Consumer Unit

[DandGNWales]

Hi All,

The boat re-fit is about to gather pace, so here is yet another question:

 

What size consumer unit do I need for the 240v electrics?

 

At the moment she is wired just like a caravan but with no curcuit breakers, so to get her through her Boat Safety we will need to start afresh and fit a new consumer unit, so what little knowledge I have, I thought the following

 

1 for 240v sockets

1 for 240 Lights

as we have no invertor I will have to read up a lot (Just ordered the book How to fit out a narrowboat)

 

So would a 5 channel unit suffice or is bigger better?

[matty40s]

Forget 240v lights, stick to 12v and get led.

You have a lot of reading to do!

[by'eck]

I used a small unit purchased from CEF with space on the DIN rail for two RCBO's and four MCB's.

 

[jonathanA]

you would need to think about what your 'AC' system should look like. will you have shore power now or in the future ? will you want to hook up a generator ?

 

If you don't know or just need a 'basic' system to get you going using an inverter or shorepower only then look for a 'garage' type consumer unit with a main RCD and space for 2 MCBs. I would recommend a 16A MCB for your sockets and a 6A for 'anything else' even if you don't know what that is yet. This is what a typical garage/shed consumer unit will come with and they can be had for around £25 from the usual suspects.

You can worry about complicating the set up to accomodate shore power/generators etc in the future

 

Its worth looking at these pages for some idea of the issues around AC systems I doubt any book on boat fitting comes near these pages for authoritive design information.

 

http://www.smartgauge.co.uk/nb_ac_sys.html

[nicknorman]

Our boat just has one RCD and one 16A MCB. But then we only have mains sockets and no mains lighting (why would you want mains lighting, unless you are permanently marina based?). This has the advantage that the one MCB represents the maximum current from the 16A shore power lead / connectors. Once you start to have several MCBs with an overall rating higher than the shore lead connectors etc, you can overload the connectors without anything blowing, which is not a good way to do things IMO.

[Happy Go Lucky]

I like to see the main isolator (usually what people think of as the RCD) with a rating no higher than the supply connector. This is usually 16 Amps so you may have to replace the one that comes with the unit.

 

There are a lot of firms selling what are called 'garage' consumer units. These contain the RCD incomer and space for two or three MCBs. This will fulfil most people's needs.

[Alastair]

why have 'mains' lighting?

 

Because fittings and spares are affordable, widely available and (compared to marina 12V stuff) cheap! You also don't have to worry about voltage drops on long runs.

 

A few 12V lights for 'instant on' lighting in key areas, and some 240V lighting is a good mix, imo.

[DandGNWales]

Well, I have just been on another spending spree, new Leasure Batts, new starter batt and ended up getting a unit with 5 MCB's to future proof the system and agree with Alastair a good mix of 12v for instant and like the option of some 240Vac as my eyes tend to suffer in low light if trying to read etc, so will get it installed and fingers crossed when I secure the batts get a BSC pass, then get her licensed ready for the mega journey Wales bound, wish us luck, we are going to need it

[nb Innisfree]

We have all 240v lighting, triphosphor tubes run from a Victron, they are ecomical and give off loads of light.

[DandGNWales]

We have all 240v lighting, triphosphor tubes run from a Victron, they are ecomical and give off loads of light.

I will look into them thanks for the info

[nb Innisfree]

I will look into them thanks for the info

 

Got ours from B&Q, expensive at £17.95 for the largest one (20 watt)

[smileypete]

I like to see the main isolator (usually what people think of as the RCD) with a rating no higher than the supply connector. This is usually 16 Amps so you may have to replace the one that comes with the unit..

If I'm reading right, you might be getting RCDs a little mixed up with RCBOs

 

RCDs only detect current imbalance

MCBs only detect current overload

RCBOs do both.

 

But RCDs do have a rated maximum working current. So they must be used with separate overcurrent protection, like an MCB, to ensure this maximum isn't exceeded.

 

cheers, Pete.

~smpt~

Edited October 1, 2013 by smileypete

[alan_fincher]

(deleted)

Edited October 1, 2013 by alan_fincher

[jonathanA]

I like to see the main isolator (usually what people think of as the RCD) with a rating no higher than the supply connector. This is usually 16 Amps so you may have to replace the one that comes with the unit.

 

There are a lot of firms selling what are called 'garage' consumer units. These contain the RCD incomer and space for two or three MCBs. This will fulfil most people's needs.

Incomer RCDs tend to come in 40/63/80A versions. The incoming wiring/connector will be protected by the 'bollard' or equivalent for shore lines - usually a mximum of 16A mcb possibly as little as 5 or 6 Amps though. Point is its the upstream device that needs to be sized accordingly. The main point of the RCD in these installations is for earth leakage detection,

[nicknorman]

Incomer RCDs tend to come in 40/63/80A versions. The incoming wiring/connector will be protected by the 'bollard' or equivalent for shore lines - usually a mximum of 16A mcb possibly as little as 5 or 6 Amps though. Point is its the upstream device that needs to be sized accordingly. The main point of the RCD in these installations is for earth leakage detection,

I'm not sure you have grasped Pete's point that the current rating of an RCD is the max current it can safely pass and interrupt. It's not a figure at which the RCD will trip (sorry if you have indeed grasped that!)

 

Bearing in mind the general principle that the fusing is to protect the cable not the appliance, I maintain that a boat supplied via 16A connectors and cable, should have a 16A breaker. One. Ok if you really want to, after that 16A breaker you could have several other ones in series for lighting immersion heater etc but really, is there much benefit from so doing? It doesn't even mean that an overload on the sockets won't put the 240v lights out because with two 16A breakers in series, which one will blow first? It does mean that an overload on the lighting circuit won't kill the sockets, but as I said, does it really matter?

[DHutch]

We have, one for ring main, one for charger, one for mains lights, single RCD up front.

- We only have one mains light, its never used, and only then because (because its there) the low voltage engine room lights are a bit naff for the job.

- Mains lighting is a very valid option if you plan to have an inverter running 24/7, although i would always retain a skeleton low voltage circuit, and/or twin inverters.

 

Cant see you needing any more, charger could be taken off the ring main, no real point it going for individual RCBOs as it basically is anyway!

 

Your limited to 16amp incoming, which should be protected at the bollard and/or before, and you cant really get any discrimination if you tried, certainly not on the ring main. Which is why new installations all have to have the 16amp 'bolloard mcb/rcd/rcbo' accessible and one per berth.

 

Are you having an inverter, if so, how does that integrate?

 

 

 

Daniel

[DandGNWales]

We have, one for ring main, one for charger, one for mains lights, single RCD up front.

- We only have one mains light, its never used, and only then because (because its there) the low voltage engine room lights are a bit naff for the job.

- Mains lighting is a very valid option if you plan to have an inverter running 24/7, although i would always retain a skeleton low voltage circuit, and/or twin inverters.

 

Cant see you needing any more, charger could be taken off the ring main, no real point it going for individual RCBOs as it basically is anyway!

 

Your limited to 16amp incoming, which should be protected at the bollard and/or before, and you cant really get any discrimination if you tried, certainly not on the ring main. Which is why new installations all have to have the 16amp 'bolloard mcb/rcd/rcbo' accessible and one per berth.

 

Are you having an inverter, if so, how does that integrate?

 

 

 

Daniel

I think we have bought the right unit then, so as it only has one leisure battery I will need to fit an Invertor so as we won't be running a washing machine but do have a 240 vac fridge so what size would I need ?, also what would I need to fit to get hot water from the engine?

[Alastair]

depends on your fridge. there will be a panel on the fridge giving the max current draw or wattage

[Happy Go Lucky]

If I'm reading right, you might be getting RCDs a little mixed up with RCBOs

 

RCDs only detect current imbalance

MCBs only detect current overload

RCBOs do both.

 

But RCDs do have a rated maximum working current. So they must be used with separate overcurrent protection, like an MCB, to ensure this maximum isn't exceeded.

 

cheers, Pete.

~smpt~

 

I should have made it clear that I like the main isolator to be a residual current device with overload protection (i.e. an RCBO) with a rating no higher than the supply connector. Most people I come across will refer to it as the RCD which, technically, it is!

 

I know that the supply connector should be protected by the upstream fuse but I am wearing a belt, braces and have a piece of string in my pocket just in case

[jonathanA]

I'm not sure you have grasped Pete's point that the current rating of an RCD is the max current it can safely pass and interrupt. It's not a figure at which the RCD will trip (sorry if you have indeed grasped that!)

 

Bearing in mind the general principle that the fusing is to protect the cable not the appliance, I maintain that a boat supplied via 16A connectors and cable, should have a 16A breaker. One. Ok if you really want to, after that 16A breaker you could have several other ones in series for lighting immersion heater etc but really, is there much benefit from so doing? It doesn't even mean that an overload on the sockets won't put the 240v lights out because with two 16A breakers in series, which one will blow first? It does mean that an overload on the lighting circuit won't kill the sockets, but as I said, does it really matter?

I have grasped the point.

 

I guess we'll agree to disagree as I would maintain that the cabling/connector ARE protected by the upstream (bollard) breaker which may not even be as high a rating as 16A.

 

 

Edited to remove a senior moment !

Edited October 3, 2013 by jonathanA

[nicknorman]

I have grasped the point.

 

I guess we'll agree to disagree as I would maintain that the cabling/connector ARE protected by the upstream (bollard) breaker which may not even be as high a rating as 16A.

 

 

Edited to remove a senior moment !

ARE? Or SHOULD BE? Yes, you are right they should be. At our marina I have no idea whether there are16A breakers in the bollards because you can't see them - I guess there are, behind a locked panel. It is probably a bit OTT but one could argue for self sufficiency regardless of whether or not the bollard is designed and installed correctly, especially if you are in the habit of roving to different marinas etc.

 

Another minor point is that if I turn on too many things I might blow the breaker inside the bollard. I wouldn't be able to reset it outside marina office hours. It would be better to have a lower rated breaker on the boat that I could reset. Yes, with 2x16A breakers in series, who knows which will blow first, but if the boat has multiple breakers exceeding 16A total I can be certain that it will be the bollard that blows first. Just a thought.

[by'eck]

ARE? Or SHOULD BE? Yes, you are right they should be. At our marina I have no idea whether there are16A breakers in the bollards because you can't see them - I guess there are, behind a locked panel. It is probably a bit OTT but one could argue for self sufficiency regardless of whether or not the bollard is designed and installed correctly, especially if you are in the habit of roving to different marinas etc.

 

Another minor point is that if I turn on too many things I might blow the breaker inside the bollard. I wouldn't be able to reset it outside marina office hours. It would be better to have a lower rated breaker on the boat that I could reset. Yes, with 2x16A breakers in series, who knows which will blow first, but if the boat has multiple breakers exceeding 16A total I can be certain that it will be the bollard that blows first. Just a thought.

 

Having used and abused power hook-ups in marina's between longitude 35°E and 90°W, it seems on average that marina owners/managers tend to err for the easy life and overrate power pedestal breakers (assuming there are any )

 

The only exceptions were in France where I couldn't boil a 1.2kW travel kettle without tripping the breaker. Probably also installed correctly at Antigua Yacht Club where they offer up to 400 amp 380 volt three phase hook ups, since an error there could take the whole island out

Edited October 5, 2013 by by'eck

[smileypete]

For a narrowboat a reasonable solution would be an RCCB (often referred to and labelled as an RCD) followed by a 16A MCB, both can often be had in a 'garage consumer unit'

 

I think it's good practice to ensure the boat loading cannot exceed the rating of the shoreline socket, on a narrowboat feeding everything through a 16A MCB will achieve this.

 

A better solution for an narrowboat and very likely mandatory for boats that travel further afield, would be an RCCB followed by a 2 pole MCB, in case a supply is reversed.

 

RCBOs can be a bit of a minefield so probably best stick to separate RCCB and MCB if at all poss.

 

cheers, Pete.

~smpt~

[NMEA]

As you are wish to conform the BSS you may as well do it to BS EN ISO 13297:2012 Small craft - Electrical systems - Alternating current installations which is the current standard we have to adhere to. Therefore you must fit a double pole trip free circuit breaker with RCD within 500mm of the incoming plug (unless you are encasing the cable in conduit) so make sure any CU you buy has DP trip free RCD, not just DP. Remember that any IP rating on consumer units is meaningless unless they are correctly installed with the proper cable glands to the same IP rating and also gaskets on the mounting hardware. As you appear to be regularly on shore power then a galvanic isolator should be used too in order to protect your immersed metalwork. As for the CU overcurrent protection, both in number and values then provided no individual MCB or RCBO exeeds 16a then fit what ever number you wish provided the are matched to the conductor rating. Oh, don't forget to bond the PE to the hull, afther the GI if used.

Edited October 6, 2013 by NMEA

[smileypete]

Dunno if you really need breaker 'diversity' on a boat with a 16A mains supply.

 

I s'pose if there's a inaccessible 16A shoreside breaker you could put any lighting and a few bits on a 6A breaker and the rest on a 10A breaker.

 

ETA another 'gotcha' with boat wiring is the need to use ferrules on the ends of fine stranded cable when used with standard electrical accessories.

 

cheers, Pete.

~smpt~

Edited October 6, 2013 by smileypete