How to tell if your AC wiring needs an upgrade

@Ozzy This isn’t a lab grade device and may over estimate by 1-2 volts, but it is relatively accurate. A well wired home can have a couple of volts on the neutral and all is pretty much normal. It happens because you wire homes for safety and cost effectiveness and 2V is just fine.

You want to make sure your home isn’t much higher than that though, AND if you want to know if your audio system is causing your AC to sag (drop in voltage) this is a good way to measure it.

It is rare, but dangerous, that a home’s neutral becomes corroded or fails, in which case that N-E voltage will suddenly rise, and that’s why it’s a good thing to have an eye on now and then. Also, the testing I suggest helps you measure where the problem is. Putting in a new branch circuit is not going to help you if you already have an elevated neutral. Fix that first!

It may help to understand things this way:  The higher the neutral voltage the lower your outlet voltage (assuming you don't have something else wildly wrong).

Thinking about this some more, I'd say the most common error you'll find is an outlet with the hot and neutral reversed.  In that case the n-e will show 118 V or so.  Easy to fix.

The higher the neutral voltage the lower your outlet voltage (assuming you don't have something else wildly wrong).

Can you explain this above?

I did the test with a multimeter on kitchen outlets with nothing connected. I measured 0.9V. I plugged in a 25W incandescent lamp and the voltage dropped to 0.4. Was the 0.9 noise?

@deludedaudiophile - Things get a little complicated, since the V on the neutral may be the opposite phase of your circuit, but if you assume everything else in the house is off, the Hot to N is usually <= Hot to ground. As your circuit draws more current, the N voltage will rise, the Hot will drop, and the V drop across either will balance.

Try the same with a coffee pot instead! :)