I've got some 3-core armoured cable, 7 copper strands, each measures
0.48mm diameter. By my calculations the size is 7*PI*(0.48/2)^2 which
comes out at 1.25mm^2 - is this a normal size?

Anyway, there is a 45m run of this to my from gate - I plan to put in
a socket and a gate opener. Is a 15A MCB OK?

--
Nigel M

On Thu, 20 Jul 2006 17:59:29 +0100, Nigel Molesworth wrote:

from gate

D'OH! * front gate
--
Nigel M

The message
from Nigel Molesworth contains these words:

Anyway, there is a 45m run of this to my from gate - I plan to put in
a socket and a gate opener. Is a 15A MCB OK?

That would depend on how much current the gate opener draws!

--
Skipweasel
Pay no attention to that man behind the curtain.

On Thu, 20 Jul 2006 18:21:44 +0100, Guy King wrote:

Anyway, there is a 45m run of this to my from gate - I plan to put in
a socket and a gate opener. Is a 15A MCB OK?

That would depend on how much current the gate opener draws!

Does it? I want to know the correct MCB for this cable. But they draw
under 1KW.

--
Nigel M

Nigel Molesworth wrote:

I've got some 3-core armoured cable, 7 copper strands, each measures
0.48mm diameter. By my calculations the size is 7*PI*(0.48/2)^2 which
comes out at 1.25mm^2 - is this a normal size?

No. Perhaps it's 1.5 mm^2, which would be 7/0.52 mm, or an old imperial
size (pre-1970) but I'd expect 3/0.029" in that case.

Anyway, there is a 45m run of this to my from gate - I plan to put in
a socket and a gate opener. Is a 15A MCB OK?

No, because of voltage drop over that length. What's the socket for?
For the gate opener alone you could use a 6A MCB in which case the cable
would be OK. If you really need a 16 A circuit (13 A socket + 3 A gate
motor) then you'll need 4 mm^2 cable.

You might want to think about the earthing arrangements for the gate,
especially if the house supply is PME.

--
Andy

On Thu, 20 Jul 2006 18:51:18 +0100, Andy Wade wrote:

No. Perhaps it's 1.5 mm^2, which would be 7/0.52 mm, or an old imperial
size (pre-1970) but I'd expect 3/0.029" in that case.

It's less than 0.52 - my calipers say 0.50 and my micrometer says
0.020" = 0.508. I rounded to 0.48 as it matched 1.25mm!

No, because of voltage drop over that length. What's the socket for?
For the gate opener alone you could use a 6A MCB in which case the cable
would be OK.

I need to run a car vac or a pressure washer, so about 1KW max, and
not at the same time as the gate. I've opted for a 10A MCB, as that's
all I could get on eBay (old MK Sentry).

You might want to think about the earthing arrangements for the gate,
especially if the house supply is PME.

Yes, on PME. Would another earth rod be a good idea? However, if you
are going to tell me to isolate the earth, I'm going to ignore you ;-)

--
Nigel M

Nigel Molesworth wrote:

I need to run a car vac or a pressure washer, so about 1KW max, and
not at the same time as the gate. I've opted for a 10A MCB, as that's
all I could get on eBay (old MK Sentry).

Label the socket "Max. load 1.5 kVA" or similar.

Yes, on PME. Would another earth rod be a good idea? However, if you
are going to tell me to isolate the earth, I'm going to ignore you
;-)

You need to feed through a 30mA RCD at the house end. Earth the cable
armour at the house end in the normal way and *isolate* it at the gate
end. Provide a suitable earth electrode for earthing the gate and
socket (resistance to earth should be 1.6k ohm and preferably less
than 200 ohm).

If you do not do this then should the combined neutral and earth (CNE)
feed to the house become o/c your gate will be live at full phase
voltage (not protected by the RCD) which is a trifle dangerous. OK, on
an urban supply the risk of this is very low, but not zero. The risk is
higher on rural overhead supplies.

An alternative strategy would be to export the house earth via the
armour and provide the lowest resistance earth electrode system you can
manage, connected to the main earth terminal in the house (suggest 2 or
3 rods each sunk to 8 or 12 ft.) That would help reduce the touch
voltage at the gate in the case of the o/c CNE feed. The RCD is still
required, because of the socket provided for portable equipment outdoors.

--
Andy