16 or 32 amp...which can I use?

[MapisM]

in any boat installation its save / a obligation to have one main cirquit breaker, in order to cut the shore supply in case of a problem.
this should be rated the size of the supply cable and connectors.

I wholeheartedly agree that a master breaker onboard, downstream of the dock socket(s), should always be installed.
I don't think that's somehow mandatory for boat builders, though.
In fact, I've seen some boats (also CE-A rated, btw!) where the main leads go straight to a master RCD-only device, and from there to all the specific breakers (in parallel, so to speak).
And in these installations, the scenario that seastoke envisaged in his post #13 definitely has a chance to materialize.

 

[Seastoke]

Correct M also take a scenario where a boat has a 16amp inlet also a 16amp breaker on board, is all safe ,yes if you are plugged into a 16amp socket on dockside and have a 2.5 cable. Now take the same boat but plugged into a32amp socket with 2.5 cable and 16 amp outlet to the boat , the inlet starts to melt as it has a fault in it sets fire to boat and the next boat . Would insurance pay out ,big gamble.

 

[petem]

Correct M also take a scenario where a boat has a 16amp inlet also a 16amp breaker on board, is all safe ,yes if you are plugged into a 16amp socket on dockside and have a 2.5 cable. Now take the same boat but plugged into a32amp socket with 2.5 cable and 16 amp outlet to the boat , the inlet starts to melt as it has a fault in it sets fire to boat and the next boat . Would insurance pay out ,big gamble.

Yeah but as we keep saying, any half decent boat will have a breaker adjacent to the shore power socket. If it doesn't then it would be wise to fit one as you should not be reliant on the marina breakers to be correctly rated. Does your boat not have one?

 

[Seastoke]

Yeah but as we keep saying, any half decent boat will have a breaker adjacent to the shore power socket. If it doesn't then it would be wise to fit one as you should not be reliant on the marina breakers to be correctly rated. Does your boat not have one?

Yes it does Pete but you are missing the point, the inlet on your boat is rated at 16amps if it is supplied by a 32 amp breaker , there is the problem , no short circuit protection it could cause a fire ,

 

[MapisM]

Nope seastoke, the circuit is protected anyway, in the setup that myself, petem and bartw are describing - it just isn't very intuitive.
So, since I think we are a bit at cross-purposes, I made a (pathetic, sorry) drawing, to try to sort this out.

First of all, let's assume to have a boat whose AC circuit is designed for 16A max.
This means that the dark red cable with its plugs, and also the red cable that goes from the stern socket to the electrical panel, are all sized for 16A.
Let's also assume (as is normally the case) that the single RCDs in the electrical panel (i.e. the small rectangles in the electrical panel "2"), all together, account for MORE than 16A.

As I understand, what you are saying is that if you attach the dark red cable to a 32A socket on the dock, and you use all the onboard appliances, you might draw much more than 16A (say for instance 30A) without tripping any RCD, because the dockside RCD is rated for 32A, and the single RCDs in the electrical panel are - individually - still within their rated max current.
So, this condition can indeed happen, and can potentially last forever, allowing plenty of time to overheat both the dark red cable outside the boat and the red cable inside, eventually risking to set the boat on fire.
Otoh, if you would have attached the dark red cable to the 16A socket on the dock, you would have been protected by the RCD inside the service bollard.
Now, if this is the point you are making, I think you are 100% correct.

But, and it's a big but, our objection is that in a properly designed boat electrical system, there should be also a master RCD in position "1", just downstream of the external socket, rated for the max current that the circuit is designed to withstand - in this example, 16A.
So, if you assume to have such RCD, you can see why it becomes irrelevant whether you are connected to a supply capable to provide only the 16A which you will need, or 32A, or also much more.
In fact, as soon as you turn on enough devices onboard that all together demand 30A, the onboard master 16A RCD will immediately trip off, even if the dockside RCD could supply 32A or whatever.
Theoretically, I guess you might still argue that if the external (dark red) cable+plug is rated for 16A, it isn't correctly protected when connected to a dockside 32A RCD.
But in practice, it's totally irrealistic to think that the current in excess of 16A potentially flowing through it for just a fraction of a second (before the onboard master RCD trips off) could be enough to damage it - let alone overheating it.

Just as a last consideration, what I already said in my post #21 still stands: in a boat that does NOT have the master RCD "1" (and indeed I have seen some!), your concern is absolutely valid.
To anyone who doesn't have such master RCD, my personal recommendation is to fit it PDQ, regardless of whether they always use a dockside socket of the same capacity or not.
In fact, I'd rather not trust the dock service bollards alone, because I've seen all sorts of malarkies inside them, including bypassed RCDs just because "they kept tripping off"...! :ambivalence:

 

[BartW]

Mapism, I think that Seastoke's point is;
even, if you have the master breaker "1" (16A) on the stern of boat, and all dark red cabling rated 16A, when youn plug that in to a 32A shore socket,
you might have a problem in case there is fe a short in the stern plug, creating a curent of more than 16A, and less then 32A ... and potential risc of fire,

I have no defense to that statement, he is ofcause correct,
I can only say that this is situation that my boat is almost permanently in, and that I can sleep well with it.

cabling, and stern sockets, stern cirquit breakers are all 40A,
and these are currently connected to the 90A shore supply.

but I'm sure that in the med there are many many more situations that are much more riscfull.

 

[petem]

Thanks Seastoke, MapisM and Bart, feels like we're getting there now! As for insurance paying out, I'd say the scenario described by Bart above would still be classified as an accident and therefore insurance would still pay out.

 

[Seastoke]

Just one point , or two an rcd detects earth faults not amperage the amperage on a red is what amps it can switch, it is the circuit breaker that protects overload and short circuit , you can have a device that does both it's called RCBO . But just remember that most faults on boats are in the leads and plugs with being in the elements.

 

[Seastoke]

Now i have said before when you wander around marinas the leads are very poor, and I discuss this with our marina as they have a duty of care to people and boats , I think boat leads should be pat tested annually as in factories and no I don't want the job. By the way map have you thought of going in to boat design.

 

[RupertW]

Now i have said before when you wander around marinas the leads are very poor, and I discuss this with our marina as they have a duty of care to people and boats , I think boat leads should be pat tested annually as in factories and no I don't want the job. By the way map have you thought of going in to boat design.

You said “pat tested” - it’s deja vu all over again. To help me calm down I’ll go and get one of those free pizza pies being given away.

 

[Andy Cox]

I'd like to add an extra dimension to this , which is is quite typical for a lot of us........a genny.

I have a 32A socket on the transom and a 12kva genny which should be able to chuck out circa 50A. What is the defined protection for this type of set up? Would it be a 32A RCBO next to the input socket at the transom and a 50A RCBO at the genny output, to give overload / short as well as earth leakage fault protection to the cabling between the two input sources and the individual circuit breakers on the 240 distribution panel?
Would I need any other type of RCD protection in the system.
Maybe this should be in a new thread?
Andy

 

[MapisM]

an rcd detects earth faults not amperage

Apologies, my mistake.
In all points where I wrote "RCD" in post #25, it's actually a breaker that I was referring to.
In most boats that I've seen, there is indeed also a master RCD, inside the electrical panel, downstream of the breaker "1" and upstream of all line-specific breakers.
I can't remember to have ever seen RCBOs on boats, at least not those built by IT yards.
In fact, while RCBOs are indeed available also here, they are nowhere near as frequently used as the combination of two separate devices in cascade.
Btw, funnily in my post #21 I did mention RCD correctly... I'm just not enough used to debate this stuff in EN to use the correct terms "automatically", so to speak!

 

[MapisM]

I have a 32A socket on the transom and a 12kva genny...

I have a very similar setup on my boat (11 rather than 12kVa genset, buts still not far from 50A anyway, while the dock socket is 32A).
And no RCBOs on the genset line, as well as I have none on the dock line.
There is only an integrated 50A breaker on the (Kohler) genset panel.
Obviously, the wiring is sized accordingly, and it goes to the "dock/genset/none" isolating switch in the electrical panel.
The only master RCD is in the electrical panel, downstream of the isolating switch.
Which in turn means that such RCD protects the whole onboard AC circuit regardless of whether the current is provided by the dock or the genset.

 

[Seastoke]

You said “pat tested” - it’s deja vu all over again. To help me calm down I’ll go and get one of those free pizza pies being given away.

Can you enlighten me please.