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Since the 17th Edition we have had “Every installation shall be divided into circuits, as necessary, to reduce the possibility of unwanted tripping of RCDs due to excessive protective conductor currents produced by equipment in normal operation.” However the active word is normal.
Under normal operation how big can a circuit be? 3.5 mA is the limit where a plug and socket can be used, so normal earth leakage is less than 3.5 mA the 30 mA RCD can trip between 15 and 30 mA so with no fault, i.e. normal operation 10 sockets is within the rules, however clearly 100 sockets is over egging it.
So it would seem 25 sockets is likely considered as reasonable, but as fixed appliances are added which do not have the 3.5 mA limit like cookers, immersion heaters, and lights then we it seems are over stepping the mark.
My old house had just two RCD’s and they would have a batch of tripping, could go a year without a trip, then trip once a week for a month then another year without tripping, since been fitted for some 25 years now, it is clear they did not comply, they did trip in normal operation, two RCD’s were not enough. That is in a 3 bedroom house.
Mothers house had 6 RCD’s two for whole of house except for kitchen, and 4 RCBO’s for kitchen, and I seem to remember only one unwanted trip, so it would seem likely 3 RCD’s with the kitchen on it’s own RCD would have been enough.
This house when we moved in had one RCD with most of house unprotected, it now has 14 RCBO’s as experience with last house had shown 2 RCD’s are not enough, and consumer units may have three neutral bars, but not really designed for 3 RCD’s and also 3 RCD’s take 6 slots, so the consumer unit becomes much larger. However 4 slots are taken up with surge protection and an isolator, and since must be able to isolate else where under HSE rules, never really worked out why we have an independent isolators to isolate else where plus one in the consumer unit that is I suppose going OTT, no real need for an isolator in the consumer unit.
So from my own experience it does seem a few RCBO’s for kitchen and then 2 RCD’s for rest of house is enough for normal operation, however then we have “Take account of danger that may arise from the failure of a single circuit such as a lighting circuit.” We it seems don’t put lights and sockets in the same room on the same RCD, for this house that forced my hand, sockets split front/back and lights split up/down so could not possibly get away with two RCD’s, maybe putting lights on RCBO would have been enough.
However this is all about design, and the electrician is trying to design the installation when in real terms he has no idea what will be plugged in, so where it seems the requirements of division of installation has not been met, can he be called on to correct and add more RCD’s? We sign to say we have designed, not simply followed tradition, so at what point could the house holder blame the designer and say I want to claim for the loss of a freezer of food as you got the design wrong? And if one person is successful claiming from a designer would that open the flood gates?
I would say clearly a caravan has all on one RCD (although it does have battery back up) and a two up, two down clearly two RCD’s are enough, but as the person who designs the installation at what point do we need more that 2 RCD’s?
Under normal operation how big can a circuit be? 3.5 mA is the limit where a plug and socket can be used, so normal earth leakage is less than 3.5 mA the 30 mA RCD can trip between 15 and 30 mA so with no fault, i.e. normal operation 10 sockets is within the rules, however clearly 100 sockets is over egging it.
So it would seem 25 sockets is likely considered as reasonable, but as fixed appliances are added which do not have the 3.5 mA limit like cookers, immersion heaters, and lights then we it seems are over stepping the mark.
My old house had just two RCD’s and they would have a batch of tripping, could go a year without a trip, then trip once a week for a month then another year without tripping, since been fitted for some 25 years now, it is clear they did not comply, they did trip in normal operation, two RCD’s were not enough. That is in a 3 bedroom house.
Mothers house had 6 RCD’s two for whole of house except for kitchen, and 4 RCBO’s for kitchen, and I seem to remember only one unwanted trip, so it would seem likely 3 RCD’s with the kitchen on it’s own RCD would have been enough.
This house when we moved in had one RCD with most of house unprotected, it now has 14 RCBO’s as experience with last house had shown 2 RCD’s are not enough, and consumer units may have three neutral bars, but not really designed for 3 RCD’s and also 3 RCD’s take 6 slots, so the consumer unit becomes much larger. However 4 slots are taken up with surge protection and an isolator, and since must be able to isolate else where under HSE rules, never really worked out why we have an independent isolators to isolate else where plus one in the consumer unit that is I suppose going OTT, no real need for an isolator in the consumer unit.
So from my own experience it does seem a few RCBO’s for kitchen and then 2 RCD’s for rest of house is enough for normal operation, however then we have “Take account of danger that may arise from the failure of a single circuit such as a lighting circuit.” We it seems don’t put lights and sockets in the same room on the same RCD, for this house that forced my hand, sockets split front/back and lights split up/down so could not possibly get away with two RCD’s, maybe putting lights on RCBO would have been enough.
However this is all about design, and the electrician is trying to design the installation when in real terms he has no idea what will be plugged in, so where it seems the requirements of division of installation has not been met, can he be called on to correct and add more RCD’s? We sign to say we have designed, not simply followed tradition, so at what point could the house holder blame the designer and say I want to claim for the loss of a freezer of food as you got the design wrong? And if one person is successful claiming from a designer would that open the flood gates?
I would say clearly a caravan has all on one RCD (although it does have battery back up) and a two up, two down clearly two RCD’s are enough, but as the person who designs the installation at what point do we need more that 2 RCD’s?