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.




AC voltage, harmonic distortion and line frequency are all measurable. If there is a difference between night and day listening, and it's related to power delivery, we should be able to measure it. Personally I think some of this is psychological. Evening and night time listening hours are typically environmentally quieter, and your brain possibly adjusts to this. I've personally never measured any difference in power quality in my home environment between daytime listening and night time listening. One of my main listening rooms is down in my basement. The environment is intentionally blacked out all of the time (of course except when I light it), so that if this is a psychological thing, I can have a "night" environment whenever I want it. 

When I was a Radio Broadcast Engineer, I had a rack full of equipment in a transmitter room. This rack contained the audio processor for the FM transmitter. It created the audio signature of the FM station. The rack of equipment had a 20 plug power strip, and it was almost full. I plugged in my Fluke 43B Power analyzer, and discovered the Harmonic Distortion for this power strip was 0.0%. I kid you not. I was never able to find another AC plug that ever gave me that low of a Harmonic Distortion reading. The 3 phase power transformer for the building was on a pole right outside the door to this transmitter room.  

AC voltage, harmonic distortion and line frequency are all measurable


Indeed, but most of us can only measure AC voltage.  Harmonic distortion is definitely not something you get with your average multimeter, and the one thing I have the most faith in is the AC frequency.  So in the absence of anything else, it would be nice to correlate AC voltage with listening experience.

When I built my house, I had two dedicated lines wired with 10/2 gauge with ground, both going to hospital grade receptacles. Each one is connected to the same buss side at the breaker box. I’ve never heard any noise except a fluorescent light starter in my room where I store cables etc. I replaced it with a solid state starter which corrected the problem. All other low amperage equipment is connected to another line that are daisy chained. The two dedicated lines power two Krell FV-600 monoblocks.