Hi,

I am going to be running SWA cable out to the garage soon (Total run is
a little under 20em from the house CU to the garage CU)

I will also be installing a generator point on the garage, which will be
connecting to a proper transfer switch in the house.

It will be easier and cheaper if I just run a single SWA cable with 4
cores, two for the generator and two for the feed into the garage.

Is this permitted, or do I have to have two separate cables?

The SWA will be terminated in the house and garage in a metal box, then
the two circuits taken from there to there respective places.

Thanks!

Toby...

Toby wrote:
Hi,

I am going to be running SWA cable out to the garage soon (Total run is
a little under 20em from the house CU to the garage CU)

I will also be installing a generator point on the garage, which will be
connecting to a proper transfer switch in the house.

It will be easier and cheaper if I just run a single SWA cable with 4
cores, two for the generator and two for the feed into the garage.

Is this permitted, or do I have to have two separate cables?

The SWA will be terminated in the house and garage in a metal box, then
the two circuits taken from there to there respective places.

The main complexity sounds like it is going to be dealing with earthing
and possibly main equipotential bonding. What earthing scheme do you
have in the house?

--
Cheers,

John.

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

John Rumm wrote:
Toby wrote:
Hi,

I am going to be running SWA cable out to the garage soon (Total run
is a little under 20em from the house CU to the garage CU)

I will also be installing a generator point on the garage, which will
be connecting to a proper transfer switch in the house.

It will be easier and cheaper if I just run a single SWA cable with 4
cores, two for the generator and two for the feed into the garage.

Is this permitted, or do I have to have two separate cables?

The SWA will be terminated in the house and garage in a metal box,
then the two circuits taken from there to there respective places.

The main complexity sounds like it is going to be dealing with earthing
and possibly main equipotential bonding. What earthing scheme do you
have in the house?


The idea was to use the SWA armour as the earth for both and have an
additional earthing rod next to the generator point connected via 10mm
cable (Generator is only 7.5KVA).

The generator transfer switch This one -
http://www.briggsandstrattongenerato...ertransfer.htm
does not have the facility to switch the earthing, so I am assuming all
the earth connections can stay connected all the time?

My main earth is supplied by the armour of the incoming supply cable (TN-S)

Is there any reason the earth connection to this can't be left connected
in the event of a power failure with the generator running?
(I assumed it is OK as the transfer switch does not have the facility to
switch the earth connection)
The generator has one leg of it's output tied to ground, so there will
be no potential difference between neutral and earth in the system. If
live found it's way to earth, this would just create a short, tripping
the MCB, so, as far as I can see it, there is no risk to anyone working
on the power grid here (just like the power company ties their neutral
to earth everywhere)

Also any reason the earth rod can't stay "in circuit" during normal
operation (considering the lead water pipe is connected to the earthing
system 24/7 via 10mm cable and this will be acting the same, if not better)

In reality the generator won't be running very often, as the mains power
supply should be reliable, but I already have the generator, so am just
making provision for it's use "just in case" - If I move out, it will be
coming with me too, so nothing to worry about later on either, it will
simply be disconnected.

Toby...

Toby wrote:
John Rumm wrote:
Toby wrote:
Hi,

I am going to be running SWA cable out to the garage soon (Total run
is a little under 20em from the house CU to the garage CU)

I will also be installing a generator point on the garage, which will
be connecting to a proper transfer switch in the house.

It will be easier and cheaper if I just run a single SWA cable with 4
cores, two for the generator and two for the feed into the garage.

Is this permitted, or do I have to have two separate cables?

The SWA will be terminated in the house and garage in a metal box,
then the two circuits taken from there to there respective places.

The main complexity sounds like it is going to be dealing with
earthing and possibly main equipotential bonding. What earthing scheme
do you have in the house?


The idea was to use the SWA armour as the earth for both and have an
additional earthing rod next to the generator point connected via 10mm
cable (Generator is only 7.5KVA).

The generator transfer switch This one -
http://www.briggsandstrattongenerato...ertransfer.htm
does not have the facility to switch the earthing, so I am assuming all
the earth connections can stay connected all the time?

My main earth is supplied by the armour of the incoming supply cable (TN-S)

Is there any reason the earth connection to this can't be left connected
in the event of a power failure with the generator running?
(I assumed it is OK as the transfer switch does not have the facility to
switch the earth connection)
The generator has one leg of it's output tied to ground, so there will
be no potential difference between neutral and earth in the system. If
live found it's way to earth, this would just create a short, tripping
the MCB, so, as far as I can see it, there is no risk to anyone working
on the power grid here (just like the power company ties their neutral
to earth everywhere)

Also any reason the earth rod can't stay "in circuit" during normal
operation (considering the lead water pipe is connected to the earthing
system 24/7 via 10mm cable and this will be acting the same, if not better)

In reality the generator won't be running very often, as the mains power
supply should be reliable, but I already have the generator, so am just
making provision for it's use "just in case" - If I move out, it will be
coming with me too, so nothing to worry about later on either, it will
simply be disconnected.

Toby...

I think John is alluding to concerns about "exporting" the earth from
your TN-S main supply out to the garage and "re-importing" the generator
earth back from the garage to the house.

see here for more info:

http://wiki.diyfaq.org.uk/index.php?...i ng_an_earth

Given that you have a TN-S supply and are proposing properly buried SWA
cabling and this garage is presumably a building of substance rather
than a rickety shed, then I would probably be inclined to (permanently)
connect all the earths together and run an additional main-bonding
conductor alongside your SWA cables. You should consider getting a duct
to run your cables rather than direct burial, because you would need to
upgrade your main bonding earth wire further if it was direct buried.

e.g.
http://www.polypipe.com/polypipe/con...ategoryID=7598

Dave Osborne wrote:
Toby wrote:
John Rumm wrote:
Toby wrote:
Hi,

I am going to be running SWA cable out to the garage soon (Total run
is a little under 20em from the house CU to the garage CU)

I will also be installing a generator point on the garage, which
will be connecting to a proper transfer switch in the house.

It will be easier and cheaper if I just run a single SWA cable with
4 cores, two for the generator and two for the feed into the garage.

Is this permitted, or do I have to have two separate cables?

The SWA will be terminated in the house and garage in a metal box,
then the two circuits taken from there to there respective places.

The main complexity sounds like it is going to be dealing with
earthing and possibly main equipotential bonding. What earthing
scheme do you have in the house?


The idea was to use the SWA armour as the earth for both and have an
additional earthing rod next to the generator point connected via
10mm cable (Generator is only 7.5KVA).

The generator transfer switch This one -
http://www.briggsandstrattongenerato...ertransfer.htm
does not have the facility to switch the earthing, so I am assuming
all the earth connections can stay connected all the time?

My main earth is supplied by the armour of the incoming supply cable
(TN-S)

Is there any reason the earth connection to this can't be left
connected in the event of a power failure with the generator running?
(I assumed it is OK as the transfer switch does not have the facility
to switch the earth connection)
The generator has one leg of it's output tied to ground, so there will
be no potential difference between neutral and earth in the system. If
live found it's way to earth, this would just create a short, tripping
the MCB, so, as far as I can see it, there is no risk to anyone
working on the power grid here (just like the power company ties their
neutral to earth everywhere)

Also any reason the earth rod can't stay "in circuit" during normal
operation (considering the lead water pipe is connected to the
earthing system 24/7 via 10mm cable and this will be acting the same,
if not better)

In reality the generator won't be running very often, as the mains
power supply should be reliable, but I already have the generator, so
am just making provision for it's use "just in case" - If I move out,
it will be coming with me too, so nothing to worry about later on
either, it will simply be disconnected.

Toby...

I think John is alluding to concerns about "exporting" the earth from
your TN-S main supply out to the garage and "re-importing" the generator
earth back from the garage to the house.

see here for more info:

http://wiki.diyfaq.org.uk/index.php?...i ng_an_earth


Given that you have a TN-S supply and are proposing properly buried SWA
cabling and this garage is presumably a building of substance rather
than a rickety shed, then I would probably be inclined to (permanently)
connect all the earths together and run an additional main-bonding
conductor alongside your SWA cables. You should consider getting a duct
to run your cables rather than direct burial, because you would need to
upgrade your main bonding earth wire further if it was direct buried.

e.g.
http://www.polypipe.com/polypipe/con...ategoryID=7598


Thanks for the reply.

The garage is indeed a proper building (brick) and is only about 6m from
the house, so this is why I am choosing to export the house earth there
- if it were down the other end of the garden, then I expect a separate
TT system would be better for the garage. - It will have an earthing rod
for the generator too, so it will be both TN-S and TT I suppose!

I was planning on using 4mm XPLE SWA cable, and having the feed to the
garage via a 32A MCB (Not RCD protected) and then have a 5 way CU in the
garage, with a main switch, RCBO's for sockets and exterior lights and a
MCB for the freezer circuit (All the wiring in the garage will be done
in surface mount conduit, so nothing will be buried in the walls)

How do I find out the CSA of the armour in the 4mm SWA cable - is there
a chart somewhere showing the values?, I am happy to use 6mm if I need
to, to get the CSA up on this cable, and save having to run another duct
(I will be running a green duct for comms cables anyway, but would
rather not run another duct just for a separate earth cable if I can
help it.

Toby...

Toby coughed up some electrons that declared:

How do I find out the CSA of the armour in the 4mm SWA cable - is there
a chart somewhere showing the values?, I am happy to use 6mm if I need
to, to get the CSA up on this cable, and save having to run another duct
(I will be running a green duct for comms cables anyway, but would
rather not run another duct just for a separate earth cable if I can
help it.

Toby...

Send me your email address (mine's valid) - I have a datasheet I can send
you on XLPE with actual and copper-equivalent CSAs.

Can't find the source though, otherwise I would have just posted a link...

Cheers

Tim

Toby wrote:
Dave Osborne wrote:
Toby wrote:
John Rumm wrote:
Toby wrote:
Hi,

I am going to be running SWA cable out to the garage soon (Total
run is a little under 20em from the house CU to the garage CU)

I will also be installing a generator point on the garage, which
will be connecting to a proper transfer switch in the house.

It will be easier and cheaper if I just run a single SWA cable with
4 cores, two for the generator and two for the feed into the garage.

Is this permitted, or do I have to have two separate cables?

The SWA will be terminated in the house and garage in a metal box,
then the two circuits taken from there to there respective places.

The main complexity sounds like it is going to be dealing with
earthing and possibly main equipotential bonding. What earthing
scheme do you have in the house?


The idea was to use the SWA armour as the earth for both and have an
additional earthing rod next to the generator point connected via
10mm cable (Generator is only 7.5KVA).

The generator transfer switch This one -
http://www.briggsandstrattongenerato...ertransfer.htm
does not have the facility to switch the earthing, so I am assuming
all the earth connections can stay connected all the time?

My main earth is supplied by the armour of the incoming supply cable
(TN-S)

Is there any reason the earth connection to this can't be left
connected in the event of a power failure with the generator running?
(I assumed it is OK as the transfer switch does not have the facility
to switch the earth connection)
The generator has one leg of it's output tied to ground, so there
will be no potential difference between neutral and earth in the
system. If live found it's way to earth, this would just create a
short, tripping the MCB, so, as far as I can see it, there is no risk
to anyone working on the power grid here (just like the power company
ties their neutral to earth everywhere)

Also any reason the earth rod can't stay "in circuit" during normal
operation (considering the lead water pipe is connected to the
earthing system 24/7 via 10mm cable and this will be acting the same,
if not better)

In reality the generator won't be running very often, as the mains
power supply should be reliable, but I already have the generator, so
am just making provision for it's use "just in case" - If I move out,
it will be coming with me too, so nothing to worry about later on
either, it will simply be disconnected.

Toby...

I think John is alluding to concerns about "exporting" the earth from
your TN-S main supply out to the garage and "re-importing" the
generator earth back from the garage to the house.

see here for more info:

http://wiki.diyfaq.org.uk/index.php?...i ng_an_earth


Given that you have a TN-S supply and are proposing properly buried
SWA cabling and this garage is presumably a building of substance
rather than a rickety shed, then I would probably be inclined to
(permanently) connect all the earths together and run an additional
main-bonding conductor alongside your SWA cables. You should consider
getting a duct to run your cables rather than direct burial, because
you would need to upgrade your main bonding earth wire further if it
was direct buried.

e.g.
http://www.polypipe.com/polypipe/con...ategoryID=7598


Thanks for the reply.

The garage is indeed a proper building (brick) and is only about 6m from
the house, so this is why I am choosing to export the house earth there
- if it were down the other end of the garden, then I expect a separate
TT system would be better for the garage. - It will have an earthing rod
for the generator too, so it will be both TN-S and TT I suppose!

I was planning on using 4mm XPLE SWA cable, and having the feed to the
garage via a 32A MCB (Not RCD protected) and then have a 5 way CU in the
garage, with a main switch, RCBO's for sockets and exterior lights and a
MCB for the freezer circuit (All the wiring in the garage will be done
in surface mount conduit, so nothing will be buried in the walls)

How do I find out the CSA of the armour in the 4mm SWA cable

http://wiki.diyfaq.org.uk/index.php?...rmour_as_a_CPC

- is there
a chart somewhere showing the values?, I am happy to use 6mm if I need
to, to get the CSA up on this cable, and save having to run another duct
(I will be running a green duct for comms cables anyway, but would
rather not run another duct just for a separate earth cable if I can
help it.

Toby...

I've done a bit more homework...

For a line CSA of 4mm2, the minimum earth CSA is 10mm2 if using the
steel armour of a buried SWA cable, provided that there is mechanical
protection[1]. (Table 54.1).

For a 4mm2 2-core SWA cable, the CSA of the armour is about 20mm2, so
you are OK in principle and don't need an additional earth wire.

[1] - dig a trench at least 550 deep. Lay about 50mm of sand
blinding[2]. Lay SWA on sand blinding (if laying two cables, keep them
separated laterally[3]). Check that top of cable is at least 450 deep.
Add 150mm sand blinding on top of cable; place mechanical protection on
top of sand blinding (roof slate, concrete tiles, clay half pipe, etc),
back fill another 150 or so; Place yellow "Electrical Service Below"
tape; Backfill to top.

[2] Use soil in lieu of sand if soil is "free of sharp stones and other
materials that might damage the cable".

[3] Note that two SWA cables sharing the trench incurs a current rating
factor of:

(Table 4C2)
0.8 (one cable diameter lateral separation);
0.85 (125mm lateral separation);
0.9 (250mm lateral separation);

Two-core 4mm2 70deg armoured cable buried direct has current capacity of
37A (Table 4D4A) so you should up-rate your line conductors to 6mm2 or
have a minimum lateral separation of 250mm to get 32A current rating.

Dave Osborne wrote:

I think John is alluding to concerns about "exporting" the earth from
your TN-S main supply out to the garage and "re-importing" the generator
earth back from the garage to the house.

I was more concern about the difficulty that may occur should one end up
with a TN-S system that has to become a TT for use with the genset. That
would them mean the need for RCD protection on all circuits to maintain
the fault protection.

However - more info from Toby suggests that the genset will be
configured to supply a TN-C-S style supply.



--
Cheers,

John.

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

John Rumm wrote:
Dave Osborne wrote:

I think John is alluding to concerns about "exporting" the earth from
your TN-S main supply out to the garage and "re-importing" the
generator earth back from the garage to the house.

I was more concern about the difficulty that may occur should one end up
with a TN-S system that has to become a TT for use with the genset. That
would them mean the need for RCD protection on all circuits to maintain
the fault protection.

However - more info from Toby suggests that the genset will be
configured to supply a TN-C-S style supply.



This is correct.

The transfer switch can also have an RCD fitted if I need it - do I (I
would rather not if I can get away with it to be honest) but if I do
need one, can I fit a 100mA one?

Thanks again!

John Rumm wrote:

However - more info from Toby suggests that the genset will be
configured to supply a TN-C-S style supply.

That's not allowed - using any combined neutral and earth (CNE)
conductor in a consumer's installation is illegal in the UK, under the
ESQC regulations [1].

Configure the generator to make a TN-S system. Here's a blast from the
past which includes an ASCII wiring diagram:

http://groups.google.co.uk/group/uk....n&dmode=source

I would very strongly discourage the 4-core SWA approach here, because
its unconventional nature could be quite dangerous for the unwary.
Using two 2-core SWAs will bolster up the armour CSA nicely too.


[1] http://www.opsi.gov.uk/si/si2002/20022665.htm#8 - regulation 8(4)

--
Andy

In article ,
Toby wrote:
Also any reason the earth rod can't stay "in circuit" during normal
operation (considering the lead water pipe is connected to the earthing
system 24/7 via 10mm cable and this will be acting the same, if not
better)

Using a water pipe to provide the earth isn't allowed these days.

--
*Plagiarism saves time *

Dave Plowman London SW
To e-mail, change noise into sound.

Dave Plowman (News) wrote:
In article ,
Toby wrote:
Also any reason the earth rod can't stay "in circuit" during normal
operation (considering the lead water pipe is connected to the earthing
system 24/7 via 10mm cable and this will be acting the same, if not
better)

Using a water pipe to provide the earth isn't allowed these days.


I realise that, but as the lead water pipe is bonded, it will be acting
as an earth (but not the primary one!) too!

Toby wrote:
Hi,

I am going to be running SWA cable out to the garage soon (Total run is
a little under 20em from the house CU to the garage CU)

I will also be installing a generator point on the garage, which will be
connecting to a proper transfer switch in the house.

It will be easier and cheaper if I just run a single SWA cable with 4
cores, two for the generator and two for the feed into the garage.

Is this permitted, or do I have to have two separate cables?

The SWA will be terminated in the house and garage in a metal box, then
the two circuits taken from there to there respective places.

Thanks!

Toby...

I have to say, I wouldn't recommend it on principle (i.e. run both
services on a single cable). From a safety point of view, it would not
be usual or expected that you would have a source of energy at each end
of a single cable. If you do choose to go this route, then make sure
your labelling is permanent, clear and unambiguous.