How to set up for 240v?
QI am planning the electrics for a Dutch barge (supported by an electrician!) and looking for guidance. Would it be all right to wire the boat, sockets, lights, appliances etc, using 240v as follows:
Shore power, galvanic isolator, inverter charger unit (with RCD), leisure batteries, inverter charger then feeding various services (sockets, interior lights, exterior lights, bilge pumps, water pump, fridge etc.) The inverter charger unit will be connected to engine and a portable generator and solar panels. CONALL PLATTS, via email
ATONY REPLIES... I can give general pointers, but not specific advice on mains power systems on boats, your (qualified) electrician should give you that.
A galvanic isolator should prevent any stray earth currents corroding the hull, but I would prefer an isolation transformer if the boat were to be connected to the shoreline for long periods.
There should be one single earth point between the onboard 240v electrical system and the hull, but the isolator or transformer will isolate this from the shore-side company mains earth. You need this hull bond so the RCD will operate in the event of a fault.
The generator and/or inverter might cause complications if either use a centre tapped floating earth, but an experienced marine qualified electrician should know how to deal with this correctly.
A combined charger / inverter might not be such a good idea on two counts. Firstly, if it fails, you lose both systems and secondly, you need to ensure that, in the event of a power cut when on shore power, the inverter will not try to power the battery charger system – otherwise you will end up with very flat batteries.
Ordinary twin and earth mains cables (using one or a few thick conductors) are likely to snap under vibration and are not suitable for boat use. Most people use arctic grade flex. Use bootlace ferrules when making screw connections to flex.
Using 240v for things such as lighting means extra battery losses because the inverter will not be 100% efficient (we usually reckon on 80% for calculations). Also, if the inverter fails you will have no lights. I am not sure how easy it will be to get mains water pumps, shower drain pumps etc. I would use 12v or 24v lighting and pumps, with mains for the rest.
You need to ensure only one of your three AC sources (shoreline, generator, invertor) is connected to the boat’s mains wiring at any one time, otherwise the phases will probably not be in sync (although some inverter models can sync themselves) and expensive damage may result.
This could be as simple as one mains socket for each supply, with the boat’s wiring connected to a single plug; or there are manual and automatic systems that can select one at a time.
Use a galvanic isolator