Summary

I designed these little display adapter covers to fit over a single gang electrical box. I measured the box at 4” X 2 1/8” X 2 1/8” deep. It is very square. You need to break off the little tabs or ears that stick into the box to mount a light switch or receptacle so the PZEM will fit into the electrical box. This is why I went around the box.
One of the covers has a square hole that measures 87 X 46 mm’s to hold a PZEM-022 energy monitor. The other cover has (2) 22mm holes to hold various meters.
They both fit tight over the electrical box, no screws are necessary to hold them in place. I had to really fight one of them to get it on, wiggle and angle and it eventually went on. If you are you are using a handy box with the rounded corners then the cover will slide on. If you are using a box like I show in the pictures, stamped and formed, then you might have to squeeze the box a little bit with a pair of channel lock pliers, Then the cover will slide on.
The back lid will fit either cover but the 22mm meters won’t fit because of their depth. So the back cover is good for the PZEM only I think. I had to round the corners a little with a dremel to get the back cover to fit into the display adapter. Then it’s a nice tight fit, no glue. There is a small hole in the corner to pass a small 4 conductor cable through. I secured the cable with a wire tie.
I have one of these mounted in an electrical box near my generator input and it will display the generator electrical data. I have another one mounted in the stand alone box and I will use this one to monitor the energy used in my home office.
I printed these in ABS at 50% infill.