AC Power / Energy Meter

A surprisingly competent AC power-line voltage / current / energy / power meter fits neatly into a mud ring atop a 4×4 inch square electrical box:

AC Power Meter – assembled

The inside view shows the wiring, such as it is:

AC Power Meter – interior

The square black block is the split-core current transformer around the hot line wire, which sticks up just enough in any orientation to require an extension ring, thus a second trip to the Big Box store.

The mud ring has two tabs with threaded screw holes for the device (switch / GFCI / whatever): grab those with a Vise-Grip, flex until they break off, then file down the stub.

Generous globs of hot-melt glue secure the meter in the mud ring. I added a strip of duct tape under the connections in the hope it might avert disaster should either of the AC wires come loose, but my real hope is in the safety ground to the metal box.

The line cord comes from the Box o’ IEC cords, minus its IEC connector, plus the bright yellow USA-ian connector.

Yes, the three metal box pieces and the Leviton connector cost far more than the meter.

Not to code, but good enough for my purposes.

Comments

3 responses to “AC Power / Energy Meter”

2025-11-20

pardobsso

Those meters are extremely cheap and nice.

The only complaint I have with mine is that they don’t care about the current transformer orientation and always report positive power flow.

Reply
1. 2025-11-20
  
  Ed
  
  The transformer even has a directional arrow inside the aperture and the meter obviously uses the phase to get the power factor, but “positive power” makes sense for nearly all applications.
  
  Net metering for solar power would be an exception, although I betcha the utility would get twitchy about finding one of those things clamped around their wiring. :grin:
  
  Reply
2025-11-23

pardobsso

Yep.
At least it’s fool-proof.
I was surprised at how accurate/close enough mine was when reading power factor.

Reply