[floresjc]

I have a Double 240 and a Double 240/3 which I use to power my home theater. Just bought a new home and will be finishing the basement. Essentially, I will be doing a hidden install, placing a dedicated 20amp line into the room beneath my staircase and putting the amps in there. I will have a standard door to access the space, and so I could go in there and turn them on or off.

My question would be if I made that outlet switchable (as in putting a light switch outside the door to that room), could I leave the amps "on" all the time and just switch the outlet on/off as needed? I'm wondering if there would be too much current rush initially or if turning on the amps in that fashion would be detrimental. Also want to know if you think it would be worth the extra effort to run shielded wire to the outlet, or if I should consider shielded wire for any other outlets, like say the plasma tv or receiver etc...

[Wayner]

No shielding of AC wire should be necessary. As for operating the amps with a wall switch, they really should be sequentially turned on and off. In other words, the amps should be the last things turned on in the system, and first things turned off in the system.

There are some power outlet units (with "treated power") that will do this. My old Monster Cable, HTS3000 does this, turning the preamp and other low level devices on first, then with delay, switches on the amplifiers. In shut down mode, it kills power to everything instantly. The reason for doing the sequential on/off is to prevent speaker thumping. To use such a unit, it usually has 2 power cords. One goes to the 20 receptacle in your case and the other would plug into your switched outlet of your preamp or processor. The second plug to processor controls the delay timed outlets on the power unit, that you would plug your amps into, but not their current capacity. That comes from the power outlet source.

I also suggest a lighted switch for this outlet, but you will have difficulty finding a switch rated for 20 amps. If you install a 4 plex, 20 amp dedicated outlet, you could switch one duplex but it would then have a 15 amp rating. Your other outlet would be 20 amp rated. You could use this unswitched 20 amp outlet to operated low amperage devices that you would plan on leaving on all the time, like a VCR, DVD or cable box.

Wayner

[Wayner]

Like this:

 

Wayner

[Wayner]

You could switch the second duplex and add a second switch and sequence on and off manually with the switches. I'd add a third duplex to cover those components you'd want to leave on all the time.

Wayner

[floresjc]

Thanks for the info Wayner. One thing I'm confused about.

I was checking around AVAhifi and Parasound and some other amp manufacturers web pages. For something like the Parasound A21, it says that peak current is something like 60 amps per channel. I'm wondering, with the kind of current that AVA can throw around (and other manufacturers), is a single 20 amp line enough? Are people putting in 50 amp lines or some other work around?

I've had all 5 channels of 240 power (240 and 240/3) on a 20 amp line with no problems (Frank said this was ok), yet I would have to think that peak current would be much higher than 20 amps. I'm not an electronics guru and I guess I'm confused at how a 20 amp line could handle the current dished out by 5 channels of double die power.

[srb]

I was checking around AVAhifi and Parasound and some other amp manufacturers web pages. For something like the Parasound A21, it says that peak current is something like 60 amps per channel. I'm wondering, with the kind of current that AVA can throw around (and other manufacturers), is a single 20 amp line enough? Are people putting in 50 amp lines or some other work around?

The AC line can supply 20A at 120V (USA).  Just because the amp can deliver peak current of 60A doesn't mean the AC line has to be rated as such.
 
Look at the Maximum Power Consumption of the amp(s) to determine the current that the AC line will need to deliver.  For example, the Parasound A21's power requirement is rated at 1500W for full power at 4 ohms.  That would require 1500W/120V = 12.5A from your AC line.
 
Steve

[floresjc]

srb -

Thanks, that does help.

[Wayner]

Steve has pointed out quite well what's going on with the power. Just to blow your mind a little, that little outlet can deliver 50,000 amps for a couple of milliseconds with a dead short, in which a smaller arc flash explosion would occur. Amperage has to always be considered with time as the control element to the equation. The power amps can deliver such power because their own built in power supplies have that ability (with capacitors, etc.) to deliver high current for short periods of time, (again in milliseconds) to get thru a demanding musical passage. If you are playing your music that loud, you have other issues to be concerned with.

Wayner

[floresjc]

Wayner -

No I was more curious than anything. As a non-electrical engineer, seeing something like 60 amps per channel peak on a 20 amp line (even if its just a stereo amp) was a little confusing. And I also know that for most listening, very little power draw is necessary, maybe a couple watts at most, its those instaneous transients you are talking about that seem to be the sticking point.

Would you by chance happen to know what the maximum power consumption is for the Insight line of amps? I have a double of the 240, 240/3, and 440. The 240 and 240/3 get along just fine on a single 20amp line (just as Frank said they would) and I'm going to put the 440 on a line of its own. I'd be curious though to do srb's little division and see what kind of current they draw.

[Wayner]

Let's do some simple math here. The 240 can put out about 120 watts per channel, or about 240 watts of musical power. The "line" fuse, before everything else is 7 amps. This is an internal fuse for the entire amplifier in front of everything even the power transformer. I'm pretty sure the 240/3 is about the same power, but If you want to feel good, let's say it's a 8 amp (guessing) and the 440 may have a 10 amp.

So, the 240 and 240/3 adds up to 15 amps and the 440 is about 10 amps. Now, this is not even the maximum power consumption for these amps as the fuse is a slo-blow. That means the old time element is brought in again. In normal use, the amps may be drawing as little as a few amps each, it depends on how loud you play your music.

Please keep in mind that amplifiers have tremendous inrush current when they are turned on and depending on the condition of the circuit breaker and other additional loads, the 20 amp breaker may trip.

When I consider circuit loads, the amps are the main consideration. If you have only one single 20 amp line, and have these 3 amps on that same circuit, the math says we're 5 amps over, cause the 3 amps are fused to 25 amps. However, again, those fuses will blow at failure mode over time (again, in milliseconds). I was taught that a good rule of thumb on devices like these amps that have variable power consumption is to use 65% as a power factor correction, some suggest 55%. That put's total draw at 16.25 amps @ 65%. Now CD players, preamps and the like can't hardly draw a 1/2 and amp so as it appears to me, the circuit amperage should be OK, unless you have a bunch of these devices. Most CD players are under 25 watts so 25/120 = .2 amps so there is still room.

The problem here is that these amps have a variable power consumption. Let's say we had 20, 100 watt light bulbs on a 15 amp circuit breaker. That would be 20 X 100 or 2,000 watt. Watts divided by volts would be 2,000/120 = 16.666 amps and we would have circuit failure (breaker trips). If we had 18, 100 watt light bulbs, that would be 1800 watts, so 1800/120 = 15. This could be a trip point as well, depending on breaker style (class) and it's trip condition (is it worn). Every time a circuit breaker is tripped, it looses it's holding power a little bit so next time it trips, it may only take 14.95 amps, as an example.

To sum it all up, you have your 20 amp line pretty well consumed. If you plan on adding more equipment, you probably will start to end up in the nuisance tripping mode and it may be necessary to add another branch circuit.

Wayner

[Wayner]

Also, don't get any ideas about changing the breaker size. The breaker is there to protect the outlet and the wire to it. I'll also ass/u/me that you are using a 20 amp receptacle?

 

[floresjc]

I was planning on using a 20amp receptacle. I'm actually not doing any of the work myself. My dad's a contractor and has a good electrician friend he's known for some 30 years. So he does all the work in our homes.

So I'll probably have him put in a 20 amp line in the living room for the 440 (sounds like a dedicated 15 would work), and another 20 amp line to the basement for just the 240's. The other gear, tvs and processors and stuff, will go on another circuit. I just wanted to have the amps separate because I know they would be high current draw compared to the other stuff. I didn't want to have to worry about my wife turning on a lamp and having the circuit trip because I was watching a movie or something. 

Right now I have the 240's on a non dedicated line. But they may be the only things besides a light bulb on that circuit, and I've had no problems. I'm not even sure if its a 15 or 20 amp line, most likely 15. I don't crank it up to unreasonable levels though.

I'm not going to mess with breakers, but I may get a buddy box for more circuits or even a new panel altogether. I have a 150 in right now with 8 circuits left, which should be plenty to finish off the basement. My dad can get a 200 panel or something like that (maybe 220) for pretty much free so maybe I'll just have that installed before we get started, Rick (the electrician) is going to have to check whats coming in the home, the wire may be thick enough but I'm certain we're not provisioned that high.