confused about 20 amp power cables

@williewonka said:

A single receptacle installed on an individual branch circuit shall have an ampere rating not less than that of the branch circuit.

True, not less than. The single receptacle installed on an individual branch circuit can have an ampere rating greater than the ampacity rating of the branch circuit. Therein a single NEMA 5-20R (20 amp) receptacle can be installed on a 15 amp branch circuit.

As for this:

NEC 210.21 (B)(1)

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@ditusa said:

First, the discussion is in regards to a 15A male plug of a power cord with a 20 female IEC connector. NEC is not involved.

The power cord @ditusa Linked in his post may not be a Listed power cord. There are ones just like it manufactured that are Listed. UL Listed.

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@erik_squires said:

Check the fuse rating on the back of your amp. It’s probably a lot less than 20A. :) I don’t have access to the manual but I saw an image which specified 1500W on the back. This should be around 12 Amps. A 15A circuit is generally rated to 1800W, a 20A circuit for 2400, so definitely a good thing you are using a 20A circuit!

No fuse on the back of the amp. Fuses are inside. Accessed from removing the bottom cover of the amplifier. I couldn’t find anywhere on the Net what the ampere rating is for the fuse(s).

I don’t have access to the manual but I saw an image which specified 1500W on the back. This should be around 12 Amps.

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This should be around 12 Amps.

Agree. 1500W/120Vac (nominal) = 12.5A

On HiFi Engine Web Site you can access the owner’s manual. Listed in the specs it says AC power consumption max 1500 watts. Not sure exactly how the 1500W max power consumption number is applied. Max continuous watts???. I don’t think so. There is only one power transformer. 1000Va, 1KVa.

@blisshifi said:

I am an authorized T+A dealer, and I can tell you that the most powerful fuse in the unit is 10A,

I take him at his word.

YouTube video. The Formidable T+A 3100HV Integrated Amp from Germany

The power transformer in the amp is a 1000Va "torodal" transformer.

Two 500Va 115Vac primary windings. For the U.S. the two windings are wired in parallel. 1000Va. Using the data given on the transformer.

Available FLA = 1000Va / 115Vac = 8.7A

U.S.connected 120Vac nominal AC mains amps, 1000Va / 120V = 8.3A.

Available short term overload of the 1000Va transformer??? Just a guess, there is a rated overload percentage. (service factor). Look at the specs for head room for 8 ohm and 4 ohm max power ratings.

The amplifier has to have a soft start circuit, imo, to limit inrush current. If not the electrical panel circuit breaker would see a dead short on turn-on of the amplifier and trip on its short circuit protection.

So back to the overload protection AC line fuse in the amplifier. 10A, I assume slow blow.

IF the FLA is 8.3A the fuse was sized at a little over 120% of 8.3A. (Good chance the circuit designer of the amplifier sized the power transformer at 80% of the of the FLA of the amplifier. That leaves 20% head room for playing/listening to music with high dynamic music passages.)

It would be nice if a reviewer took the time to measure the AC line current at power output clipping.

From the owner’s manual specs:

Output Power* (Peak)
8 ohm 380 W
4 ohm700 W

Peak is not max continuous output power.

Just for a rough AC mains current draw calculation using 4 ohm 700W.

700W / 120V = 5.8A + unknown loses.

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Bottom line... why the 20 amp IEC inlet connector? Better contact surface area???

Beats me why it was used.

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Food for thought.

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Dynamic Headroom.

@almarg Said:            02-08-2010 at 08:00am

It refers to the ability of an amplifier to deliver a greater amount of power on brief musical peaks than the amount of power it is rated to deliver continuously.

That can be good in the sense that the peak power levels required by a lot of music can be vastly higher than the average levels that are required. Classical symphonic music is one of the most extreme examples of that.

However, high dynamic headroom can also be an indication that the amplifier's power supply and/or its thermal design are "weak," because it indicates that the amplifier cannot sustain its maximum power capability for very long.

Regards,
-- Al

https://forum.audiogon.com/discussions/dynamic-headroom

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kijanki  Said:           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

 

It's not just the ampere rating size of the AC power fuse used in a power amp that determines the wire size needed for branch circuit wiring and the size of the wire used in a power cord.

The power supply of a power amplifier likes/needs a steady state AC mains voltage.

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@mintakax Said

I read the recent thread you participated in (AC Power in misc-audio), lots of good info in that thread. I may end up putting in a Furman P-2400 at some point.

I don’t know enough about P-2400 to recommend it one way or the other. Especially if you would be plugging the T+A PA 3100 HV integrated amp into it.

The T+A PA 3100 HV integrated amp has a very robust power supply.

"1000VA toroidal transformer with 120,000µF of filter capacitance."

Jmho the amp should be plugged directly into the 20A dedicated branch circuit wall outlet.

Available power at the wall outlet for this,

for very short time (millisecond pulse) at the peak of full wave rectified sinewave.

03-18-2025 at 01:02pm

is pretty much unrestricted. A 20A circuit will easily pass very short time (millisecond pulse) s many times the 20 amp breaker’s handle rating. (Same for the 10A slow blow fuse in the PA 3100 amp.

Limiting factor? VD, (Voltage Drop) on the AC mains caused by the load of the power supply on the branch circuit wiring. Therein the connected load of the amplifier playing high dynamic music at a high volume level. (Not a steady continuous load... This load, "very short time (millisecond pulse) at the peak of full wave rectified sinewave."

What determines VD on the branch circuit wiring? Connected load in amperes, length of the branch circuit wiring X two, and wire gauge size. (Remember the 20A breaker will pass short pules of current well over its’ handle rating, all day long.)

Question.

What AWG wire size did the electrician install for the 20A dedicated branch circuit? #12AWG? #10AWG?

Guesstimate length of the wiring from the electrical panel to the wall receptacle outlet? Try to include up, down, over and around lengths to the total length of the branch circuit wiring.

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https://www.stereophile.com/content/ta-pa3100-hv-integrated-amplifier-measurements

T+A specifies the PA 3100 HV’s maximum continuous power as 300W into 8 ohms (24.8dBW) and 500W into 4 ohms (24.0dBW). With both channels driven and using our definition of clipping, which is when the output’s percentage of THD+noise reaches 1%, fig.4 indicates that the amplifier clipped at 318Wpc into 8 ohms (25.0dBW). The T+A amplifier also exceeded its specified power into 4 ohms, clipping at 525Wpc (24.2dBW), again with both channels driven (fig.5).

(I don’t hold the AC wall voltage constant for these tests. With the amplifier idling, it was 121.6V; with the amplifier clipping into 4 ohms, the AC supply voltage had dropped to 117.9V.)

Just a guess measurement were taken with an RMS multimeter.

What was the base line for the AC VD measurements? What did the current, in amperes, measure on the branch circuit wiring?

What determines VD on the branch circuit wiring? Connected load in amperes, length of the branch circuit wiring X two, and wire gauge size.

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Edit:

It would be nice if a reviewer took the time to measure the AC line current at power output clipping.

From the owner’s manual specs:

Output Power* (Peak)
8 ohm 380 W
4 ohm700 W

Peak is not max continuous output power.

Just for a rough AC mains current draw calculation using 4 ohm 700W.

700W / 120V = 5.8A + unknown loses.

700W / 120V = 5.8A + unknown loses would be for one channel.

Both channels driven peak watts would be 1400W / 120 = 11.67A + loses.

Problem is my above calculations are flawed and do not express what is actually happening on the AC mains branch circuit wiring.

It doesn’t account for this.

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.

I’m not sure what type of current measuring test equipment would be used to measure for dynamic short spurts of current draw on the AC mains branch circuit wiring caused by high dynamic music passages for music being played. A regular Clamp Amp meter will not catch, register, the current draw event fast enough, imo. Unless several peaks were close together. ??? Not even sure then. Maybe an Oscilloscope?

@kijanki might be able to answer the question. And, more than likely, rephrase it better, what I’m trying to say.

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@mintakax said:

Thanks!  I believe the wire was 12AWG and the run is roughly 60ft.  Most of the advice I've received has been to plug the amp into the 20A wall outlet.

Hindsight is 2020. I wish I had asked you earlier in the thread about the AWG wire size of the branch circuit wiring. Especially before you had, bought, a 10ft 10AWG power cord made.

  60ft 12ga branch circuit wiring feeding the PA 3100 HV integrated amp may be sounding fine, good, to your ears. That is all that really matters.

(#12AWG is the bare minimum required for a 20A branch circuit.)

IF you ever decide to have another 120V 20A dedicated branch circuit installed for a 60ft - 70ft run, I would recommend using solid core #10AWG wire.

My first preference is 10/2 Solid core MC (Metal Clad) aluminum armored cable. Second choice is 10/2 NM sheathed Cable. (Romex, Trade Name). 

FYI, the circuit breaker will be 20A. The circuit breaker determines the size, amperage rating, of the branch circuit. Therein even if the branch circuit wiring is #10AWG the circuit breaker cannot be bigger than 20A. The connected 20A duplex wall outlet is Listed for use on a 20A circuit only. Cannot be installed on a 30A circuit.

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@mintakax said:

Are you saying the 10AWG power cord could have been 12 AWG and would have been less expensive?

No, not saying that at all.

My thinking was, If I had ask about the size of the wiring of the existing 20A dedicated branch circuit, before you bought the 10ft power cord, and I found it was #12awg 60ft long, I would have recommended you have a new 20A dedicated branch circuit installed using #10AWG solid wire installed closer to your audio system. Forget buying a 10ft power cord and use the money instead toward the cost of a new 20A dedicated branch circuit for the PA 3100 HV integrated amp.

You could have hired the electrician to extend the existing 20A dedicated branch circuit closer to your audio system equipment for any digital equipment you have. Including any SMPS equipment you have.

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