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Old 01-07-2018, 07:01   #1
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Join Date: Mar 2012
Location: Boston, MA
Boat: 1981 Bristol 32 Sloop
Posts: 13,417
120vac System - New Shore Power

Resources - I found these useful
Shore Power Upgrade - Sail Magazine
Safe Shore Power - Boat us - Don Casey
DIY Shore Power - West Marine
Don't get tripped up by New Shore Power ---> Inverter issues
ELCI a Primer
RCD vs ELCI what is the difference?

For this small boat with an old minimal 120vac system and no breaker panel new components are needed:

Shore Power Plug
  • Existing 30a plug & cord is ok.
Galvanic Isolation/Transformer
  • Isolation Transformer would be best, but are heavy & expensive and totally isolates the boat from shore power and ground (eliminates ABYC requirement for ELCI), 30a $500
  • Galvanic Isolator is more commonly used, 30a, new $300
  • Check existing device and wiring. Test it.
  • There are wiring diagrams for the Isolator in the links above
Main 120vac Panel
  1. Replace single inaccessible breaker/trip, find location.
  2. ELCI Test (new ABYC standard)
  3. Main Breaker
  4. Polarity Indicator
  5. Breakers (5)
    1. Outlets ---GFI ---outlet---outlet
    2. Water Heater (120v coil, not used)
    3. Refrigeration (240v/120v 50/60hz cord, not used)
    4. Battery Charger (new device)
    5. Spare
See Blue Sea Main 30A Double Pole plus 2 positions + 3 spares $270

Inverter and Generator? -No

Wiring should be sized and wired properly & carefully with good connectors and multi strand tinned marine wire. Remove any solid house wiring and replace it. Receptacles should be GFI in plastic boxes.
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Old 01-07-2018, 07:19   #2
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Join Date: Mar 2012
Location: Boston, MA
Boat: 1981 Bristol 32 Sloop
Posts: 13,417
Re: 120vac System - New Shore Power

Those with Generator and Inverters who do not have an Isolation Transformer should read

ELCI - A Primer
An excerpt:
Aboard a boat, the above code requirements mean that both the hot line(s) and the neutral line(s) must be switched “out” when the boat is connected to a shore power “derived source” and switched “in” when the “derived source” is the onboard genset or inverter. I know of many boats that only switch the hot conductor, which is a clear code and safety violation. (Refer to footnote 1, below in this article, for configurations involving isolation transformers.)

This is related to the diagram that Pelagic uploaded in an earlier thread showing a clever generator interlock, I believe.

If a boat has no generator or main inverter and has a properly wired galvanic isolator (not an isolation transformer) is there a problem if you plug in a 12vdc socket inverter, and have not "switched out" hot and neutral as stated above?

These complicated systems need to be designed to be fool safe IMHO.
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shore power

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