High quality in-wall UL-C2 rated 10-gauge A/C wiring ?

Headroom loss for 14ga vs 10ga is less than ¼db @ ≈14A / ≈1600W
See http://ielogical.com/Audio/CableSnakeOil.php#ACWiring

Voltage drop calculator.
http://www.windsun.com/Hardware/Voltage_Calc.htm

Distance or Conductor Size: .... (Distance)

Single or Three phase: ........... (Single)

Conductor Type: .... (Copper)

Installation: ............. (Conduit)   .... Same for Romex
Voltage: .................... (120V)

Maximum Voltage Drop: ... (Already set for 3%. You can change the percentage to what ever you want.)
3% of 120V = 3.6V VD
2% of 120V = 2.4V VD

Conductor size: ...... (14 gauge)

Current: ...................(12 amps)

Max length of branch circuit for a 3% VD (Voltage Drop) 55.97ft.
Max length of branch circuit for a 2% VD 37.32ft

Remember, up, down, and all around when figuring the entire length.

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

Here’s a quote from a Pro Audio web site, old post.

Around 1984 when I bought my first QSC power amp I called QSC after reading that it has 3db of headroom. I was told that the 300 watt rms rated amp could produce 600 watts of peak power when needed.


That means if I did a rim shot on the snare drum to make it louder or kick the bass drum harder when hitting a crash cymbal there would be enough power reserve for this and the amp would not clip. I remember the guy telling me its like snapping my fingers and then waiting a few seconds and snapping them again.

https://forums.prosoundweb.com/index.php?topic=139460.10

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I guess if all you listen to is elevator music at a moderate listening level #14 wire is all you need.

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Note:
When a load is known the NEC says the wire shall be sized at 125% of the connected load. Again when the load is known. Using #14awg copper wire, #14 has an ampacity rating of 15 amps. 80% of 15 = 12 amps.
(For a continuous load. Continuous load is defined by the NEC for a load lasting 3 hours or more.)

(ieales there’s your reserve you are looking for. )

That does not mean you can’t load a convenience receptacle outlet circuit to the 15 amp max until the 15 amp breaker trips..... If it trips..... With a receptacle convenience outlet circuit the loads are not known. The limiting factor is the circuit breaker.

In a dwelling unit there is no limit on the number of receptacle outlets that can be installed on a 15 or 20 amp branch circuit.


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Other than Class A, HiFi is not a continuous load. A ’typical’ tube amp is about 1A per 70W sum of both channels.

Peak power can be a numbers game. The 1974 FTC rule mandated an amplifier provide 1/3 rated power for 1 hour @ rated distortion without shutting down. Peak power is the greater of power supply or protection circuit voltage and current. Into a complex load, i.e. loudspeaker and cables, rated power maybe a fantasy.

Most every home over 1500ft² in America fails the 3% rule in some area, being wired with 14/2. Obviously if one has a very heavy continuous draw, a heavier circuit should be installed.

However, for the vast majority of systems, the load is neither heavy or continuous.

I guess if all you listen to is elevator music at a moderate listening level #14 wire is all you need.

and if you listen to Def Leppard @100db, your hearing is so screwed as to make HiFi irrelevant ~<;-P

For nearly ½ century, I’ve used an oscilloscope to determine undistorted power at the load. Musical peaks of 100db are handled easily. Said oscilloscope also determines that line voltage is always more than sufficient to keep the power supplies at full charge!

As mentioned previously: A large transient at line zero crossing depends 100% on amplifier power supply. 4/0 cable will not make one iota difference.

And 3% drop is only about -¼db

ieales

361 posts
06-17-2019 8:59am

Other than Class A, HiFi is not a continuous load. A ’typical’ tube amp is about 1A per 70W sum of both channels.

No kidding? I would never of known that without you telling me.

Is that what you took away from reading my entire post?
Hell, in the link you provided the guy used 14 amps for a purely resistance load for his bench tests for testing of dynamic headroom of a power amp. Why didn’t he use a real world testing? You know a power amp, connected to a load like speakers. Push the amp feeding it with a high dynamic source. Maybe the sound track from the John Wick Movie. That’s pretty intense.

Much ado is made in some circles about the inadequacy of 14ga wiring and how it will diminish dynamics.

14ga Copper wire has an ampacity of 28 amps. The U.S. National Electrical Code [NEC] rates 14ga THHN for 20A @ 75°C. Romex 14/2 is electrically equivalent to THHN. NEC limits 14ga to 15A circuits for a very adequate safety margin. See NEC 310.15(B)(16).

To find how much loss is incurred on a heavily loaded 14ga circuit, a Semi Professional espresso machine, plugged into the first socket on a circuit and the only device, was measured. It has a 1600w heating element with a resistance of ≈8.25Ω or ≈14A current draw. The heating element is PID controlled. This duty cycle is a square wave and presents transients far in excess of anything in a HiFi system. Using a digital sampling oscilloscope [DSO], 100%, ≈50% and 0% duty cycle load voltages were recorded.

No load measured 117.81vrms, load 114.02vrms integrating samples over 1 period for periods

with the highest and lowest peaks respectively. Over several minutes, 50% or 100% duty cycle made no difference in the loaded voltage peaks.

14ga Copper wire has an ampacity of 28 amps. The U.S. National Electrical Code [NEC] rates 14ga THHN for 20A @ 75°C. Romex 14/2 is electrically equivalent to THHN. NEC limits 14ga to 15A circuits for a very adequate safety margin. See NEC 310.15(B)(16).

Another guy that doesn’t understand how to read the NEC.

14ga copper wire is rated for 28 amps...... Maybe in free air. What is the length of the circuit for a 2% VD or even a 3% VD at 28 amps? Use the VD calculator... What is it at 20 amps.

Not continuous, ........ but say for a quick short draw of 28 amps or even 20 amps. Now please use a realistic number for the distance, length, of the circuit conductors.

Professional espresso machine

Really, an espresso machine? Does that espresso machine have a power transformer,  bridge rectifier and electrolytic caps in it?
I wonder if Ralph Karsten would agree you can substitute an espresso machine for one of his power amps for such a test.

No load measured 117.81vrms, load 114.02vrms integrating samples over 1 period for periods
with the highest and lowest peaks respectively. Over several minutes, 50% or 100% duty cycle made no difference in the loaded voltage peaks.

What was the length of the wire in the circuit? Did I miss it?
117.81V - 114.02V = 3.79V VD. What’s that going to do to the power supply of a power amp as the caps are trying to recharge? Read Ralph Karsten quoted material below.

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I should have never mentioned the part about the NEC and the definition of continuous load for the 125% for sizing a branch circuit when the load is known. Way too much info for you. I should have left that whole thing out.

The VD calculator was meant to shown how current and the length of the wire are directly proportional to VD. NOTICE: No mention of the type of insulation used on the wire. NO 60C or 75C or 95C. Why? Because the copper conductor in 60C wire is exactly the same as the copper conductor in 75C and 95C insulated wire.
VD on THHN 75C insulated wire will be the same as TW 60C insulated wire.


What the hell do you think the rest of my post was about? Continuous load of a power amplifier? NO it was not!

The second issue is the high frequency current limiting. This is a bit trickier to understand, but its not quite rocket science. Almost any power supply consists of a power transformer, rectifiers and filter capacitors. When the the transformer voltage is higher than the capacitor voltage, the rectifier commutates (a fancy word for turns on and conducts). At that point the filter capacitors can charge up and will do so until the power transformer voltage falls low enough that the rectifiers cut off.

At that point the circuit using the power supply drains the filter caps. Since this happens 60 times a second, the drain is usually not very much at all, so its only at the very peaks of the AC waveform that the caps are be replenished. There might be only a few microseconds or milliseconds that this can happen, and quite a bit of current might have to flow during that time, essentially a high frequency event.

If the power cord limits current during this period, the performance of the circuit using the power supply might suffer, possibly due to increased IMD since the DC might have a bit more of a sawtooth on it than if the current was not limited.

That means if I did a rim shot on the snare drum to make it louder or kick the bass drum harder when hitting a crash cymbal there would be enough power reserve for this and the amp would not clip. I remember the guy telling me its like snapping my fingers and then waiting a few seconds and snapping them again.

Can you see any correlation in the two quotes? Any?

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ieLogical is my domain.

I used an espresso machine precisely because it is a resistor and a near constant load. I wasn't testing the dynamic headroom of an amp. That is a property of the amplifier and not the line. I could run the identical test on my HiFi, but it's much more of a PITA. Additionally, amplifier peak output has the inconvenient habit of occurring when the A/C line is not at peak, so the line cruises merrily along unperturbed. BTDT.

3.79V VD What’s that going to do to the power supply of a power amp as the caps are trying to recharge?

A 200w power amp is going transform that down to about 2V on the caps. 10ga is going to give +1V more on the caps @ 14A line draw

So assuming the transpistors are full on and running off the transformer because the caps are flat, which they never are, instead of 40V at the speaker, there will be 39V. 20log(39/40) = -0.22db <OUCH!>

There might be only a few microseconds or milliseconds that this can happen, and quite a bit of current might have to flow during that time, essentially a high frequency event.

The line provides 60Hz. Full stop. It does not know diddly about any other frequency, distortion components aside. The power supply provides DC. The control devices modulate that DC to provide the AC to the speaker.

When the load current drops as the signal alternates phase, the draw from the capacitors decrease and the capacitors charge. If the load amplitude peaks when the line is 0v,all the current is supplied by the capacitors.

Please have a look at http://ielogical.com/assets/CblSnkOil/HFoverLine.png to see what is happening with high frequency and the line. The capacitors supply ALL the power when the transformed voltage is below the capacitor voltage + the diode drop.