Voltage at wall outlet

[Gunny]

What tolerance is acceptable? I never paid attention until I plugged in a surge protector with a display on it, 100 volts. Checked a few outlets around the house with a meter and all consistently 100 volts. I know a 10% tolerance can be normal, but this is almost strange to me.

I hardly matters. AC is an efficient transport for electricity but most devices in your home will use a transformer to convert it to a [much lower] DC voltage. That voltage is then delivered to the respective devices at the voltage they specify.

Now if you're talking about [class AB] amplifiers then P = IxE will always apply but you're still in tolerance and need not worry.

 

[Speedskater]

They're in range if the voltage is +/- 10%. It seems like nit-picking, but they sell power, not voltage. 10% won't hurt anything unless it's extremely sensitive and the voltage peaks sharply, often. Remember- it can peak negative, too.

I don't worry about the 125V reading. But those with legacy equipment designed for a 110-115V line might have some unhappy equipment.

 

[Johnny2Bad]

Normally with an unloaded circuit in my home I will have 127V AC, but if I put a load on it (turn on a toaster in the kitchen or run a TV or fire up the HiFi) it will drop to 120V pretty much right on the nose. Western Canada. That's +5.8% / -0

The above via a Kill-A-Watt and confirmed by a Fluke 87-V

 

[TLS Guy]

What tolerance is acceptable? I never paid attention until I plugged in a surge protector with a display on it, 100 volts. Checked a few outlets around the house with a meter and all consistently 100 volts. I know a 10% tolerance can be normal, but this is almost strange to me.

10% tolerance is not normal and against Federal law. The voltage to you house must be +/- 5%.
That means the single phase voltage has to be between 116 and 126 volts. For two phase 240 circuits that 238 to 252 volts.

Get rid of that ghastly Monster unit. If you want protection get an APC UPS and whole house surge protection. My units let me know right away if the voltage is out of spec and will raise and lower out of spec voltage.

I recently had my units show over voltage. It got up to 138 volts. I got hold of the power company and a roadside voltage regulator had failed about a mile and a half away.

 

[Speedskater]

Note that the US does not have federal electrical laws. The National Electrical Code (NEC) is just a set of rules. It's up to the Authority Having Jurisdiction (AHJ) which is the city or state to make the laws. The AHJ is free to chose which year and which parts of the code to make law. The AHJ is also free to add other rules to their law.

 

[highfigh]

I don't worry about the 125V reading. But those with legacy equipment designed for a 110-115V line might have some unhappy equipment.

Depends on what's inside. Even tube equipment is usually OK and that stuff wasn't designed to tight tolerances. On most schematics, it will show something like "All voltages +/- 20% and 125VAC is within that range, even after the increase from the power transformer's secondary. I have a guitar amp from the late-'30s and when I measured the B+ and secondary voltages after replacing the rectifier, electrolytics, power cord, and adding a fuse, the voltage at each test point was within range for each tube.