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Old 03-10-2008, 16:33   #1
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AC electrical refit

Hi Everyone,

I'm in the process of planning an electrical upgrade for our boat. We live aboard full time and are always plugged in when at the dock, so I'd like to start with the AC system (currently 30 year old 14/2 household wire to the outlets, so definitely time for an upgrade). Our electrical system is pretty simple, we have 6 outlets and one battery charger (no inverter) that run on the AC. Currently power comes from the shore power outlet to the AC panel and then out on 2 separate circuits, one for the port outlets and one for the starboard outlets. The battery charger is plugged into an outlet in the engine compartment. I've purchased a new panel from Blue Sea and I'm planning on ordering new wire and some GFCI outlets, but I have a few questions first.

1. Currently the AC system is not connected to the DC ground, I've been reading Calder's book, and he recommends this to give the AC a path back to the shore power ground if there is a leak into the DC system. For us the only connection between AC and DC is the battery charger, so I'm not sure how much of a concern this is. Also we have no galvanic isolator. If I connect the AC system to the DC ground I would be worried about corrosion of our shaft and propeller. I guess my question is how much risk is there with our current setup? Is it likely that the AC can short into the DC system via the battery charger? also is galvanic corrosion possible with our current setup since the battery charger is grounded in the DC system? I'm considering rewiring things as they are (ie not adding a galvanic isolator and not connecting the AC to the DC ground), but I'd like to know if I'm being a total idiot. If the AC and DC were completely separate I wouldn't see a problem, but the charger being in there makes me worry.

2. What gauge of wire would be best to use? I'd like to go up to at least 12 gauge for the outlets, especially since we often have an electric space heater plugged in, but I'm wondering if I should bite the bullet (economically speaking) and use 10 gauge wire.

I hope that's all clear.


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Old 03-10-2008, 17:01   #2
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personally as a master electrician i would use 14 ( 15 amp )gauge wire for most oultets then maybe put 2 outlets on 12 ( also on 15 amp ) gauge on a different circuit. maybe one near the engine, and one near a roof hatch for topside work that way under high load you loose less to resistance ( which in boat lenght terms is nothing) under high load stuff . as for using heaters the largest portable heater you can buy is 1500 watts, or 12.5 amps. you would also be better served by a few heaters spread around on a lower wattage. if you wired like i said you might need to uplug some large draw items if you used power tools, but it would avoid tripping the breaker. also yes 10 gauge is way over kill.

as for the inverter an easy way is a double pole double throw switch that ties one of the circuits in to either the shore power or inverter, its basicly a transfer switch. you dont want to have every outlet in the boat on the inverter, because when you switch over you can easily have something plugged that you forgot about drawing power too. even better in my mind it just 2 outlets, one on each end of the boat completely seperate from shore power

grounding and isolation with the exception of the shore power ground i have no clue whats best

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Old 03-10-2008, 17:30   #3
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I would suggest you go to the Professional Boatbuilder site and find Nigel Calder's article on AC systems. It is worth the read.
The Blue Dot Campaign. This Changes Everything.
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Old 03-10-2008, 18:57   #4
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here is some good information

Preventing Hazardous Ground Faults on Boats - Resources - Blue Sea Systems
Chesapeake Bay, ICW Hampton Roads To Key West, The Gulf Coast, The Bahamas

The Trawler Beach House
Voyages Of Sea Trek
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Old 03-10-2008, 18:58   #5
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And here is a ton of information

Lessons In Electric Circuits
Chesapeake Bay, ICW Hampton Roads To Key West, The Gulf Coast, The Bahamas

The Trawler Beach House
Voyages Of Sea Trek
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Old 04-10-2008, 02:09   #6
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Marinco has a basic, but excellent, publication: “Boater’s Guide to AC Electrical Systems” at:
Guides for Marinco Electrical Group Brands | Marinco

See particularly diagrams (1, 2, & 3) on pages 19 - 21.

See alco ABYC E-11 (circa 2003 - now superceded by 2008 re-issue)

Gord May
"If you didn't have the time or money to do it right in the first place, when will you get the time/$ to fix it?"

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Old 04-10-2008, 02:26   #7
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We just got done doing the same thing on our boat. We had that $%^$%$ solid core household wire strung all over the boat. Ripped the works out and used heavy duty industrial extension cords (cut-up) to wire in the new system. We used a 12-gauge wire cord for the hot water heater circuit although that may have been over-kill. The AC is grounded directly to the shore power ground while the DC portion is grounded to the boat. We have a galvanic isolator that came with the boat that separates the two.

I personally would consider adding the isolator if you're going to be tied up in a marina most of the time. I don't especially understand all of the electrical black magic going on underwater, but I do know that some marinas seem to have problems with stray current running all over the place chewing up zincs. We also kept our receptacles to a minimum because we don't use the AC circuit that much and mostly because it's a PITA to get the new wire run. We left some of the old household wire abandoned in place because it was such a hassle trying to get it out. We're talking very inflexible wire here!!!

Good luck! From what I've read there seems to be a lot of opinions on the best way of doing the electrical, some of which might even be correct. I sometimes think it would be a lot simpler just to use candles!!!!

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Old 09-10-2008, 15:21   #8
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try to replace your wiring with tinned wires. That will stand for long time.

Try to use only gold plated terminals (cheaper than you think), will stand against corrosion extremely long time.

If you want to top: Place a small tin point between the wires very end and the terminal. Do NOT let run the tin into the terminal.

This will be a lot of work. I am corrosion free since 6 years (Caribbean). I replaced the whole Volvo wiring (trash) and most oft the “normal European” not tinned and after 3-6 years black wiring.

comin' soon
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