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Monday, November 16, 2015

What Was I Thinking?

Over the last a few weeks, two events occurred revealing two flaws in my electrical wiring design and implementation. One AC and one DC kind...

AC wiring flaw

It is close to winter again. Which means space heaters get run when I am inside the boat. Large power tool operation inside the boat is happening more often these days. While I put careful thought to ensure there would always be an AC outlet nearby(I hate running extension cords throughout the boat), I clearly wasn't thinking when I wired them all through ONE 15 amp breaker.

The problem? Run a power tool while the space heater is on HIGH, or better yet, run TWO space heaters (fore and aft), and the breaker will trip. Climb back to the engine room and reset the switch. Repeat a few minutes later. Grrr.

Solution: add a second breaker for the AC outlets. Since all wiring runs are homed to the engine room, re-configuring this is not a problem. Now, there are two AC outlet circuits: port and starboard. Each run through their own GFCI outlet mounted on the engine room electrical panel. All fixed.

DC wiring flaw

Recall we have FOUR electric bilge pumps. Two in each sump, fore and aft. In each pair, one is a "Crash" pump (expensive, high capacity for that time when you have a really BIG leak, hopefully never), the other is a "Dry" pump (cheaper, low capacity, for keeping the bilges dry). They are mounted such that, the dry pumps start first, and then, if water ingress is overpowering for the dry pumps, the crash pumps kick in.

My original wiring had all pumps powered through one 24 volt buss, which in turn was powered through one Mastervolt channel.

Well, a few weeks ago, something happened to the forward "dry" bilge pump causing it to overload the circuit (stuck impeller or something). This caused an overcurrent condition in the Mastervolt system which, in response, shut down the circuit. Now the 24 volt buss has no power, along with all the other pumps connected. I think you can see the flaw.

If one were in a real emergency, where the boat was taking on water, the last thing you want is one of the cheap low capacity pumps to fail, and take out the rest of the pumps with it.

Furthermore, as handy and fancy as the Mastervolt system is, I don't feel comfortable having it be the SOLE source of power for the bilge pumps. Some sort of electrical bypass is necessary in case the Mastervolt system goes down.

The solution is to wire all four pumps into the Mastervolt system, each with their own channel. Between the channel output and the (physical) pump switch, each tap into the positive side of one circuit of a multi-circuit fuse block. The entire fuse block, in turn is powered directly from the battery terminals, through an override switch.

The result is that, should the Mastervolt system shut down, turning on the one override switch will energize the fuse block, bringing all pumps back on-line.

Pretty easy huh? Like I said, "What was I Thinking?" when I originally wired this thing. Oh well, best catching this now instead of waiting for a true emergency situation.

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