RCDs, RCBOs & MCBs

[diyhell]

Have read the DIY info FWL_Engineer has hosted at the Franklin Wood site and it raised my techie interest in the subject of RCDs etc.

I'm guessing the provision of a RCD-equipped socket outlet (as suggested for an internal socket used for external equipment) on a circuit protected by an MCB at the (RCD equipped) Consumer Box is important due to different ratings of the two RCDs.

But what's the difference between using an RCD equipped socket outlet with a MCB at the CB and just using a RCBO? Doesn't the latter fulfill the services of both an RCD and MCB?

 

[plugwash]

yeah rcbo and normals socket or mcb and rcd socket makes no real difference

can you paste the exact bit of advice you were looking at you may be misunderstanding it

 

[diyhell]

Difficult to post the whole thing because it's loads of pages, but FWL recommends in his scenario at http://www.franklin-wood.co.uk/diyindex.htm:

Kitchen Ring 32A 30mA RCBO
External Socket #1 16A Type B MCB

the latter including a 'RCD protected socket-outlet adjacent to the Front Door of the premises in order to provide power externally at the front of the house should this be required. This socket-outlet will be protected by a 16A Type B MCB in the distribution board'

Now, you can buy a 16A RCBO http://www.tlc-direct.co.uk/Main_Index/Consumer_Units_Index/Mk_Sentry_Contactors_and_RCBO/index.html so why not just use one of those instead of an RCD protected socket and MCB?

 

[plugwash]

fwl hates split boards....
if you have a normal split board (with 30ma rcd) in your house then just put the outdoor socket on the rcd side and there is no need for any further rcds (there is no point in putting 2 rcds of the same trip value one after the other you will most likely just trip both)

if you are dedicating a rcd to one socket it is imo better to use a rcd socket than a rcbo becuase it means the reset point is closer to the point of use

 

[ban-all-sheds]

fwl hates split boards....

And RCD incomers, except where required with TT supplies.

RCBOs everywhere is his mantra - a man of expensive tastes.....

 

[kendor]

having local rcd's as opposed to one covering the whole installation would also be preferable to cover the regs about protective devices(mcb's and rcd's alike) and discrimination, better the circuit in question trips rather than the whole installation goes down!

 

[plugwash]

i do see his point in a way

but unless you are runnign stuff that both needs rcd protection and needs a very reliable supply i think more than one rcd is overkill in a normal house