Correct RCD

[Ex- Member]

Our consumer unit came with a mains swich already fitted, however it's a MBC switch/fuse.

 

I'm told We should have an RCD instead of the MBC but I'm unsure what one to get and the amperage, any help much appreciaed

 

 

Red double switch is a MBC

[nicknorman]

Our consumer unit came with a mains swich already fitted, however it's a MBC switch/fuse.

 

I'm told We should have an RCD instead of the MBC but I'm unsure what one to get and the amperage, any help much appreciaed

 

Red double switch is a MBC

You might be better to keep the double pole red switch, and replace the MCBs (the black switches) with RCBOs which combine the function of an MCB and an RCD. That way, a fault in one area of the circuitry won't take everything else out as well. I suppose it depends on how many different mains things you have, but if you think you need a 4 way consumer unit, presumably you plan a fair few. I think RCBOs are pretty standard at 30mA fault current trip or less, and you should chose a rating appropriate to the circuits connected to them.

 

Alternatively if you want to have one RCD instead of the red switch, it should be double pole ie switching live and neutral and rated to the max current - typically 16A from a normal shoreline, but possibly more if you have a powerful generator.

Edited October 10, 2012 by nicknorman

[steelaway]

You might be better to keep the double pole red switch, and replace the MCBs (the black switches) with RCBOs which combine the function of an MCB and an RCD. That way, a fault in one area of the circuitry won't take everything else out as well. I suppose it depends on how many different mains things you have, but if you think you need a 3 way consumer unit, presumably you plan a fair few. I think RCBOs are pretty standard at 30mA fault current trip or less, and you should chose a rating appropriate to the circuits connected to them.

 

Alternatively if you want to have one RCD instead of the red switch, it should be double pole ie switching live and neutral and rated to the max current - typically 16A from a normal shoreline, but possibly more if you have a powerful generator.

 

 

 

I think you will have to buy one that fits your consumer unit - there are many different makes.

I also think you may have to buy a bigger one than you need but the circuit breakers will keep every thing safe

This one is smallish ....RCD

 

Alex

[Chalky]

When I last bought one it was cheaper to buy an 80A RCD than a lower rated one. RCBOs aren't cheap. It may even be cheaper to change the whole consumer unit - there are often deals for units fully populated with switches, RCDs & MCBs at the biy DIY stores.

[nicknorman]

When I last bought one it was cheaper to buy an 80A RCD than a lower rated one. RCBOs aren't cheap. It may even be cheaper to change the whole consumer unit - there are often deals for units fully populated with switches, RCDs & MCBs at the biy DIY stores.

The only trouble with having no overall correctly rated breaker is that typically if you put on too many services on the boat, each of which is protected by a correctly rated breaker, you exceed the rating of the shore supply and it trips at the bollard rather than the boat (presuming the supply is correctly protected). This might mean just getting wet whilst you pop out to reset it, or it might mean calling out the marina staff to reset it if it beneath a locked panel - which might result in loss of power overnight etc.

 

I would therefore recommend having a double pole breaker (whether RCBO or MCB) that is rated to the max supply - as I said typically 16A for a shore line.

Edited October 10, 2012 by nicknorman

[Ex- Member]

The only trouble with having no overall correctly rated breaker is that typically if you put on too many services on the boat, each of which is protected by a correctly rated breaker, you exceed the rating of the shore supply and it trips at the bollard rather than the boat (presuming the supply is correctly protected). This might mean just getting wet whilst you pop out to reset it, or it might mean calling out the marina staff to reset it if it beneath a locked panel - which might result in loss of power overnight etc.

 

I would therefore recommend having a double pole breaker (whether RCBO or MCB) that is rated to the max supply - as I said typically 16A for a shore line.

 

Thanks for the replies, we will be on shore line for tthe next few months. The problem we have as Nick has sussed is that any overload on the boat causes a trip in the adjasent warehouse we get our power from. If this happens at night we have to wait for the depot to open in the morning to reconnect. So we want any trip to occur on the boat.

 

Although there's 4 outlets we don't acttually have that much 240. one trip is dedicated to the calorifier 1 KW element 2 are dedicalte to 4 single sockets port and the same starboard, the 4th dedicated to the twin tum washing maching max 600 wats. I do like the idea of tripping individually but that might be a bit OTT considering our light usage.

 

 

Something like this. Seems cheap compared to others, is tthis a trusted brand?

http://www.ebay.co.uk/itm/DOUBLE-POLE-16-AMP-TYPE-B-RCBO-2-MODULE-NEW-/160846619001?pt=UK_BOI_Materials_Supplies_Electrical_ET&hash=item257334a179#ht_600wt_1037

[Ex- Member]

The only trouble with having no overall correctly rated breaker is that typically if you put on too many services on the boat, each of which is protected by a correctly rated breaker, you exceed the rating of the shore supply and it trips at the bollard rather than the boat (presuming the supply is correctly protected). This might mean just getting wet whilst you pop out to reset it, or it might mean calling out the marina staff to reset it if it beneath a locked panel - which might result in loss of power overnight etc.

 

I would therefore recommend having a double pole breaker (whether RCBO or MCB) that is rated to the max supply - as I said typically 16A for a shore line.

 

Thanks for the replies, we will be on shore line for tthe next few months. The problem we have as Nick has sussed is that any overload on the boat causes a trip in the adjasent warehouse we get our power from. If this happens at night we have to wait for the depot to open in the morning to reconnect. So we want any trip to occur on the boat.

 

Although there's 4 outlets we don't acttually have that much 240. one trip is dedicated to the calorifier 1 KW element 2 are dedicalte to 4 single sockets port and the same starboard, the 4th dedicated to the twin tub washing maching max 600 wats. I do like the idea of tripping individually but that might be a bit OTT considering our light usage.

 

 

Something like this. Seems cheap compared to others, is tthis a trusted brand?

http://www.ebay.co.u...9#ht_600wt_1037

Edited October 11, 2012 by Julynian

[nicknorman]

Something like this. Seems cheap compared to others, is this a trusted brand?

http://www.ebay.co.u...9#ht_600wt_1037

 

Rolec is a reasonably well known manufacturer, but whether their RCBOs are a good product I don't know - they do seem quite cheap. Of course just because it has ROLEC and CE painted on, doesn't necessarily mean anything... At least it is a British seller so you will know where to post the charred remains if it doesn't work properly!

[jonathanA]

Hi never heard of the make myself but it appears to be an ok spec.

 

Most 'shop' bought consumer units come with 63 or 80A RCDS finding the smaller ones is more difficult, and you'd pay about the same (£10-15) for an individual RCBO to replace one of your 4 MCBS, I would say its worth a goo.

 

Most if not all these MCBs/RCBO/RCD's use a standard mounting (DIN rail) so you should be able to swap it easily enough.

 

I should point out I don't purport to be an expert and this is just my personal opinion - no warranty is implied or inferred !

[Ex- Member]

Rolec is a reasonably well known manufacturer, but whether their RCBOs are a good product I don't know - they do seem quite cheap. Of course just because it has ROLEC and CE painted on, doesn't necessarily mean anything... At least it is a British seller so you will know where to post the charred remains if it doesn't work properly!

 

Cheers Nick

 

I found this model

 

http://www.meteorelectrical.com/consumer-units_16amp-30ma-dp-rcbo.html?tax_val=1&country_id=222

 

Seems a bit better qualiy and only a few quid dearer and states BS EN 61009

Think i'll go for it.

[smileypete]

I found this model

 

http://www.meteorelectrical.com/consumer-units_16amp-30ma-dp-rcbo.html?tax_val=1&country_id=222

 

Seems a bit better qualiy and only a few quid dearer and states BS EN 61009

Think i'll go for it.

Looks good. If space is tight, some people get a 'garage consumer unit' containing an RCD, 16A MCB and 6A MCB, but leave the 6A MCB unused.

 

Only slight advantage of separate RCD and MCB over an RCBO, is that it's easier to tell if the trip was due to an earth fault, or an overload.

 

cheers,

Pete.

[nb Innisfree]

Looks good. If space is tight, some people get a 'garage consumer unit' containing an RCD, 16A MCB and 6A MCB, but leave the 6A MCB unused.

 

cheers,

Pete.

 

That's what we use but 6A for lighting circuit.

[Ex- Member]

Looks good. If space is tight, some people get a 'garage consumer unit' containing an RCD, 16A MCB and 6A MCB, but leave the 6A MCB unused.

 

Only slight advantage of separate RCD and MCB over an RCBO, is that it's easier to tell if the trip was due to an earth fault, or an overload.

 

cheers,

Pete.

 

Cheers Pete

 

Have ordered it,

 

I also have one of those plug in testers with lights in it to check weather wiring is correct, so use this every tiime I do any electtrical work on the 240 system, it does check for correct earthing I recall.

Edited October 12, 2012 by Julynian

[steelaway]

Cheers Pete

 

Have ordered it,

 

I also have one of those plug in testers with lights in it to check weather wiring is correct, so use this every tiime I do any electtrical work on the 240 system, it does check for correct earthing I recall.

 

 

 

I'm not sure this will test the integrity of the ELCB and eathing.

ELCB should trip if it see's a fault, so you need a tester that will trip it.

 

Alex

[Paul C]

Have a look at 3.5.1 in the BSS requirements. I'm not sure if the examiner would be needlessby picky if he applied it, but it says "...circuit breakers must be rated less than the current carrying capacity of the cable protected".

 

Interpreting this....if you have a single RCD in a consumer unit which has 4x MCBs, then the sum of the amperage rating of those MCBs can't be more than the current carring capacity of the cable - in this case the shoreline hookup cabling eg from the socket to the RCD. For this reason, I think "simpler is better" and just having one RCD and one MCB is nice to have on a boat. An alternate might be using a 10A and a 6A circuit breaker, eg 10A for the sockets and 6A for battery charger?

 

I'm not 100% on this so if anyone with more experience with this can add anything useful, would be appreciated.

[nicknorman]

Have a look at 3.5.1 in the BSS requirements. I'm not sure if the examiner would be needlessby picky if he applied it, but it says "...circuit breakers must be rated less than the current carrying capacity of the cable protected".

 

Interpreting this....if you have a single RCD in a consumer unit which has 4x MCBs, then the sum of the amperage rating of those MCBs can't be more than the current carring capacity of the cable - in this case the shoreline hookup cabling eg from the socket to the RCD. For this reason, I think "simpler is better" and just having one RCD and one MCB is nice to have on a boat. An alternate might be using a 10A and a 6A circuit breaker, eg 10A for the sockets and 6A for battery charger?

 

I'm not 100% on this so if anyone with more experience with this can add anything useful, would be appreciated.

I think the idea behind Julynian's proposal is to replace the red double pole switch in the photo with an RCBO rated at 16A. The other MCBs on the right are in series with this "master" RCBO so even if the individual MCBs add up to more than 16A (which they might well do, since it is normal to have more appliances on a boat than the total capacity of the system - ie you can't turn on everything at once) it doesn't matter since if he exceeds 16A demand, the RCBO will trip, thus satisfying your point. Depending on how the boat is wired, it might be helpful to have several MCBs as one does in a house, so that a fault on one circuit, say sockets, doesn't take out another circuit, say lights.

 

Of course anyone who worked on the wiring for say sockets, isolating them using the single pole MCB, whilst keeping the other circuits powered for say lighting, would be very foolish.....

 

That's me then!

[Paul C]

I think the idea behind Julynian's proposal is to replace the red double pole switch in the photo with an RCBO rated at 16A. The other MCBs on the right are in series with this "master" RCBO so even if the individual MCBs add up to more than 16A (which they might well do, since it is normal to have more appliances on a boat than the total capacity of the system - ie you can't turn on everything at once) it doesn't matter since if he exceeds 16A demand, the RCBO will trip, thus satisfying your point. Depending on how the boat is wired, it might be helpful to have several MCBs as one does in a house, so that a fault on one circuit, say sockets, doesn't take out another circuit, say lights.

 

Of course anyone who worked on the wiring for say sockets, isolating them using the single pole MCB, whilst keeping the other circuits powered for say lighting, would be very foolish.....

 

That's me then!

 

Yep if a double pole RCBO is used to do the first isolation, then each circuit was protected by an appropriate MCB, that would be all okay. Its if the initial isolation was by RCD (which only trips on residual current ie between live and earth, not overload current) then this may happily pass say 6 + 10 + 10 + 10 = 36 A while the input cabling is only rated at 16A.

[Chalky]

 

Most if not all these MCBs/RCBO/RCD's use a standard mounting (DIN rail) so you should be able to swap it easily enough.

 

 

Whilst they've standardised on DIN rail there are actually 3 different versions.

 

http://en.wikipedia.org/wiki/DIN_rail

 

Most of the ones I've come across are the top hat section however I have come across all the others (and some more) in test rigs and control cabinets. The one major difference is where the connections are. The manufacturers have their own standards for bus bar connections and it's often difficult to connect devices from different manufacturers on to the same bus bar.

 

 

"...circuit breakers must be rated less than the current carrying capacity of the cable protected".

 

 

That applies to all fuses and circuit breakers. They're there to protect the cable not the load.

[smileypete]

I'm not sure this will test the integrity of the ELCB and eathing.

ELCB should trip if it see's a fault, so you need a tester that will trip it.

I think it should show up a floating/disconnected earth, (the test button on the RCD will test the RCD itself but not the earthing).

 

There's a circuit diagram of a socket tester here:

 

http://coxengineering.sharepoint.com/Pages/Boreglazing.aspx

 

cheers, Pete.

~smpt~

[nicknorman]

 

There's a circuit diagram of a socket tester here:

 

 

Or maybe not...

[smileypete]

Or maybe not...

Oops here it is:

http://www.marcspages.co.uk/pq/4511.htm

 

cheers, Pete.

~smpt~

[Ex- Member]

I found the model I have used for years, it was recommended to me by a friend who's a qualified electrician.

 

http://www.tool-net.co.uk/p-360050/defender-13a.html?gclid=CNjhwbPp_bICFWXJtAodCR0A9w

 

Being on dry land for some years and with 240 on the boat as well as power extension leads outside the boat for numerous power tools, this unit checks for faults, so whenever I fit a new plug or use a new found exension lead, I check it with this. Must work as I haven't electrocutted my self or anyone else yet

 

It is very useful though and on one occasion did detect a shoolboy wiring error after I'de fitted some sockets.

[Lucien]

A couple of points here.

 

First, as I understand it, the OP wants to fit residual current protection (i.e. protection against electric shock) where there currently is none. This is a good idea. However there will already be (or at least jolly well ought to be) an RCD fitted to the shore supply into which the boat is plugged. In which case, in the event of a leakage, e.g. you get one of your appliances wet, it's pure luck which breaker will trip, just as likely to be the one on the shore as the one in the boat as they will have the same characteristics.

 

Secondly, when you come to look at the rating of an RCD, the tripping sensitivity for normal purposes is 30mA and that is the type you need. What this means is that if more than 30mA escapes from the circuit, it will trip in the specified time, making fatal shock unlikely. The current rating in amps is merely how heavy a load the breaker will carry, it has no effect on the tripping characteristics. If your shoreline is rated 16A then you need an RCD equal or greater, 63A is very common and may be cheapest. The smallest in general use is 25A and this would do equally well, as you will be unable to use its full capacity owing to your 16A shoreline limit.

 

Regarding limiting the overall current with an MCB on the incoming circuit on the boat, again the shoreline should be protected at source by an MCB no greater than 20A if it is a 16A socket outlet, more commonly it will be a 16A MCB. In this case you will have the same situation as with the RCD, that the breaker on the boat has the same rating as the one on the shore and it will be down to luck as to which trips first. Although with identical MCBs it might well be whichever is in the warmer location.

 

Moving on to the point about distinguishing what caused a trip on an RCBO, many modern RCBOs will be found to have an indicator that shows up only when a residual trip has occurred (i.e. one due to leakage) not when an overcurrent or short circuit has tripped the breaker. Hence there is no advantage of separate breakers on this score.

 

Final thought for now; those plug-in socket testers vary widely in effectiveness, in fact there are different standards for the different grades, however most of the DIY store ones are the basic grade. What these all have in common is that they do not tell you whether your earthing is good. They will tell you if it is absolutely useless, for instance if you don't connect the cable in the back of the socket. But in a narrowboat installation, I bet if you disconnect the earth from your shoreline and plug one of those in, it will still show good. So please don't rely on them too much, they are a poor substitute for a proper electrical test. Much as a nose is a poor substitute for a manometer when testing for gas leaks!

 

Lucien

[nicknorman]

A couple of points here.

 

First, as I understand it, the OP wants to fit residual current protection (i.e. protection against electric shock) where there currently is none. This is a good idea. However there will already be (or at least jolly well ought to be) an RCD fitted to the shore supply into which the boat is plugged. In which case, in the event of a leakage, e.g. you get one of your appliances wet, it's pure luck which breaker will trip, just as likely to be the one on the shore as the one in the boat as they will have the same characteristics.

 

Secondly, when you come to look at the rating of an RCD, the tripping sensitivity for normal purposes is 30mA and that is the type you need. What this means is that if more than 30mA escapes from the circuit, it will trip in the specified time, making fatal shock unlikely. The current rating in amps is merely how heavy a load the breaker will carry, it has no effect on the tripping characteristics. If your shoreline is rated 16A then you need an RCD equal or greater, 63A is very common and may be cheapest. The smallest in general use is 25A and this would do equally well, as you will be unable to use its full capacity owing to your 16A shoreline limit.

 

Regarding limiting the overall current with an MCB on the incoming circuit on the boat, again the shoreline should be protected at source by an MCB no greater than 20A if it is a 16A socket outlet, more commonly it will be a 16A MCB. In this case you will have the same situation as with the RCD, that the breaker on the boat has the same rating as the one on the shore and it will be down to luck as to which trips first. Although with identical MCBs it might well be whichever is in the warmer location.

 

Moving on to the point about distinguishing what caused a trip on an RCBO, many modern RCBOs will be found to have an indicator that shows up only when a residual trip has occurred (i.e. one due to leakage) not when an overcurrent or short circuit has tripped the breaker. Hence there is no advantage of separate breakers on this score.

 

Final thought for now; those plug-in socket testers vary widely in effectiveness, in fact there are different standards for the different grades, however most of the DIY store ones are the basic grade. What these all have in common is that they do not tell you whether your earthing is good. They will tell you if it is absolutely useless, for instance if you don't connect the cable in the back of the socket. But in a narrowboat installation, I bet if you disconnect the earth from your shoreline and plug one of those in, it will still show good. So please don't rely on them too much, they are a poor substitute for a proper electrical test. Much as a nose is a poor substitute for a manometer when testing for gas leaks!

 

Lucien

Not really sure of the points you are trying to make in the 1st couple of paras since the OP is not planning to fit an RCD nor an MCB, but an RCBO. However your point about which breaker would trip first is valid - it does of course depend on what breaker is fitted shore-side, something we don't know. As far as the need for an RCD function at all, bearing in mind it should be fitted to the shore power outlet, this is of course true in theory but, bearing in mind a boat can be plugging into all sorts of shore power, both well installed and maintained, and not, most people think it a good idea to provide their own protection.

[Paul C]

Not really sure of the points you are trying to make in the 1st couple of paras since the OP is not planning to fit an RCD nor an MCB, but an RCBO. However your point about which breaker would trip first is valid - it does of course depend on what breaker is fitted shore-side, something we don't know. As far as the need for an RCD function at all, bearing in mind it should be fitted to the shore power outlet, this is of course true in theory but, bearing in mind a boat can be plugging into all sorts of shore power, both well installed and maintained, and not, most people think it a good idea to provide their own protection.

 

The title of the topic suggests that an RCD is to be fitted. However I think we all agree, an RCBO would be a better option here. They are a bit more expensive, though (in my searching around for similar).