Recommended current leakage in mA for RCBO on boat?

[Vega1447]

My surveyer has rightly insisted that I install an RCBO between my 220V shore power supply and the below decks consumption (battery charger, dehum...).

A friend who is wiser than I suggested something between 30 and 50 mA current leakage rating so that I won't get too many false positives.

What does the forum think?

The boat will be afloat on fresh water from next week - as fresh water is a poor conductor does that suggest something like 40-50 mA?

Thanks in advance for any replies.

 

[Boater Sam]

30 mA is the recommended for personal protection.

 

[Gumpy]

I have never seen a false positive with an RCBO, if it trips there is a fault or several faults adding up to above the trip current.
30ma will be fine any higher and it's a waste of time.

 

[Channel Sailor]

In the UK, possibly elsewhere too (including the EU), the marina trip on the pontoon will be 30mA (and it will operate within maybe 40mS depending on the amount of fault current). Also if on the Hard in a quality yard it is likely there is a 30mA trip somewhere in the supply. So if the one of the yacht is a 30mA then it will be a race as to which one trips first, depending on the manufacturers operating time characteristics) . If boat one is greater than 50mA then it is unlikely to trip first. If less then 30mA then it probably will operate before the marina pontoon pillar trip.

In some yards (and non UK marinas) it could be there is not a 30mA RCD installed. So I would say in these cases, having your own 30mA on board is good for when you hook up your 16A supply in a location without a 30mA trip. UK and other safe properly provided supplies will use their own RCD on your socket that, when it trips, will break both the Live and the Neutral.

Your RCD if on board should also break the live and neutral together, just in case it does trip first. Because you do not want the Neutral left connected after your on board RCD has tripped out. Also if you have an RCD on board and you rely on it, then test it quarterly with the test button. If you know for sure there is not a shore side RCD, then I suggest ask a professional to check your on board RCD every few years. They do fail.

Basically, if in a UK or similar standard marina or a quality yard supply, then an on board 30mA RCD probably adds some confusion or is unnecessary. This is because behind the marina pillar socket is your own RCD anyway, that is tested by the operator every quarter and professionally tested every few years. I would guess this applies in a reasonable quality EU marina/yard as well, but others here I am sure have first hand experience of non UK marina/yards electrics.

But.... .. there is always a but.... some appliances on board such as largish de humidifier, single induction hob and switch mode chargers can confuse RCDs. So there are various types of RCD available to get around this problem. A "Type AC" RCD is your standard inexpensive device which is for resistive loads (e.g. kettle, heater and small electronic appliances) only. Available more commonly at reasonable prices is the Type A RCD, which is better for anything with and electric motor, single ring induction hob, modern house battery chargers and if you have a lot of computer equipment. So if you had a Type A RCD on board and a vessel with more than the just basics to power, then your Type A 30mA RCD will trip first (and safely) before the probably marina/yard Type AC 30mA RCD (which may not trip at all). This is because the Type AC RCD can be baffled by the electronic and inductive loads. Hence why leading quality manufacturers of RCDs for domestic use now offer only Type A RCDs or other more technical products, they do not bother producing the basic old Type AC.

To avoid a "race" issues between RCDs in series, the upstream RCD (for example on the Pontoon) can have a delay configured so it does not trip first. Though I think it is unlikely a pontoon socket would have a delay RCD on it. Maybe another in series 30mA RCD upstream again at the pontoon to shore connection point might/would have a delay configured, this would be sensible.

The 30mA value has been decided on because it has been deemed that above this level of current one could be electrocuted to cause injury or death.

100mA RCDs were mostly intended to protect against fire risks. 10mA RCD trips are available though not all that common.

Once you go above 16A max supply on a socket, house boat supplies, and larger installations. Then a marine professional I would say is needed, and maybe there is someone here that is exactly that.

 

[Vega1447]

Many thanks to all who answered!

 

[davidpbo]

30ma is the usual RCCD (Residual Current Circuit Device) trip current for a final circuit and is intended to prevent a fatal electric shock. RCCDs with higher trip currents are usually used in the distribution network.

A 10ma trip might be used on a final curcuit in agricultural buildings and other wet locations.

As far as I know the different Type ratings relate to the current handling characteristics of over current protection devices such as MCBs (Miniature Circuit Breakers) . You can if course get combined MCB and RCCDs.

On my simple installation (2 doubles and 1 single socket, no battery charging or connection to the boat 12V system) I did use a 10ma trip in the distribution board, it has never tripped and I do check it both with the test button and occasionally an installation tester.

 

[PaulRainbow]

My surveyer has rightly insisted that I install an RCBO between my 220V shore power supply and the below decks consumption (battery charger, dehum...).

A friend who is wiser than I suggested something between 30 and 50 mA current leakage rating so that I won't get too many false positives.

What does the forum think?

The boat will be afloat on fresh water from next week - as fresh water is a poor conductor does that suggest something like 40-50 mA?

Thanks in advance for any replies.

The RCD, RCBO etc on a boat should have a maximum sensitivity of 30ma.

But, before you rush and and buy one, what other protection does your shore power installation have ? Do the individual circuits have MCBs, or is there just a single circuit, with everything plugged into sockets, suitably fused ?

 

[lustyd]

Just remember that whichever you fit it won’t make your installation safe, it makes it less dangerous. It’s entirely possible on a boat to get electrocuted without tripping one of these devices. Remember that they only trip if there’s a difference in current so you can pass 16A through yourself and it will be more than happy to oblige. I’ve had several failures on boats which didn’t trip the system. In one case my shore power cable burned £5 of electric while cut in half and dangling in the water. I’m sure it was quite spectacular for a while!

 

[davidpbo]

The RCD, RCBO etc on a boat should have a maximum sensitivity of 30ma.

But, before you rush and and buy one, what other protection does your shore power installation have ? Do the individual circuits have MCBs, or is there just a single circuit, with everything plugged into sockets, suitably fused ?

To clarify, RCCD sensitivity increases as the leakage current rating decreases. E.g. a 10ma trip will trip at a lower current imbalance than a 30ma trip.

Be wary of RCBOs they are often single pole devices and only break the (Hopefully) Live leg of the circuit. Likewise the commonly available single gang MCBs.

And yes, other fusing needs to be appropriate for the size of the cables used in the installation, probably 16A for anything using 2.5mm cable and less for smaller.

I’ve had several failures on boats which didn’t trip the system. In one case my shore power cable burned £5 of electric while cut in half and dangling in the water. I’m sure it was quite spectacular for a while!

That is the fault of the tripping arrangements to the supply socket on shore if the faults did not trip the power. Fuses are intended to protect the circuits after them, not before, so any arrangement on the boat is would not protect the shore power cable before it.

 

[PaulRainbow]

To clarify, RCCD sensitivity increases as the leakage current rating decreases. E.g. a 10ma trip will trip at a lower current imbalance than a 30ma trip.

Be wary of RCBOs they are often single pole devices and only break the (Hopefully) Live leg of the circuit. Likewise the commonly available single gang MCBs.

And yes, other fusing needs to be appropriate for the size of the cables used in the installation, probably 16A for anything using 2.5mm cable and less for smaller.

Not sure why you would think i didn't know any of that David

There are plenty of double pole RCBOs available and it's a requirement under current reg's to fit them, it isn't a requirement to fit double pole MCBs though.

 

[davidpbo]

Not sure why you would think i didn't know any of that David

You may know that, other people may not which is why I wrote "For clarification"

It was interesting using a search for RCBO on the CPC web site. Many initial descriptions said single pole, others said single module, going to the description some single module RCBOs (At least) stated 2 pole. So it would seem single pole is single pole, single module is (Maybe) 2 pole, but best to check.

 

[PaulRainbow]

You may know that, other people may not which is why I wrote "For clarification"

It was interesting using a search for RCBO on the CPC web site. Many initial descriptions said single pole, others said single module, going to the description some single module RCBOs (At least) stated 2 pole. So it would seem single pole is single pole, single module is (Maybe) 2 pole, but best to check.

I think you'll find that single module, double pole, RCBOs are only double pole for the RCD part of the device, for CPD purposes they behave the same as a single pole MCB.

 

[lustyd]

That is the fault of the tripping arrangements to the supply socket on shore if the faults did not trip the power. Fuses are intended to protect the circuits after them, not before, so any arrangement on the boat is would not protect the shore power cable before it.

No it’s because the return path goes via the rcd so the two wires have the same current. Rcd trips if there’s a mismatch. A cable in the water can work exactly like a kettle element, and a human between two wires will quite happily fizz away if insulated properly to avoid leaked current

 

[davidpbo]

I find it difficult to believe the flow and return current in a severed cable dangling in water would be sufficiently well balanced to not trip a correctly functioning RCCD. l am not saying it is not theoretically possible.

 

[lustyd]

Surprised the heck out of me too. It did eventually trip but only after burning £5 of electric. The other incident was a 4 gang socket that filled with water from condensation. That one also eventually tripped and took the marina days to locate.
Regardless, the point is that and RCD makes it less dangerous, not safe. You can and will still get electrocuted on a protected circuit!

 

[Channel Sailor]

re 230V single pole v double pole trips/isolators/switches on a boat on a marina shore power. The reason Marina electrical installation regulations state RCDs must be double pole is because in a Marina the neutral might not be at the same voltage as the earth. A Single pole RCD or RCBO on board might well trip out for an earth leakage fault, but if a person is still holding the neutral in one hand and the Earth of an appliance in the other, then they could still get an electric shock of more than 30mA.

You might wonder how one could end up with a neutral in your hand. Well, if the original fault on board was a Live wire exposed on a heater and you grabbed it (with other hand on the heater chassis) then the 30mA RCD would probably trip. But if the trip is only single pole in the Live, then your hand is now connected to the Neutral because of the low resistance back via the heater element. If the neutral is not sufficiently bonded to earth at the Marina end, then a small voltage exists between the chassis in one hand and the wire in the other. If more than 30mA flows then risk of death! Also you are hung up on it because there is nothing except a 16A fuse to cut off the electricity. Hence why a double pole is needed.

Same applies to 230V switches/isolators on board, bear in mind that if for maintenance purposes you switch off an MCB or a single pole switch in the live, then the neutral is still connected through to the Marina and it might not be at the same voltage as the onboard earth. So if switching off for maintenance of safety reasons, then use a double pole switch or unplug the appliance, or unplug the boat from the pontoon supply.

In a house, in most cases, the neutral is bonded to earth with a hefty connection. This keeps the earth and neutral at the same voltage. In exceptional cases where the neutral is not bonded to the earth, then Regulation states that double pole RCDs shall be employed.

 

[PaulRainbow]

re 230V single pole v double pole trips/isolators/switches on a boat on a marina shore power. The reason Marina electrical installation regulations state RCDs must be double pole is because in a Marina the neutral might not be at the same voltage as the earth. A Single pole RCD or RCBO on board might well trip out for an earth leakage fault, but if a person is still holding the neutral in one hand and the Earth of an appliance in the other, then they could still get an electric shock of more than 30mA.

You might wonder how one could end up with a neutral in your hand. Well, if the original fault on board was a Live wire exposed on a heater and you grabbed it (with other hand on the heater chassis) then the 30mA RCD would probably trip. But if the trip is only single pole in the Live, then your hand is now connected to the Neutral because of the low resistance back via the heater element. If the neutral is not sufficiently bonded to earth at the Marina end, then a small voltage exists between the chassis in one hand and the wire in the other. If more than 30mA flows then risk of death! Also you are hung up on it because there is nothing except a 16A fuse to cut off the electricity. Hence why a double pole is needed.

Same applies to 230V switches/isolators on board, bear in mind that if for maintenance purposes you switch off an MCB or a single pole switch in the live, then the neutral is still connected through to the Marina and it might not be at the same voltage as the onboard earth. So if switching off for maintenance of safety reasons, then use a double pole switch or unplug the appliance, or unplug the boat from the pontoon supply.

In a house, in most cases, the neutral is bonded to earth with a hefty connection. This keeps the earth and neutral at the same voltage. In exceptional cases where the neutral is not bonded to the earth, then Regulation states that double pole RCDs shall be employed.

This is incorrect. Marina shore power systems are required to have double pole Earth leakage protection and the neutral must be bonded to Earth at the pontoon.

It is also a regulatory requirement for all new builds that all onboard power sources,( generators or inverters) have their neutral and earth bonded at source. All vessels must have a double pole earth leakage protection device.

 

[Channel Sailor]

The is getting very technical and is a subject area I am not specifically familiar with, but in the interests of my own enlightenment because I could be wrong, here goes. Re PaulRainbow post above. My post was informed by BS7671 2018 Section 709 , Marinas and Similar Locations, (Possibly slightly out of date as I have not cross checked all the recent amendments), Regulation 709.411.4 says that in accordance with Electrical Safety, Quality and Continuity Regulations “Prohibit the connection of a PME earthing facility to any metalwork in a boat.”

PME meaning a shore supplied system where somewhere on the marina premise the neutral is bonded to the safety earth conductor/wire that is also used to supply pontoons..

Now it could be I have mis interpreted the regulation here and if so then I would be pleased to be corrected.

what happens onboard with generators is different and I get that a neutral or some part of the windings, would need to be bonded to earth, as paulrainbow says. Without it, the usual safety devices would not work as expected.

 

[PaulRainbow]

The is getting very technical and is a subject area I am not specifically familiar with, but in the interests of my own enlightenment because I could be wrong, here goes. Re PaulRainbow post above. My post was informed by BS7671 2018 Section 709 , Marinas and Similar Locations, (Possibly slightly out of date as I have not cross checked all the recent amendments), Regulation 709.411.4 says that in accordance with Electrical Safety, Quality and Continuity Regulations “Prohibit the connection of a PME earthing facility to any metalwork in a boat.”

PME meaning a system where the neutral is bonded to the safety earth conductor/wire.

Now it could be I have mis interpreted the regulation here and if so then I would be pleased to be corrected.

All AC power sources must have the neutral bonded to Earth, so for shore power, that means at the marina, not on the boat. But inverters and generators must be bonded at source too, so that's obviously on the boat.

In post #16 you seem to be under the impression that the marina supply might not be bonded, which would be incorrect (or it should be).

So, in short, all AC supplies should be bonded at source and both the marina and the onboard consumer unit must be fitted with double pole RCD/RCBOs.

 

[VicS]

All AC power sources must have the neutral bonded to Earth, so for shore power, that means at the marina, not on the boat. But inverters and generators must be bonded at source too, so that's obviously on the boat.

In post #16 you seem to be under the impression that the marina supply might not be bonded, which would be incorrect (or it should be).

So, in short, all AC supplies should be bonded at source and both the marina and the onboard consumer unit must be fitted with double pole RCD/RCBOs.

That is correct but its not that simple

There are basically three earthing systems that are used in the UK: TT, TNCS and TNS

A TNCS system must not be for marina pontoon supplies ( nor for caravans or things like marquees at outdoor events

PME, to which channel sailor refer, is a TNCS system with multiple earthing of the combined PEN conductor. He is therefore correct in saying that a PME system must not be connected to boats
A TNS ( or TT) system must therefore be used .