RCBO's ...

R

Rabbit Rabbit

New Member
The MK 45 amp 30mA RCBO's come with neutral and cpc wires and the cable I put in is 10mm csa. I phoned MK Tech and asked what csa the neutral was (it was less than 10mm thats for sure). He did not know so I asked it the neutral cable should be same as the phase (i.e. balance the two) within the CU. I know it is only a short distance for this neutral to run (to the neutral block with the CU) but should it be the same? The guy at MK said "..well it should be OK" (hardly instills confidence)
 
I think the type you are talking about is a braided type of cable inside a insulated sheath. The most impotant think is what current that tail is dessigned to withstand and presumably MK have flash tested that rcbo
 
Very good point Lectric Man. One assumes 45 amps since its a 45 amp RCBO its for a 10.5kW shower supply so I guess it don't matter much the mere fact I am using 10 mm csa and the supplied neutral is less than 10mm is sort of irrelevant provided it can carry the 45 amps - I take your point. It's Saturday and my brain must be resting! Many Thanks for waking me up
 
I'm surprised that you didnt know that cpc's in all of our 6242Y T&E standard cable is smaller than the main conductors except the 1mm which is the same size. I think 10mm has a 4mm cpc.

See Table E1 in Guidance note 1.
 
Cors I knew that unphased! (hence the 1.67 multiple) what the cpc has to do with my query I have no idea. To re-interate or make clear - I have wired in a 10mm cable to the CU, I want to use a MCBO to provide both MCB and RCD capability the MK MCBO (45A 30mA) unit is supplied with a short neutral cable of a LESSER csa than the 10mm neutral cable (and phase for that matter and yes the cpc is smaller). My query is that since I am using 10mm cable and since the MK MCBO neutral is of a smaller csa will there be an imbalance since the RCD effects (under Kirchoff's second law) may be imbalanced and hence not work properly. Hoppe I make myself clear and sorry about any confusion.
 
sure that applies to the size of rcbo this guy is fitting

but iirc the statement in the mk catalogue applied to the whole range of 1 module rcbo's

said statement seems to have dissapeared from the current catalogue though
 
well its regardless of what it is at end of day, highest current consumption should always be staged correctly from main switch, but i wouldnt expect you to know that unless you was installing etc.
 
yes i did know that actually

but i remember the rcbos explictly stateing they can only be fitted in the first 4 positions (the whole range of 1 module ones not just the high rateings)

said comment seems to have gone in the current mk catalogue though

the only possible reason i can think of would be length of the neutral wire
 
Thank you for all the comments guys. In fact the situation is worse than I feared, having read your comments. It is an old MK CU using the old MCB's all enclosed along with the meter, tails, fuse, the lot in a metal surrround with metal front door. A real ugly thing. Anyway, I am addding a 10.5kW shower using 10 mm cable to this old CU. Than main switch is a 4 pole (yes 4 pole!) 100mA 80 A RCD and the reasion for this is that all the MCB's are the the LEFT of the main RCD! Real wierd. Anyway, I am also having to use an MK converter such that I can use the MCBO new type of bus bar connection. No way can it get nearer to the main isolator RCD. Yes I know fit a complete new CU, thats what MK said, but punter has no money for that. Maybe I should forget the MCBO and simply but in a 45 amp MCB and rely on the main 100mA RCD - yes I know it should be a 30mA one but the regs don't specify this it is only a nice and proper thing to do. Problem is will I sleep at night? The issue about positioning is interesting, obvious when one thinks about due to power consumption.
 
Probably because you are supposed to fit the highest-rated circuits as close to the Main switch as you can.

So they say.

They also say (but can't remember where) that you shouldn't put lots of high-current MCBs next to each other because of localised heat build-up.

?:|?:|
 
Long chat with MK today on the subject. The part is 6938s (45A 30mA). "The Sentry RCBOs may be installed ANYWHERE along the length of the busbar..." that is what the installations instructions say (see their website). I follow the logic of positioning, heating, loading etc. but the installation instructions were also verbally confirmed. Now my next problem is getting one! no-one round here stocks 'em!! Thnx guys.
 
Long chat with MK today. I aslo downloaded from their web site installation instructions for the 6938s (45A 30mA RCBO). "The Sentry RCBOs may be installed ANYWHERE alonmhg the length of the busbar..." that is what the leaflet shows and this was verbally confirmed by MK. I understand thbe logic of limited positioning, heating etc. but now I can fit one and sleep with peace of mind. Now all I have to do is get one, no-one stocks them round here - is it worth it all? I knew I should have been a plumber! Thnx guys.
 
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