Question about: "With a TT install you will need to use an insulated CU "

[DICEGEORGE]

I have several consumer units around the house but before them all is a new 100ma 100ms RCD in a box, so must only this box be insulated?

ukdiy wiki says: "With a TT install you will need to use an insulated CU since this minimise s the possibility of a phase to earth fault occurring inside the CU before the RCD (which due to the high earth fault loop impedance of the local eart h spike, may result in a fault that would never be cleared). " at

quipment

[george]

[John Rumm]

Subsequent boxes will have earth fault protection from the RCD, so they can be any type. The RCD itself would traditionally have been in a plastic box, but with the 3rd amendment of the 17th edition you may find that harder to find.

[DICEGEORGE]

thats good news, I can keep my plastic RCD consumer units and only replace the wooden ones, thanks John. [George]

[John Rumm]

I think you may be conflating two issues here...

For TT installs, plastic used to be the norm to mitigate against the potential for an earth fault before the type S RCD.

17th edition amendment 3 mandates that new CUs installed should be of a non combustible material. Meaning that if you use a metal clad CU for a TT install (and where there are multiple CUs; the CU that contains the non RCD protected incomers) you would need to use a double insulation kit for the incomers to reduce the possibility of an earth short before the RCD.

Irrespective of that, you can keep what you already have. Just when installing new CUs they need to be non combustible. If they are downstream of an RCD anyway, then its a non issue at that point.

[bruce]

You could put a single time delayed rcd in a plastic box by itself in front of everything. It can be in plastic rather than metal because one rcd by itself does not meet the 7671 definition of 'switchgear'.

[John Rumm]

It sounds to me like that is what he already has...