Where do you stop with this rcd malarkey?

[hoover]

I'm wiring a mates house at the minute which will be supplied from a tt system. The suppliers meter will be resessed into the outside wall. The consumer unit's will be located in a utility room some seven or eight meters away. They'll be supplied by a split con centric cable run in an underground duct. I'll have about 13 or 14 circuits (big house) which i'll split over two consumer units. So i'm thinking i'll need a 30 ma rcd protecting the underground cable, a 30 ma rcd protecting the cu supplying the sockets, cooker etc, a 30 ma rcd protecting the cu supplying the lights, heating etc and then 2 seperate 30 ma rcd's protecting the fire alarms and fridge/freezer. Thats 5 30 ma rcd's i'll need to cut down on inconvenience if something trips. Your thoughts would be helpful.

 

[ryanryan]

i think youll need two dual split load consumer units, the submains dont need a rcd!

 

[hoover]

i think youll need two dual split load consumer units, the submains dont need a rcd!

You sure the sub mains dont neen an rcd? I thought as they were under ground and a tt system with the lenght being about 8 meters they would need to be rcd. I'm also installing a 80 amp fuse switch to protect the sub mains.

 

[monkeyelectric]

You sure the sub mains dont neen an rcd? I thought as they were under ground and a tt system with the lenght being about 8 meters they would need to be rcd. I'm also installing a 80 amp fuse switch to protect the sub mains.

Put a 100mA at the other side of your switchfuse that will protect the cable and you have to do it for a tt anyways

 

[Christech]

Hi
100ma RCD does not discriminate against a 30ma RCD thus not complying to 17th Edition Regs . Personally i would opt for a 100ma Time Delayed incoming RCD controlling 5 zones made up of maybe 2 RCD's & 3 RCBO's as most manufacturers offer High Integrity CU's now.

 

[scotsparky]

whats the Ze at panel?? a 200ma main rcd for supply as long at ZexIn<50 then split 5d.b with 30ma for final circuits
remember the 50v mximum for fault voltage it will also give you discrimminaton
Basic discrimmination rule is miss 1 size

 

[ian.settle1]

Hi
100ma RCD does not discriminate against a 30ma RCD thus not complying to 17th Edition Regs . Personally i would opt for a 100ma Time Delayed incoming RCD controlling 5 zones made up of maybe 2 RCD's & 3 RCBO's as most manufacturers offer High Integrity CU's now.

Why do you say there is no discrimination between the 30mA and 100 mA?

 

[monkeyelectric]

Hi
100ma RCD does not discriminate against a 30ma RCD thus not complying to 17th Edition Regs . Personally i would opt for a 100ma Time Delayed incoming RCD controlling 5 zones made up of maybe 2 RCD's & 3 RCBO's as most manufacturers offer High Integrity CU's now.

How do you make that out? the 30mA would trip before the 100mA would'nt it?

 

[scotsparky]

there is a slim possibility that at 5x tripping current that the 100ma rcd will trip

 

[ian.settle1]

there is a slim possibility that at 5x tripping current that the 100ma rcd will trip

30mA at x5 it should trip in less than 40ms where the 100ma at x1 would trip in less than 300ms, would be sensitive to trip before 30mA

 

[scotsparky]

+at 5x under 40ms on a 30ma rcd which overlaps the 100ma rcd so as i said a slim chance if the 30ma rcd has not beed manually tested it is possibel. but a slim chance

 

[andekoch]

I agree an 100ma time delay pre distribution circuits to the 2 CU's and protect those cables with a switch fuse. Then a std split rcd board(s) as required, the second board can be fed from a mcb in the first board if required or its own switch fuse. I assume the 2 boards are some distance appart.
NB check that the IxV<50V (as per previous post).