Reliance ControlsMB125 Indoor 50-Amp Wattmeter Box

Very well made, small box that does exactly what it is designed to do. I am using the 50amp box. There was no problem installing the current transformers over 6 gauge wires but the wires from the transformers to the meters in the box are pretty short! I installed it all myself in about 2 hours but could easily be done faster. I had to be somewhat creative with installing the box in-wall beside the flush mounted breaker panel and used a primed (unpainted yet) access door to conceal the box within the wall. I did an initial operational test using a 5500W heater and confirmed that the meters showed 5500W within the precision of the markings on the meter. Note that the precision of the 12.5kw (50amp version) is around 125W or half-way between each marking. I also used the PowerBACK (not completely installed yet) which works just fine. All parts were obtained on Amazon for a reasonable price.

A bit expensive for what it is BUT it's well built and serves a very important purpose. Reviews that suggest there is no room in the box to bring your generator wire into it, through the CTs and then into your panel/generator switch are wrong. I used 6 gauge wire and had no real issues. I brought the cable down through the top knockout and then out into the generator switch/main panel through the left knockout. 6 Gauge is not easy to work with as it is so I dont think the size of this meter added any add'l difficulty - just the standard difficulty in bending 6 gauge wire.

This unit is just the ticket to help manage electrical loads while using your generator or solar power system. I used to use a clamp meter, measure the amps, multiply by the voltage and get Watts. Now I read it right from the dual meters.It was easy to install, simply turn off the power, break the hot wire in the L1 and L2 sides of the breaker box, slide a current sensing transformer over each hot wire, reconnect them, turn the power back on and you're good to go. It took me less than 20 minutes including punching out knockouts in both boxes. So far, quite accurate as well.

The box that the gages are in was a lot of extra plastic that I didn’t need. But if you have the space to mount it, then it doesn’t matter. It does what I need it to do.

I am a master electrician, self employed electrical contractor. I ordered this product to install for a customer as part of a generator installation. I found this product to be extremely frustrating to install, the CT leads are way too short forcing you to route your feeders through the tiny box. The space in the box is very limited due to the design of the meters. Once installed one of the meters failed to function properly. I swapped the CT leads to verify it was the meter and it was. I have no way to get a replacement without ordering a new unit (Customer delayed project start beyond 30 days of purchase) and my customer is over an hour away. So I am stuck loosing half a day of productivity, two hours of travel (10 MPG van), and the cost of purchasing this failed product yet again. I strongly advise against purchasing this product, continue your search for alternatives.

The leads are WAAAAAAaaaY too short. Whatever your measuring with this meter should be within 6 inches of the box, otherwise you'll have to do an unauthorized modification and void the warranty! Also the cover for the wiring underneath the meters is some sort of cheap paper-plastic hybrid that feels pretty flimsy. Granted, it's not going to get a lot of use, and that's good because it's not good for much. The unit seems to work fine, though.

Nice little unit. I am using it on a sub-feed panel that I hook my generator to for powering the house during power outages. This lets me see what load I am putting on the generator. Works Great!!

The design and dimensions of the Reliance Controls MB125 (50-Amp) and MB75 (30-MB) meter boxes are the same; 4 * combination 1/2" & 3/4" knockouts - both right-left sides (1.25" from bottom to center of KO), bottom (dead center), and top (1.25" from left side to center of KO). My biggest complain is the length of the current transformer (CT) connector wires which are 4 * 12" 20 AWG stranded wires (black-yellow) connected to 2 * CT terminals @ one end and 4 * 1/4" female insulated flag (i.e. right-angle) disconnect crimp terminal connectors @ the other end. Depending on which KO used you will have only ~6-8" of usable wire. I noticed some like to butt their meter box directly to their panel, I think the wires are delicate and I would recommend (& per NEC) using a small raceway such as a box spacer connector (a.k.a. back-to-back connector), off-set nipple connector, etc.. I could not get the flag terminals to fit thru 1/2" box spacer & off-set nipple connectors; I did not test but I think they would fit thru 3/4" connectors.I wanted extra wire length but I did not want to splice into the CT wires - so I created 4 * male-female flag terminal extension wires. Lowes and Home Depot (HD) do not sell female flag terminals so you will need to order them from Amazon or get the at Radio Shack. The blue flags are 16-14 AWG and the red flags are 22-18 AWG - you will need the flag type cause there is not enough room in the meter box for the straight type. Either the blue or red flags will work and driver to the decisions is the gauge size wire you have - I used 20 AWG solid copper bell wire (red-white) which was $.29 per foot at Lowes; I mapped black-to-red and yellow-to-white wires. Crimping flag terminals is a little tricky - make sure the crimper tool crimps at the tip of the tool (versus having a wire cutter) else you may destroy the terminals. I used a 14 AWG solid copper wire from the meter box's green grounding screw to my panel's ground bar - although using a metal raceway would have been sufficient for grounding the meter box.The manufacture's instructions are weak and I hope someone can learn from my example.