I've read the FAQ and I think I'm alright but...

I have a garage fed from the house consumer unit a 32A MCB and a 100mA
RCD and 10m of 2 core 2.5mm SWA. The house earth is TN-S and the armour
of the SWA is used for the earth in the garage. There are no services
in the garage.

At the garage end this goes into a split load CU with 16A and 6A MCBs on
both the (30mA) RCD and non-RCD side.

The non-RCD circuits feed a freezer and lights - The RCD circuits feed
two double sockets , a socket for a tumble drier and 240W of external
external lighting.

I now want to put in a 3.5m x 2.5m log cabin approx 2m behind the garage
to use as a garden office. The loading in here will be lights, a couple
of PCs and monitors and upto 2kW of heating.

Part P aside, is it OK to run a 16A radial from the existing garage
circuit using 2.5mm T&E round the inside of the garage and extend out to
the cabin with either 2.5mm SWA or 2.5mm Arctic flex clipped to the
fence posts?

Thoughts?

Thanks,

Peter

Peter Watson wrote:
I've read the FAQ and I think I'm alright but...

I have a garage fed from the house consumer unit a 32A MCB and a 100mA
RCD and 10m of 2 core 2.5mm SWA. The house earth is TN-S and the
armour of the SWA is used for the earth in the garage. There are no
services in the garage.

At the garage end this goes into a split load CU with 16A and 6A MCBs
on both the (30mA) RCD and non-RCD side.

The non-RCD circuits feed a freezer and lights - The RCD circuits feed
two double sockets , a socket for a tumble drier and 240W of external
external lighting.

I now want to put in a 3.5m x 2.5m log cabin approx 2m behind the
garage to use as a garden office. The loading in here will be
lights, a couple of PCs and monitors and upto 2kW of heating.

Part P aside, is it OK to run a 16A radial from the existing garage
circuit using 2.5mm T&E round the inside of the garage and extend out
to the cabin with either 2.5mm SWA or 2.5mm Arctic flex clipped to the
fence posts?

The 100mA RCD at the house end seems to serve no purpose.

Personally I would not clip to the fence posts, however a 16A or 20A radial
would be fine for your suggested load.

--
Adam

Peter Watson wrote:
I've read the FAQ and I think I'm alright but...

I have a garage fed from the house consumer unit a 32A MCB and a 100mA
RCD and 10m of 2 core 2.5mm SWA. The house earth is TN-S and the
armour of the SWA is used for the earth in the garage. There are no
services in the garage.

At the garage end this goes into a split load CU with 16A and 6A MCBs
on both the (30mA) RCD and non-RCD side.

The non-RCD circuits feed a freezer and lights - The RCD circuits feed
two double sockets , a socket for a tumble drier and 240W of external
external lighting.

I now want to put in a 3.5m x 2.5m log cabin approx 2m behind the
garage to use as a garden office. The loading in here will be
lights, a couple of PCs and monitors and upto 2kW of heating.

Part P aside, is it OK to run a 16A radial from the existing garage
circuit using 2.5mm T&E round the inside of the garage and extend out
to the cabin with either 2.5mm SWA or 2.5mm Arctic flex clipped to the
fence posts?

The 100mA RCD at the house end seems to serve no purpose.

Personally I would not clip to the fence posts, however a 16A or 20A radial
circuit would be fine for your suggested load.

--
Adam

On 30/04/2011 16:33, John Rumm wrote:
On 30/04/2011 13:42, Peter Watson wrote:
I've read the FAQ and I think I'm alright but...

I have a garage fed from the house consumer unit a 32A MCB and a 100mA
RCD and 10m of 2 core 2.5mm SWA. The house earth is TN-S and the armour
of the SWA is used for the earth in the garage. There are no services in
the garage.

What is the 100mA RCD for?

A mis-guided attempt to offer some protection for the SWA run - Easy to
rmeove!


At the garage end this goes into a split load CU with 16A and 6A MCBs on
both the (30mA) RCD and non-RCD side.

The non-RCD circuits feed a freezer and lights - The RCD circuits feed
two double sockets , a socket for a tumble drier and 240W of external
external lighting.

I now want to put in a 3.5m x 2.5m log cabin approx 2m behind the garage
to use as a garden office. The loading in here will be lights, a couple
of PCs and monitors and upto 2kW of heating.

Unconnected with your question, but based on my experience with a
similar sized insulated timber building, you will probably need less
heating than that most of the time.

That's good to hear - The cabin will have insulated floor, roof and
walls so I'm hoping it won't need much. 2kW was a guess - i haven't
calculated the requirement...

Part P aside, is it OK to run a 16A radial from the existing garage
circuit using 2.5mm T&E round the inside of the garage and extend out to
the cabin with either 2.5mm SWA or 2.5mm Arctic flex clipped to the
fence posts?

Thoughts?

Yup that should be ok. Clipping to fence posts is not "ideal" - but that
rather depends a little on the permanence of the fence.

There's a short run of a couple of low concrete posts that I can use
(The sort that were used for three wire dividing fences)


Given your intended usage, I would probably take a 20A radial from the
non RCD side of the CU in the garage. Run it on the surface or in
visible trunking and then it does not need RCD protection. Then
transition to SWA for the outside bit (using weather proof boxes or
outside sockets). and slap a dinky split load CU in the office.



Other potential options for the external run? Hi-tuf perhaps, or T&E in
flexible conduit?

Thanks for your help...

Peter

On 30/04/2011 20:14, Peter Watson wrote:

Other potential options for the external run? Hi-tuf perhaps, or T&E in
flexible conduit?

Well, definitely not arctic flex! Hi-tuf seems to be disappearing from
the market(?) so that leaves SWA, NYY-J, T&E in rigid PVC conduit, or
pyro. I'd avoid flexible conduit outdoors - or at least check the
manufacturer's data to make sure it's suitable.

Don't forget that an outdoor conduit system needs to have drainage
hole(s) at the lowest point(s) to avoid trapping water.

--
Andy

On Mon, 02 May 2011 09:30:18 +0100, Andy Wade
wrote:

On 30/04/2011 20:14, Peter Watson wrote:

Other potential options for the external run? Hi-tuf perhaps, or T&E in
flexible conduit?

Well, definitely not arctic flex!

What's the problem with arctic?


--

On 04/05/2011 08:08, The Other Mike wrote:

What's the problem with arctic?

There's arctic and 'arctic'. Yellow arctic, made to BS 7919 Table 44 is
OK for outdoor use, but only on 110 V (55-0-55 V) systems. This can be
handled down to -25 deg. C.

The blue 'arctic' stuff is made to BS 6500 and is OK for 230 V, but
should not be handled below +5 deg. C. However it's only an 'ordinary
duty' cable and for the application here I'd recommend at least a heavy
duty (H07) cable. Also for a permanent installation there's a general
preference for non-flexible cables so Hi-Tuf or SWA would be much better
choices, IMO.

Chapter and verse on Arctic in this /Wiring Matters/ article:
http://electrical.theiet.org/wiring-...s.cfm?type=pdf

--
Andy