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Posts: n/a
Default Shed wiring - OK

Sorry in advance for a common post.

I've Googled and checked and it seems to be OK, but could somebody just
have a read through and confirm if the set-up below is as per the
regulations.

Old set up:
Remote brick built shed, originally wired up by a previous owner. Fed via
a 13 fused spur from the downstairs ring main and terminated in a two way
fused CU in the shed. Power use in minimum - occasional hand tool, LV
garden lights. Internal 13A socket accessible for garden use as required.

Proposed new set up:
3core 4mm SWA - earth is taken through the yellow wire - with the armour
sleeving bonded to the yellow wire at both ends.

Two way CU in the shed with mcbs and protected by integral 30mA RCD.
Sockets (probably three) in the shed, either as a ring main or as a radial
circuit, plus an external socket mounted externally on the shed wall for
garden use.
- 2.5mm T&E fed from a 16A mcb

Shed lighting plus external light
- 1.25mm T&E fed from a 6A mcb

In-house connection is to a 32A mcb on a split CU and is protected by the
integral 30mA RCD in the CU (there are two split CUs in the house, this CU
only feeds shower and outside lights, so if it trips it's not a problem).

SWA terminated in the shed and indoors in a metal knockout box using
suitable glands. Metal box is also earthed (I assume that a plastic box
could be used instead if required?)

6mm T&E is used to complete the circuit from the SWA to the CU at both
ends.

I realise that this means that the shed light will be lost if the RCD
trips in the shed. I could solve this by using a separate CU in the shed
for lighting only (I have a spare CU) or is this not permissible as the
light would still be lost if the 32A mcb tripped in the house CU?

An alternative would be to use the existing supply from the fused spur on
the ring main to feed a separate CU in the shed just for the lighting,
using a 5A fuse in the spur instead of the current 13A one. However, I
would have liked to have got rid of that cable altogether.

I assume that if a separate CU was used in the shed for the lighting, that
this would also require its own RCD?

Thanks

Roger
(my reader sometimes loses mail/newsgroup messages
- if you think you should have had a reply/comment,
please e-mail me again. Ta!)
  #2   Report Post  
 
Posts: n/a
Default

PS

Does SWA have to be buried underground, or can it lay on the top?. I could
just run it along the top of the ground near the bottom of the fence. It
wouldn't get disturbed there. I could then use cleats to secure it to the
external house and shed wall as necessary.

Roger


In article ,
() wrote:

Sorry in advance for a common post.

I've Googled and checked and it seems to be OK, but could somebody just
have a read through and confirm if the set-up below is as per the
regulations.

Old set up:
Remote brick built shed, originally wired up by a previous owner. Fed
via a 13 fused spur from the downstairs ring main and terminated in a
two way fused CU in the shed. Power use in minimum - occasional hand
tool, LV garden lights. Internal 13A socket accessible for garden use
as required.

Proposed new set up:
3core 4mm SWA - earth is taken through the yellow wire - with the
armour sleeving bonded to the yellow wire at both ends.

Two way CU in the shed with mcbs and protected by integral 30mA RCD.
Sockets (probably three) in the shed, either as a ring main or as a
radial circuit, plus an external socket mounted externally on the shed
wall for garden use.
- 2.5mm T&E fed from a 16A mcb

Shed lighting plus external light
- 1.25mm T&E fed from a 6A mcb

In-house connection is to a 32A mcb on a split CU and is protected by
the integral 30mA RCD in the CU (there are two split CUs in the house,
this CU only feeds shower and outside lights, so if it trips it's not a
problem).

SWA terminated in the shed and indoors in a metal knockout box using
suitable glands. Metal box is also earthed (I assume that a plastic box
could be used instead if required?)

6mm T&E is used to complete the circuit from the SWA to the CU at both
ends.

I realise that this means that the shed light will be lost if the RCD
trips in the shed. I could solve this by using a separate CU in the
shed for lighting only (I have a spare CU) or is this not permissible
as the light would still be lost if the 32A mcb tripped in the house CU?

An alternative would be to use the existing supply from the fused spur
on the ring main to feed a separate CU in the shed just for the
lighting, using a 5A fuse in the spur instead of the current 13A one.
However, I would have liked to have got rid of that cable altogether.

I assume that if a separate CU was used in the shed for the lighting,
that this would also require its own RCD?

Thanks

  #3   Report Post  
John Rumm
 
Posts: n/a
Default

wrote:

Remote brick built shed, originally wired up by a previous owner. Fed via


How remote?

Proposed new set up:
3core 4mm SWA - earth is taken through the yellow wire - with the armour
sleeving bonded to the yellow wire at both ends.


What type of earthing do you have at the house?

You may not want to export the house earth if it is either a TT setup,
or if the shed is a long way from the house. If this were the case then
you could connect the earth to the shield at the source end, but
terminate in a plastic CU at the shed end and provide a local earth via
a rod.

Two way CU in the shed with mcbs and protected by integral 30mA RCD.
Sockets (probably three) in the shed, either as a ring main or as a radial
circuit, plus an external socket mounted externally on the shed wall for
garden use.
- 2.5mm T&E fed from a 16A mcb

Shed lighting plus external light
- 1.25mm T&E fed from a 6A mcb


1mm sq will be more than adequate for the lights on a 6A MCB.

What sort of work are you planning to do in the shed - how critical is
the loss of light on a RCD trip going to be?

If it is an issue you could fit a battery backed emergency light (about
30 quid from TLC).

In-house connection is to a 32A mcb on a split CU and is protected by the
integral 30mA RCD in the CU (there are two split CUs in the house, this CU
only feeds shower and outside lights, so if it trips it's not a problem).


Since it is protecting the shower, changing it for a higher trip rating
or a time delay version is not really an option. So that kind of negates
any benefit of the one in the shed.

SWA terminated in the shed and indoors in a metal knockout box using
suitable glands. Metal box is also earthed (I assume that a plastic box
could be used instead if required?)


If you are not going to export the house earth then plastic somewhere
(i.e. either the box or the CU) will be needed to isolate the shield.
You can usually take a SWA straight into a CU - it should have a 20mm
knock out that will take a gland)

I realise that this means that the shed light will be lost if the RCD
trips in the shed. I could solve this by using a separate CU in the shed
for lighting only (I have a spare CU) or is this not permissible as the
light would still be lost if the 32A mcb tripped in the house CU?


It is not the house MCB that is likely to trip, but the house RCD. A
imbalance fault at the shed could trip either the shed, the house or
both RCDs

An alternative would be to use the existing supply from the fused spur on
the ring main to feed a separate CU in the shed just for the lighting,
using a 5A fuse in the spur instead of the current 13A one. However, I
would have liked to have got rid of that cable altogether.


Battery backed light in the shed sounds like a whole lot less fuss.

--
Cheers,

John.

/================================================== ===============\
| Internode Ltd -
http://www.internode.co.uk |
|-----------------------------------------------------------------|
| John Rumm - john(at)internode(dot)co(dot)uk |
\================================================= ================/
  #4   Report Post  
 
Posts: n/a
Default

In article ,
(John Rumm) wrote:

wrote:

Remote brick built shed, originally wired up by a previous owner. Fed
via


How remote?


The shed is about 25 feet from the house. The total length of SWA/T&E
from CU to CU is probably around 20m or less


Proposed new set up:
3core 4mm SWA - earth is taken through the yellow wire - with the
armour sleeving bonded to the yellow wire at both ends.


What type of earthing do you have at the house?


Sorry, forgot to mention that - it's the standard TN-S with the earth
supplied by the electric co.

You may not want to export the house earth if it is either a TT setup,
or if the shed is a long way from the house. If this were the case then
you could connect the earth to the shield at the source end, but
terminate in a plastic CU at the shed end and provide a local earth via
a rod.

Two way CU in the shed with mcbs and protected by integral 30mA RCD.
Sockets (probably three) in the shed, either as a ring main or as a
radial circuit, plus an external socket mounted externally on the
shed wall for garden use.
- 2.5mm T&E fed from a 16A mcb

Shed lighting plus external light
- 1.25mm T&E fed from a 6A mcb


1mm sq will be more than adequate for the lights on a 6A MCB.

What sort of work are you planning to do in the shed - how critical is
the loss of light on a RCD trip going to be?


Not a lot - it's the odd bit of drilling or (electrical) soldering and
that's about it.

If it is an issue you could fit a battery backed emergency light (about
30 quid from TLC).


OK

In-house connection is to a 32A mcb on a split CU and is protected by
the integral 30mA RCD in the CU (there are two split CUs in the
house, this CU only feeds shower and outside lights, so if it trips
it's not a problem).


Since it is protecting the shower, changing it for a higher trip rating
or a time delay version is not really an option. So that kind of
negates any benefit of the one in the shed.

SWA terminated in the shed and indoors in a metal knockout box using
suitable glands. Metal box is also earthed (I assume that a plastic
box could be used instead if required?)


If you are not going to export the house earth then plastic somewhere
(i.e. either the box or the CU) will be needed to isolate the shield.
You can usually take a SWA straight into a CU - it should have a 20mm
knock out that will take a gland)

I realise that this means that the shed light will be lost if the RCD
trips in the shed. I could solve this by using a separate CU in the
shed for lighting only (I have a spare CU) or is this not permissible
as the light would still be lost if the 32A mcb tripped in the house
CU?


It is not the house MCB that is likely to trip, but the house RCD. A
imbalance fault at the shed could trip either the shed, the house or
both RCDs

An alternative would be to use the existing supply from the fused
spur on the ring main to feed a separate CU in the shed just for the
lighting, using a 5A fuse in the spur instead of the current 13A one.
However, I would have liked to have got rid of that cable altogether.


Battery backed light in the shed sounds like a whole lot less fuss.

--
Cheers,

John.

/================================================== ===============\
| Internode Ltd -
http://www.internode.co.uk |
|-----------------------------------------------------------------|
| John Rumm - john(at)internode(dot)co(dot)uk |
\================================================= ================/


Thanks for the advice

Roger
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Junior Member
 
Posts: 28
Default

[ Remote brick built shed, originally wired up by a previous owner. Fed
via[/i][/color]

The shed is about 25 feet from the house. The total length of SWA/T&E
from CU to CU is probably around 20m or less


Proposed new set up:
3core 4mm SWA - earth is taken through the yellow wire - with the
armour sleeving bonded to the yellow wire at both ends.



Sorry, forgot to mention that - it's the standard TN-S with the earth
supplied by the electric co.


Two way CU in the shed with mcbs and protected by integral 30mA RCD.
Sockets (probably three) in the shed, either as a ring main or as a
radial circuit, plus an external socket mounted externally on the
shed wall for garden use.
- 2.5mm T&E fed from a 16A mcb

Shed lighting plus external light
- 1.25mm T&E fed from a 6A mcb





Not a lot - it's the odd bit of drilling or (electrical) soldering and
that's about it.

If it is an issue you could fit a battery backed emergency light (about
30 quid from TLC).


OK

In-house connection is to a 32A mcb on a split CU and is protected by
the integral 30mA RCD in the CU (there are two split CUs in the
house, this CU only feeds shower and outside lights, so if it trips
it's not a problem).


SWA terminated in the shed and indoors in a metal knockout box using
suitable glands. Metal box is also earthed (I assume that a plastic
box could be used instead if required?)


I realise that this means that the shed light will be lost if the RCD
trips in the shed. I could solve this by using a separate CU in the
shed for lighting only (I have a spare CU) or is this not permissible
as the light would still be lost if the 32A mcb tripped in the house
CU?



Battery backed light in the shed sounds like a whole lot less fuss.

--
Your original prposal with swa sounds ok dont forget to bond the sheath at both ends in your metal adaptable boxes to the yellow core used as earth ( needs yellow / green sleeve on that) If your swa is 4mm which is a 32A max cable you can also use 4mm twin and earth but the 6mm is ok, just that someone in the future may assume swa is 6mm as well. Th emergency light is called a non maintained eml, this only comes on with supply failure, go to any wholesaler and it should cost about £16.50.


  #6   Report Post  
Christian McArdle
 
Posts: n/a
Default

Proposed new set up:
3core 4mm SWA - earth is taken through the yellow wire - with the armour
sleeving bonded to the yellow wire at both ends.


I'd prefer to see 2 core SWA, with armour isolated at shed end, with shed TT
earthing by earth rod. I would also use 6mm minimum. 4mm is only just on the
limit for 20m, leaving no voltage drop left over for wiring within the shed,
if you design for the full 32A, which may be required in the future.

- 2.5mm T&E fed from a 16A mcb


Use a 20A MCB. That makes it one of the standard socket circuit types.

Shed lighting plus external light
- 1.25mm T&E fed from a 6A mcb


I've never seen 1.25mm T&E. Use 1mm or 1.5mm, whichever you have lying
about.

In-house connection is to a 32A mcb on a split CU and is protected by the
integral 30mA RCD in the CU (there are two split CUs in the house, this CU
only feeds shower and outside lights, so if it trips it's not a problem).


Feed it from the non-RCD side. In the event of an earth trip, you don't want
to have to return to the house to get the lights restored. There is no
requirement to RCD protect the SWA cable and the shed itself has its own RCD
protection.

6mm T&E is used to complete the circuit from the SWA to the CU at both
ends.


That sounds fine.

I realise that this means that the shed light will be lost if the RCD
trips in the shed. I could solve this by using a separate CU in the shed
for lighting only (I have a spare CU) or is this not permissible as the
light would still be lost if the 32A mcb tripped in the house CU?


If you want separate RCD protection for the lighting circuit, you have
several options, in descending order of desirability.

1. Use RCBOs in a non-split isolator incomer CU.
2. Use a split load with time delay 100mA RCD incomer and 30mA instant for
sockets.
3. Use two CUs, each with its own RCD.

An alternative would be to use the existing supply from the fused spur on
the ring main to feed a separate CU in the shed just for the lighting,
using a 5A fuse in the spur instead of the current 13A one. However, I
would have liked to have got rid of that cable altogether.


Yes, avoid this idea.

I assume that if a separate CU was used in the shed for the lighting, that
this would also require its own RCD?


Yes, especially with TT earthing.

Christian.


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