Introduction: DIY Circuit Breaker Panelboard With Automatic Transfer Switch (ATS), Metering and Computer Control.

I needed a mini circuit breaker panelboard to protect and segregate the loads from my solar inverter. I wanted a small form factor, transparent cover to view the breakers and adequate protection for all my house electrical loads.

I am a power system (electrical) engineer for the past 19 years to present. I have the knowledge, experience and physical skills to design, build, test and commission large (up to 132kV) power systems. DO NOT ATTEMPT WHAT I HAVE DONE IF YOU DO NOT POSSESS SIMILIAR CAPABILITIES LIKE I DO.
Electrical energy is highly dangerous and you must accept all risks when you modify any power system.

Step 1: Install Din Rail Into Enclosure and Have Cable Entry Way.

I used a 6inch din rail to mount the din circuit breakers. The din rail I secured using two bolts and nuts. I used a hole saw to cut a 1.5inch hole to allow cables to pass into the enclosure. The enclosure has outer tabs to allow securing to a wall.

Step 2: Install the Neutral and Ground Bus Bars.

For 120 volt ac distribution you need breakers, a neutral bus and a ground bus. The loads off this panel will be few and load wattage. The small size bars I'm using will be perfect for my application.

Step 3: Create and Connect the Live Bus.

In order to safely provide my Loads with 120 volt power at less than 2% voltage drop, I used a length of 4mmsq stranded wire. I made loops and inserted into each breaker on the line side. Now live, neutral and ground supply connections can be made.

Step 4: Add Led Indicators Per Sub Breaker and Incoming Supply.

I wanted visual indication if a breaker is closed. On Amazon I obtained 120vac leds and I mounted one per breaker and one on the incoming live bus. One side of each led I soldered to the breaker or bus. The other I tied together and connected to the neutral bus via a crimp fork lug.

Step 5: Add the ATS and AC Meter

I used a two pole double throw relay with NO NC contacts per pole as my ATS. The common of of one pole I wired to the live side of the circuit breakers. This pole I dedicated to the live 120vac conductor from my utility supply (via a 20amp breaker).

The common of the other pole I sent to the neutral bus bar.

The NO contacts were wired to the utility live and neutral conductors. The NC contacts were wired to my solar inverter respective live and neutral. I switch both live and neutral since my inverter does not produce a grounded neutral.

The coil I wired to the utility live since in power failure I wanted the ATS to default to inverter power. I installed a toggle switch to manually select utility power in the case of inverter failure. I also put in series with the coil another relay to remotely switch between utility and inverter. This relay is part of my labjack u3 pc home controller as shown in the screen pic. Anywhere in the world I can monitor and select which power source I want plus several other parameters in my home.

An AC volt and current meter I included on the inside face of the enclosure lid. The current transformer is around the output of the ATS. As always with current transformer connections it must be tight and secure since an open circuit with cause rapid failure and blowout of the transformer.

Step 6: Commissioning and Appreciation.

Finally after some serious hours of work, my DIY panelboard is complete with meter, led indicators per breaker and an interface back to my home controller software. The last pic shows the software I made using FLOWSTONE. Our power utility is call TTEC. Currently I have the ATS selecting solar power. Via software or a physical switch on the side of the panelboard I can select TTEC or solar power.

I took a thermal scan and the resistor leads showed any appreciable heat. The wires from the MCBs were relatively cool.

Step 7: Add On: Enclosure Light.

I felt the need to have internal lighting in order to install future wires. I put a 2 Watt led lamp at the inside top of the enclosure. Cool eh?