Measurements for a dedicated line

The question of whether a homeowner should get a dedicated line is often like "should I get bangs." It’s a little complicated. Here are a couple of reasons to consider not:

I. My experience is that you won’t eliminate all the other noise coming from your home even if you do run a dedicated line. I still hear motors switching on and off despite being on completely different circuits.

II. A little resistance and a little inductance may actually be a good thing in keeping noise out of your line, so overkill on the wire gauge may not help this.

Why you definitely should get a dedicated line, with thicker wiring:


Less voltage sag.


Voltage sag means that under load the resistance in the line will cause the AC cabling int he wall itself to consume some of the AC voltage, giving your gear less volts to work with. This sag is proportional to current, so the more amps your gear is drawing the more sag.

This sag is something you can measure. There are two things you need to look: The hot to neutral voltage and the neutral to ground.

With nothing on the circuit your N-E (neutral to earth or ground) should be 2V or less. If it’s significantly higher than that stop and call an electrician. That’s true for any circuit in your home. High N-E values are indicators of a problem which may be in the circuit or in the service wiring from outside to the panel.

What happens when you turn your equipment on and play music is that the line will sag. The H-N (hot to neutral) voltage will drop, and the N-E will go up. Some sag as you turn on big amps is normal. So long as you are not tripping breakers you are fine. What you want to measure is the sag after your system has stabilized and while it’s playing music.

Keep an eye on the N-E value, as this will be a good indicator of the sag independent of the incoming line voltage. It may also point out where you may have issues. That is, if you measure an extra 2V of N-E, your sag is probably around 4V, so you went from 120V to 116V and you can be relatively comfortable it isn’t outside influences.

Of course, any good multimeter will work for this but I like plug in meters with built in N-E measurements. This one is cheap, and the N-E may not be hyper accurate, but it is the only device I’ve found on Amazon that will show you both the H-N and N-E voltages at the same time.

The nice thing about any plug-in type voltage meter is you can watch it over  a couple of days without hand holding probes in the socket.

If you find another which does both please post.



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(I assume the audio branch circuit is 2 wire with ground...)


It’s still not clicking in my brain what you’re trying to say about voltage drop across the neutral and EGC. No offense, but if I already have a low impedance EGC, why should I even care about voltage drop, or voltage difference, between the neutral and EGC?

Now draw a symbol for a voltmeter connected from the neutral on the load end of the circuit and connect the other end of the voltmeter to the EGC.

If assuming the load is plugged into one half of a typical duplex wall outlet, and consuming current; you’re saying 1) place the voltmeter on AC volts 2) one probe in the neutral on the other half of the outlet not being used by the load 3) and the other probe touching the EGC. Is that correct? If so, I’ve already tried this before you posted, and the reading is around 28 millivolts. I’ve even tried breaking the EGC connection from the load to the wall outlet, and placing my meter across it - still the same, about 28 millivolts.

BTW, thanks for taking the time to explain this to me. If neutrals were oversized (compared to the hot conductor), would I be seeing less voltage drop in some of my presented scenarios?



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I ran some tests for VD on a convenience receptacle outlet branch circuit.

Wiring is 12/2 with ground NM cable, (Romex trade name). Length, distance, from panel to wall outlet used for test is approximately 65 ft. Nothing was plugged into any outlet. Nothing but wall outlets on the circuit.

DMM for first test was a Fluke 87.

Load is a 1875 watt hair dryer. Calculated amp draw is 15A @125Vac.

1875W / 125Vac (data name plate) = 15A.

No load, L to N, 123V.

N to EGC measured 3.4mV ( 0.0034V)

With load, L to N, 118.2V... VD, 4.8V.

N to EGC, 2V. (Half of 4.8VD = 2.4V)

/ / / /

2nd test I used a Klein CL800 clamp amp meter. I used this meter because it has two AC voltage switch settings. One works like a regular DMM. Therein it has an internal input resistance is 10megohm or greater. Same as the Fluke 87 DMM.

The other selector switch AC voltage setting is LoZ, (Low Impedance). This setting puts a small load internally across the digital voltmeter circuit. I used the Fluke 87 to measure the resistance of the LoZ setting on the CL800 and measured 3.6K ohms. (3,600 ohms).



Klein CL800. (Meter set to LoZ AC

No load, L to N, 122.5V. .. (I did a quick check with the Fluke 87. It also measured 122.5V.) A point in time...

N to EGC, 0.00V (The Fluke measured 3.4mV ( 0.003V) Ghost Voltage.

With load connected. Hair Dryer same settings.

L to N, 117.8V. VD 4.7V.

N to EGC, 2V. (Half of 4.7VD = 2.35V)