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.




@erik_squires Since I do pay a considerable amount of attention to power quality, bonding and grounding (bordering on OCD), and because of your provided link, I have now ordered this tester (mainly just for the N - E figure). I'm not sure I'm going to trust this device though after reading the 1 star reviews on Amazon. How do you think the tester obtains the N - E figure? Is the tester possibly converting ohms to volts for this test? Do you have to push a test button to see this figure, or is it always displayed?  

I agree completely with getting a dedicated line with thicker wiring. I would add that an Equitech 2Q or higher will be a wonderful complement. 


>>>once current is flowing through your circuit an excessively high N-E indicates excess resistance on the neutral.<<<


OK, this is starting to make a little more sense now. A device on the circuit being tested has to be consuming *some* current for the N - E figure to take place or appear. Got it.  

@dpop The N-E measurement is the same as the H-N, just volts. You can do the same with any multimeter. The ground wire normally has zero current, and remains at 0 V. The neutral though carries the same current as the hot. It’s that current that creates an elevated voltage. Consider:

V = A * R

So, on a lightly loaded circuit, with 1 Ohm, the neutral will be:

V = 5A x 1 Ohm = 5V.

The trick here is that the Hot will suffer the same voltage drop, 5V. So while the panel may be 120V, you have dropped 5V on the hot and 5 at the neutral so your wall socket will be 110 V just from voltage sag.


OK, this is starting to make a little more sense now. A device on the circuit being tested has to be consuming *some* current for the N - E figure to take place or appear. Got it.

The neutral wire has to have current to elevate the voltage above zero, yes, but you can still measure the voltage even if the voltage is zerol