SMALL BOATS ELECTRICAL INSTALLATIONS

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.

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.

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.

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

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.

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. 

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

Z.

Well you can't connect to any metalwork if the craft is not made of metal can you.

Z.

The metal kettle in the boat would qualify.

But in general the cases of shore power and generated on board are very different. Only the shortest of voyages will be made while plugged in, and I suspect it is almost never the dno who makes any such connection.

It will be the small/ medium boatyards dealing with narrow boats and so on that are most likely to fall foul of this rule and maybe private moorngs at the ends of gardens on inland waterways. And probably most likely for the saturday lad  to throw the extension lead much as you would a mooring rope when a boat pulls in and occasionally miss and splosh it  into the water.

Oddly only last summer we hired a boat on the Caledonian canal and the number of caravan style hookup leads flapping about  in the elements and drooping into the water mid span was something to behold. Lots of RCDs in clear plastic boxes, so there is ADS, but it still feels more continental than I am used to in the UK.

Mike.

Mike

Are you sure Mike? In that case use a plastic bodied auto jug kettle.

"A risk associated with an electrical supply to a craft at a marina includes the possibility of an open circuit fault of the PEN conductor were a PME supply to be used. This would raise the potential of all metalwork (including that of the craft, if connected) to a dangerous level above true earth and hence the connection of a neutral conductor to the metal body of a boat or caravan is specifically prohibited in legislation (Electricity Safety, Quality and Continuity Regulations (ESQCR) Regulation 9(4))."

Z.

And the "Distributor" will not be connecting his combined earth and neutral to the kettle anyway.

rotective multiple earthing

9.—(1) This regulation applies to distributors' low voltage networks in which the neutral and protective functions are combined.

(2) In addition to the neutral with earth connection required under regulation 8(3)(b) a distributor shall ensure that the supply neutral conductor is connected with earth at—

(a)a point no closer to the distributor’s source of voltage (as measured along the distributing main) than the junction between that distributing main and the service line which is most remote from the source; and

(b)such other points as may be necessary to prevent, so far as is reasonably practicable, the risk of danger arising from the supply neutral conductor becoming open circuit.

(3) Paragraph (2)(a) shall only apply where the supply neutral conductor of the service line referred to in paragraph (2)(a) is connected to the protective conductor of a consumer’s installation.

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

Z.

Most small boats that I have been involved with have gas stoves to boil water, not electric kettles. Or larger craft may have a sold fuel stove.

Z.

Yachts have sacrificial anodes to prevent corrosion of props and structural nuts and bolts.

I was told its not a good idea to attach the negative side if the 12V system to the metalwork of a yacht.

Good chance of damaging the on board navigation equipment and other electronics.