Having just laid a concrete pad to install a summer house, I would like
to carry out the following work.
Currently there is a power cable (conduited T&E) to the area I want to
go to, but it is a spur from the attached garage, and I would prefer
the external power to be on a seperate circuit. This circuit will be
disconnected once the replacement is in place

1. Run a power feed from the house consumer unit to a secondary
consumer unit in the summer house using armoured cable. Cable to be
buried (Depth?)

2. Run (alongside the armoured cable but in a conduit) 2 data cables,
a front door bell, and a telephone cable. I will include a length of
thin Polyprop rope to allow for futher cables to be pulled later.

3. From the secondary consumer unit:-
i. Individual Power for the pond pump and UV. To be security
switched and needs some kind of visual indicator (like an led switch
without the switch)
ii. Individual Power run to each of 4 Garden lights (each to be
individually switched from within the summer house. These will be spurs
rather than a ring.
iii. Individual Power run to each of 2 waterproof power outlets
in the Garden.
iv. A small 'ring-main' within the summer house (to be capable
of running total comsumption of c10A).
v. Lighting for the summer house itself.

I am intending protecting the circuits from the summer house with
individual Residual Current breakers on the secondary Consumer unit.
One breaker for the external lights, one for the power outlets, one for
the pond stuff, one for the internal ring, and one fro the internal
lighting.

With all the above in mind.....

Should I protect the Power run from the main consumer unit to the
secondary consumer unit with an Residual Current breaker at the Main
Consumer end?

Should the whole of the secondary consumer unit be protected at the
inlet point with a resudual current breaker (I would prefer to avoid
the pond stuff going off due to a fault on one of the other circuits)

Is conduited T&E sufficient for the external power runs to the pond,
garden lights and power outlets.

Is the earth on the armoured cable sufficient or do I require an earth
rod in the garden?

I intend to do alll the trenching and laying in of cabling and get a
local sparks in to do the final hook-up. Can anyone think of anything
I have ommitted? (I'm sure this is a common enough project that someone
will have done something similar.

Sorry for all the detail, 1st posting here and would prefer to get as
much info down as possible.

wrote:

1. Run a power feed from the house consumer unit to a secondary
consumer unit in the summer house using armoured cable. Cable to be
buried (Depth?)

Present advice in the IEE EGBR is 500 mm (or 600 mm if under a vegetable
plot). Marker tape should be placed while back-filling, so as to be at
approx 150 mm below the finished ground level.

2. Run (alongside the armoured cable but in a conduit) 2 data cables,
a front door bell, and a telephone cable. I will include a length of
thin Polyprop rope to allow for futher cables to be pulled later.

Use some sort of seamless duct (intended for underground use), rather
than electrical conduit, so it stays dry. I used green cable TV duct,
scrounged from a helpful man working in the road, for mine. Blue MDPE
water pipe (suitably marked) is another option.

3. From the secondary consumer unit:-
i. Individual Power for the pond pump and UV. To be security
switched and needs some kind of visual indicator (like an led switch
without the switch)
ii. Individual Power run to each of 4 Garden lights (each to be
individually switched from within the summer house. These will be spurs
rather than a ring.
iii. Individual Power run to each of 2 waterproof power outlets
in the Garden.

A grid switch system (e.g. MK Grid Plus) is your friend here. Make
yourself a control panel with switches (I'd suggest DP for all the
outdoor stuff), secret key switches, neon indicators and fuses as
required. Make sure everything is clearly labelled.

iv. A small 'ring-main' within the summer house (to be capable
of running total comsumption of c10A).

If you only want a few sockets, a 16 A or 20 A radial circuit in 2.5
mm^2 will suffice. No need for a ring.

v. Lighting for the summer house itself.

I am intending protecting the circuits from the summer house with
individual Residual Current breakers on the secondary Consumer unit.

RCBOs, you mean (combined MCB and RCD). An expensive option: are you
sure that's not a little OTT?

One breaker for the external lights, one for the power outlets, one for
the pond stuff, one for the internal ring, and one for the internal
lighting.

Another option would be a split-load unit with a 100 mA RCD for all the
fixed equipment and a 30 mA one for the two socket circuits. You'd then
have (say) 5 MCBs: summerhouse sockets, outdoor sockets, pond (sub-fused
if necessary at the control panel with BS 1362 fuses), summerhouse
lights, outdoor lights.

With all the above in mind.....

Should I protect the Power run from the main consumer unit to the
secondary consumer unit with an Residual Current breaker at the Main
Consumer end?

Not unless that's necessary to protect the submain cable (unlikely in
most cases). If you did use an RCD here is would have to be a
time-delayed type.

Should the whole of the secondary consumer unit be protected at the
inlet point with a resudual current breaker (I would prefer to avoid
the pond stuff going off due to a fault on one of the other circuits)

Not if you use individual RCBOs, or multiple RCDs.

Is conduited T&E sufficient for the external power runs to the pond,
garden lights and power outlets.

Yes, if it will stay dry and the T&E won't be exposed to direct
sunlight. Generally though, it's a lot less bother to use direct buried
1.5 or 2.5 SWA for this sort of thing - and it's quite cheap.

Is the earth on the armoured cable sufficient or do I require an earth
rod in the garden?

More information required: cable size; length of run; circuit rating (32
A might be about right?); type of house earthing; any accessible Class 1
(metal cased, earthed) equipment to be installed outdoors; any
electrical supply to a metal-framed greenhouse? Also "earth on the
armoured cable" subdivides into two options - 2-core with armour as
earth, and 3-core with one core plus armour as earth.

I intend to do alll the trenching and laying in of cabling and get a
local sparks in to do the final hook-up. Can anyone think of anything
I have ommitted? (I'm sure this is a common enough project that someone
will have done something similar.

You'll find plenty of previous threads on this in the Google archive.

--
Andy

Andy Wade wrote:
wrote:

1. Run a power feed from the house consumer unit to a secondary
consumer unit in the summer house using armoured cable. Cable to be
buried (Depth?)

Present advice in the IEE EGBR is 500 mm (or 600 mm if under a vegetable
plot). Marker tape should be placed while back-filling, so as to be at
approx 150 mm below the finished ground level.

Thanks, should all be at 0.5m then.


2. Run (alongside the armoured cable but in a conduit) 2 data cables,
a front door bell, and a telephone cable. I will include a length of
thin Polyprop rope to allow for futher cables to be pulled later.

Use some sort of seamless duct (intended for underground use), rather
than electrical conduit, so it stays dry. I used green cable TV duct,
scrounged from a helpful man working in the road, for mine. Blue MDPE
water pipe (suitably marked) is another option.

I am getting some undergound condiut (courtesy of my father who works
for a major electrical company - they dig a lot of roads up). It is
seamless and I will be able to do the entire run in one piece.


3. From the secondary consumer unit:-
i. Individual Power for the pond pump and UV. To be security
switched and needs some kind of visual indicator (like an led switch
without the switch)
ii. Individual Power run to each of 4 Garden lights (each to be
individually switched from within the summer house. These will be spurs
rather than a ring.
iii. Individual Power run to each of 2 waterproof power outlets
in the Garden.

A grid switch system (e.g. MK Grid Plus) is your friend here. Make
yourself a control panel with switches (I'd suggest DP for all the
outdoor stuff), secret key switches, neon indicators and fuses as
required. Make sure everything is clearly labelled.

Had looked at these. Nice to know I was on the right tracks.


iv. A small 'ring-main' within the summer house (to be capable
of running total comsumption of c10A).

If you only want a few sockets, a 16 A or 20 A radial circuit in 2.5
mm^2 will suffice. No need for a ring.

Thats nicer. Saves a lot of cable


v. Lighting for the summer house itself.

I am intending protecting the circuits from the summer house with
individual Residual Current breakers on the secondary Consumer unit.

RCBOs, you mean (combined MCB and RCD). An expensive option: are you
sure that's not a little OTT?

Thats what I had in mind. Would rather be OTT than underprotected.
May now revise if it is way OTT though.


One breaker for the external lights, one for the power outlets, one for
the pond stuff, one for the internal ring, and one for the internal
lighting.

Another option would be a split-load unit with a 100 mA RCD for all the
fixed equipment and a 30 mA one for the two socket circuits. You'd then
have (say) 5 MCBs: summerhouse sockets, outdoor sockets, pond (sub-fused
if necessary at the control panel with BS 1362 fuses), summerhouse
lights, outdoor lights.

Not sure I understand the difference here.


With all the above in mind.....

Should I protect the Power run from the main consumer unit to the
secondary consumer unit with an Residual Current breaker at the Main
Consumer end?

Not unless that's necessary to protect the submain cable (unlikely in
most cases). If you did use an RCD here is would have to be a
time-delayed type.

Thanks, thought it was a bit overkill. The armoured cable is *tough*


Should the whole of the secondary consumer unit be protected at the
inlet point with a resudual current breaker (I would prefer to avoid
the pond stuff going off due to a fault on one of the other circuits)

Not if you use individual RCBOs, or multiple RCDs.

Thats good. Would rather the pump didn't cut out if anyhing else did.


Is conduited T&E sufficient for the external power runs to the pond,
garden lights and power outlets.

Yes, if it will stay dry and the T&E won't be exposed to direct
sunlight. Generally though, it's a lot less bother to use direct buried
1.5 or 2.5 SWA for this sort of thing - and it's quite cheap.

Doh! Didn't think of using smaller gauge. Direct burial would be a
lot easier.


Is the earth on the armoured cable sufficient or do I require an earth
rod in the garden?

More information required: cable size; length of run; circuit rating (32
A might be about right?); type of house earthing; any accessible Class 1
(metal cased, earthed) equipment to be installed outdoors; any
electrical supply to a metal-framed greenhouse? Also "earth on the
armoured cable" subdivides into two options - 2-core with armour as
earth, and 3-core with one core plus armour as earth.

You are correct in that the Circuit is to be fused at 32A.
Type of house earthing. No idea (how do I tell?)
Multiple equipment types, but will include a mini server farm so will
need to be earthed.
No supply to green house. Summer House is wooden construction.
Mains supply to summer House will be 3 core one core + armour as earth.


I intend to do alll the trenching and laying in of cabling and get a
local sparks in to do the final hook-up. Can anyone think of anything
I have ommitted? (I'm sure this is a common enough project that someone
will have done something similar.

You'll find plenty of previous threads on this in the Google archive.

Google is my best friend at the moment.


--
Andy

Thanks for your time,
Mike

wrote:

I am getting some undergound condiut (courtesy of my father who works
for a major electrical company - they dig a lot of roads up). It is
seamless and I will be able to do the entire run in one piece.

That sounds fine.

Thats what I had in mind. Would rather be OTT than underprotected.
May now revise if it is way OTT though.

Some might say it's way OTT, I only said it might be a little OTT. If
_you_ don't think it's OTT then /ipso facto/ it isn't, as you obviously
think the cost's acceptable.

Another option would be a split-load unit with a 100 mA RCD for all the
fixed equipment and a 30 mA one for the two socket circuits. You'd then
have (say) 5 MCBs: summerhouse sockets, outdoor sockets, pond (sub-fused
if necessary at the control panel with BS 1362 fuses), summerhouse
lights, outdoor lights.

Not sure I understand the difference here.

Your proposal is individual RCBOs, i.e. you'd have a main switch feeding
the busbars, from which each final circuit would be taken off via an
individual single device (one or two modules wide, depending on
manufacturer) providing both residual current and overcurrent protection
for that circuit only.

My suggested alternative option would involve a single main switch
feeding two two-module-wide RCDs (providing only residual current
protection); each RCD than feeds its own busbar and neutral bar, from
which final circuits are taken off via individual MCBs, which provide
the overcurrent protection. This way the (relatively expensive) RCDs
are shared between a number of circuits.

I suggest you get hold of copies of the IEE On-Site Guide (ISBN
0863413749) and Electrician's Guide to the Building Regs (ISBN
086341463X) - both available from Amazon - as you'll find them useful
references for this sort of thing.

Thanks, thought it was a bit overkill. The armoured cable is *tough*

Yes, but you still need to be sure that the fuse/MCB at the house end
would blow if someone dug through it.

You are correct in that the Circuit is to be fused at 32A.

Just guessing. We still need to know the run length, and details at the
house end (fuse or MCB, and what type) to select an appropriate cable
size. For SWA submain cables this is seldom determined by current
rating considerations, voltage drop and earth fault loop impedance are
usually the determining factors.

Type of house earthing. No idea (how do I tell?)

See the FAQ. Basically there are three types:

TN-S - where the main earthing conductor from the CU is connected to the
metal (usually lead) sheath of the supply cable with an earthing
clamp. Normally found on older supplies (pre-mid-1970s) in urban areas.

TN-C-S (aka PME) - where the main earthing conductor is connected to a
special sealed terminal in the supplier's fused cut-out unit. (Here the
supply cable is 2-core and your earth is taken from the supply neutral,
which is earthed at many points in the street.) Normally found on newer
premises, or where the service cable has been replaced. Frequently
there will be a PME warning label.

TT (obsolescent) - where the supplier provides no earth connection and
you rely on an local earth rod (etc.) in conjunction with RCD(s) or an
older ELCB ('earth leakage trip'). Normally found in rural areas with
overhead supplies, although the overhead networks are being upgraded for
PME, so recent overhead connections are likely to be TN-C-S.

Don't confuse the main bonding conductors, which go to the water and gas
pipes, with the main earthing conductor. If in doubt post a picture of
the supply position on some web space somewhere and the panel will offer
opinions.

Multiple equipment types, but will include a mini server farm so will
need to be earthed.
No supply to green house. Summer House is wooden construction.
Mains supply to summer House will be 3 core one core + armour as earth.

.... and the length is?

--
Andy

big snip
Multiple equipment types, but will include a mini server farm so will
need to be earthed.
No supply to green house. Summer House is wooden construction.
Mains supply to summer House will be 3 core one core + armour as earth.

... and the length is?

15-20Metres (depending on precise route the cable takes) measured from
the main consumer unit to the secondary consumer unit. Each of the
power outlets will be about 10m from the secondary, the lights will be
between 15mteres (furthest), and 5 metres (nearest). Pond is about 5
metres from the secondary. Will get back on the earth type.


--
Andy