Power Consumption (Semi-Technical)

[Quickley17]

Alright, this is my first post, and I realize that I will be making some shocking and rash generalizations here, but I am looking into setting up a home theater (I am a pretty handy dude, so I will most likely do it myself).

My question stems from my basic understanding of home wiring and electricity, and I figured I would use LARGE numbers (which do not in any way accurately reflect my purchase intentions) for the sake of clarity.

Let us say I want to power my mains with two McIntosh MC2KW's producing 2000 W to each speaker (I think the speaker choice is unimportant for this excercise, suffice to say that the speakers can "handle" this amount of power). My understanding of RMS values for a sine wave indicate to me that I would peak at a little over 2800 Watts. My understanding of home electricity is that to develop 2800 Watts of 120V power, I would need a 25 AMP circuit.

Am I to infer by this math that in order to properly utilize the power available in this amplifier, I would need a 25 AMP circuit for each amplifier? And subsequently, if I were to have equipment this powerful, I would need to wire AT LEAST 3 circuits (2x 25 amp and a third) to this room in order to power those two speakers and associated HiFi equipment?

(Reality: I have two Polk Rti4 bookshelf speakers and a Pioneer Elite VSX-90TXV reciever and am looking to develop my system... but that is a different post)

 

[Rickster71]

My understanding is that each unit has two modules.
Each McIntosh MC2KW has two 120v AC plugs.
So you would need two 15-Amp, (or better yet) two 20-Amp circuits per unit.
120 Volts, 50/60Hz, 12 Amps
Also remember you'll never have it turned up to full volume

That's my understanding, let's wait for the Mac experts to add their thoughts.

 

[nick1000000]

Also understand that the amp may have the 2000W ready to deliver to the speakers, but the speakers will never use all that power at once. Speakers can be run at 1W.
Yes you are right though. Each amp would need its own outlet to draw the power without tripping the circuit. You would have a steep electric bill if you had your system on a lot.

 

[highfigh]

Alright, this is my first post, and I realize that I will be making some shocking and rash generalizations here, but I am looking into setting up a home theater (I am a pretty handy dude, so I will most likely do it myself).

My question stems from my basic understanding of home wiring and electricity, and I figured I would use LARGE numbers (which do not in any way accurately reflect my purchase intentions) for the sake of clarity.

Let us say I want to power my mains with two McIntosh MC2KW's producing 2000 W to each speaker (I think the speaker choice is unimportant for this excercise, suffice to say that the speakers can "handle" this amount of power). My understanding of RMS values for a sine wave indicate to me that I would peak at a little over 2800 Watts. My understanding of home electricity is that to develop 2800 Watts of 120V power, I would need a 25 AMP circuit.

Am I to infer by this math that in order to properly utilize the power available in this amplifier, I would need a 25 AMP circuit for each amplifier? And subsequently, if I were to have equipment this powerful, I would need to wire AT LEAST 3 circuits (2x 25 amp and a third) to this room in order to power those two speakers and associated HiFi equipment?

(Reality: I have two Polk Rti4 bookshelf speakers and a Pioneer Elite VSX-90TXV reciever and am looking to develop my system... but that is a different post)

Make sure the amp actually runs on 120VAC. At this power level, I would have designed it for 220/240VAC.

If it does run on 120V, you can use 8AWG- 10AWG on a dedicated 40A circuit if it's not too far from the panel.

 

[PENG]

My understanding of RMS values for a sine wave indicate to me that I would peak at a little over 2800 Watts. My understanding of home electricity is that to develop 2800 Watts of 120V power, I would need a 25 AMP circuit.

Sorry, your calculations is not quite right. You are right about Peak value=1.414XRMS value but a 25A cct at 120V will get you 3,000 watts average power, not peak power. The MC2KW's power module is rated for 1,000 watts rms output so assuming at rated load the overall efficiency is close to 70%:

Input power required=1000/.7=1,428.6 watts=11.9A

I chose 70% as the efficiency at rated load because according to McIntosh each power module requires 12A at 120V. So as shown above, at 70% efficiency the current draw at 1,000 watts is approx 12A. Other using this basis I do not know what the overall efficiency is for that amp.

To conclude, as Rick suggested, two 15A (of course 20A preferred) used solely for this beast will be fine.

 

[lsiberian]

Alright, this is my first post, and I realize that I will be making some shocking and rash generalizations here, but I am looking into setting up a home theater (I am a pretty handy dude, so I will most likely do it myself).

My question stems from my basic understanding of home wiring and electricity, and I figured I would use LARGE numbers (which do not in any way accurately reflect my purchase intentions) for the sake of clarity.

Let us say I want to power my mains with two McIntosh MC2KW's producing 2000 W to each speaker (I think the speaker choice is unimportant for this excercise, suffice to say that the speakers can "handle" this amount of power). My understanding of RMS values for a sine wave indicate to me that I would peak at a little over 2800 Watts. My understanding of home electricity is that to develop 2800 Watts of 120V power, I would need a 25 AMP circuit.

Am I to infer by this math that in order to properly utilize the power available in this amplifier, I would need a 25 AMP circuit for each amplifier? And subsequently, if I were to have equipment this powerful, I would need to wire AT LEAST 3 circuits (2x 25 amp and a third) to this room in order to power those two speakers and associated HiFi equipment?

(Reality: I have two Polk Rti4 bookshelf speakers and a Pioneer Elite VSX-90TXV reciever and am looking to develop my system... but that is a different post)

You don't need mcintosh amps for sure.

Go pro amp and get some the Yamaha amps. They are very quiet.

 

[Quickley17]

Peng, I was under the impression that a circuit didn't have any concept of rms. I had always assumed that if a total load exceeded the available current, the circuit would break. This would mean that for a 20 AMP circuit at 120 volts, a load in excess of 2400 watts would cause the circuit to break, ESPECIALLY because we're talking about peaks, which is what circuit breakers are designed to protect against. This is not the way it works? What happened to the 80% rule?

Highfigh. You're absolutely right. I think they do design them to operate at 240 volts, which makes a whole lot of sense.

 

[PENG]

Peng, I was under the impression that a circuit didn't have any concept of rms. I had always assumed that if a total load exceeded the available current, the circuit would break. This would mean that for a 20 AMP circuit at 120 volts, a load in excess of 2400 watts would cause the circuit to break, ESPECIALLY because we're talking about peaks, which is what circuit breakers are designed to protect against. This is not the way it works? What happened to the 80% rule?

Let me answer in point form.

1. When we say 15A in residential wiring we always mean 15A rms unless otherwise specified.

2. So you are right about a 10A sinewave will yield approx. 14A peak but then the 15A cct is rated for approx. 15X1.414=21.2A without tripping (See 3. below).

3. A 15A breaker, like a 15A fuse, will not trip as soon as the load reach 15A. It has a thermal characteristics that typically allow a higher current for a short duration in order to avoid nuissance tripping due to initial surge resulted from powering up a motor or transformer such as those found in a 2 KW power amps. McIntosh amps typically are equipped with what they call a powerguard that mitigate such transformer current inrush currents.

4. The 80% rule you refer are respected if you use two dedicated 15A circuits. McIntosh calls for 12A, 15X0.8=12A. Further, we (me and Rick) both said 20A is preferred.

I hope this answers you questions.

 

[Quickley17]

Well apparently I can't post links, but if you google "circuit breaker sizing" the first link does not imply that there is anything RMS about the circuits. It states that you have to build in the tolerance yourself.

According to the National Electric Code (USA):

OCPD = 100% non-continuous + 125% continuous = capacity.

2000 watts / 120 v = 16.66 Amps

1.25 x 16.66 = 21.833 Amps continuous.

ADD approx 800 Watts non-continuous:

800 watts / 120 v = 6.66 Amps

1 x 6.66 + 1.25 x 21.83 = 28.49

Do you have a link or source to show me that these circuits are rated at RMS? I don't mean to doubt you, but I've never heard that.

 

[PENG]

Do you have a link or source to show me that these circuits are rated at RMS? I don't mean to doubt you, but I've never heard that.

http://books.google.ca/books?id=Z4D-0J9R4QMC&pg=PA217&lpg=PA217&dq=does+nec+use+rms+currents&source=bl&ots=UectBkuje7&sig=H_7_-poqEq4XZjix7xSr9DhLqTw&hl=en&ei=SgxlSr6UGpHOM6Ou2Z4M&sa=X&oi=book_result&ct=result&resnum=9

I can't find anything explicit either but you will see that everywhere they show examples of current currents they use 120V as the voltage. If they were talking peak currents they would have to use 120X1.414V.

In the example in the link (page 9), they use 120V/10 ohms=12A. Since the voltage use is 120V that is obviously RMS, then the derived 12A must be RMS, agree?

In general, unless stated otherwise, RMS is the norm. One of the problems with specifying peak value is that it is dependent on the waveform.

Again if you 2X15A or better still 2X20A you will have plenty of reserve. If you really want to go with 2X25A for peace of mind then do it.

 

[Quickley17]

So I guess my confusion lies in the fact that I have always assumed that the amp will always ask for 120 volts. Is it true then that at peaks the amp will ask for 130, 150, 170? volts and thus offset the otherwise higher currents? I didn't think electronic equipment strayed from the 120 VAC (sometimes 240) provided by normal breakers.

 

[mtrycrafts]

Well apparently I can't post links, but if you google "circuit breaker sizing" the first link does not imply that there is anything RMS about the circuits. It states that you have to build in the tolerance yourself.

According to the National Electric Code (USA):

OCPD = 100% non-continuous + 125% continuous = capacity.

2000 watts / 120 v = 16.66 Amps

1.25 x 16.66 = 21.833 Amps continuous.

ADD approx 800 Watts non-continuous:

800 watts / 120 v = 6.66 Amps

1 x 6.66 + 1.25 x 21.83 = 28.49

Do you have a link or source to show me that these circuits are rated at RMS? I don't mean to doubt you, but I've never heard that.

RMS is understood. All you have to do is see the voltage ratings you posted, 120V. That is an RMS voltage, not a peak voltage of 120V. Slap on an O scope and see this explicitly.
Everything is assumed RMS unless otherwise stated. Plug in a voltmeter and see what you get. Then read the voltmeter instructions how it reads voltages, RMS. Why would current be different?

Besides, it would be not very productive to use and rate things in peak value as that doesn't produce power long enough at the peaks
Call up NEC.

 

[nick1000000]

If you already have the equipment you are talking about then plug it into whatever your house has provided for you. If nothing bad happens you are set. If you continually have reset your breaker then you need to run more current to your amps.
Most amps run fine on 120V 15A lines. These amps have capacitors and correct me if I am wrong but those capacitors are there for those intenses when there is a peak in the power consumption from the speakers and the capacitor gives that extra power the amp cannot.