Dual RCD Board on TT system

[padmore12345]

Hi guys

been working on new builds for the last ten years so havent had much experience with tt supplies for a while and need some advice on a tt job ive been asked to have a look at.

the situation is this, gone to a mates house whos had his consumer unit changed by girlfriends uncle or someone and noticed its a tt supply. the unit is an mk 16th edition board ie 100a main switch, breaker, breaker, breaker, RCD, breaker, breaker, breaker etc. pretty sure from college memories that the whole install has to be cover by an RCD before the consumer unit, which it isnt. ie its suppliers cut out fuse, tails, meter, tails, consumer unit.

was after advice from you guys what do you thinks the best option to get over this

1) stick a 17th edition dual rcd board in, will this cover the all circuits with rcd protection matter and discrimination???

2) get another Rcd and split load kit to cover front half of board ie main switch, new rcd, breaker, breaker, rcd, breaker breaker etc

3) get new rcd and enclosure to front the whole install between meter and ccu, cut meter seals etc(not to keen on this)

4) or your suggestion

also ive seen the rod has been installed under the floor in the hallway a couple of metres away from ccu in understairs cupboard, is this okay or should it be accessable outside somewhere in an inspection pit or will this suffice as long as the loop readings are in acceptable range.

cheers in advance for any replies.

 

[Mac]

Can't you just use RCBO's for all the circuits.The rod is ok indoors as long as it's accessible.Oh and welcome to the forum

 

[willosparky]

dont need an rcd before the board. to be 17th just need to have in the board, main switch, then rcd, some mcb's then another rcd and the rest of the mcb's meter tails should be 25mm and earth 16mm hope this of help to you

 

[patricklondon]

as mac says or option 1. option 2 is no cheaper and probably a lot more of a pfaf. and yes all terminations must be accessible, if you can get to it ok then its not a problem

 

[padmore12345]

thanks for your quick reply chaps. if i was to go the buy new rcd and fit to existing board route, would i be right in saying to discrimate between the two one would need to be say an 80A/30ma rcd and the other a 63A/30ma rcd. both fed from the load side of the main switch and not in parallel. or am i barkin up the wrong tree?

thought about the rcbo route but about 8 breakers to change, could be a bit pricey at 30 squid a pop or whatever they are now. doing it on mates rates to so every penny counts.

 

[patricklondon]

sounds pretty spot on mate have a look at your local supplier they usually have deals on

 

[willosparky]

there is no need to worry about descimination betwwen rcd's in the board as the 2nd one is not in circuit with the first one. they will trip individualy no matter what. An mk sentry split load board would be best, with an 80A and 63A rcd both 30mA
Endmundsons electrical wholesalers sell them.

 

[amp]

Regs state all circuits on TT system to have 30 m/a protection.

Just change the MCB'S after the main switch for RCBO's and its sorted. Especially if all the light circuits are on the RCBO'S. You need to keep the lights and sockets from the same floor on different RCD'S to meet 17th edition.

 

[pushrod]

, would i be right in saying to discrimate between the two one would need to be say an 80A/30ma rcd and the other a 63A/30ma rcd. both fed from the load side of the main switch and not in parallel. .

In what you describe there would be no rcd discrimination between the two unless one was a time delay type,

But as willosparky says in a 17th edition board they are not in series so no issues with discrimination .

 

[amp]

Read this carefully please ! from what you have described you will only need three RCBO'S for the circuits after the main switch there is not going to be a discrimination issue at all! you are making this job more complicated than it needs to be. 10 mins to change and and some testing. changing a board is couple of hours and test everything. not to mention neeeding the main cut out fuse removed and building regs if you want it legal.

 

[Des 56]

Read this carefully please ! from what you have described you will only need three RCBO'S for the circuits after the main switch there is not going to be a discrimination issue at all! you are making this job more complicated than it needs to be. 10 mins to change and and some testing. changing a board is couple of hours and test everything. not to mention neeeding the main cut out fuse removed and building regs if you want it legal.

I agree

The simple solutions are hard to accept sometimes
Double pole rcbos perhaps to re complicate the matter?

 

[padmore12345]

thanks for all the advice chaps. think im going to get another rcd and split load kit for the front half of the board and do some circuit jiggerling, up lights, down sockets etc. seems the cheapest option at £35 from screwfix. thanks again.