Project: Fast Acting Circuit Breaker

Today's model trains are more sophisticated then ever, relying on complex computer circuit boards and lots of easily damaged LEDs and other components. The old reliable Lionel postwar transformers had internal circuit breakers but they were only good to protect the equipment from that era. They won't protect today's trains, and it is very likely that a short circuit from a derailment would fry your internal circuit boards before the transformer's breaker would trip. Replacing burnt out electronic boards is expensive when they are available surplus, and impossible when they are out of stock. A simple in-line external circuit protector system is cheap peace of mind. So, I built one as a fun project.

I found plans on the OGR's Youtube channel for a fast-acting circuit breaker box. This is an upload of an older video that I believe originally was filmed about 15-20 years ago. As designed, it had four sets of banana jack binding posts on each side for the input and output wires (a Lionel ZW has four sets of outputs) and it all just barely fit.  

When I priced everything through the video's updated recommended parts sources, the banana jack plugs alone were $90! Since I don't even use that style of connector, I asked on the OGR forum if they were required and found out that they weren't. So, I switched to using inexpensive terminal strips and saved a lot of money. 

The parts I used were: 

(1) fast acting circuit breakers (W28-XQIA-10) that I sourced from Ebay. The numbers in the circuit breaker part number designation actually represent something... the last "10" means 10 amps", and not being an electrical wizard I decided not to deviate from what they called for here. They were $3 each.  

(2) heavy duty terminal strips from Ebay for about $8 total.

(3) a project box. The plans called for a box that today costs $25 and it was only barely large enough to fit everything in it. In fact, you had to solder it all up and then bend the wires out of the way. I looked on Amazon and found a substitute box that is a roomy 8"x5"x3" with external mounting tabs for about $10. Larger, cheaper, and more convenient. Sold!

(4) Red and black 16g wire. I bought a five foot long piece of red/black speaker wire on Ebay for $6.

(5) 14/16g wire terminals. I bought a box of 20 for less than $4.

I started with a scrap of plywood I found in my garage that I cut to size and sanded smooth. I could have left it natural but I decided to paint it black. The project box was marked by placing blue tape on the sides and then laying out the four 1/4" clearance holes for the wires on each side. Because the box is so large, I had a lot of flexibility in where to locate things. I probably could have located them lower down on the sides. I found the drill bits constantly grabbed the plastic box, and the only solution was to very slowly drill down through the side walls. Then, I spun a hobby blade around the holes to remove the burrs.

The project box was screwed to the wood. Then, I attached the terminal blocks to the sides near the holes I had drilled.

The top of the box needed four holes to mount the breakers, and each hole had to be about 5/8" diameter. My largest drill bit was 1/2", but I did have a spade bit that was 11/16" which helped. I should have been smart and bought the correct size bit, or a tapered reamer, but I did neither. I mostly used my metal burr bit to make the holes. As a result, one of my holes was slightly too large and the breaker rotated in it slightly once installed. To prevent this, I glued small strips of styrene around each breaker just to prevent movement. I later painted them black.

The five feet of wire allowed for each of the four channels to be 15" long, which was just about perfect. Honestly, though, another couple of inches of red wire would have made things easier later on. There is plenty of space in the box to cram the extra wires.

Wiring it up was pretty simple. The black wires had some spade terminals crimped on their ends and then they were screwed to the corresponding terminals on each side of the box. For the red wires, I clamped the lid onto the side of my workbench to hold it in place and then soldered on the eight wires. After that, I used some heat-shrink tubing for security. It wouldn't short if the two red wires touched, but they would just jumper over the circuit breaker and defeat its purpose.

Right before I screwed it all up, I took a picture for posterity. 

Well, upon screwing it together I discovered the circuit breakers wanted to pop up out of the lid. My holes I drilled were a little too loose to retain them, and there was so much extra wire down below that it acted like a spring to push them up. I pushed them down and screwed down the lid, but if I were to do it again I might install them on the front of the box as its depth is longer than its height. Or maybe just buy a proper reamer for the holes. 

I haven't tested it yet, as my layout is still in the benchwork stage. But, it was a fun project to work on in the meantime.