.

A must read before you call the electrician.
Bill Whitlock, President of Jensen Transformers Inc.
http://centralindianaaes.files.wordpress.com/2012/09/indy-aes-2012-seminar-w-notes-v1-0.pdf
Pay close attention to pages 31 through 36
.
Jim

they want me to use a 30 amp single pole breaker so that my amp will run smoother, less heat, draw more current on demand, my sound stage will sound bigger and taller, and everything else, remember, all this is what krell swears too, they run my amp and the 750mcx amps on a 30 amp breaker thier at the factory, also,
11-11-14: Audiolabyrinth

Audiolabyrinth'

"They" told you wrong. First off the current carrying guts inside of a 20 amp breaker are the same as a 30 amp breaker. Only the trip unit settings are different. A 20 amp breaker will pass short bursts of current of over 100 amps all day long.

Per NEC Code a 20 amp NEMA 5-20R receptacle can only be connected to a 20 amp breaker. Minimum size branch circuit wire, #12 awg. The breaker size determines the size of the branch circuit. If # 10 wire is used the breaker still has to be a 20 amp if the receptacle is a NEMA 5-20R receptacle.

IF by chance the breaker is tripping occasionally on start up from high inrush current most breaker manufactures make a breaker with a longer lag time for high inrush current.
Example
>http://www.cesco.com/b2c/product/33471?gdftrk=gdfV25445_a_7c1847_a_7c7081_a_7c33471&gclid=CIurm-rygMICFY6EaQodj0MAvg


Two or more 15 amp NEMA 5-15R receptacles can also be installed on a 20 amp branch circuit. Per Code a 20 amp receptacle cannot be installed on a 15 amp branch circuit.
Audiolabyrinth,

Were you told by a Tech at Krell over the phone or through an email? Just guessing it was over the phone. See if the guy will send you an Email stating "Krell" recommends you use a 30 breaker to feed a 20 amp rated receptacle. Tell him you want to post it here on Agon.

As I said in my previous post the current carrying guts of a 20 amp breaker are the same as a 30 amp breaker, exactly the same.In fact they are the same as 40 amp breaker. Only the thermal and magnetic trip settings are different. And of course the number printed on the breaker handle.

As for the FLA rating of the Amp IF the amp is UL/CSA Listed the most continuous power the amp can draw is 16 amps, 80% of 20 amps. If it is over 16 amps the manufacture would then have to use a 30 plug mated to a 30 amp receptacle connected to a 30 amp branch circuit to get the UL/CSA Listing.
There are a lot of good comments in this thread. I recently had some work done in my new house. I started calling electricians to get some estimates. I knew I had the right guy when he said, "music room? Then you will be wanting isolated 20 amp circuits."
11-22-14: Brownsfan
Brownsfan,

Isolated circuits? Do you mean dedicated circuits?
If isolated what type of wiring method was used? Is the wiring inside of a metal conduit?
Jim