Advice on shorepower?

[Colvic Watson]

Currently we have a hotch potch of systems and I'm going to sort it out. Any advice on the planned installation would be very helpful please:

1. Close to the shorepower entry into the wheelhouse a garage consumer unit with two 16amp MCB breakers and a master RCD
2. One of those MCB's circuits for the ring main, this is an existing insalation and is the ring of 4 single sockets and two tube heaters.
3. The second MCB circuit will connect to a double socket to allow me to switch the calorifier and battery charger on and off.

I can't see the benefit of connecting the earth from the incoming 240v supply to the battery negative? At present there is a galvanic isolator with a mess of wiring from it to the two battery banks. The MCB's surely protect all the outlets for a short between live and neutral? For a short between live and earth then surely the marina power is earthed? I have a plug in socket tester to check the supply and all sockets currently show three leds for good connection.

Anything I've missed and what about that earth/battery neutral issue?

 

[nigelmercier]

Any advice on the planned installation would be very helpful please...

If you have room, add space for a couple more MCBs. For example, I've got one for the fridge, the computer, the immersion heater, and the battery chargers. I've also got all 13A sockets on separate circuits. Ring mains are not a sensible idea, even in a house!

Make sure that the earth wire passes through the GI before it goes anywhere else (including the CU), no need to ground it to the battery.

 

[Colvic Watson]

Thanks. Some questions:

Why not a ring main?
Why bother with the galvanic isolator at all? If no shorepower is connected via it to anodes then there's nothing to fizz the anodes?

 

[nigelmercier]

Thanks. Some questions:

Why not a ring main?
Why bother with the galvanic isolator at all? If no shorepower is connected via it to anodes then there's nothing to fizz the anodes?

Ring mains were invented in the UK solely for the purpose of saving copper after WW2. It is much better to have an MCB on each socket, as they do in Europe. If you want to keep the ring, then fine, but it is in no way mandatory to have one providing you have 2.5mm cable on a 16A MCB.

You don't need to connect the earth to the battery ground, but some equipment may do this for you, by design or due to a fault. It's a good idea to have the GI as protection. On my boat, they are connected; but if I had advised this then there would have been an avalanche of contrary opinions.

 

[VicS]

Garage consumer units usually have 1x 6 amp and 1x 16 amp MCBs plus of course the RCD. One circuit being for lights and one for power.

I think you will find that a ring main would normally be connected to a 32amp MCB.

You should have double pole isolation within 0.5m of the inlet connection or the cable to the consumer unit should be enclosed ( eg in a conduit)

The shorepower earth should normally be bonded to the DC negative ( except with fully isolated DC systems) and the anodes etc.
There is provision in ISO 13297 for this not to be so provided the whole vessel is protected by an RCD. Other standards do not allow this, it is not recommended and the concession will probably be dropped when ISO 13297 is next revised.

When the shorepower earth is bonded to the DC negative and anodes etc an galvanic isolator is next to essential if the shorepower connection will be left plugged in, even if not in use, for prolonged periods.


ISO 13297

.

 

[Colvic Watson]

Thanks for that. What does bonding the negative to the battery DC achieve in terms of protection?

 

[VicS]

Thanks for that. What does bonding the negative to the battery DC achieve in terms of protection?

A small improvement in electrical safety ... perhaps.

The pros and cons have been hotly debated in the past.

 

[Boathook]

If I was redoing my system it would be with RCBO's - RCD and circuit breaker combined, as long as they switch off both positive and negative. This sorts out the problem with wires being reversed sometimes in France.
At present I have a radial / ring type system (16 amp cable) on board for the sockets protected by a 16A circuit breaker but the master RCD is a double pole unit. The firdge is supplied from a 5 amp circuit breaker. Somewhat unusual but all well protected.

 

[nigelmercier]

If I was redoing my system it would be with RCBO's - RCD and circuit breaker combined, as long as they switch off both positive and negative. This sorts out the problem with wires being reversed sometimes in France...

It shouldn't matter, a RCD measures an imbalance between neutral and phase.

 

[KellysEye]

> galvanic isolator with a mess of wiring from it to the two battery banks

There is something wrong there. We have GI's on both our 12v and 240 circuits. There should be only one wire attached to the GI, the earth wire.

 

[Colvic Watson]

> galvanic isolator with a mess of wiring from it to the two battery banks

There is something wrong there. We have GI's on both our 12v and 240 circuits. There should be only one wire attached to the GI, the earth wire.

Is this the same earth that also goes to the battery negative?

 

[sailorman]

Is this the same earth that also goes to the battery negative?

Hi Simon do a ybw search there is lots bed time reading on the subject.
i would suggest you ask "Little Stewie" local boat sparkie (he is almost always around the yard he has a white escort) he will give you the definitive answer & any advice relating to your set-up. Ralph or JJ would give you his mobi No.
my preference would be to keep them separate as i have o/b

 

[nigelmercier]

We have GI's on both our 12v and 240 circuits...

Where would you put a GI on a 12V circuit, and why?

 

[Boo2]

Ring mains are not a sensible idea, even in a house!

Sorry, but why is this ?

Boo2

 

[nigelmercier]

Sorry, but why is [a ring main not a sensible idea, even in a house] ?

I'm probably repeating myself, but here goes ...

The idea of a ring main was purely to save copper after WW2; is is not better, merely cheaper. It relies on the idea that you can make a shorter circuit of an area with a ring (thus saving copper) which is effectively doubled in capacity by the return loop.

However, if one of the conductors becomes detached or damaged, the sockets continue to function normally - so the user is unaware of the problem. Now you have a circuit with (say) 20A capacity cable, being fused by a 30A fuse or 36A MCB - not good! In addition, each circuit encompasses many sockets, often an entire floor of a house. If the breaker goes, you lose all power to the entire area.

Using radial circuits, the MCB is rated below the cable capacity, so is safer. In addition, in a fault condition only a small number of sockets are affected; it is thus easier to locate and rectify the fault.

 

[prv]

The shorepower earth should normally be bonded to the DC negative ( except with fully isolated DC systems) and the anodes etc.

What does "fully isolated" mean in this context? In a car, I'd assume it meant "not using the body as a return path" but that's irrelevant on a plastic boat (and nobody does it on metal boats either).

Pete

 

[VicS]

What does "fully isolated" mean in this context? In a car, I'd assume it meant "not using the body as a return path" but that's irrelevant on a plastic boat (and nobody does it on metal boats either).

Pete

It means a fully insulated 2 wire DC system in which the d.c. negative is isolated from the ground (earth), i. e. not connected to the water through a metallic hull or the propulsion system, nor earthed through the a.c. protective conductor.

See the definition 3.16 of ISO 10133

To be honest this the first time I have bothered to look at ISO 10133. Some other interesting stuff in there to read. ... Enjoy!

.

 

[Jean]

It shouldn't matter, a RCD measures an imbalance between neutral and phase.

But if there is only single pole protection, and the line and neutral are reversed at supply, then circuit/apparatus "neutral" stays at line potential, even with the single pole RCBO tripped.

 

[VicS]

But if there is only single pole protection, and the line and neutral are reversed at supply, then circuit/apparatus "neutral" stays at line potential, even with the single pole RCBO tripped.

But shouldn't there still be a double pole RCD in the system which will afford the same protection as normal even if the MCBs are replaced with single pole RCBOs

What's the reasoning behind fitting RCBOs in place of MCBs ?

Or am I wrong about retaining a common 2 pole RCD?

 

[Jean]

VicS: Yes agree, but Boathook made no mention of a double pole RCD. Shore power is likely to have its own RCD, but unless the trip current discrimination is adequate (or time delayed), no guarantee which one trips first.

RCBO normally takes up just one width slot in the consumer unit (although one width slot RCBO’s may by now be available, I've not checked recently). So it’s a degree of extra protection if space in the consumer unit is limited. And of course makes nuisance tripping of RCD’s serving multiply circuits easier to trace if using RSBO’s instead, with one per each circuit.Thanks for your ISO document links, I’d not seen them, must read through them over Christmas.