Hi all,
I want to extend my ring main through a wall to another room.
Is it acceptable to pick-up from an existing socket and run the cable
behind the skirting then through the wall to the new socket? distance
will be about 2 mtr.
The room has concrete floor with drops from the roof which is
inaccessible, single story so would have to rip the roof up.

Match

Matchlock wrote:
Hi all,
I want to extend my ring main through a wall to another room.
Is it acceptable to pick-up from an existing socket and run the cable
behind the skirting then through the wall to the new socket? distance
will be about 2 mtr.
The room has concrete floor with drops from the roof which is
inaccessible, single story so would have to rip the roof up.

Match

It's OK so long as the cable is running at the same height as the
socket. Whilst you can do what you like within 150mm of the ceiling,
this is not the case for the floor (basically because people tend to
fit skirting boards and the like in this area and could therefore
damage the cable. Going through the wall into the back of the socket is
fine, it's just that you can't go down from the existing socket and
then across, only straight across.

Alternatively you could run behind the skirting if there was enough
room to put the cable under metal protection which is earthed.

Hope this helps.

Fash

Fash wrote:
Matchlock wrote:
Hi all,
I want to extend my ring main through a wall to another room.
Is it acceptable to pick-up from an existing socket and run the cable
behind the skirting then through the wall to the new socket? distance
will be about 2 mtr.
The room has concrete floor with drops from the roof which is
inaccessible, single story so would have to rip the roof up.

Match

It's OK so long as the cable is running at the same height as the
socket. Whilst you can do what you like within 150mm of the ceiling,
this is not the case for the floor (basically because people tend to
fit skirting boards and the like in this area and could therefore
damage the cable. Going through the wall into the back of the socket is
fine, it's just that you can't go down from the existing socket and
then across, only straight across.

Alternatively you could run behind the skirting if there was enough
room to put the cable under metal protection which is earthed.

Hope this helps.

Fash

Thanks for the quick reply Fash.
The existing socket is 100mm above the skirting so I will have to make
the drop down to the centreline of the skirting, around an internal
corner then through the wall.
I assume from your reply that if I chase the wall behind the skirting
and cover in grounded metal not plastic? I should be OK.
Would I also need to go through the wall in metal?

Match

Matchlock wrote:

The existing socket is 100mm above the skirting so I will have to make
the drop down to the centreline of the skirting, around an internal
corner then through the wall.

If the new socket is to be at the same height as the one that you're
taking the spur from then it will be easier not to drop down but to run
the cable on a direct horizontal line between the two sockets.

I assume from your reply that if I chase the wall behind the skirting
and cover in grounded metal not plastic? I should be OK.

It needs to be thick metal that you couldn't easily drill or nail
through. Steel conduit is OK, but the thin metal capping certainly isn't.

Would I also need to go through the wall in metal?

Protection is needed where the cable is less than 50 mm from either
surface of the wall AND is not in the defined horizontal safe zone.

--
Andy

Andy Wade wrote:
Matchlock wrote:

The existing socket is 100mm above the skirting so I will have to make
the drop down to the centreline of the skirting, around an internal
corner then through the wall.

If the new socket is to be at the same height as the one that you're
taking the spur from then it will be easier not to drop down but to run
the cable on a direct horizontal line between the two sockets.

I assume from your reply that if I chase the wall behind the skirting
and cover in grounded metal not plastic? I should be OK.

It needs to be thick metal that you couldn't easily drill or nail
through. Steel conduit is OK, but the thin metal capping certainly isn't.

This isn't quite true, the point is if the protection is earthed then
you are safer as you're always in contact with earth before reaching
the live and therefore the low resistance path won't include the
operator. I have reproduced the relevant bit from th regs below.

Protection, as permitted by Regulation 522-06-06 (i), (ii) and (iii),
may be provided in a number of ways. The cable may be protected by an
earthed metal conduit, trunking or ducting satisfying the requirements
of BS 7671 for a protective conductor, or the cable should incorporate
an earthed metal sheath complying with the requirements of BS 7671 for
a protective conductor of the circuit concerned. Alternatively,
mechanical protection sufficient to prevent penetration of the cable by
screws or nails may be used.

The point is that it is very hard to satisfy the mechanical penetration
requirement hence why it's earthed.

Would I also need to go through the wall in metal?

Protection is needed where the cable is less than 50 mm from either
surface of the wall AND is not in the defined horizontal safe zone.

I agree with Andy here except that you don't have a problem on the side
of the wall where your new socket is since the cable will be vertically
below the fitting and therefore in a safezone.

--
Andy

Take a look at http://www.niceic.org.uk/approved/quest3.html which
shows graphically all the safe zones.

Fash

Fash wrote:

Andy Wade wrote:
It needs to be thick metal that you couldn't easily drill or nail
through. Steel conduit is OK, but the thin metal capping certainly isn't.

This isn't quite true, the point is if the protection is earthed then
you are safer as you're always in contact with earth before reaching
the live and therefore the low resistance path won't include the
operator.

I'm not sure exactly which bit you're saying isn't quite true. I accept
it's a little simplified but maintain that metal capping (earthed or
not) does not provide adequate protection. 522-06-06 (iii) requires
earthed conduit, trunking or ducting (satisfying the requirements for a
CPC) and capping is none of those things. But you're quite right to
point out that "mechanical protection sufficient to prevent penetration
of the cable by nails, screws and the like" would not need to be earthed.

There are also the options of using cables incorporating an earthed
covering, or concentric cables as permitted in 522-06-06 (i) and (ii).
We discussed that possibility recently in this thread
http://groups.google.com/group/uk.d-...72f29b 55e948.

I have reproduced the relevant bit from the regs below.

The bit you reproduced was copied from the NICEIC page you cited and not
from BS 7671, so is not "the regs".

FAOD, here's the whole of 522-06-06 (again):

Quote from BS 7671:2001, Amendment no. 2

*522-06-06* A cable concealed in a wall or partition at a depth of less
than 50 mm from the surfaces of the wall or partition shall:

(i) incorporate an earthed metallic covering which complies with the
requirements of these Regulations for a protective conductor of the
circuit concerned, the cable complying with BS 5467, BS 6346, BS 6724,
BS 7846, BS EN 60702-1 or BS 8436, or

(ii) be of insulated concentric construction complying with BS 4553-1,
BS 4553-2 or BS 4553-3, or

(iii) be enclosed in earthed conduit, trunking or ducting satisfying the
requirements of these Regulations for a protective conductor, or be
mechanically protected sufficient to prevent penetration of the cable by
nails, screws and the like, or

(iv) be installed in a zone within 150 mm from the top of the wall or
partition or within 150 mm of an angle formed by two adjoining walls or
partitions. Where the cable is connected to a point, accessory or
switchgear on any surface of the wall or partition, the cable may be
installed in a zone either horizontally or vertically, to the point,
accessory or switchgear. Where the location of the accessory, point or
switchgear can be determined from the reverse side, a zone formed on one
side of a wall of 100 mm thickness or less or partition of 100 mm
thickness or less extends to the reverse side.
/quote

Incidentally, from June 2008 the 17th Edition is likely to allow
unprotected runs outside the safe zones provided that the circuit is 30
mA RCD protected and "the normal methods of protection [...] cannot be
employed".

The point is that it is very hard to satisfy the mechanical penetration
requirement hence why it's earthed.

Mmm, OK - I see what you're getting at. Fair point.

--
Andy