Upgrading / Rewiring Electrics On A Boat

Bikertov · May 31

As I am starting to plan the electrical upgrades on my boat, and have some queries on how things should be done, I though a general thread would be useful rather than getting into specifics of my own boat - so feel free to hijack with your own queries and experience !

Bikertov · May 31

My first area to consider is the 240V side of things, as I'm looking to add some more mains sockets. The idea would be to add extra sockets to the existing ring that goes round the saloon, galley and berth, and then run a new ring to the engine bay for tube heaters and such like. As in a domestic situation, the immersion heater would be on it's own radial circuit.

So the first question is what size and type cable to use ?

I know it should be stranded wires and not solid core. But as for the cable size ? If the shore line and supply is only rated at 16A, is there any need to wire the sockets with 2.5mm cable (25A) or can it be done in 1.5mm cable (16A)

From what I have gathered, if insulated flex is used (eg 3183Y cable) rather than individual wires, the cable doesn't strictly have to run in conduit - but do correct me if I'm wrong

annv · May 31

Hi Biker You need to use Artic blue cable for 240 volt as per reg's. I would advise 2.5 for all circuits as per a house it may be larger than you actually need but you will only need one roll and it will be future proofed and the cost between 2-5 and 1-5 is not much. If you run it in the bilge you need to run it in conduit and be supported by clips to keep it out of any water that might be there.It dosn't need conduit in the cabins but must be clipped/supported,also good practice to dip exposed ends of wire and the screws in Vaseline (not ordinary grease) to prevent corrosion John

annv · May 31

Hi Biker Just to add Hep 2 o water pipe is very good for ducting as it's very flexible. John

dom · May 31

Mains is a bit of a minefield, not least because in theory you ought to be working to 18th Edition and BSS standards, but the former will probably never get considered, except maybe in the case of an accident or insurance claim.

I'd cable the domestic ring in 2.5mm, purely because if you switch to a 32A hookup, you can run a couple of 3Kw devices on a ring without having to upgrade cabling. It may not be something you plan on doing immediately, but if you start making a lot of use in winter, you can then run a heater and an electric cooker at the same time (a Ninja Foodie or similar is brilliant for use on a boat and avoids the moisture issues from gas cookers).

The engine bay ring is probably fine in 16A, as long as you're only going to run lighting and tube heaters.

I'd probably be inclined to run a dedicated radial/spur socket for a mains charger, so it keeps running (and supporting the bilge pump) uninterrupted if anything else develops a fault on the main ring.

Be aware you MUST use dual pole RCBOs to be safe. It's not unheard of for hookup posts to be reverse polarity, which could render single pole breakers unsafe.

Rover · May 31

Ring circuits are not generally used on small boats. There is no point if it is being supplied from a 16A shore supply. There should be an AC incoming panel with RCD and incoming breaker. From there a radial circuit with its own breaker to each cabin.

If you want to do it properly, have a read of ISO 13297. It is quite a short document and not difficult even for non-technical people. Most of it is common sense. You (and your insurance company) will have the satisfaction of knowing you have a fully compliant installation.

Woodie · May 31

If fitting a new mains distribution board, make sure the RCD is a type A and not the previous more common type AC.

Bikertov · May 31

4 hours ago, dom said:

Be aware you MUST use dual pole RCBOs to be safe. It's not unheard of for hookup posts to be reverse polarity, which could render single pole breakers unsafe.

33 minutes ago, Woodie said:

If fitting a new mains distribution board, make sure the RCD is a type A and not the previous more common type AC.

In this instance, I'm not looking to change the existing 240V shore power panel - it is a Brian Ward unit with a Hager CD 240U (40A / 30mA trip) RCD, and 4 breaker switches.

But useful to know for a full rewire

grendel · May 31

dont ask me to supply a length of brass connection strip for a boats wiring- I do reckon though that a 400A busbar from one of these may be a bit overkill (see the bar across the top above the breakers(its about 3/4" square cross section)

and yes its fitted in a boat

dom · May 31

1 hour ago, Bikertov said:

In this instance, I'm not looking to change the existing 240V shore power panel - it is a Brian Ward unit with a Hager CD 240U (40A / 30mA trip) RCD, and 4 breaker switches.

Looks like it should be a CDA240U if it's type A. If it's an older RCD, there may be a possibility a new one might fit in the same footprint and they're not especially expensive.

Looking at Brian Ward's current offerings, does the panel have a correct polarity indicator?

The danger with reverse polarity is that with a single pole breaker or switch off, the neutral cable can still be live. It's especially dangerous if there's also an earth defect - a neutral short to case can electrify the whole device. It takes more than one factor for it to occur, but a UK distributor in the caravan market had an issue along these lines.

Personally, with the cost of them now, I'd rather have RCBOs on everything, but understandable if you don't want to change the panel. The main advantage with RCBOs is things are more resilient and a fault only affects one circuit, but with a boat, you've obviously still got 12v lighting, etc throughout anyway.