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

@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

@erik_squires noise is often mentioned but I would never install a dedicated line for noise control. to me the only real reason is to make is a size bigger to accomodate your amps rapid power needs. Mine is 10 awg. I admit I was lucky to have an abandoned 240V 10awg line for a dryer in the wall behind my system.

For noise I am a big believer in a rectifier/inverter such as the PSA PP.

Jerry

@carlsbad2  - The one thing about the Class D power plants is that they do in fact output quite a bit of noise.  Personally I prefer to use an old-school voltage regulator. 

@erik_squires I assume you're referring to the new PP12 that weighs 1/3 what my PP10 does.  I'm still surprised that they output noise but I'm pretty sure my 90 lb behemoth isn't class D.  --Jerry

@carlsbad2 Honestly haven't kept up with them that closely.  I remember there was an original generation that was essentially using linear amplifiers, then they switched to Class D.

At the same time the founder of Jensen Transformers (really nice guy) founded another power conditioning company, Perfect Power?  Forgot the exact name, that used buck/boost transformers.  Very efficient compared to the PP, but still based on a linear amp.  Sadly that didn't really go anywhere. Sounded like an excellent compromise IMHO.