4mm armoured electrical cable
Steve Gontarek
armoured cable that the likes of screwfix supply - in particular the
4mm 3 core . Can anyone tell me what ampage 4mm is rated at ? I think
it is 32 amps but ain't sure. Also, would there be any advantage of
getting the 4 core version of the cable, or is that for 3 phase
installations only?
Steve
Dave Plowman
2-Core 4mm armoured is rated at 39amps - 3 and 4 core at 34 amps.
IIRC, the safest way would be to use 2 core and provide a local earth/RCD
at the garage.
--
* Plagiarism saves time *
Dave Plowman dave....@argonet.co.uk London SW 12
RIP Acorn
Rick Hughes
Not sure what Screwfix prices but for comparison TLC sell it at £1.40 per
metre or £62.50 /50m £100 /100m
HTH
Rick
"Steve Gontarek" <st...@dml.ac.uk> wrote in message
news:5jjo2uockggh0u3cf...@4ax.com...
Andy Hall
"Dave Plowman" <dave....@argonet.co.uk> wrote in message
news:4aefe9ca2d...@argonet.co.uk...
> In article <5jjo2uockggh0u3cf...@4ax.com>,
> Steve Gontarek <st...@dml.ac.uk> wrote:
> > I'm thinking of putting electricity into our garage. I'll need the
> > armoured cable that the likes of screwfix supply - in particular the
> > 4mm 3 core . Can anyone tell me what ampage 4mm is rated at ? I think
> > it is 32 amps but ain't sure. Also, would there be any advantage of
> > getting the 4 core version of the cable, or is that for 3 phase
> > installations only?
>
> 2-Core 4mm armoured is rated at 39amps - 3 and 4 core at 34 amps.
>
> IIRC, the safest way would be to use 2 core and provide a local earth/RCD
> at the garage.
>
Dave, I can remember we had that debate a few months ago with all the usual
suspects on electrical stuff chipping in from experience and the wiring
regs.
For my installation where the house is on TN-C-S (PME), we arrived at the
conclusion that creating a separate equipotential zone by running armoured 2
core, grounding one end of that only and then providing a separate local
earth rod at the detached garage was the safest solution.
This was partly due to my wanting outlets for a freezer that would not be
RCD protected at the house end, but to have the remaining sockets, used for
portable appliances outside, fully protected with 30mA RCDs.
Steve, presumably where you are you're on a TT system with local earth rod
anyway?? If so then having a separate rod and RCD for the garage would be
a good idea.
.andy
Steve Gontarek
>
<snip>
>For my installation where the house is on TN-C-S (PME), we arrived at the
>conclusion that creating a separate equipotential zone by running armoured 2
>core, grounding one end of that only and then providing a separate local
>earth rod at the detached garage was the safest solution.
>
>This was partly due to my wanting outlets for a freezer that would not be
>RCD protected at the house end, but to have the remaining sockets, used for
>portable appliances outside, fully protected with 30mA RCDs.
>
That's exactly what I want to do
>Steve, presumably where you are you're on a TT system with local earth rod
>anyway?? If so then having a separate rod and RCD for the garage would be
>a good idea.
>
Yes, the Earth runs down from the supply pylon into the ground.
I was basically going to run the cable from a spare 100mA DP isolater
in my split box in the house. This would connect, in the garage, to a
two way consumer unit protected by a 80A\30mA RCD. My only problem was
that we want to eventually put a chest freezer out there, which is
obviously not a good idea to protect via a RCD, so I was going use a
seperate isolater for that circuit (as it happens I have an older
metal-clad ceramic (2x15A) box that I can use). So final questions :
1. what diameter of 2-core cable did you eventually use in the end
(4mm, 6mm ??) ? I guess the 2-core rated at 39 amps is probably more
than sufficient for that garage, but I reckon I would probably have to
connect that through a 40 Amp MCB as well as the 100A DP isolater at
the house end.
2. When you talk about grounding one end of the armoured cable, are
you talking about grounding the armoured sheath at the house end, but
*not* connecting it up at the garage end (instead using a seperate rod
for earthing at the garage) ?
Steve
Dave Plowman
Steve Gontarek <st...@dml.ac.uk> wrote:
> 2. When you talk about grounding one end of the armoured cable, are
> you talking about grounding the armoured sheath at the house end, but
> *not* connecting it up at the garage end (instead using a seperate rod
> for earthing at the garage) ?
Personally, I'd connect the sheath at the garage end. It would then be
clear to anyone working at the main house installation that the garage has
a separate earth.
Standing by to be told why this isn't a good idea. ;-)
--
* Why do psychics have to ask you for your name? *
Andy Hall
>
> I was basically going to run the cable from a spare 100mA DP isolater
> in my split box in the house. This would connect, in the garage, to a
> two way consumer unit protected by a 80A\30mA RCD. My only problem was
> that we want to eventually put a chest freezer out there, which is
> obviously not a good idea to protect via a RCD, so I was going use a
> seperate isolater for that circuit (as it happens I have an older
> metal-clad ceramic (2x15A) box that I can use). So final questions :
>
I guess that's OK. I did another split one in order to have everything in
one box.
> 1. what diameter of 2-core cable did you eventually use in the end
> (4mm, 6mm ??) ? I guess the 2-core rated at 39 amps is probably more
> than sufficient for that garage, but I reckon I would probably have to
> connect that through a 40 Amp MCB as well as the 100A DP isolater at
> the house end.
>
I used 6mm and there's a 40A MCB protecting it. You certainly need to
protect for fault current
considering the cable in question.
> 2. When you talk about grounding one end of the armoured cable, are
> you talking about grounding the armoured sheath at the house end, but
> *not* connecting it up at the garage end (instead using a seperate rod
> for earthing at the garage) ?
>
I grounded it at the house end and not the garage end. I take Dave's point
though, but I guess
you can argue that both ways. I did it that way because I thought of it
intuitively like a TT system
with the garage considered as another "house" and only the L & N coming in.
I can't find anything in the wiring regs. that says either way.
.andy
Chris French
<st...@dml.ac.uk> writes
>
>I was basically going to run the cable from a spare 100mA DP isolater
>in my split box in the house.
Hmm, no protection for the cable? You will need a fuse or MCB to protect
the cable.
>This would connect, in the garage, to a
>two way consumer unit protected by a 80A\30mA RCD. My only problem was
>that we want to eventually put a chest freezer out there, which is
>obviously not a good idea to protect via a RCD, so I was going use a
>seperate isolater for that circuit (as it happens I have an older
>metal-clad ceramic (2x15A) box that I can use).
Exactly the sort of thing I have done.
>1. what diameter of 2-core cable did you eventually use in the end
>(4mm, 6mm ??) ? I guess the 2-core rated at 39 amps is probably more
>than sufficient for that garage, but I reckon I would probably have to
>connect that through a 40 Amp MCB as well as the 100A DP isolater at
>the house end.
>
I used 6mm for my supply. But I was also governed by voltage drop
conditions as well. 40A fuse, through a 45A DP switch to islolate the
supply. I didn't want to use a MCB. I didn't want that tripping as well
if something tripped the garage CU
>2. When you talk about grounding one end of the armoured cable, are
>you talking about grounding the armoured sheath at the house end, but
>*not* connecting it up at the garage end (instead using a seperate rod
>for earthing at the garage) ?
>
That's what I've done.
--
Chris French, Leeds
Andrew Gabriel
Dave Plowman <dave....@argonet.co.uk> writes:
>
> Personally, I'd connect the sheath at the garage end. It would then be
>clear to anyone working at the main house installation that the garage has
>a separate earth.
No, you must connect it at the house end.
The house earth is providing the protective earthing for the
interconnecting cable, and has to be rated to handle the fault
current in the event of a cable fault. Whilst you could go to
the effort of making sure the out-building's earth in conjunction
with the fault current protective device(s) at the house did
provide suitable protection, it would be a very non-conventional
arrangement which would be sure to trip someone up in the future.
If you are making the out-building a TT system with own earth
rod, make sure all the electrical fittings from the supply
entry to the out-building up to and including the RCD are plastic.
(You can use metal, but you have to convert them to be double
insulated since a short to that metalwork would probably just
leave it live - easiest to just stick with plastic fittings at
that point.)
--
Andrew Gabriel
Consultant Software Engineer
Andy Wade
> Whilst you could go to
> the effort of making sure the out-building's earth in conjunction
> with the fault current protective device(s) at the house did
> provide suitable protection, it would be a very non-conventional
> arrangement which would be sure to trip someone up in the future.
It would also violate wiring regulation 542-01-09: "[...] if the
protective conductor forms part of a cable [it] shall be earthed only in
the installation containing the associated protective device." The
associated protective device, in this context, is clearly the one at the
supply end of the cable, and not any downstream device in the
outbuilding.
> If you are making the out-building a TT system with own earth
> rod, make sure all the electrical fittings from the supply
> entry to the out-building up to and including the RCD are plastic.
> (You can use metal, but you have to convert them to be double
> insulated since a short to that metalwork would probably just
> leave it live - easiest to just stick with plastic fittings at
> that point.)
Alternatively MK offer an 'RCD insulation kit' accessory for their metal
CU's for just this purpose. It comprises a beefy plastic bushing for the
incoming cable and a cable clamp which is used to prevent the incoming
live conductors coming adrift and touching the case should the terminal
screws work loose. I've used this item on a couple of occasions on TT
installations where a metal housing is more appropriate than plastic.
I've not seen equivalent products listed by any other manufacturer, but
they may exist.
A happy new year everyone
--
Andy