Just twenty or thirty years ago the electrical system on the average sailboat was very simple. It had two batteries connected to an OFF-1-2-BOTH battery switch, and all the loads were fed from there:
On the back of the battery switch were three studs: one for each battery, and one for the common, that is, the terminal that connects to the alternator and all the loads:
The battery switch for this Catalina 30 is this way. In addition to the connection to each battery, the battery studs on the back of the switch are good places to connect the outputs for the shore power charger, the voltmeter, and the bilge pump, all things we want permanently connected to a battery, and never turned off.
On the common terminal of course is the big cable connected to the engine’s starter, and the feed wire to the main distribution panel, which in this case is just a 10 gauge wire: ah, the days of such simplicity. The back of this switch might be a little crowded, but all of these wires fit.
Today the electrical system on the average sailboat is more robust and complex. With just the aforementioned connections to the battery terminals – voltmeter, charger, bilge pump, maybe the memory wires from a stereo or other electronics – the studs are already too crowded. On the common terminal, forget it. You might have the big cable to the starter, a big cable to an inverter or inverter/charger, big cable to the windlass, and a good-sized cable to feed the main distribution panel, which now supplies a radar, a refrigerator, and a range of modern comforts.
All these cables simply won’t fit, and according to the ABYC standard, you shouldn’t stack more than four ring terminals on a stud anyway.
Enter the bus bar. Give yourself some breathing room!
A bus bar simply expands your single stud into four or more. A large gauge cable, and nothing else, connects to the common stud on the battery switch. The other end connects to the bus bar, where you’ve got a row of big studs for all the other connections. The same could be done for one of the battery connections if you find you’ve got too many cables and wires that need to be connected directly to a battery, without a switch in between. Generally speaking, we want to keep our battery terminals clean. Manufacturers sometimes dictate otherwise, as with some electrical system monitors and chargers, but we should endeavor to have nothing but the supply cables connected to our batteries.
The bus bar is even more necessary on the negative side, where the negative cables from the batteries, negative ground from the engine, inverter, windlass, corrosion ground (green wire), and feed to main distribution panel, all must connect. Might also note here that bus bar covers are equally important, as they make for a lot of exposed, live metal:
Many older boats foresaw this scenario, but it was before off-the-shelf bus bars, so they just added distribution studs, or what Blue Sea Systems now calls a Power Post, but one stud just isn’t enough. These are overcrowded and a bus bar would create more room, make circuits easier to trace, and ahem, that thing about no more than four ring terminals to a stud?:
Remember, good wiring is not only electrically sound, but easy to follow. Wherever you find yourself running out of room and trying to cram too many terminals in a tight space, even if it’s electrically sound, it will be difficult to service and trace in the future. A relatively cheap and simple bus bar is often the solution.
This article was syndicated from The Adventures of the Vessel Condesa