[C320-list] Ground Bus Bar - Perkins M30 Alternator

[Jack Brennan]

Let’s see whether I can explain this without goofing up. Corrections are welcomed. A caveat is that while I have completely rewired other boats, I haven’t dived into all of the wiring on the 320.

The grounding bolt on the engine is the main grounding point for the boat. Through the prop shaft and the prop, it provides a path to ground in the water.

All of the negative cables on the batteries are connected. Another cable there should run to the grounding bolt on the engine. One more should run to the main negative buss behind the circuit breaker panel. That means all 12-volt appliances share the same ground.

The starter, alternator and some other equipment may also be connected directly to the bolt rather than the main buss just because the wire run is shorter. There’s no reason to run cable all the way back to the circuit-breaker panel.

Creating a second ground buss bar shouldn’t affect anything.

It’s possible just to use the batteries for the ground, but there’s a danger. 

That’s because if something goes wrong and 110 volts gets into the 12-volt system, you could get electrocuted.  Even if the 12-volt buss bar is connected to the engine bolt, you could electrocute anyone in the water. If you connect the green wire from the AC system to the main 12-volt buss, that provides another path to ground that lessens the danger.

The downside to this is that if you don’t have a galvanic isolator, connecting the green wire can increase the risk of corrosion if there is another boat with bad wiring that is plugged into the dock. Every boat plugged in at the dock shares the same ground, and stray current can eat away at your zinc, prop, etc.

So, ideally, everything is linked together and, if you plug in regularly, you use a galvanic isolator to block corrosion. I avoid this by using solar panels and relying on the alternator during cruises. When I do plug in, say in Key West, my zinc inevitably needs to be replaced.

I assume that means there is no galvanic isolator buried in the boat.

Jack Brennan
Sonas, 1998 Catalina 320
Tierra Verde, Fl.
Dolphin Cruising Club of Tampa Bay
















Sent from Mail for Windows 10

From: Jeff Smith
Sent: Wednesday, July 1, 2020 2:19 PM
To: C320-List at Catalina320.com
Subject: [C320-list] Ground Bus Bar - Perkins M30 Alternator

To all with a Perkins,

Has anyone installed a ground bus bar for the M30 alternator? The common ground for the Perkins M30 is a bolt at the back of the engine. When I removed the bolt to ground my electric lift pump, I inadvertently severed three ground wires that were also attached to that point (alternator and something else I have not traced). My thought is to install a ground bus bar with one wire from the back of the engine and mount the bus bar somewhere close. Then I can simply connect my grounds on the bar.

Amazon sells a Blue Sea Systems Common BusBar (rated up to 250A, though I am looking at the 150A version), with 10 screws and a cover. I am curious if anyone has done something similar. I think I have at least five different wires grounded to the back of the engine.

Thanks,
Jeff
’94, #121