RCD's In TT Systems

[Gavthesparky]

I am quoteing to change an old consumer unit to 17th edition on a TT installation. I have checked the regs and it looks like the preffered option is to give added protection by changing the 100A main switch to a 100A 100mA RCD together with the 30mA RCD protection already in the board. Firstly is this correct or havr I miss read it? and secondly I believe (though I will have to double check) that the supplier or previous sparky has fitted an RCD as an isolation device before the board. I have no idea of its age so should I rely on it. I geuss testing it both manually and electronically will give me that answer?

Many thanks in advance

 

[A-Non-eMouse]

100ma rcd if the board is metalclad to protect the tails otherwise dual rcd 17th edition board 'plastic' with 100a main switch is fine as direct replacement. the two 30ma rcds will cover all circuits with protection required.

 

[vitoboy]

how will a rcd in a consumer unit protect tails..? metal unit or plastic..?
where this in regs?

 

[Spudnik]

You would need 100mA to protect the tails before entering a MC CU, basically, as it is now.

 

[Sintra]

A single RCD protecting a TT system must be installed at the origin of the installation unless the part of the system between the origin and the RCD fulfills the requirements for protection by Class II equipment or equivalent insulation. 531.4.1

 

[Spudnik]

Dont confuse the matter