RCD on a TT system

[NigelKing]

Hi,
Can anyone tell me if I have to have a separate RCD fitted to my incoming electricity supply between the meter tails and the new split load CU that we had fitted 3 years ago.

 

[andy]

Hi,
Can anyone tell me if I have to have a separate RCD fitted to my incoming electricity supply between the meter tails and the new split load CU that we had fitted 3 years ago.

everything sould be protected by an RCD. depends how your existing board is as to what RCD's you need and where

 

[NigelKing]

new 12 way split load consumer unit was installed straight from meter tails so the whole circuit is not RCD protected. (lights and heating are not RCD protected)

 

[1974stephen]

It is my understanding that a TT supply has to have a 100mA RCD device on the WHOLE installation, usually installed prior to the CU. Although I'm open to any differences of opinion.

 

[andy]

best thing to do is have a standard isolator feeding 2 RCD's. 30mA for sockets etc, and 100mA for lights, smoke alarm etc. that way, if 1 RCD trips, you dont loose everything

if you dont have room to do this, you could add a 100mA time delay RCD to the meter tails

 

[fastJedi]

See my posting of a few days ago. Are you sure the main switch in the CU isn't an RCD? Assuming it isn't you can either replace the DP switch in your CU or add an RCD in a separate enclosure. Getting an appropriate RCD device can be a bit tricky. Not all manufacturers supply a suitable device, hence you may have to resort to a separate enclosure (as I did).

To achieve proper discrimination between your existing RCD(s) and the new one you need .....
100mA trip (or 300mA if you have a good earth)
Time Delay (To ensure the whole lot doesn't trip unnecessarily)
80A or 100A rating ... depending on your installation

Electricians make a big thing about the dangers of not having a main RCD!

 

[NigelKing]

Thanks for the info Fastjedi, reading your post was what got me spooked in the first place.
I paid £3000 to get a 3 bed bungalow 'professionally' rewired 3 years ago so i'm a bit ****ed to say the least that this could have been missed.

 

[NigelKing]

Thanks for replies.

I have :-

100A main switch on the non RCD side covering 4 lighting circuits (one in the garage) and the central heating.

30mA hager CD284U 30mA RCD covering the rest.

Is the best course of action to replace the main switch with say a hager CE284U 100mA RCD or to add a separate type S time delayed RCD ?

Should the earth rod be checked out (tested)

i'm not going to do this myself I just need to know that the Sparks that I employ will say the right things when asked bearing in mind my previous experience.

 

[Qedelec]

Electricians make a big thing about the dangers of not having a main RCD!

Fastjedi
There is avery good reason for this...... YOUR SAFETY!!!

 

[viewer]

Why not leave the split board as it is and put RCBOs on the currently non-protected part?

 

[NigelKing]

an RCBO is roughly the same price as an RCD but wouldn't I need an RCBO for each unprotected circuit ?

 

[salem2000]

You could ask your supplier to convert from TT to PME. In some areas they will do it for free, mine did.

And it is cheeper to replace the main isolator with a RCD than fit RCBO's to all unprotected circuits

Salem.

 

[viewer]

Salem's right. It would be cheaper, but very easy (although some are double width) and would give discrimination. You pays your money and....

 

[salem2000]

One thing to remember..........

Replacing the main isolator requires the Company Fuse to be pulled. please get it done properly by someone who knows what to do.

Salem.

 

[NigelKing]

I fully agree Salem.
The whole point of this thread is to find out the best/correct way of doing this so that the Sparks that I call in to quote for it won't give me duff info like the 'professional' that rewired it 3 years ago.