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SMALL BOATS ELECTRICAL INSTALLATIONS

John Peckham

I have been asked about electrical installations in small boats. Now I know they are out of scope for BS 7671 but I do not know if there is a similar standard for small boats. Could I ask the forum please if you do installations in small boats? If so do you install to a specific standard or best practice and do you certify the end result after inspecting and testing to the standard or best practice? I thinking here about canal boats, yachts and cabin cruisers not bigger vessels such as ships as these are covered by an IET publication and insurance company requirements. I have looked at a canal boat and it was more like a floating domestic installation in twin and earth and a domestic consumer unit! Given the amount of boats and pleasure craft around I cannot believe there is not a common standard or publication, or maybe there is?

Thanks

JP

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  • 0

    For a small and simple installation at mains voltage on a boat, I would proceed as for a caravan.

    For an ELV installation I would follow accepted good practice, including 2 pole wiring, NOT earth return as is used on motor vehicles. In many cases, oversized cables will be needed to minimise voltage drop.

    On all but the most basic craft, essential equipment should be duplicated with no common point of failure. For example duplicated feeds from two batteries to radio equipment, bilge pumps, and navigation lights.

    For small and simple circuits, a good rule of thumb is to size the fuse at twice the running current, and then size the cable at twice the fuse size.

    Example, bilge pump uses 8 amps. Use a fuse of about twice that, 15 amps or 16 amps. Then select cable good for about 32 amps, probably 4mm.

  • 0 in reply to broadgage

    Consider possible corrosion at electrical terminals, especially if the boat is used in salt or brackish waters. Protect all cable ends and do not allow joints to get wet. Use appropriate gunge like grease or silicon sealant etc. Duplicate bilge pumps in case one becomes blocked, seized or fails in another way. Have independent torches and backup of essential equipment like the marine radio etc. in case of 12 Volt failure or a dead or dying battery.

    Consider corrosion of external parts like propellers and steering gear due to electrolysis.

    Only supply steel hulled craft via a mains TT earthed supply, NOT P.M.E.

    Z.

  • 0 in reply to Zoomup

    The PME restriction applies to all craft, not just steel hulls.

  • 0 in reply to GeoffBlackwell

    But is more critical to all metal hulled boats as there is more exposure of metal parts. Glass fibre (GRP) hulled or wooden hulled boats pose less risk.

    Z.

  • 0 in reply to GeoffBlackwell

    It not a case of critical - it is prohibited in law by the Electricity Safety, Quality and Continuity Regulations.  These are statute - compliance is not optional.  They will probably send you to the colonies if you transgress.  To be more exact - the Regulation 9.4.  Places a duty on the distributor - the text is:

    The distributor shall not connect his combined neutral and protective conductor to any metalwork in a caravan or boat. 

  • 0 in reply to GeoffBlackwell

    Yes I knew that, why did you think that I didn't?

    Z.

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