Shore power consumer unit question

[Boo2]

Hi,

Shore power consumer units has cropped up as a topic in the past so apologies if this seems like unnecessary repition. I am thinking of installing a garage unit like this one from Screwfix : http://www.screwfix.com/p/mk-sentry...liateWindow-_-Sub+Networks-_-DeepLink-_-78888

My understanding is that boat shore-power useage needs dual pole RCBOs because you cannot tell which way up the supply will be (ie live might be swapped with neutral by someone's splitter cable). My understanding also is that the generally available dual pole RCBOs are double module, ie you can only fit one of them into a 4-way garage CU like that linked.

My understanding is that lighting is preferred to be run off of a different circuit from everything else so you are not left in the dark when things go wrong.

So for a typical boat install, what is the best thing to do ? Run everything, including fixed wired charger from a single circuit off one dual pole RCBO ? Or go for a 6-way garage unit (if these are available ?) ? Or polarise the on-board mains by tying neutral to the ship's earth ? Or what ?

Concrete recommendations preferred, along with links to suitable equipment on the UK web.

Many thanks,

Boo2

 

[David2452]

The unit you show already has the correct DP RCD and is the one I use for simple small installs, you can easily replace the 16a & 6a MCBs with double pole ones, they are available the same size as the single one's so no need for a larger unit. The MK is IP65 which is about as much as you can hope for a consumer unit, bur be sure to retain that integrity with the mounting screws and cable entries. Normal practice is to use the 16a for the power circuit and if you have low voltage AC lighting then use the 6a, if your lighting is extra low voltage DC then use the 6a (or appropriate replacement) for another circuit, e.g. charger or immersion. There is no need for RCBOs with that RCD present.

 

[Boo2]

The unit you show already has the correct DP RCD and is the one I use for simple small installs, you can easily replace the 16a & 6a MCBs with double pole ones, they are available the same size as the single one's

Sorry, where ? I looked and all the double pole RCBO / MCBs I could find were double width.

<Edit: Actually, I have seen these http://www.electricalcomponentsdire...t-RCBO-2-pole-C-curve-16A-RCBO-30mA--235.html which do fit the bill...>

Boo2

 

[David2452]

Sorry, where ? I looked and all the double pole RCBO / MCBs I could find were double width.

Boo2

The ones I use are Schneider Merlin Gerin, I'm sure a search will find some retail.

 

[Lon nan Gruagach]

Hi,

Shore power consumer units has cropped up as a topic in the past so apologies if this seems like unnecessary repition. I am thinking of installing a garage unit like this one from Screwfix : http://www.screwfix.com/p/mk-sentry...liateWindow-_-Sub+Networks-_-DeepLink-_-78888

My understanding is that boat shore-power useage needs dual pole RCBOs because you cannot tell which way up the supply will be (ie live might be swapped with neutral by someone's splitter cable). My understanding also is that the generally available dual pole RCBOs are double module, ie you can only fit one of them into a 4-way garage CU like that linked.

My understanding is that lighting is preferred to be run off of a different circuit from everything else so you are not left in the dark when things go wrong.

So for a typical boat install, what is the best thing to do ? Run everything, including fixed wired charger from a single circuit off one dual pole RCBO ? Or go for a 6-way garage unit (if these are available ?) ? Or polarise the on-board mains by tying neutral to the ship's earth ? Or what ?

Concrete recommendations preferred, along with links to suitable equipment on the UK web.

Many thanks,

Boo2

You will only need one RCD since there will almost certainy never be a situation where several partial earth leaks add upto enough to trip the main incomming.
In the unit you linekedthe large switch on the left is the RCBO, as David2452 states the MCBs should be changed for double pole.
Given your apparet lack of understadng of mains wiring I strogly sugest you have an electrcian do the installation.

 

[Boo2]

You will only need one RCD since there will almost certainy never be a situation where several partial earth leaks add upto enough to trip the main incomming.
In the unit you linekedthe large switch on the left is the RCBO, as David2452 states the MCBs should be changed for double pole.
Given your apparet lack of understadng of mains wiring I strogly sugest you have an electrcian do the installation.

Ah, actually...

The CU, like all CUs, does only have one RCD. It has the facility for several MCBs / RCBOs. The need for more than one MCB/RCBO has nothing to do with the earth leaks, it has to do with not wanting to trip all circuits owing to an overcurrent in one of them.

The large switch on the left in the picture on the page I linked to is the RCD.

Boo2

 

[nigelmercier]

I've just fitted a new consumer unit. Standard 30mA RCB and MCBs, I don't understand the need for the dual-pole devices.

 

[Boo2]

I don't understand the need for the dual-pole devices.

AIUI, if the mains is reversed then a tripped single pole MCB/RCBO can leave a line live while at the same time the equipment connected to it is showing dead and the MCB/RCBO switch is down indicating the same. Of course the RCD should save your life, but do you really want to get a jolt ?

Boo2

 

[prv]

The need for more than one MCB/RCBO has nothing to do with the earth leaks, it has to do with not wanting to trip all circuits owing to an overcurrent in one of them.

If it's not about earth leaks, then why the separate RCBOs instead of just using MCBs and a single RCD?

Pete

 

[Boo2]

If it's not about earth leaks, then why the separate RCBOs instead of just using MCBs and a single RCD?

Yes, you can do that and I don't think there's anything particularly preferable about individual RCBOs rather than MCBs, personally (so long as there's an overall RCD, obviously).

Boo2

 

[VicS]

AIUI, if the mains is reversed then a tripped single pole MCB/RCBO can leave a line live while at the same time the equipment connected to it is showing dead and the MCB/RCBO switch is down indicating the same. Of course the RCD should save your life, but do you really want to get a jolt ?

Boo2

Perhaps if you are concerned about reversed polarity then you should incorporate a "reversed polarity warning light"

The diagram below shows a simple low voltage AC installation incorporating a reversed polarity warning light, N

E is the 2 pole RCD/ isolator and H the two mcbs in your Garage unit.

I could be your battery charger ( or AC lights)

J would be your 3 pin 13 amp sockets

If you carry a polarity reversing adapter lead you can then correct the reversed polarity when warned by the warning light

If you want the idea can be extended to include a second indicator light between live and earth to show when the polarity is correct

 

[prv]

Yes, you can do that and I don't think there's anything particularly preferable about individual RCBOs rather than MCBs, personally (so long as there's an overall RCD, obviously).

Ah, ok, I'd got the impression you were determined to use RCBOs.

For what it's worth, my system uses an overall RCD and then a single pole MCB for each of battery charger, water heater, and socket circuit (which is radial rather than ring). Standard small UK domestic system really. Next to the (double pole) master on/off switch is a panel with a momentary "test" button that connects in the guts out of one of those tester plugs; this can be used to check the polarity (among other things) before turning on the rest of the system. I have a short (and well-labelled) lead which swaps polarity to be inserted if required.

Admittedly this goes against my usual principle that wherever possible systems should just work without manual intervention, so the polarity-agnostic system you have in mind would be better. But so far on the UK south coast and adjacent bits of France, I haven't found a backwards supply anyway. Perhaps there was a time when French marinas frequently offered a tatty domestic 2-pin socket wired up at random, but perhaps those days are past, at least in the places most of us visit?

Pete