When landscaping my back garden, I decided to install some electric
cable for future lighting and power requirements. I was advised to
install 4-core cable which would run from a separate consumer unit in a
shed, itself fed from the main consumer unit positioned in the house.

I am now at the point of wanting to connect the electrics up, but have
now been told that I needed a 5 core cable to feed both lighting and
power sockets. Originally, I was told that it would be acceptable to
operate a common neutral, leaving me with 2 lives (one for lighting and
one for power), and the earth.

If this method really can't be used, is it acceptable to use the outer
armour as the earth, freeing up a cable for a second neutral?

Forgive my apparent ignorance, but I want to try and understand my best
options (short of digging up the garden and replacing the cable with a
5 core!)

Thanks for any advice.

MB wrote:

If this method really can't be used, is it acceptable to use the outer
armour as the earth, freeing up a cable for a second neutral?

In simple terms, and assuming that the cable is a steel wire armoured
one, then yes you can use the armour for the earth.

Forgive my apparent ignorance, but I want to try and understand my best
options (short of digging up the garden and replacing the cable with a
5 core!)

Outdoor electrics are not always straightforward, and there are a few
gottchas. We would need a bit more background to give any really useful
advice. In particular, what sort of lights and sockets are you feeding?
How is the shed CU fed with power, and what sort of earthing system does
your house use. Also what cable lengths are involved.

--
Cheers,

John.

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MB wrote:

When landscaping my back garden, I decided to install some electric
cable for future lighting and power requirements. I was advised to
install 4-core cable which would run from a separate consumer unit in a
shed, itself fed from the main consumer unit positioned in the house.

I am now at the point of wanting to connect the electrics up, but have
now been told that I needed a 5 core cable to feed both lighting and
power sockets. Originally, I was told that it would be acceptable to
operate a common neutral, leaving me with 2 lives (one for lighting and
one for power), and the earth.

If this method really can't be used, is it acceptable to use the outer
armour as the earth, freeing up a cable for a second neutral?

Forgive my apparent ignorance, but I want to try and understand my best
options (short of digging up the garden and replacing the cable with a
5 core!)

Thanks for any advice.

Life is so much simpler if you run 12v around instead. No regulations,
no significant safety issue, no rcd trips, no wiring failures due to
water ingress, run the cable where you want, fuse it how you want,
plenty of lights readily available that will run on it etc. You could
keep your cable for 240 power and add another for 12v lighting.


NT

John Rumm wrote:
MB wrote:

If this method really can't be used, is it acceptable to use the outer
armour as the earth, freeing up a cable for a second neutral?

In simple terms, and assuming that the cable is a steel wire armoured
one, then yes you can use the armour for the earth.

I would still be tempted to put an earth spike in and earth to that AS WELL.

wrote:
MB wrote:

When landscaping my back garden, I decided to install some electric
cable for future lighting and power requirements. I was advised to
install 4-core cable which would run from a separate consumer unit in a
shed, itself fed from the main consumer unit positioned in the house.

I am now at the point of wanting to connect the electrics up, but have
now been told that I needed a 5 core cable to feed both lighting and
power sockets. Originally, I was told that it would be acceptable to
operate a common neutral, leaving me with 2 lives (one for lighting and
one for power), and the earth.

If this method really can't be used, is it acceptable to use the outer
armour as the earth, freeing up a cable for a second neutral?

Forgive my apparent ignorance, but I want to try and understand my best
options (short of digging up the garden and replacing the cable with a
5 core!)

Thanks for any advice.

Life is so much simpler if you run 12v around instead. No regulations,
no significant safety issue, no rcd trips, no wiring failures due to
water ingress, run the cable where you want, fuse it how you want,
plenty of lights readily available that will run on it etc. You could
keep your cable for 240 power and add another for 12v lighting.


NT

Except that 3KW at 12v is about 300A, which requires twin cables
slightly thicker the mains water pipes to do any distance without losing
most of the voltage. And a ****ING big 12v transformer at the other end,

Whereas its well within even modest dimesnions of underground armored
cable at 240V.

wrote:
MB wrote:

When landscaping my back garden, I decided to install some electric
cable for future lighting and power requirements. I was advised to
install 4-core cable which would run from a separate consumer unit in a
shed, itself fed from the main consumer unit positioned in the house.

I am now at the point of wanting to connect the electrics up, but have
now been told that I needed a 5 core cable to feed both lighting and
power sockets. Originally, I was told that it would be acceptable to
operate a common neutral, leaving me with 2 lives (one for lighting and
one for power), and the earth.

If this method really can't be used, is it acceptable to use the outer
armour as the earth, freeing up a cable for a second neutral?

Forgive my apparent ignorance, but I want to try and understand my best
options (short of digging up the garden and replacing the cable with a
5 core!)

Thanks for any advice.

Life is so much simpler if you run 12v around instead. No regulations,
no significant safety issue, no rcd trips, no wiring failures due to
water ingress, run the cable where you want, fuse it how you want,
plenty of lights readily available that will run on it etc. You could
keep your cable for 240 power and add another for 12v lighting.

.... and you need very thick cable for any runs more than a few metres
long which have significant power consumption through them.

--
Chris Green

Thanks everyone for your comments.

In answer to the queries:

1. I don't know what type of earthing the main house uses - sorry, I am
not an electrician (and it probably shows). However, if it helps, the
house is only a few years old - so this might indicate the type of
earthing used?

2. The CU in the shed would be supplied from a spare 32A fuse on the
main CU in the house. I ran a 6mm 3 core armoured cable underground to
supply this from the house to the shed.

3. The distances involved are quite large. I don't have the figures to
hand, but it is c. 40 metres from the house to the shed. From the shed
5 cables radiate out across the garden. The furthest point that I am
looking to supply is about 80 metres from the shed. The cable for these
runs is 4 core 2.5mm. Voltage drops were calculated at the time, and I
know that it worked out considering the likely level of loading.

4. I intend to use low voltage lighting, but due to the distances
involved, I had to run 240v to as near as possible to the point of use.
Naturally, I needed 240v for the power outlets.

I am intrigued about this idea of using separate lives for switching -
my original intention was to have separate lighting zones in the
garden, being able to turn each on independently. However, as I want to
incorporate power sockets in these same zones using the same 4 core
cable this is where the problem starts.

If I am allowed to wire both lives from the 4 core into the same MCB in
the shed, then presumably to allow the switching, I would pass the live
for the lighting through a separate switch, while the live for the
power sockets runs uninterupted?

Alternatively, is it possible to 'link' two MCBs (a bit like the
di-pole switch) so that if any maintenance is to carried out on one
circuit, both have to be switched off at the same time?

Thanks everyone for their interest - please let me know if you need any
more clarification.

Best regards

Michael.

MB wrote:

1. I don't know what type of earthing the main house uses - sorry, I am
not an electrician

Then you should fix both of these (to a small, but useful extent). Go
to your local wholesaler and splash out a tenner or so for a copy of
"The On-site Guide". This explains pretty much all you ever need to
know regularly for most situations, including the rules you need to
follow for your earthing here. Well worth a read.

Thank you for your advice.

I should make it clear that I have no intention of installing this
myself - and will be looking for the help of a qualified electrican - I
value my life too much. However, I do like to understand broadly what
can and can't be done before paying the professional.

Sorry, John, I neglected to answer one of your questions.

The power sockets to be supplied would be single gang 13Amp sockets,
probably the MK Masterseal type which have a good IP rating.

I intend to use low volatge lighting, probably 12v - no SBS or SES type
arrangements.

wrote:

Life is so much simpler if you run 12v around instead. No regulations,

Incorrect. The requirements of Part P and BS 7671 apply to the whole of
an electrical installation, including ELV circuits. There's an
exemption in Part P (Schedule 2B paragraph 3(a) for:

"telephone wiring or extra-low voltage wiring for the purposes of
communications, information technology, signalling, control and similar
purposes, where the wiring is not in a special location;"

but not for ELV power circuits. The work would still be notifiable
since wiring in a garden counts as a "special installation" (as defined).

no significant safety issue

Significant risks of overheating and fire could exist if proper
overcurrent protection is not provided. Protection against electric
shock requires correct application of the many regulations in BS 7671
relating to SELV (or other ELV) systems.

--
Andy

The Natural Philosopher wrote:
wrote:
MB wrote:

When landscaping my back garden, I decided to install some electric
cable for future lighting and power requirements. I was advised to

Life is so much simpler if you run 12v around instead. No regulations,
no significant safety issue, no rcd trips, no wiring failures due to
water ingress, run the cable where you want, fuse it how you want,
plenty of lights readily available that will run on it etc. You could
keep your cable for 240 power and add another for 12v lighting.

Except that 3KW at 12v is about 300A, which requires twin cables
slightly thicker the mains water pipes to do any distance without losing
most of the voltage. And a ****ING big 12v transformer at the other end,

I'd be surprised if the OP intended to put 3kW of lighting in his
garden


Chris Green:

... and you need very thick cable for any runs more than a few metres
long which have significant power consumption through them.

Very thick cables are one way, but not a necessity. Now that I know the
OP is looking at long wiring runs, this is one point against 12v, but
its still quite doable without resorting to monster cables.

For very long runs the OP talks about, put one 12v light on each 2
cores, calculate the Vdrop on the cable, and set your 12v supply to
deliver 12v + cable Vdrop. Calcs are needed to see what the Vdrop is,
or I suppose it could be measured if preferred.

Another option is to put lamps in groups of 2 in series, and run them
from 24v.


Andy Wade:
NT:

Life is so much simpler if you run 12v around instead. No regulations,

Incorrect. The requirements of Part P and BS 7671 apply to the whole of

no significant safety issue

Significant risks of overheating and fire could exist if proper
overcurrent protection is not provided.

Correct fusing is elementary. Plus 12v PSUs normally have some sort of
overcurrent protectiion built in.


Protection against electric
shock requires correct application of the many regulations in BS 7671
relating to SELV (or other ELV) systems.

Since one can hold 12v without feeling a thing, its hard to see all
those regs being relevant to shock protection IRL.


The main real life advantage of 12v systems is their ability to survive
water contamination. Generally speaking outdoor 240v lighting is prone
too being troubled by water, and does not have the long term
reliability of survivability that indoor kit has. 12v gets round this
because it will continue to function (safely) when wet, and dry itself
out. Plus at just 6v from ground, the risk is so low one could put a
tongue ontoa bare wire and be unharmed.


NT

Except that 3KW at 12v is about 300A, which requires twin cables slightly
thicker the mains water pipes to do any distance without losing most of
the voltage. And a ****ING big 12v transformer at the other end,

It's garden lighting, not a floodlighting for a Premiership football field.

Christian.

Thanks for your reply Owain. A couple of questions.......

Very careful consideration will have to be given to equipotential zones.

Can you explain what you mean by this?

You can still do this if you use X10 or similar mains-borne remote
control switching. This would allow you to control your lights etc from
the house, or multiple locations.

I don't understand how the X10 or similar would allow me to use a
common neutral. Or are you assuming that both lives would be wired
through the same MCB?

I like the idea behind the X10 product - originally, I had intended to
use a remote switch panel which used similar technology to that used in
remote garage doors and gates etc. However, the range on these can be a
bit limited.

Thanks for your help.

MB wrote:

In answer to the queries:

1. I don't know what type of earthing the main house uses - sorry, I am
not an electrician (and it probably shows). However, if it helps, the
house is only a few years old - so this might indicate the type of
earthing used?

A fair chance you have TN-C-S then... however to confirm, have a read of
a couple of pages starting he

http://www.diyfaq.org.uk/electrical/....html#earthing

If it is still not obvious then post a picture of your supply
installation (i.e. where the supply cable enters the house and connects
up to the meter etc) for us to have a look at.

2. The CU in the shed would be supplied from a spare 32A fuse on the
main CU in the house. I ran a 6mm 3 core armoured cable underground to
supply this from the house to the shed.

Cable wise that sounds ok. The length of the cable would suggest that
your shed will need to be a TT install (i.e. local earth spike with RCD
protection on all circuits). In which case you would not usually use the
exported earth from the house (it would be there to protect the cable,
but not connected to the CU in the shed). If you do have a TN-C-S
installation then that is another strong indication that the shed supply
should be TT since otherwise you would need to export and continue the
equipotential zone in the shed. Depending on its construction this may
be difficult.

3. The distances involved are quite large. I don't have the figures to
hand, but it is c. 40 metres from the house to the shed. From the shed
5 cables radiate out across the garden. The furthest point that I am
looking to supply is about 80 metres from the shed. The cable for these
runs is 4 core 2.5mm. Voltage drops were calculated at the time, and I
know that it worked out considering the likely level of loading.

With that long run you will need to watch voltage drop. A 2kw appliaance
for example would pull the voltage down below spec even without
including the 6mm SWA run to the shed. For lighting however it will
probably be fine.

4. I intend to use low voltage lighting, but due to the distances
involved, I had to run 240v to as near as possible to the point of use.
Naturally, I needed 240v for the power outlets.

In this circumstance you don't actually gain much advantage from the low
voltage lighting.

I am intrigued about this idea of using separate lives for switching -
my original intention was to have separate lighting zones in the
garden, being able to turn each on independently. However, as I want to
incorporate power sockets in these same zones using the same 4 core
cable this is where the problem starts.

Can't see why. With 4 cores and a shield used as an earth you have
plenty of options. For example you could have a live and neutral for a
lighting circuit and use the other two wires for the socket. You could
have three switched lives (starting at the same MCB) and one neutral to
provide three discrete lighting zones (and no socket).

If I am allowed to wire both lives from the 4 core into the same MCB in
the shed, then presumably to allow the switching, I would pass the live
for the lighting through a separate switch, while the live for the
power sockets runs uninterupted?

Yes, with the caveat that the lighting fixtures you use will need to be
of a design that allows the use of a supply with a high protective
device current rating. (i.e. a 16A MCB), Many lamp holders require lower
rating protective devices than this.

Alternatively, is it possible to 'link' two MCBs (a bit like the
di-pole switch) so that if any maintenance is to carried out on one
circuit, both have to be switched off at the same time?

No, absolutely not.

--
Cheers,

John.

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\================================================= ================/

wrote:
The Natural Philosopher wrote:
wrote:
MB wrote:

When landscaping my back garden, I decided to install some electric
cable for future lighting and power requirements. I was advised to

Life is so much simpler if you run 12v around instead. No regulations,

Chris Green:

... and you need very thick cable for any runs more than a few metres
long which have significant power consumption through them.

Very thick cables are one way, but not a necessity. Now that I know the
OP is looking at long wiring runs, this is one point against 12v, but
its still quite doable without resorting to monster cables.

For very long runs the OP talks about, put one 12v light on each 2
cores, calculate the Vdrop on the cable, and set your 12v supply to
deliver 12v + cable Vdrop. Calcs are needed to see what the Vdrop is,
or I suppose it could be measured if preferred.

Another option is to put lamps in groups of 2 in series, and run them
from 24v.

Using 2.5T&E @ 0.019 ohms/mtre/conductor, for 10 metre run we get a
total cable R of 2x 0.19 ohms = 0.38 ohms.

With a 20w 12v halogen lamp (i=20/12=1.66A) that gives us a Vdrop of
0.38 x 1.66 = 0.63v. This is not a problem.

1.5mm T&E would give 1v drop, again not a problem.

Putting the unused bare wire in parallel with the black wire would drop
these figures further. So too would the options of lower power bulbs,
LEDs, CFLs, or 24v working would lower the perectnage drop. But no
reduction is needed.


NT

MB wrote:

Thanks for your reply Owain. A couple of questions.......


Very careful consideration will have to be given to equipotential zones.


Can you explain what you mean by this?

I alluded to this in my ealier post as well. If you have a TN-C-S
install, it is very important that your equipotential bonding is up to
current standards. This is because there are some fault conditions, like
for example a break in the neutral connection to your property, that
could leave all exposed earthed metalwork in your house sat at mains
voltage. This is because with TN-C-S the connection between neutral and
earth is made at your house and not at the substation. Take away the
neutral and everything floats up to mains voltage. The solution to this
problem is to ensure that any metalwork that you are likely to come into
contact with is all electrically bonded together, keeping it all at the
same fault voltage, and hence unlikly to give rise to a serious shock
hazard.

Now when you take power outside, things become much more trickey. Access
to an independant earth is in many cases now easy (you are standing on
it!) So it is much harder to prevent you from simultaneously coming into
contact with an electrical earth sat at a fault voltage, and a another
local earth at a much lower potential. It is possible to do this in a
well made shed or garrage with an insulating floor for example, but
almost impossible in a building sat directly on the ground. For most
practical applications it is simpler to disconnect from the house earth
and use your own local one.

You can still do this if you use X10 or similar mains-borne remote
control switching. This would allow you to control your lights etc from
the house, or multiple locations.


I don't understand how the X10 or similar would allow me to use a
common neutral. Or are you assuming that both lives would be wired
through the same MCB?

You don't have a common neutral as such, you just have one live and an
associated neutral. There is no need to have multiple switched circuits
anymore to achieve control of the lights.

Basically you daisy chain your lights between a live and neutral on a
circuit. The X10 device provides switching for the light local to the
switch (not for the whole circuit necessarily - unless that is what you
want). The control information that instructs a X10 device to swithc on
or off passes down the mains wiring to it.



--
Cheers,

John.

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Owain & John

Thank you for your very useful advice.

One final question (for now at least), would the X10 system work across
multiple consumer units? For example, were I to plug the controller in
somewhere in the house, the signal would have to pass through the main
house CU, to the proposed shed CU and then down the cable to the
lights.

Thanks once again for your help.

Michael.

Thanks - I'll probably give that a go.

In article . com,
"MB" writes:
Owain & John

Thank you for your very useful advice.

One final question (for now at least), would the X10 system work across
multiple consumer units? For example, were I to plug the controller in
somewhere in the house, the signal would have to pass through the main
house CU, to the proposed shed CU and then down the cable to the
lights.

Connect the X10 sender to a socket near to the CU if possible.
That will give best possible chance of coverage to everywhere.

--
Andrew Gabriel