Since having a meltdown of a 22 AWG accessory wire about a month ago due to a short, I have been wrestling with how to properly protect all these runs of small wire. The main 14 AWG feeds are protected by 15 amp fuses, but after things branch out to other sub-terminal strips, then to smaller wires feeding individual accessories, these fuses don't protect adequately. I wanted a compact way to do this with individual branch line fuses of 5 amp or so, which will protect the smaller wires.
At the local Princess Auto (similar to Harbor Freight Tools) I found this: It has a single heavy duty supply bolt, 10 individual sub-circuits, and up to 100 amps total load @ 32 VDC. It uses micro blade fuses so it's compact. Dimensions are 3-1/4" x 3-3/4" overall.
And the cool thing is each sub-circuit has an LED to indicate if the respective fuse is blown. I simulated this by removing a fuse as shown. The LED's are non-polar, and work with AC as well. I figured this will be a handy feature for troubleshooting a blown fuse under the layout.
Since I don't need 10 circuits for any of my accessory supply voltages, I decided to disassemble it and see if I could maybe split it into two units, maybe one of 6 circuits and another of 4 circuits. Here is what I found inside:
This is the view after lifting the LED circuit board. You can see the single hefty common supply bus running along the bottom.
I cut the bus simply enough with tin snips as below. Presto: two separate supply buses. Then to separate the LED indicators I used my dremel cutting wheel to cut the outside common traces at the two points marked with black sharpie just to the right of the center of the circuit board. I then ran a small common wire (not shown) from the short supply bus to the now isolated common outside traces on the right end of the board. This effectively makes the 4 right LED's respond to open fuses on the short bus end of the board only, completely isolated from the 6 remaining LED's on the longer left bus, which still operate exactly as they did originally.
After reassembly it looks like this. And some simple testing indicated that all LED's work as expected. I replaced all the distribution circuits fuses with 5 amp ones, which will protect the smaller 22 AWG wiring from disasters. The upper right connector on the 12VAC end will be the feed, and is according fused with a 15 amp fuse, just to get power to the common bus feed to the other 3 fuses.
Here it is all finished and ready to go on (or rather under) the layout. Will try to get that done soon, depending on what's on the "honey do" list.
Just thought this may be of interest to others that have similar issues adequately protecting smaller accessory power wiring.
Rod
