Neutral to Ground
Next, check from neutral to ground. That should read very close to 0 volts, but up to 2 volts is acceptable according to the electrical code.
If, however, you read around 120 volts from neutral to ground, then the polarity of the power outlet is reversed. Don’t plug in. Again, this can cause a dangerous hot-chassis condition depending on how your guitar or PA system is wired.
As a final check, a run-of-the-mill outlet tester from your local home center will confirm that the polarity of the outlet is correct.
Plug it into the power outlet on stage and you should see only the two yellow/amber lights light up. If you see any other combination, do not plug in your guitar amp. Once you’re familiar with the procedures, all this can be done in a minute or two.
It’s a very small inconvenience that will help ensure the safety of you and your band.
Measuring Neutral to Ground.
—Always set your meter to read AC volts using the 400-, 600- or 750-volt scale
—Hot (short slot) to neutral (tall slot) should read approx 120 volts (between 110 and 125 volts AC)
—Hot (short slot) to ground (U-shape) should read approx 120 volts (between 110 and 125 volts AC)
—Ground (U-shape) to neutral (tall slot) should read approx 0 volts (less than 2 volts AC)
Mike Sokol is the chief instructor for the HOW-TO Sound Workshops and the HOW-TO Church Sound Workshops. He is also an electrical and audio expert with 40 years in the industry. Visit the No Shock Zone Website for more electrical safety tips.
This article is provided as a helpful educational assist with sound system setup and musical performance, and is not intended to have you circumvent an electrician or qualified audio technician. The author and the HOW-TO Sound Workshops will not be held liable or responsible for any injury resulting from reader error or misuse of the information contained in these articles. If you feel you have a dangerous electrical condition in your PA system or instruments, contact a qualified, licensed electrician or audio installer.