Electrical RCD consumer units onboard

[All_at_Sea]

Currently I have one breaker in the incoming 240v supply shorepower line. I am just about to add a generator to this so thought l would upgrade the 240v system. My plan is to put in a garage consumer unit, 6 way. So far so good. However I note that most marinas run on a 16amp supply, so is there any need for any MCB to be any bigger than this? Most boxes I see have a domestic 63A incomer, but l was going to reduce this to either 30 or even 16 amp supply.

The genny will be a 4kw unit.

Having done that I was going to have the interior circuits as, sockets 16amp, immersion 6amp, batt charger 10amp. Does this seem ok or do you use a different regime?

 

[prv]

I have a 16-amp main breaker, as ideally I'd rather the one on board trips than one somewhere on the pontoons or ashore, possibly in a locked box that I can't get at. Of course, if the shore one is also 16 amps I can't be sure which will pop first, but it might help.

10 amps seems a lot for a battery charger; is that what it's rated at?

Pete

 

[VicS]

Currently I have one breaker in the incoming 240v supply shorepower line. I am just about to add a generator to this so thought l would upgrade the 240v system. My plan is to put in a garage consumer unit, 6 way. So far so good. However I note that most marinas run on a 16amp supply, so is there any need for any MCB to be any bigger than this? Most boxes I see have a domestic 63A incomer, but l was going to reduce this to either 30 or even 16 amp supply.

The genny will be a 4kw unit.

Having done that I was going to have the interior circuits as, sockets 16amp, immersion 6amp, batt charger 10amp. Does this seem ok or do you use a different regime?

Garage consumer units are usually just RCD plus 1x 16 amp mcb and 1x 6amp mcb I fyou want more than two circuits then I dont think a garage consumer unit is what you want


Either connect your genny via the incoming shorepower connector or make sure you have it connected via an appropriate "transfer switch" if permanently wired in

 

[All_at_Sea]

Thanks for the replies. Does it matter about the actual ampage of the incomer unit, as this is the rcd bit it would trip if a fault happened in the system onboard?

 

[Lon nan Gruagach]

In theory it is bad practice to have a downstream breaker of higher rating, it can confuse fault finding in large systems. That said then there is no issue provided that all downstream wiring and equipment is protected by any breaker. So, to construct a bad installation you might have 16A shore supply, 32A shore cable (good so far), 100A master breaker (still good)r, 32A bus bar (thats the bad bit, its downstream of a 100A breaker even though your shore supply can only do 16A)

Thanks for the replies. Does it matter about the actual ampage of the incomer unit, as this is the rcd bit it would trip if a fault happened in the system onboard?

Now, this is worrying and will lead many people to say "get an electrician". Why? you seem to be confusing RCD and master circuit breaker (sure you can get them combined, but you give the impression you dont really know) RCD is residual current device, it will detect any lost current (regardless of where it may go, so its not just an earth leakage trip [ELCB]) where as a master circuit breaker (possibly MCCB, not to be confused with MCB a miniature circuit breaker) will measure the current in the circuit. One detects a wire touching something it shouldnt and will trip at low currents to prevent electric shocks, whereas the other will prevent circuits being overloaded.

 

[All_at_Sea]

No l don't think l was as the RCD covers all the system - my question was does it matter what rating this bit has because it will sense lost current and trip, surely regardless of the rated amps of that RCD? ie Are you saying that if l had a 1000 amp RCD it would never trip out?

 

[Lon nan Gruagach]

No l don't think l was as the RCD covers all the system - my question was does it matter what rating this bit has because it will sense lost current and trip, surely regardless of the rated amps of that RCD? ie Are you saying that if l had a 1000 amp RCD it would never trip out?

Ahh. OK all that matters is that it trips at the right current and right timing, usually 30mA 30mS (provided it can manage anything that might normally pass the nearest upstream current trip.)
However you did originally mention MCB, then incomer unit then rcd. These can all be different.

 

[Aurai]

One part

Of your approach is to work out what you want to power and where, distances on a boat are usually relatively short. In your case whatever you plan for your 13A sockets, 6A Immersion, Battery Charger (checking rating?) and from this work out "demand characteristics".

Anything over 2kW for instance should be run off its own dedicated radial circuit, not sockets.

This will tell you what you are expecting to use and can then be used to select your Main Switch, with each circuit having a correctly rated MCB and all the circuits protected by RCD.

Small Garage units tend to dispense with a Main Switch and use the MCB for isolation purpose.

 

[nigelmercier]

Alternatively, skip the incoming breaker entirely. My boat wasn't wired with one originally, so when I added a CU I saw no reason to add one, just MCBs on the various circuits.

 

[VicS]

Garage consumer units are usually just RCD plus 1x 16 amp mcb and 1x 6amp mcb I fyou want more than two circuits then I dont think a garage consumer unit is what you want

Incorrect
6 way ones, and others, avaialble

 

[lumphammer]

Currently I have one breaker in the incoming 240v supply shorepower line. I am just about to add a generator to this so thought l would upgrade the 240v system. My plan is to put in a garage consumer unit, 6 way. So far so good. However I note that most marinas run on a 16amp supply, so is there any need for any MCB to be any bigger than this? Most boxes I see have a domestic 63A incomer, but l was going to reduce this to either 30 or even 16 amp supply.

The genny will be a 4kw unit.

Having done that I was going to have the interior circuits as, sockets 16amp, immersion 6amp, batt charger 10amp. Does this seem ok or do you use a different regime?

The RCD and 63A incomer you refer to is normally the max current the switch will take. It is for isolation and leakage protection and doesn't provide any over current protection. That is done by the individual mcbs that protect each circuit.

 

[VicS]

Currently I have one breaker in the incoming 240v supply shorepower line. I am just about to add a generator to this so thought l would upgrade the 240v system. My plan is to put in a garage consumer unit, 6 way. So far so good. However I note that most marinas run on a 16amp supply, so is there any need for any MCB to be any bigger than this? Most boxes I see have a domestic 63A incomer, but l was going to reduce this to either 30 or even 16 amp supply.

The genny will be a 4kw unit.

Having done that I was going to have the interior circuits as, sockets 16amp, immersion 6amp, batt charger 10amp. Does this seem ok or do you use a different regime?

I take it this is the sort of thing you have in mind

It has a 30mA double pole RCD rated at 63amps max load, which is not an overcurrent protection device, and 6 mcbs rated at 2x 20 amps, 1x 16 amps and 3x 6amps all in an IP65 weatherproof enclosure

I imagine you can change the mcbs to ones of different, more appropriate, ratings or even start with a similar blank enclosure and fit an RCD and mcbs of your choice.

With this your overall overcurrent protection relies on circuit breaker on the pontoon supply

 

[All_at_Sea]

just the job. Thanks VicS