A couple of questions about wiring an external socket fixed to the
outside wall of the house.

1. What type of wiring is used to pass through the cavity wall to the
socket (just TWE ?)
Cavity is aircrete, fibreglass batt, brick.

2. Tilt hole in wall down toward outside to stop water getting in from
the outside,
or tilt hole down toward inside to prevent water running down the
inside of the cavity (in theory !) and tracking into the socket box ?

3. If I use an exterior RCD socket (with the active feature that trips
off with loss of power),
are these usually 10mA RCDs, so you have discrimination from a 30mA
RCD that may be protecting the wiring from the consumer unit to the
socket ?
Or do I have to use armoured cable from the consumer unit to avoid two
RCDs ?

4. General question based on (3).
Latest regs, wiring has to be protected by RCD or amoured (unless
buried deep enough or in metal conduit etc). If you are wiring
something remote with remote RCD (consumer unit in shed etc), does
the TWE wiring through the house (before you go outside) have to be
RCD protected ?
Or do you really have to use armoured cable right from the consumber
unit to avoid having RCDs in series and therefore lack
discrimination ?

Thanks,
Simon.

On 2 July, 10:23, sm_jamieson wrote:
A couple of questions about wiring an external socket fixed to the
outside wall of the house.

1. What type of wiring is used to pass through the cavity wall to the
socket (just TWE ?)
Cavity is aircrete, fibreglass batt, brick.

2. Tilt hole in wall down toward outside to stop water getting in from
the outside,
or tilt hole down toward inside to prevent water running down the
inside of the cavity (in theory !) and tracking into the socket box ?

3. If I use an exterior RCD socket (with the active feature that trips
off with loss of power),
are these usually 10mA RCDs, so you have discrimination from a 30mA
RCD that may be protecting the wiring from the consumer unit to the
socket ?
Or do I have to use armoured cable from the consumer unit to avoid two
RCDs ?

4. General question based on (3).
Latest regs, wiring has to be protected by RCD or amoured (unless
buried deep enough or in metal conduit etc). If you are wiring
something remote with remote RCD (consumer unit in shed etc), *does
the TWE wiring through the house (before you go outside) have to be
RCD protected ?
Or do you really have to use armoured cable right from the consumber
unit to avoid having RCDs in series and therefore lack
discrimination ?

Thanks,
Simon.

sm_jamieson wrote:
A couple of questions about wiring an external socket fixed to the
outside wall of the house.

1. What type of wiring is used to pass through the cavity wall to the
socket (just TWE ?)
Cavity is aircrete, fibreglass batt, brick.


yes.

2. Tilt hole in wall down toward outside to stop water getting in from
the outside,
or tilt hole down toward inside to prevent water running down the
inside of the cavity (in theory !) and tracking into the socket box ?


Neither. Use mastic.

3. If I use an exterior RCD socket (with the active feature that trips
off with loss of power),
are these usually 10mA RCDs, so you have discrimination from a 30mA
RCD that may be protecting the wiring from the consumer unit to the
socket ?
Or do I have to use armoured cable from the consumer unit to avoid two
RCDs ?

pass.

4. General question based on (3).
Latest regs, wiring has to be protected by RCD or amoured

I think you man armoured :-)

(unless
buried deep enough or in metal conduit etc). If you are wiring
something remote with remote RCD (consumer unit in shed etc), does
the TWE wiring through the house (before you go outside) have to be
RCD protected ?

No.To the best of my knowledge. Howver an overall say 100mA RCD on the
whole instalation is usual.


Or do you really have to use armoured cable right from the consumber
unit to avoid having RCDs in series and therefore lack
discrimination ?

No.

Use big RCD on main incoming. Then RCBOs on spurs that need proper
protection. Or remote RCD.Armour outside underground.


Thanks,
Simon.

sm_jamieson wrote:
A couple of questions about wiring an external socket fixed to the
outside wall of the house.

1. What type of wiring is used to pass through the cavity wall to the
socket (just TWE ?)
Cavity is aircrete, fibreglass batt, brick.

I used 20mm PVC conduit and passed T&E through that.

2. Tilt hole in wall down toward outside to stop water getting in from
the outside,
or tilt hole down toward inside to prevent water running down the
inside of the cavity (in theory !) and tracking into the socket box ?

Not a problem if you use conduit and make sure it is well sealed to the
box.

Colin Bignell

On Jul 2, 10:23*am, sm_jamieson wrote:
A couple of questions about wiring an external socket fixed to the
outside wall of the house.

1. What type of wiring
2. Tilt hole in wall down toward outside

Flat Twin & Earth of suitable rating through conduit through hole.

One way would be...
- 1G 20A DP Switch on inside in 1G 47mm backbox (wiring space)
- Female 20mm conduit fitting into wall
- 20mm conduit through wall
- Female 20mm conduit into rear of exterior box

Now, the conduit should ideally slope downwards to stop water tracking
from the outer leaf to inner leaf. To do this with rigid conduit you
slightly warm the conduit over a kettle to get a double bend to create
an incline in the middle but horizontal to enter the conduit adapters.
Alternatively you can buy flexible conduit which will slip inside
female 20mm conduit fittings - look for 20mm *outside* diameter on
Ebay, it is usually grey or white convoluted. Very useful to have some
on the shelf for this kind of thing.


3. If I use an exterior RCD socket (with the active feature that trips
off with loss of power), are these usually 10mA RCDs, so you have
discrimination from a 30mA RCD that may be protecting the wiring
from the consumer unit to the socket ?

Exterior RCD socket are normally 30mA.
You do not fit an external RCD socket to a 30mA RCD protected circuit,
because there would be no discrimination - either or both would trip.
A 30mA trip typically goes at 23mA and a particular number of
milliseconds, another may trip at 22mA and slightly slower - but that
does not matter because earth fault currents are usually much higher
and thus trip both

If you want dual inline RCD protection for health reasons, such as a
pacemaker & hedgetrimmer, I would fit a 10mA inline RCD to the hedge
trimmer cable (CPC & Farnell sell these for about £12) and not use an
RCD protected socket. Not many external sockets have 10mA protection
and would be pretty expensive (there is a 10mA non-outside metalclad
Legrand on Ebay but the price has steadily risen as they have sold
them).

4. General question based on (3).
Latest regs, wiring has to be protected by RCD or amoured (unless
buried deep enough or in metal conduit etc). If you are wiring
something remote with remote RCD (consumer unit in shed etc), *does
the TWE wiring through the house (before you go outside) have to be
RCD protected ?

So you want a remote RCD in a shed, thus no RCD at the head end?
1 - use BS8436 cable through the house buried 50mm from surface
2 - use Flat Twin Earth cable through the house on surface (not
buried)
3 - use armoured (with armour in place) through the house (but glands
must be accessible for inspection & testing, ie, you can not bury them
in plaster)

Generally most people put the RCD (RCBO) at the house end.
The shed end then gets sockets, a fused-spur off the sockets for
lights, and an emergency light fitting. If the power trips off for any
reason the light is retained.

So in summary RCD should not be "daisy-chained".
You can buy a simple plug-in RCD tester (Socket & See, Fluke) right up
to proper digital unit on Ebay quite cheaply.

On 2 July, 13:59, "js.b1" wrote:
On Jul 2, 10:23*am, sm_jamieson wrote:

A couple of questions about wiring an external socket fixed to the
outside wall of the house.

1. What type of wiring
2. Tilt hole in wall down toward outside

Flat Twin & Earth of suitable rating through conduit through hole.

One way would be...
- 1G 20A DP Switch on inside in 1G 47mm backbox (wiring space)
- Female 20mm conduit fitting into wall
- 20mm conduit through wall
- Female 20mm conduit into rear of exterior box

Now, the conduit should ideally slope downwards to stop water tracking
from the outer leaf to inner leaf. To do this with rigid conduit you
slightly warm the conduit over a kettle to get a double bend to create
an incline in the middle but horizontal to enter the conduit adapters.
Alternatively you can buy flexible conduit which will slip inside
female 20mm conduit fittings - look for 20mm *outside* diameter on
Ebay, it is usually grey or white convoluted. Very useful to have some
on the shelf for this kind of thing.

3. If I use an exterior RCD socket (with the active feature that trips
off with loss of power), are these usually 10mA RCDs, so you have
discrimination from a 30mA RCD that may be protecting the wiring
from the consumer unit to the socket ?

Exterior RCD socket are normally 30mA.
You do not fit an external RCD socket to a 30mA RCD protected circuit,
because there would be no discrimination - either or both would trip.
A 30mA trip typically goes at 23mA and a particular number of
milliseconds, another may trip at 22mA and slightly slower - but that
does not matter because earth fault currents are usually much higher
and thus trip both

If you want dual inline RCD protection for health reasons, such as a
pacemaker & hedgetrimmer, I would fit a 10mA inline RCD to the hedge
trimmer cable (CPC & Farnell sell these for about £12) and not use an
RCD protected socket. Not many external sockets have 10mA protection
and would be pretty expensive (there is a 10mA non-outside metalclad
Legrand on Ebay but the price has steadily risen as they have sold
them).

4. General question based on (3).
Latest regs, wiring has to be protected by RCD or amoured (unless
buried deep enough or in metal conduit etc). If you are wiring
something remote with remote RCD (consumer unit in shed etc), *does
the TWE wiring through the house (before you go outside) have to be
RCD protected ?

So you want a remote RCD in a shed, thus no RCD at the head end?
1 - use BS8436 cable through the house buried 50mm from surface
2 - use Flat Twin Earth cable through the house on surface (not
buried)
3 - use armoured (with armour in place) through the house (but glands
must be accessible for inspection & testing, ie, you can not bury them
in plaster)

Generally most people put the RCD (RCBO) at the house end.
The shed end then gets sockets, a fused-spur off the sockets for
lights, and an emergency light fitting. If the power trips off for any
reason the light is retained.

So in summary RCD should not be "daisy-chained".
You can buy a simple plug-in RCD tester (Socket & See, Fluke) right up
to proper digital unit on Ebay quite cheaply.

Is there any limit to how far the remote wiring (e.g. for the shed)
can be away from the RCD in the consumer unit ? I will eventually wire
up my shed, and it is about 25 metres from the house.

I wonder what the use of RCD sockets really is, since with a modern CU
everything is likely to be protected in the CU.

Thanks,
Simon.

On Jul 2, 2:26*pm, sm_jamieson wrote:
Is there any limit to how far the remote wiring (e.g. for the shed)
can be away from the RCD in the consumer unit ? I will eventually wire
up my shed, and it is about 25 metres from the house.

No.

An RCD works by detecting the imbalance between Live & Neutral.
When current goes to earth, via a nail or person in contact with the
ground, it creates an imbalance between Live & Neutral and the RCD
will disconnect an Earth Fault so preventing electrocution or fire.

There is an issue re sizing the cable based on distance.
The longer the cable the greater the voltage drop, which for fixed
wiring needs to ensure that voltage at the end for lighting is within
3% of Uo (grid supply) which can be assumed to be 230V for calculation
or actually measured (which can be higher). Sockets require the
voltage at the end to be within 5%. In unusual circumstances you can
ignore the figures where equipment is not likely to be substantially
affected by lower voltage, that way you do not need to run hugely
expensive 35mm cable to a tiny fountain pump some hundred metres away.

For 25m I would suggest 4mm 3-core, the 3rd-core & armour being for
earth.
If the shed is wet, in contact with ground, with metal tools in use
you may need to make the shed a TT-supply rather than exporting any
house earth (PME, TN-C-S) to it.

You need to pickup the Electrician's Guide to Domestic Wiring and
Onsite Guide to 17th Regulations (about £12 at Amazon UK).


I wonder what the use of RCD sockets really is, since with a modern CU
everything is likely to be protected in the CU.

In some instances you may have several sockets to which equipment may
be connected which could trip an RCD, such as in commercial premises.
In such instances it may be desireable to ensure only one socket shuts
off rather than several. An example could be several freezers, you do
not want one freezer fault taking out several (not that freezers are
likely to trip an RCD).

There is an FAQ covering this, eg, cable depth , ground preparation,
marking tape etc.

"sm_jamieson" wrote in message
...
A couple of questions about wiring an external socket fixed to the
outside wall of the house.

1. What type of wiring is used to pass through the cavity wall to the
socket (just TWE ?)
Cavity is aircrete, fibreglass batt, brick.

Yes T&E will do.

2. Tilt hole in wall down toward outside to stop water getting in from
the outside,
or tilt hole down toward inside to prevent water running down the
inside of the cavity (in theory !) and tracking into the socket box ?

Tilt hole down towards the outside. Silicone the cable entry point on the
outside box and put a drain hole in the outside box.

3. If I use an exterior RCD socket (with the active feature that trips
off with loss of power),
are these usually 10mA RCDs, so you have discrimination from a 30mA
RCD that may be protecting the wiring from the consumer unit to the
socket ?

That will not provide discrimination in most cases.

Or do I have to use armoured cable from the consumer unit to avoid two
RCDs ?

That all depends upon how much you would expect the outside sockets to trip
and the consequences of such a trip. On a rewire I would try to put the
outside sockets on their own RCBO, but if adding an outside socket to a
fully decorated house then I would just take the power from the nearest
socket (usually via a DP switch)

4. General question based on (3).
Latest regs, wiring has to be protected by RCD or amoured (unless
buried deep enough or in metal conduit etc). If you are wiring
something remote with remote RCD (consumer unit in shed etc), does
the TWE wiring through the house (before you go outside) have to be
RCD protected ?
Or do you really have to use armoured cable right from the consumber
unit to avoid having RCDs in series and therefore lack
discrimination ?

If the T&E that you intend to use to power the outside sockets/sheds is
"just behind plaster" etc then it would need to be RCD protected. And then
it would only need the one RCD at the CU and not at both ends.

Cheers

Adam

On Fri, 2 Jul 2010 11:10:26 -0700 (PDT), js.b1 wrote:

Is there any limit to how far the remote wiring (e.g. for the
shed)
can be away from the RCD in the consumer unit ? I will eventually
wire
up my shed, and it is about 25 metres from the house.

No.

Up to a limit...

An RCD works by detecting the imbalance between Live & Neutral.
When current goes to earth, via a nail or person in contact with the
ground,

Or an imbalance due to the cable charging up. I have a plugin 10mA
trip but it is a right begger to set with a long extension cable
plugged into it.

--
Cheers
Dave.