Which RCD for my consumer unit?

[Reptile Smile]

Hi all,

Am doing a 230v shorepower install. I've made the everything double pole where I can (the isolator and the two mcb's) and have organised everything except for the rcd.

I imagine this should be double pole as well, but I'm not sure about the rest of the specs. Should it be 16a? Should it be an RCBO or an RCD? Are there any other specs I should aim for?

 

[VicS]

My understanding is that the RCD should be double pole.

It should have a rating no less than the sum of all the MCBs. It should trip at 30mA.

RCBOs combine the function of an RCD with that of an MCB so you can have them in place of separate units. Not sure though about the availability of double pole RCBOs. I am sure they must exist but are not common because they are not required by the "wiring regs" AFAIK.

You say that you have an isolator. My understanding, which may be wrong, is that you should have a double pole circuit breaker. I can't see the point of a simple isolator when all you need to do is unplug the connection.

 

[David2452]

Hi all,

Am doing a 230v shorepower install. I've made the everything double pole where I can (the isolator and the two mcb's) and have organised everything except for the rcd.

I imagine this should be double pole as well, but I'm not sure about the rest of the specs. Should it be 16a? Should it be an RCBO or an RCD? Are there any other specs I should aim for?

Frankly you would struggle to find an RCD that is not DP today, unlike good quality MCBs they are double bay so take up a bit more room in the consumer unit. It should be 30 mA and 100 ms maximum trip time and of the trip free variety (that is to say it should not be possible to gaffer tape the switch in the live position as the trip is internal and the switch simply a reset) with a manual test function.

 

[nigelmercier]

Why the need for an isolator, when you have an RCD?

 

[Plevier]

It should trip at 30mV.

mA not mV.

30mA is the most common. For increased personal protection you can use 10mA but are likely to get a lot of spurious trips from noise.
Even some 30mA ones are prone to noise tripping. I've found it worth sticking to good makes like MK rather than electrical factors own brand.

 

[VicS]

mA not mV.

Whoops

 

[sailorman]

Whoops

It happens to the best of us Vic

 

[Seastoke]

Rcd can be used as main isolator it depends on how many circuits you have if you have more than four then you should go to two rcds or you could have an isolator and use rcbo,s on each circuit this would help alse tripping but costs more ,also your rcd should be tested once a month by pressing the test button and more important should be tested by a rcd tester which a 30 ma should trip under 200 miliseconds and x5 test under 40 miliseconds

 

[Reptile Smile]

I believed I'd read VicS say it was a requirement for the boat safety scheme (actually, maybe it was an ISO requirement) on one of the LustyD threads from a couple of years ago? Maybe I'm mistaken...

That said, whilst I accept that the cable can be pulled out, in my way of thinking, I would likely want to shut off this way in an emergency, in which case it would be faster to get to the consumer unit inside than scramble through the companion way to the cable. That said, I suppose it would serve the same function to trip the DP RCD than to hit the main switch..?

 

[Reptile Smile]

My understanding is that the RCD should be double pole.

It should have a rating no less than the sum of all the MCBs. It should trip at 30mA.

So on my 6A + 16A MCBs, a 25A RCD is obviously what I'm after, but is it a problem to fit a 32A, for example, or should I be seeking to be getting close to the total? Or does it not especially matter?

 

[sailorman]

So on my 6A + 16A MCBs, a 25A RCD is obviously what I'm after, but is it a problem to fit a 32A, for example, or should I be seeking to be getting close to the total? Or does it not especially matter?

as long as the amperage exceeds the total your ok, the physical size of the units will be similar, the rcd is there to cut out due to earth leakage, thus protecting you

 

[Seastoke]

To comply with electrical regs the make of the board rcd and mcbs must be of the same make if you were being to the regs each conection on mcb,s also have a set torq setting given by manufacturing.

 

[Seastoke]

What sizesupply do you have if it is 16amp then you should use 10 amp mcbs on on your boat ok the reason if you have a fault of up to 16 amp it will always trip the furthest away which will be the one protecting the supply so you may lose all your supply and the unit mite be locked where you cant reset it ,also you mention double pole mcbs what type are they as you do not use them on 230 volt system they are used in 400 volt systems or specials.if you need help please pm me

 

[David2452]

To comply with electrical regs the make of the board rcd and mcbs must be of the same make if you were being to the regs each conection on mcb,s also have a set torq setting given by manufacturing.

Where exactly in the regs that apply to boats (BS EN ISO 13297:2012) does it say that?

 

[Seastoke]

Iam quoting bs 7671 which covers electrical instalations

 

[David2452]

Iam quoting bs 7671 which covers electrical instalations

Not on boats it doesn't that is BS EN ISO 13297:2012 if we followed 7671 then we could be using solid core copper conductors, we are talking about boats and the regs that apply specifically to boats, not Wimpy bungalows.

 

[Seastoke]

Dave i will bow to your knolege but you can use flex in house wiring also so surely you cant put any junk together and surely you have to earth loop impedence tests once the instalation is done or how do you know rcds are workng right or are boat regs way behind bs 7671 we only want to try and make forumites as safe as pos

 

[Reptile Smile]

Thanks to all for their input.

Just to clarify - why should I not be using double pole MCBs? (I understand why I should be using a double pole RCD, though, as noted, the vast majority are DP anyway, I understand..?)

 

[Seastoke]

Its just that if you buy a bs consumer unit it has the copper bars supplied that to feed single mcbs or rcbos if you make your own board up and a fault developed and caused a fire your insurance could be in question but dave will be best to quote on boats

 

[l'escargot]

What sizesupply do you have if it is 16amp then you should use 10 amp mcbs on on your boat ok the reason if you have a fault of up to 16 amp it will always trip the furthest away which will be the one protecting the supply...

Surely that's the clincher. Most marina supplies are 16 amp.