Thread: Wattage calculation

Ok, so I'm looking at adding a second sub and wanted some input. My current living room is on a 15amp breaker, but the wiring could actually support a 20amp. So range is 1800 or 2400 watts total.

Sub1 = 300 watts
Sub2 = 430 watts
Plasma = 450 watts (by using the number displayed on my UPS)
Directv DVR = 55 watts
Marantz AVR = 650 watts
Oppo BDP-93 = 35 watts

Total = 1920 watts



Now, the AVR and subs, I assume is peak rating, and the Marantz is only running the two klipsch fronts and 1 klipsch center, so maybe its not pulling 600? Does it look OK, or should I get my electrician buddy to install a 20amp?

Not a question that can be answered with the info given, but 1920 W / 120 V = 16 A That would nominally be over, but...

1. Where did you get the power numbers from, especially the amplifier and sub numbers? Are these output power or input power? Peak or average? A better indicator is the input amp rating that can generally be found in the specs.

2. How high do you run your amplifiers? I am betting they are run at levels considerably lower than the rated power of the amp, thus using less power. A 650W amplifier would be pulling 5.4A. I doubt it is pulling nearly that much. You might want to buy a plug in ammeter at Home Depot to check.

3. Power factor fo the equipment. A watt isn't always a watt if it is heavily inductive (or capacitive) In these cases the power needs to be calculated using a power factor multiplier in order to capture the "imaginary" component of the power. That tends to raise calculated current.

Given what you have already said, I would bet you are OK, but if I were doing it and had access, I'd add a second 20A circuit.

DO NOT, UNDER ANY CIRCUMSTANCES replace your current 15A breaker with a 20A breaker. The wiring is rated to 15A and will (not could) overheat if too much current is drawn through it. You need 12 Ga wiring for a 20A circuit.

Another alternative is to split the equipment across two circuits. Is there another circuit in the room? How about on the other side of the wall, where you could piggyback a second outlet? These tricks can work when wiring a new circuit is not practical.

1) power numbers came from the manufacturers themselves. For the subs, they say max needed, so im assuming peak.

2) sub amps are at 9 oclock, or 1/4 gain

As far as replacing the 15amp breaker, I explained that. The wiring is 12ga (capable of a 20amp), it just has a 15amp installed. The code around here on newer homes is all 12 gauge wiring, period.

No way to split them over two circuits. I guess the meter is a good easy idea.

Is there anything simple that i could connect between the device and the outlet, to see exactly how much it pulls? (watts or amps)

Sure, an ammeter.

The breaker responds to amps so that's what you need to know.

12 amps on a 15 amp circuit or 16 max on a 20.

A "kill a watt" is what you need if you are interested in this sort of thing.
Reads watts or volt amps.

Originally Posted by Jason Whiddon

Is there anything simple that i could connect between the device and the outlet, to see exactly how much it pulls? (watts or amps)

Lowes has the Kill a Watt power meter, it's really nice. Your setup will not pull enough to trip a 15 amp breaker unless it at max power for a very long time. Breakers typically have a variable time delay set to trip at twice the amp rating after one minute or instantly with a short.

Originally Posted by inwo

12 amps on a 15 amp circuit or 16 max on a 20.

Those are maximum continuos currents allowed per code. Amps rarely pull max currents and then only for a short time at max volume.

OK, your original post was unclear on the wiring. Ask your electrician friend and verify that 12 Ga is legal for 20A breaker in your area. If they are requiring 12Ga for 15A, they may be requiring a larger Gauge for 20A as well. Also, have him inspect the romex and verify that it is actually 12/2 copper.

Originally Posted by rglore

Those are maximum continuos currents allowed per code. Amps rarely pull max currents and then only for a short time at max volume.

Exactly,

No way he will overload.

If you run a system loud enough to blow a 15 the windows will crack!