In article ,
"Robin" writes:
Does this mean that TT installations will again need an RCD before
the CU?

No.
(They never did, although that was the cheapest option before having a
single RCD protecting all circuits was explicitly called out as non-
conforming.)

Thanks but I am not clear that addresses the point I had in mind. The
ESC Q&A on this:

Question
"Is an RCD main switch (such as a 100 mA time-delayed device) still
required in the consumer unit of a new domestic installation forming
part of a TT system?"

Answer
"For a domestic installation complying with the 17th Edition where all
the final circuits are RCD-protected, an RCD main switch is no longer
required, provided that the consumer unit is of all insulated
construction."

I wondered if the new fireproof CUs were likely in practice to be "all
insulated
construction".

The other option for TT systems was to provide extra sturdy insulation
around the feed on entry and inside the CU before it becomes RCD-protected,
and kits were available to do this for some metalic cased CU's.

I don't know what Ammendment 3 will say on this topic.

--
Andrew Gabriel
[email address is not usable -- followup in the newsgroup]