In article ,
John Rumm writes:
On 04/09/2016 09:21, Andrew Gabriel wrote:
In article ,
John Rumm writes:
On 03/09/2016 21:47, DICEGEORGE wrote:
I'm thinking of installing a Wylex 2 pole RCD 100 Amp 100mA
in a box like on the TLC page linked below.

Just after the main incoming electricity company fuses,
meter and isolator switch,
but before all the henley blocks, consumer units,
solar panel connections, old fuse boxes etc

The supply is TT, I have 2 earth spikes outside the door.

Any advice for or against?

With TT all circuits need RCD protection, so yes - sounds like a good
idea unless you already have an all RCBO install.

Since you need it to discriminate with downstream RCDs it will need to
be a time delayed (aka type "S") type.

(you will still need downstram 30mA trip devices for shock protection
since 100mA trip devices only give installation and equipment protection).

Also note that this now has to be in a metal enclosure (or the whole
lot installed in a fireproof enclosure). A metal enclosure containing
the first RCD in a TT system needs to have enhanced insulation of the
supply wiring leading in to the RCD, as that's not protected by the
RCD (in effect, it needs to meet double insulation standards). You can
buy enhanced insulation kits for some metal enclosures but not others,
so you will need to make sure you choose one for which an enhanced
insulation kit is available.

What's considered the most elegant solution for TT outbuildings fed from
a non RCD protected sub main with a TN head end these days?

Traditionally the SWA would have its armour connected to the supply
earth at the source, but would then be isolated from the local TT earth
simply by connecting its gland to the plastic enclosure.

I fed the SWA in through a plastic cable gland, and cut the
armor off flush with the sheath, so there is no sheath connection.
The gland is sized to clamp the outer sheath.

This would not be good enough for a metal cased CU though - still
need the double insulation, since a short from the live feed to the
metal case is unlikely to result in disconnection of supply in 5
seconds (nor indeed, at all).

--
Andrew Gabriel
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