Mains inlet fuse?

G

guyd

Well-Known Member
Joined
24 May 2009
Messages
208
Location
Minehead
bossingtonhall.co.uk
I'm about to install a basic spur style mains from a marinco style plug which comes from the marina 16a supply.

I have just the battery charger, a small tube heater (50w) and a couple of sockets for phone chargers or Hoover's.

The marina has an RCD and a MCB rated at 16a.with a 16 socket.

However, I want to put my own fuse or.mcb at the inlet for peace of.mind. what should I use? Inlet is at stern, open to the elements.
 
guyd said:
I'm about to install a basic spur style mains from a marinco style plug which comes from the marina 16a supply.

I have just the battery charger, a small tube heater (50w) and a couple of sockets for phone chargers or Hoover's.

The marina has an RCD and a MCB rated at 16a.with a 16 socket.

However, I want to put my own fuse or.mcb at the inlet for peace of.mind. what should I use? Inlet is at stern, open to the elements.
Click to expand...

A " garage consumer unit" is an inexpensive and convenient way forward. It will contain a 2 pole RCD and a couple of mcbs. Usually a 16 amp one, which can be used for the sockets, and a 6 amp one which is convenient for a battery charger.

For examples see https://www.screwfix.com/c/electric...gedredirect-_-electrical-_-garageconsumerunit

If this is within 0.5 m of the inlet there is no requirement for any additional circuit breaker on the incomer

Presumably with a battery cahrger you will be likely to leave the shorepower supply connected for lengthy periods. It would therefore be wise to also fit a galvanic isolator.
 
Last edited:
Interesting that in UK power plugs typically have a fuse mounted in the plug. Perhaps not so common now? Anyway here in Oz you have never had a fuse in a plug and we rely entirely on the fuse or now MCB at the fuse box for protection of wiring.
So I think it entirely reasonable to rely on the MCB at the marina supply point to protect your wiring from fire risk. More MVB and RCD will provide localised protection meaning if you pop the MCB with your own problem then no one else is inconvenienced but then you may be the only one on the marina MCB anyway. olewill
 
So there is no marinised version of a garage CU. Any CU has to be open as you need to get to the switch.... And mcbs have steel springs inside them (ever taken one apart?) Which would corrode. Hence a fuse, old skool.

But then again, the marina MCB/RCD isn't in an airtight box either....


In reply to William, yes UK plugs have fuses still, in the 13a domestic style. Marinas almost exclusively use 16a round pin round plug industrial style sockets, which do not have built in fuses.
 
William_H said:
Interesting that in UK power plugs typically have a fuse mounted in the plug. Perhaps not so common now? Anyway here in Oz you have never had a fuse in a plug and we rely entirely on the fuse or now MCB at the fuse box for protection of wiring.
So I think it entirely reasonable to rely on the MCB at the marina supply point to protect your wiring from fire risk. More MVB and RCD will provide localised protection meaning if you pop the MCB with your own problem then no one else is inconvenienced but then you may be the only one on the marina MCB anyway. olewill
Click to expand...

yeah, we have fuses in the plug, that means that you dont need to use 32A cable to wire your 60w desk lamp.
 
guyd said:
So there is no marinised version of a garage CU. Any CU has to be open as you need to get to the switch.... And mcbs have steel springs inside them (ever taken one apart?) Which would corrode. Hence a fuse, old skool.

But then again, the marina MCB/RCD isn't in an airtight box either....


In reply to William, yes UK plugs have fuses still, in the 13a domestic style. Marinas almost exclusively use 16a round pin round plug industrial style sockets, which do not have built in fuses.
Click to expand...

and sadly even the boxes are all steel ITYWF now. In the past I think you'd have been able to find a plastic one.

Fitting fuses instead of the mcbs may be Ok, but you still need an RCD in the incoming supply!

Best bet would be to chose a CU weatherproof to IP65. It does not have to be permanently open and all being well you should not normally need to access the mcbs or the RCD

Alternatively either fit a circuit breaker close to the inlet connector in a weather proof enclosure or run the incoming cable in conduit to the CU in a more sheltered position.

The relevant standard to consult for guidance is ISO 13297 : 2014.
 
It’s funny that the advice is to seek a plastic box because it is a marine environment. Most boats are plastic anyway and the guts of the consumer unit the busbars, connections and MCBs and RCDs have metallic components which have not been selected as suitable for a marine environment. The box is just a box but you can go a long way to improve matters in either case by the use of glands (with the correct inserts) for each and every cable penetration.
 
JumbleDuck said:
Yes, I have just been looking for one for a new barn I've built (preen, preen) and it seems they all have to be steel nowadays.
Click to expand...

Not actually true, as I understand the regs. You can put a plastic box in a fireproof cabinet or similar.
 
On the plastic v metal rules, the Ammendment 3 changes to the 17th Edition Wiring Regulations, brought in metal eg ferrous boxes to meet fire containment needs in Domestic settings, you can use plastic anywhere else and industry and shops still use plastic, though nearly all are metal now, if you actually try and buy one!

I suggest you avoid introducing additional RCD, in series, though an accessible two pole isolation switch might be prudent. Then ensure your "box" metal or plastic is suitably protected in the chosen location. On my, spectacularly, wet boat, we boxed the box in another plastic box, with a lid.

Any design ought to be checked and tested v wiring regs. The RCD in series issue does depend on (say) achieving 30ms cut off times from the Marina one.
 
Aurai said:
On the plastic v metal rules, the Ammendment 3 changes to the 17th Edition Wiring Regulations, brought in metal eg ferrous boxes to meet fire containment needs in Domestic settings, you can use plastic anywhere else and industry and shops still use plastic, though nearly all are metal now, if you actually try and buy one!

I suggest you avoid introducing additional RCD, in series, though an accessible two pole isolation switch might be prudent. Then ensure your "box" metal or plastic is suitably protected in the chosen location. On my, spectacularly, wet boat, we boxed the box in another plastic box, with a lid.

Any design ought to be checked and tested v wiring regs. The RCD in series issue does depend on (say) achieving 30ms cut off times from the Marina one.
Click to expand...

I disagree. I have seen marina breakers taped to stop nuisance trips. I would rather trust my own breaker which I know will have been recently tested.
Of course it does not protect you from faults between your breaker and the next one upstream that actually works. Which on many boats is about 90% of the cable.
 
Aurai said:
On the plastic v metal rules, the Ammendment 3 changes to the 17th Edition Wiring Regulations, brought in metal eg ferrous boxes to meet fire containment needs in Domestic settings, you can use plastic anywhere else and industry and shops still use plastic, though nearly all are metal now, if you actually try and buy one!

I suggest you avoid introducing additional RCD, in series, though an accessible two pole isolation switch might be prudent. Then ensure your "box" metal or plastic is suitably protected in the chosen location. On my, spectacularly, wet boat, we boxed the box in another plastic box, with a lid.

Any design ought to be checked and tested v wiring regs. The RCD in series issue does depend on (say) achieving 30ms cut off times from the Marina one.
Click to expand...

17th Edition Wiring Regulations do not apply to marine installations. In a marine installation a double pole RCD must be fitted in the CU.
 
You must log in or register to reply here.

Share this page

Top