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 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)



I completely understand VD on hot and neutral. Thanks, but no further explanation is needed on that. My curiosity was always with the N to EGC. That’s where I’ve been confused all along. I’ve never paid much attention to that measurement. It’s starting to click now (as you’ve raised my awareness), especially after looking at a few websites explaining what to look for. Going forward, I'll be paying closer attention to it in the future. 

Neutral-to-Earth/ground Voltage- Causes, effects, and solution

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jea48 said:

Are you sure you have an Equipment Grounding Conductor at the outlet?

dpop response:

100% most definitely; on both outlets being discussed. I can take my multimeter and read 121.6 volts across the hot and neutral (no load), and the exact same voltage is measured across hot and the EGC.

You will get the same measurements on a bootleg ground.

L to EGC on a bootleg ground is actually from L to neutral.

N to EGC is actually From N to itself. Naturally it will measure 0.00V

What is a Bootleg Ground and Why is it Dangerous?

dpop said:

My microwave oven consumes 14.6 amps during operation (measured using the amprobe meter). Volts available at the outlet with the microwave off was between 121.3 - 121.5. Volts available at the outlet with the microwave on was 117.9. N-E volts 00 with the microwave on or off.

"N-E volts 00 with the microwave on or off. "

Sure sounds like a bootleg ground to me. (Assuming you were making a good solid connection to the N and EGC with your DMM test probes.)

dpop said:

I completely understand VD on hot and neutral. Thanks, but no further explanation is needed on that. My curiosity was always with the N to EGC.

I don’t think you do fully understand L to N VD in a current carrying circuit.

IF you have a VD on a loaded circuit. Actually measured it, (which you did (L to N), then you will, should, have measured the Voltage Drop across the length of the neutral conductor, when you measured for voltage from N to EGC. Can’t have one without the other.


Food for thought:

As for the voltage measured from N to EGC. IF the EGC is a solid low resistance/impedance connection with a high level of conductivity then it is assumed to be a good, so called earth ground. Therein at the same zero ground potential as the electrical service main Grounded Conductor, The neutral conductor. (They are Bonded together at the main panel.)

Therefore the way I look at any voltage measured from N to EGC, which is the result of a measured VD across a connected load from the Hot to neutral of a branch circuit, imo, should be considered as an above ground voltage... There’s one to ponder... Any EEs in the house?


I remember reading in the NEC (National Electrical Code) years ago there is/was a maximum allowed resistance measured from the neutral conductor to the EGC conductor at the end of a branch circuit. Just going from memory it was not more than 2 ohms or 1 ohm. I’m thinking 1 ohm.


Branch circuit de-energized. Verify circuit is dead.

For a good test:

Make sure there is not any loads connected to the circuit. Unplug everything from outlets. Check for ceiling lights that may be on the circuit. Make sure light switches are off. Measure for resistance.

I measured for resistance at the two 20 amp dedicated branch circuits in my 2ch audio room. Both measured 000.3 ohms each. (Fluke 87 DMM.)

The two branch circuit are 10/2 NM cable (Romex) 75 ft each from panel to wall outlets.



Hot-neutral is the load voltage. Voltage should read about 120 V (typically 115 V to 125 V). You measure exactly 118.5 V.

  • Neutral ground is a voltage drop (also called IR drop) caused by load current flowing through the impedance of the white wire. Let’s say you measure 1.5 V.
  • Hot ground can be thought of as the source of voltage available at the receptacle. You read 120.0 V. You note that hot-ground is higher than hot-neutral. In fact, hot-ground is equal to the sum of the hot-neutral and neutral-ground voltages.

Diagnosing Power Problems at the Receptacle - Fluke Corporation