New RCD 100 Amp 100mA after my isolator switch?

[DICEGEORGE]

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?

(Have been reading the Yellow 2015 OnSiteGuide and UKDIY FAQ)

[george]

https://www.tlc-direct.co.uk/Products/WYWRM100slash2.html?ad_position=1t1&source=adwords&ad_id=66904418597&placement=&kw=wrm100%2f2&network=g&matchtype=p&ad_type=&product_id=&product_partition_id=&test=finalurl_v2&gclid=Cj0KEQjw6am-BRCTk4WZhLfd4-oBEiQA3ydA3sWshGUzE-Y2OnznjYBUPBkE1VnLYcA5oEiUdpdS7ZwaAifH8P8HAQ

[charles]

In article <d3d72768-774a-4223...@googlegroups.com>,

DICEGEORGE <diceg...@gmail.com> 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?

when I put a new CU in this house shortly after we moved in 40 years ago,
the advice was use one RCD for the whole supply. It has serious
disdvantages* and nowadays separate RCDs or MCBOs are recommended for each
circuit.
*Major disadvantage is that if something trips the RCD everything in the
house goes out - including lights.

--
from KT24 in Surrey, England

[John Rumm]

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).

>
> (Have been reading the Yellow 2015 OnSiteGuide and UKDIY FAQ)
>
> [george]
>
> https://www.tlc-direct.co.uk/Products/WYWRM100slash2.html?ad_position=1t1&source=adwords&ad_id=66904418597&placement=&kw=wrm100%2f2&network=g&matchtype=p&ad_type=&product_id=&product_partition_id=&test=finalurl_v2&gclid=Cj0KEQjw6am-BRCTk4WZhLfd4-oBEiQA3ydA3sWshGUzE-Y2OnznjYBUPBkE1VnLYcA5oEiUdpdS7ZwaAifH8P8HAQ
>

--
Cheers,

John.

/=================================================================\
| Internode Ltd - http://www.internode.co.uk |
|-----------------------------------------------------------------|
| John Rumm - john(at)internode(dot)co(dot)uk |
\=================================================================/

[Tim Watts]

You use a single time delayed Type S RCD for fault protection on a TT
supply.

Then regular RCDs or RCBOs on the final circuits. These are guaranteed
to trip first, leaving the main RCD to handle any upstream faults or
faults on non RCD circuits.

The main RCD is there to ensure a L-E fault trips with a relatively high
impedance earth (the current would not be enough to trip an MCB).

[DICEGEORGE]

The 100ms 100ma delay RCD at the company fuse end
is also there in case of faults in the consumer units, henley blocks etc.

Yes John and Tim, there would also be 30ma 30ms RCDs downstream
(but maybe not for stair lights, freezer, and future fire alarms)

[g]

[Andrew Gabriel]

In article <E6KdnY-m29OQ3FbK...@brightview.co.uk>,

John Rumm <see.my.s...@nowhere.null> 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.

>>
>> (Have been reading the Yellow 2015 OnSiteGuide and UKDIY FAQ)
>>
>> [george]
>>
>> https://www.tlc-direct.co.uk/Products/WYWRM100slash2.html?ad_position=1t1&source=adwords&ad_id=66904418597&placement=&kw=wrm100%2f2&network=g&matchtype=p&ad_type=&product_id=&product_partition_id=&test=finalurl_v2&gclid=Cj0KEQjw6am-BRCTk4WZhLfd4-oBEiQA3ydA3sWshGUzE-Y2OnznjYBUPBkE1VnLYcA5oEiUdpdS7ZwaAifH8P8HAQ
>>
>
>

--

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

[John Rumm]

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.

[Andrew Gabriel]

In article <ps2dnW6HPv-VmFHK...@brightview.co.uk>,

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).

[Tim Watts]

Or you could enclose the plastic RCD box in something "not combustable"
or whatever the wording is. Say Euroclass B/C plywood or plasterboard
lined box, or even a metal over-box.

It's not terrible well defined, but the general idea is if the RCD
catches fire, the fire and more specifically, the cables are contained
and cannot drop out.

[John Rumm]

Yes, in effect there are two different problems to deal with here.
Ensuring disconnection of the supply once you are no longer shielded by
the head end earth, but also keeping the local and source earths separated.

If one leaves the bedding on the SWA right through the downstream
enclosure up til you separate the cores out to feed the main switch,
then you are in effect maintaining double insulation for the bulk of the
job.

[DICEGEORGE]

why have two separate earths,
one at the shed and one at the house,
why are they separate and not connected together?

That would be more fault tolerant.

[george]

[DICEGEORGE]

Andrew G wrote:
[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. ]

So not the £2.88 enclosure advertised with the 100 ms RCD at
https://www.tlc-direct.co.uk/Products/WYWRM100slash2.html?ad_position=1t1&source=adwords&ad_id=66904418597&placement=&kw=wrm100%2f2&network=g&matchtype=p&ad_type=&product_id=&product_partition_id=&test=finalurl_v2&gclid=Cj0KEQjw6am-BRCTk4WZhLfd4-oBEiQA3ydA3sWshGUzE-Y2OnznjYBUPBkE1VnLYcA5oEiUdpdS7ZwaAifH8P8HAQ

this one?
Insulated Enclosure (Rcd) IP65 Weatherproof
WY WBE4 Insulated Enclosure ( RCD ) - IP65 £21.24
https://www.tlc-direct.co.uk/Products/WYWBE4.html

But maybe as I started years ago (and notified Building Control) under the red on site guide I could use the cheap plastic box not metal?

[John Rumm]

On 04/09/2016 20:30, DICEGEORGE wrote:

> why have two separate earths,

With feeds to outbuildings, there are times when it preferable to
separate the outbuilding's earthing system from the supplies.

It was a generic question about using non insulated CUs in cases where
one would have used insulated in the past - not specific to your OP.

> one at the shed and one at the house,
> why are they separate and not connected together?

Its not always straight forward. See:

http://wiki.diyfaq.org.uk/index.php/Taking_electricity_outside#Exporting_an_earth

> That would be more fault tolerant.

With TT both ends, yup. With TN earth at the head end, it gets more
complicated.