Bypassing the Electrical Panel

[Don Casey]

I recently read that it isn’t necessary to run all electrical connections through the boat’s electrical panel when adding equipment that has its own internal switch. Thus stereos and VHF radios, for instance, might be connected in a way that bypasses the battery switch so that the appliances are always available and controlled solely by their internal switch. Do you agree, and if so, should that connection be made directly at the battery or through a bus bar that is always live?

Don Casey responds:

As a general rule, connecting any circuit directly to your battery is a bad idea. There are exceptions. The starting circuit, for example, is nearly always connected directly to the battery. (This circuit, by the way, is usually defused, but a high-amp fuse in the positive side—now readily available—makes for a safer boat.) The automatic bilge pump is typically connected directly, with a fuse in the positive leg near the battery. Some electronics, particularly Loran, are sometimes connected directly (with a fuse) to minimize interference. And SSB radios may also be connected directly with large cables to maximize the available current for long-range transmission.

Despite these exceptions, I strongly urge you to refrain from using the battery terminals as the power source for additional equipment or circuits. The power to all onboard circuits should originate downstream of the main switch so that in the event of a short or a fire you can disconnect everything with a single switch. A bus bar that is always live represents unnecessary exposure.

If your distribution panel is maxed out, it is a simple matter to install a supplemental panel, located wherever it is convenient. Breaker panels start at around $100, or you can buy a six-circuit switched-fuse panel for about $25. If you don't need switches, a simple enclosed fuse block will serve the purpose. But in all cases, pick up the supply power from the output side of the main battery switch, or better yet downstream of the main breaker if your boat has one, but not from the battery terminal.