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.




I received the test meter today that @erik_squires linked. Right off the bat I would say I’m impressed by its performance. One thing I look for in an AC voltmeter is how quickly it can measure and display voltage drops or variations. Even at ear splitting levels, one of my systems rarely consumes more than 1.5 amps on peaks, so I did not test it there, yet, as I doubt I’ll see much if any voltage fluctuation (10 AWG wire run about 15 feet from the load center). I did however put it on a variac, while quickly adjusting the power, simulating a huge momentary current draw on the line. The meter responded very quickly to this adjustment. All outlets that I’ve plugged it into so far are displaying 00 volts for the N-E figure. I am fortunate that I am fed directly from the step down transformer on the pole (I’m not at the end of the line) for my block. Even at that, during heavy summer cooling periods, I may see my total house voltage temporarily (for a few hours) drop about 2 volts. The meter doesn’t display tenths of volts for the L-N display, but using a reputable Fluke, the reading was only off by less than 1 volt. I would say it was easily worth the (roughly) $20 purchase price. My house voltage (on one leg I constantly monitor) typically remains at 120.7 volts 99% of the year.

@erik_squires you definitely got the quasi dedicated correct…. bummer…. Stromtank… and $ or € can fix that…..

Best to all in the quest for juice, AND clean juice….

Another plug in voltmeter that I really like is the Kill A Watt EZ meter. It measures a lot of things, but the voltmeter portion (which reads in tenths) is extremely accurate. 

Kill-A-Watt(Tm) Ez

@dpop Those are certainly popular, and I believe the original.  There are now dozens of watt / voltage meters out there, with a variety of smart features, including wifi connectivity.  What I've yet to find is one that measures N-E at the same time as the V.  Still, being able to chart your V over a week can really help you understand your power issues.

Using the KAIWEETS KM117B Socket Tester (the one @erik_squires linked), I took some measurements around my home:

My pizza oven consumes 11.5 amps during operation (measured using my
Amprobe ACD-10 TRMS-PLUS meter). With the oven off, AC volts available at the outlet is 121.3 - 121.5. With the oven on, volts available at the outlet dropped to 117.8. N-E volts 00 with the oven on or off.

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.

My main audio system is a 3 power amp tri-amped system. The power amps alone consume about 1.5 amps total powered on with no program material. AC volts at the outlet is 121.5 with the amps off. With the amps on, volts at the outlet are 121.0. Peak amps measured at loudest passage was 1.9 amps (or, 0.40 amps above powered up status). The feed is 15' of 10 AWG directly from the circuit breaker box. N-E volts was 00 with the amps on or off.

My furnace consumes 3.79 amps with the unit in full operation (gas burner heating, and forced air fan blowing). Volts available at the outlet with the furnace off was 121.5. Volts available with the furnace full on was 120.5. N-E volts was 00 with the furnace on or off. 

What this does prove to me is how important a dedicated run *is* for power amps, or high current consuming integrated amps or receivers.