Hi,

I am putting in a new 32A ring main that will just be for garage
internal sockets and external outside sockets. This is on a RCBO.

Reason for this if anything happens outside, it does not affect anything
else internally in the house.

I am using IP67 rated kit for all the sockets that are outside.

The garage is integral to the house, has no windows, has a upvc door and
an up and over garage door.

I am using 20mm conduit to mechanically protect the cables from
accidental damage throughout

Now do the socket face plates and pattresses that are INSIDE the garage
have to be IP rated as well or is white domestic faceplates and
pattresses inside a garage acceptable for meeting 17th Ed wiring regs?

On 15/02/2013 15:16, Stephen H wrote:

Now do the socket face plates and pattresses that are INSIDE the garage
have to be IP rated as well or is white domestic faceplates and
pattresses inside a garage acceptable for meeting 17th Ed wiring regs?

The standard faceplates are fine for a garage; but I'd be using my own
judgement as to whether they were appropriate; eg if the roof leaked or
rain blows in through cracks etc.

Personally I use the metal clad type in the workshop / garage as they're
a bit more robust bearing in mind what goes on out there.
--
David

In article ,
Lobster wrote:
On 15/02/2013 15:16, Stephen H wrote:

Now do the socket face plates and pattresses that are INSIDE the garage
have to be IP rated as well or is white domestic faceplates and
pattresses inside a garage acceptable for meeting 17th Ed wiring regs?

The standard faceplates are fine for a garage; but I'd be using my own
judgement as to whether they were appropriate; eg if the roof leaked or
rain blows in through cracks etc.

Personally I use the metal clad type in the workshop / garage as they're
a bit more robust bearing in mind what goes on out there.

agreed

--
From KT24

Using a RISC OS computer running v5.18

On 15/02/2013 15:16, Stephen H wrote:
Hi,

I am putting in a new 32A ring main that will just be for garage
internal sockets and external outside sockets. This is on a RCBO.

Reason for this if anything happens outside, it does not affect anything
else internally in the house.

I am using IP67 rated kit for all the sockets that are outside.

The garage is integral to the house, has no windows, has a upvc door and
an up and over garage door.

I am using 20mm conduit to mechanically protect the cables from
accidental damage throughout

Now do the socket face plates and pattresses that are INSIDE the garage
have to be IP rated as well or is white domestic faceplates and
pattresses inside a garage acceptable for meeting 17th Ed wiring regs?


The only requirement in the circumstance is that they are appropriate
for the situation. So assuming it does not routinly get rain blowing in
there then normal domestic ones will be fine.

Depending on what you plan to do in there you might want to consider
metal clad (and the surface pattresses will have knockout holes ready to
take a conduit terminator) since they are physically more robust.

(flush mounted plastic sockets are also quite damage resistant!)

--
Cheers,

John.

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

On 15/02/2013 16:14, John Rumm wrote:
On 15/02/2013 15:16, Stephen H wrote:
Hi,

I am putting in a new 32A ring main that will just be for garage
internal sockets and external outside sockets. This is on a RCBO.

Reason for this if anything happens outside, it does not affect anything
else internally in the house.

I am using IP67 rated kit for all the sockets that are outside.

The garage is integral to the house, has no windows, has a upvc door and
an up and over garage door.

I am using 20mm conduit to mechanically protect the cables from
accidental damage throughout

Now do the socket face plates and pattresses that are INSIDE the garage
have to be IP rated as well or is white domestic faceplates and
pattresses inside a garage acceptable for meeting 17th Ed wiring regs?


The only requirement in the circumstance is that they are appropriate
for the situation. So assuming it does not routinly get rain blowing in
there then normal domestic ones will be fine.

I have tried to take a common sense approach. So far:

I have mounted the sockets at least 0.5m away from a door/opening as a
mitigation against blown in rain when opening/closing doors.

I have used 20mm round conduit to protect the cable drops from the
ceiling to the wall mounted sockets as I believe the wall cable drops
are more likely to sustain damage than the ceiling level ring main.

The ring main has been clipped to the wall at approx 2.8 metres above
ground level so above clumsy tall people.

As mentioned earlier, the garage sockets and outside sockets are on
their own ring main with its own 32A RCBO.

In addition, the garage lighting and outside lighting is on its own 6A RCBO.

Depending on what you plan to do in there you might want to consider
metal clad (and the surface pattresses will have knockout holes ready to
take a conduit terminator) since they are physically more robust.

(flush mounted plastic sockets are also quite damage resistant!)

The pattresses are PVC which are not as brittle as moulded ones so I
believe that will be better when impact occurs.

Getting the 20mm knockouts out of the PVC pattresses seems to be an
art.... I broke two today trying to get the knockouts out. You can't
realy use a hole saw as there is pilot hole in the plastic disc to align
the drill bit with

On 15/02/2013 16:31, Stephen H wrote:
On 15/02/2013 16:14, John Rumm wrote:
On 15/02/2013 15:16, Stephen H wrote:
Hi,

I am putting in a new 32A ring main that will just be for garage
internal sockets and external outside sockets. This is on a RCBO.

Reason for this if anything happens outside, it does not affect anything
else internally in the house.

I am using IP67 rated kit for all the sockets that are outside.

The garage is integral to the house, has no windows, has a upvc door and
an up and over garage door.

I am using 20mm conduit to mechanically protect the cables from
accidental damage throughout

Now do the socket face plates and pattresses that are INSIDE the garage
have to be IP rated as well or is white domestic faceplates and
pattresses inside a garage acceptable for meeting 17th Ed wiring regs?


The only requirement in the circumstance is that they are appropriate
for the situation. So assuming it does not routinly get rain blowing in
there then normal domestic ones will be fine.

I have tried to take a common sense approach. So far:

I have mounted the sockets at least 0.5m away from a door/opening as a
mitigation against blown in rain when opening/closing doors.

I have used 20mm round conduit to protect the cable drops from the
ceiling to the wall mounted sockets as I believe the wall cable drops
are more likely to sustain damage than the ceiling level ring main.

The ring main has been clipped to the wall at approx 2.8 metres above
ground level so above clumsy tall people.

As mentioned earlier, the garage sockets and outside sockets are on
their own ring main with its own 32A RCBO.

In addition, the garage lighting and outside lighting is on its own 6A
RCBO.

Yup all sounds eminently sensible.

Depending on what you plan to do in there you might want to consider
metal clad (and the surface pattresses will have knockout holes ready to
take a conduit terminator) since they are physically more robust.

(flush mounted plastic sockets are also quite damage resistant!)

The pattresses are PVC which are not as brittle as moulded ones so I
believe that will be better when impact occurs.

Since i was dry lining my workshop I simply mounted all the sockets
flush - makes them much harder to hit in the first place, and since I
wanted lots of them, much cheaper!

Getting the 20mm knockouts out of the PVC pattresses seems to be an
art.... I broke two today trying to get the knockouts out. You can't
realy use a hole saw as there is pilot hole in the plastic disc to align
the drill bit with

Can you not drill from the outside in?


--
Cheers,

John.

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

On 15/02/2013 16:46, John Rumm wrote: On 15/02/2013 16:31, Stephen H wrote:
On 15/02/2013 16:14, John Rumm wrote:
On 15/02/2013 15:16, Stephen H wrote:
Hi,

I am putting in a new 32A ring main that will just be for garage
internal sockets and external outside sockets. This is on a RCBO.

Reason for this if anything happens outside, it does not affect
anything
else internally in the house.

I am using IP67 rated kit for all the sockets that are outside.

The garage is integral to the house, has no windows, has a upvc door
and
an up and over garage door.

I am using 20mm conduit to mechanically protect the cables from
accidental damage throughout

Now do the socket face plates and pattresses that are INSIDE the
garage
have to be IP rated as well or is white domestic faceplates and
pattresses inside a garage acceptable for meeting 17th Ed wiring regs?


The only requirement in the circumstance is that they are appropriate
for the situation. So assuming it does not routinly get rain blowing in
there then normal domestic ones will be fine.

I have tried to take a common sense approach. So far:

I have mounted the sockets at least 0.5m away from a door/opening as a
mitigation against blown in rain when opening/closing doors.

I have used 20mm round conduit to protect the cable drops from the
ceiling to the wall mounted sockets as I believe the wall cable drops
are more likely to sustain damage than the ceiling level ring main.

The ring main has been clipped to the wall at approx 2.8 metres above
ground level so above clumsy tall people.

As mentioned earlier, the garage sockets and outside sockets are on
their own ring main with its own 32A RCBO.

In addition, the garage lighting and outside lighting is on its own 6A
RCBO.

Yup all sounds eminently sensible.

That reminds me my existing two way light switches are almost at the
edge of the doors frames. As is pre-existing installation, can I leave
them as they are or should I uprate them to IP67?

Depending on what you plan to do in there you might want to consider
metal clad (and the surface pattresses will have knockout holes
ready to
take a conduit terminator) since they are physically more robust.

(flush mounted plastic sockets are also quite damage resistant!)

The pattresses are PVC which are not as brittle as moulded ones so I
believe that will be better when impact occurs.

Since i was dry lining my workshop I simply mounted all the sockets
flush - makes them much harder to hit in the first place, and since I
wanted lots of them, much cheaper!

Getting the 20mm knockouts out of the PVC pattresses seems to be an
art.... I broke two today trying to get the knockouts out. You can't
realy use a hole saw as there is pilot hole in the plastic disc to align
the drill bit with

Can you not drill from the outside in?



How do you line up the drill's holesaw blade with the groove around the
20mm knockout as there is no pilot hole in knockout for drill bit?

On Fri, 15 Feb 2013 15:16:05 +0000, Stephen H wrote:

I am putting in a new 32A ring main that will just be for garage
internal sockets and external outside sockets. This is on a RCBO.

Reason for this if anything happens outside, it does not affect
anything else internally in the house.

If there is another upstream RCD there is no guarantee that a fault in
the garage won't trip that upstream RCD and/or the garage RCBO.
Now do the socket face plates and pattresses that are INSIDE the garage
have to be IP rated as well or is white domestic faceplates and
pattresses inside a garage acceptable for meeting 17th Ed wiring regs?

I'd use metal clad but having said that the soft plastic surface back
boxes take quite a whack, rather more than the polycarbonate face
plates/boxes.

--
Cheers
Dave.

On 15/02/2013 17:30, Dave Liquorice wrote:
On Fri, 15 Feb 2013 15:16:05 +0000, Stephen H wrote:

I am putting in a new 32A ring main that will just be for garage
internal sockets and external outside sockets. This is on a RCBO.

Reason for this if anything happens outside, it does not affect
anything else internally in the house.

If there is another upstream RCD there is no guarantee that a fault in
the garage won't trip that upstream RCD and/or the garage RCBO.
Now do the socket face plates and pattresses that are INSIDE the garage
have to be IP rated as well or is white domestic faceplates and
pattresses inside a garage acceptable for meeting 17th Ed wiring regs?

I'd use metal clad but having said that the soft plastic surface back
boxes take quite a whack, rather more than the polycarbonate face
plates/boxes.


The RCBO's are all in the CU.

The entire CU has nothing but RCBO's in it.

So no MCB's or any of that split load RCD nonsense... :-)

That's why I have a new lighting circuit for garage and outside lights
and a new ring main for garage sockets and outside sockets.

On 15/02/2013 16:55, Stephen H wrote:
On 15/02/2013 16:46, John Rumm wrote: On 15/02/2013 16:31, Stephen H
wrote:
On 15/02/2013 16:14, John Rumm wrote:
On 15/02/2013 15:16, Stephen H wrote:
Hi,

I am putting in a new 32A ring main that will just be for garage
internal sockets and external outside sockets. This is on a RCBO.

Reason for this if anything happens outside, it does not affect
anything
else internally in the house.

I am using IP67 rated kit for all the sockets that are outside.

The garage is integral to the house, has no windows, has a upvc door
and
an up and over garage door.

I am using 20mm conduit to mechanically protect the cables from
accidental damage throughout

Now do the socket face plates and pattresses that are INSIDE the
garage
have to be IP rated as well or is white domestic faceplates and
pattresses inside a garage acceptable for meeting 17th Ed wiring
regs?


The only requirement in the circumstance is that they are appropriate
for the situation. So assuming it does not routinly get rain
blowing in
there then normal domestic ones will be fine.

I have tried to take a common sense approach. So far:

I have mounted the sockets at least 0.5m away from a door/opening as a
mitigation against blown in rain when opening/closing doors.

I have used 20mm round conduit to protect the cable drops from the
ceiling to the wall mounted sockets as I believe the wall cable drops
are more likely to sustain damage than the ceiling level ring main.

The ring main has been clipped to the wall at approx 2.8 metres above
ground level so above clumsy tall people.

As mentioned earlier, the garage sockets and outside sockets are on
their own ring main with its own 32A RCBO.

In addition, the garage lighting and outside lighting is on its own 6A
RCBO.

Yup all sounds eminently sensible.

That reminds me my existing two way light switches are almost at the
edge of the doors frames. As is pre-existing installation, can I leave
them as they are or should I uprate them to IP67?

To an extent, only you can answer that. How likely are they to get
rained on? Is it significantly more than say a lightswitch next to a
back door?

Getting the 20mm knockouts out of the PVC pattresses seems to be an
art.... I broke two today trying to get the knockouts out. You can't
realy use a hole saw as there is pilot hole in the plastic disc to
align
the drill bit with

Can you not drill from the outside in?



How do you line up the drill's holesaw blade with the groove around the
20mm knockout as there is no pilot hole in knockout for drill bit?

Just by eye - in the grand scheme of things it does not matter if they
do not line up perfectly (unless the knockout section is likely to fall
out once drilled close to).

(some "knockouts" are not really knockable anyway!)


--
Cheers,

John.

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

On 15/02/2013 15:16, Stephen H wrote:
Hi,

I am putting in a new 32A ring main that will just be for garage
internal sockets and external outside sockets. This is on a RCBO.

Reason for this if anything happens outside, it does not affect anything
else internally in the house.

I am using IP67 rated kit for all the sockets that are outside.

The garage is integral to the house, has no windows, has a upvc door and
an up and over garage door.

I am using 20mm conduit to mechanically protect the cables from
accidental damage throughout

Now do the socket face plates and pattresses that are INSIDE the garage
have to be IP rated as well or is white domestic faceplates and
pattresses inside a garage acceptable for meeting 17th Ed wiring regs?

Going off slightly at a tangent, I recently wanted some MK sockets for a
mate's business (normal domestic stuff keeps getting knackered), and
this guy

http://stores.ebay.co.uk/Mr-Cheapies...p2047675.l2563

has new but "shop soiled" sockets and surface mount metal boxes at a
very decent price. As far as I can see, these are genuine un-used
components. I have a few spares waiting to go into my own workshop.

On 15/02/2013 23:09, newshound wrote:

Going off slightly at a tangent, I recently wanted some MK sockets for a
mate's business (normal domestic stuff keeps getting knackered), and
this guy

http://stores.ebay.co.uk/Mr-Cheapies...p2047675.l2563

has new but "shop soiled" sockets and surface mount metal boxes at a
very decent price. As far as I can see, these are genuine un-used
components. I have a few spares waiting to go into my own workshop.

Wish I'd seen that a few weeks ago actually!

Agree that I've often bought branded electrical accessories from ebay -
it's a good source

--
David

Stephen H wrote:
On 15/02/2013 16:46,
How do you line up the drill's holesaw blade with the groove around
the 20mm knockout as there is no pilot hole in knockout for drill bit?

Remove the pilot bit and put the holesaw into the groove!

--
Adam

On 15/02/2013 15:16, Stephen H wrote:

I am putting in a new 32A ring main that will just be for garage
internal sockets and external outside sockets.

Cor, I've just been doing a bit of that today and what a bloody horrible
job it was - courtesy of the fact that the temp was about 1 deg, and the
cable was therefore almost rock solid. Very hard to bend it where I
wanted it to go, wouldn't cut or tear easily, hard to stuff down the
conduit etc...

Note to self: in future, exterior wiring is a job for the summer!

--
David

On 16/02/2013 19:07, Lobster wrote:
On 15/02/2013 15:16, Stephen H wrote:

I am putting in a new 32A ring main that will just be for garage
internal sockets and external outside sockets.

Cor, I've just been doing a bit of that today and what a bloody horrible
job it was - courtesy of the fact that the temp was about 1 deg, and the
cable was therefore almost rock solid. Very hard to bend it where I
wanted it to go, wouldn't cut or tear easily, hard to stuff down the
conduit etc...

Note to self: in future, exterior wiring is a job for the summer!


Incidentally, I was working on this new ring main today.

I have used 2.5mm2 T&E for the ring main and to the garage sockets.

Some of the external sockets are in publically accessible or child
accessible areas, so I have run the 2.5mm2 ring main to 45amp double
pole isolator switches inside the garage. 4mm2 T&E ran from the 45amp
isolators to to each individual outside double gang socket.

This has several benefits:

no one can steal electricity from the front
sockets can be turned off in garden if children are playing
if a fault develops in an outside socket, it makes fault locating down
to socket level easy
if I need garage power and a outside socket is playing up and tripping
the RCBO, I can throw the switch for that socket to Off and work in the
garage.

On 16/02/2013 19:20, Stephen H wrote:
On 16/02/2013 19:07, Lobster wrote:
On 15/02/2013 15:16, Stephen H wrote:

I am putting in a new 32A ring main that will just be for garage
internal sockets and external outside sockets.

Cor, I've just been doing a bit of that today and what a bloody horrible
job it was - courtesy of the fact that the temp was about 1 deg, and the
cable was therefore almost rock solid. Very hard to bend it where I
wanted it to go, wouldn't cut or tear easily, hard to stuff down the
conduit etc...

Note to self: in future, exterior wiring is a job for the summer!


Incidentally, I was working on this new ring main today.

I have used 2.5mm2 T&E for the ring main and to the garage sockets.

Some of the external sockets are in publically accessible or child
accessible areas, so I have run the 2.5mm2 ring main to 45amp double
pole isolator switches inside the garage. 4mm2 T&E ran from the 45amp
isolators to to each individual outside double gang socket.

(In reality a 20A plate switch and a single 2.5mm T&E would have been
adequate (i.e. in effect creating a switched unfused spur)).

This has several benefits:

no one can steal electricity from the front
sockets can be turned off in garden if children are playing
if a fault develops in an outside socket, it makes fault locating down
to socket level easy
if I need garage power and a outside socket is playing up and tripping
the RCBO, I can throw the switch for that socket to Off and work in the
garage.

Good plan.




--
Cheers,

John.

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

In article ,
Stephen H writes:
Some of the external sockets are in publically accessible or child
accessible areas, so I have run the 2.5mm2 ring main to 45amp double
pole isolator switches inside the garage. 4mm2 T&E ran from the 45amp
isolators to to each individual outside double gang socket.

My outdoor socket circuit is a TT 20A radial (with a 10mA RCBO),
but I did almost the same. I used a cooker switch with integral
socket, positioned just inside the garage door. This gives me a
socket just inside the garage which is handy when using something
just outside the garage with the door open, and separately switched
(by the cooker switch, relabeled), are all the other outdoor
sockets, which I normally keep switched off except when I'm
expecting to use them (and when I forget to turn them back off
afterwards).

This has several benefits:

no one can steal electricity from the front
sockets can be turned off in garden if children are playing
if a fault develops in an outside socket, it makes fault locating down
to socket level easy
if I need garage power and a outside socket is playing up and tripping
the RCBO, I can throw the switch for that socket to Off and work in the
garage.

Exactly same reasoning here.

--
Andrew Gabriel
[email address is not usable -- followup in the newsgroup]

On 16/02/2013 20:00, John Rumm wrote:
On 16/02/2013 19:20, Stephen H wrote:
On 16/02/2013 19:07, Lobster wrote:
On 15/02/2013 15:16, Stephen H wrote:

I am putting in a new 32A ring main that will just be for garage
internal sockets and external outside sockets.

Cor, I've just been doing a bit of that today and what a bloody horrible
job it was - courtesy of the fact that the temp was about 1 deg, and the
cable was therefore almost rock solid. Very hard to bend it where I
wanted it to go, wouldn't cut or tear easily, hard to stuff down the
conduit etc...

Note to self: in future, exterior wiring is a job for the summer!


Incidentally, I was working on this new ring main today.

I have used 2.5mm2 T&E for the ring main and to the garage sockets.

Some of the external sockets are in publically accessible or child
accessible areas, so I have run the 2.5mm2 ring main to 45amp double
pole isolator switches inside the garage. 4mm2 T&E ran from the 45amp
isolators to to each individual outside double gang socket.

(In reality a 20A plate switch and a single 2.5mm T&E would have been
adequate (i.e. in effect creating a switched unfused spur)).

I did actually sit down and think this through from a good design point
of view...

As stated, there is a 2.5mm2 ring main with a 32A RCBO.

I was not worried about L-E or N-E shorts as there is the 30mA RCD part
in the RCBO that takes care of that.

However, I had two scenarios to think about regarding my outside sockets.

I wanted to put a single external socket in the front porch.

So that meant a single 2.5mm2 spur T&E cable from the 32A ring main in
the garage to a single socket in the front porch via a bedroom.

Given that the max current available on the ring main would be 32A
before the consumer unit's 32A RCBO opens and that the maximum
in-service non-fault conditions continuous current would be 13A at the
porch socket, (limited by the 13A or less fuse in the plug of whatever
appliance plugged in)

I had thought about what could happen if there was a dead L-N short on
the single 2.5mm T&E cable running between the ring main and the single
gang socket.

Obviously this single 2.5mm cable is capable of taking a 13A current
continuously between the ring main and the single socket via the spur
cable, I felt uncomfortable with it potentially carrying up to 32A
before RCBO opens in case of a L-N short on the spur cable.

Thus, I put a 13A fused switched neon faceplate at the point where the
spur is connected to the ring main in the garage to protect the spur.

The other scenario was the double gang socket on the front driveway.

Now I could plug in two appliances. Lets say both draw up to 13A before
their individual plug fuses pops. Thats a total load of 26A which is on
a 32A rated 2.5mm ring main.

Now doing 26A continuously on a single 2.5mm2 spur cable between the
ring main and double socket I was not comfortable with, let alone a
potential up to 32A flowing in the case of a dead L-N short.

Switch isolators come rated as 20A or 45A. So 20A is less than 26A that
the double gang socket could be going up to. So I went to 45A rating for
the switch neon isolator.

So I put a 45A rated neon switch on the 2.5mm2 ring main and reasoned
that as current flows both ways round the ring, that 5.0mm2 is the same
as 2 x 2.5mm2. So I opted to run the spur cable as 4.0mm2 from the 45
amp isolator to the double gang socket. Now I am then comfortable with
up to 26A flowing continuously on this 4.0mm cable from isolator to
double gang socket.

I fully appreciate the above scenario is highly improbable and that I
have probably over-engineered my circuit but hopefully at least a sparky
can't find fault with my reasoning!

Stephen.



This has several benefits:

no one can steal electricity from the front
sockets can be turned off in garden if children are playing
if a fault develops in an outside socket, it makes fault locating down
to socket level easy
if I need garage power and a outside socket is playing up and tripping
the RCBO, I can throw the switch for that socket to Off and work in the
garage.

Good plan.

On 18/02/2013 18:18, Stephen H wrote:
On 16/02/2013 20:00, John Rumm wrote:

(In reality a 20A plate switch and a single 2.5mm T&E would have been
adequate (i.e. in effect creating a switched unfused spur)).

I did actually sit down and think this through from a good design point
of view...

As stated, there is a 2.5mm2 ring main with a 32A RCBO.

I was not worried about L-E or N-E shorts as there is the 30mA RCD part
in the RCBO that takes care of that.

However, I had two scenarios to think about regarding my outside sockets.

I wanted to put a single external socket in the front porch.

So that meant a single 2.5mm2 spur T&E cable from the 32A ring main in
the garage to a single socket in the front porch via a bedroom.

Given that the max current available on the ring main would be 32A
before the consumer unit's 32A RCBO opens and that the maximum
in-service non-fault conditions continuous current would be 13A at the
porch socket, (limited by the 13A or less fuse in the plug of whatever
appliance plugged in)

I had thought about what could happen if there was a dead L-N short on
the single 2.5mm T&E cable running between the ring main and the single
gang socket.

Obviously this single 2.5mm cable is capable of taking a 13A current
continuously between the ring main and the single socket via the spur
cable, I felt uncomfortable with it potentially carrying up to 32A
before RCBO opens in case of a L-N short on the spur cable.

Ah, right I see the line of thought you are following. In fact you are
over worrying since this exact scenario has already been thought about
in the design of unfused spurs...

As you are probably aware there are two overcurrent categories that need
to be considered with these things - that of overload, and that of a
fault. Each have their own characteristics, and each need (possibly)
separate handling.

The fault current situation is the most important - i.e. stopping the
cable vaporising or bursting into flames on a hard short. The circuit
protective device at the origin of the circuit *must* protect against
fault currents. It has been shown that a single 2.5mm^2 cable (as used
in a typical spur arrangement from a standard ring circuit) will be
adequately protected from the effects of fault current by the B32 MCB at
the origin of the circuit.

For more on this see:

http://wiki.diyfaq.org.uk/index.php?...abatic _Check

The second issue is that of overload. i.e. what happens if a load in
excess of the design current is placed on it for an extended period.
(short term overloads are permissible, and it is even desirable that a
circuit will not trip in response to them). You are correct in assuming
that you can't rely on the B32 MCB/RCBO to offer overload protection for
a single 2.5mm^2 cable. However this class of over current does not
have to be covered by the device at the origin of the circuit. In the
case of fused spurs, its enforced by the downstream fuse. In the case of
unfused spurs, then it is imposed either by the number of available
connections (e.g. a single socket can't take a load large enough) or by
the characteristics of the load itself (e.g. a fixed appliance that has
no mechanism for drawing a sustained overload)

Thus, I put a 13A fused switched neon faceplate at the point where the
spur is connected to the ring main in the garage to protect the spur.

The other scenario was the double gang socket on the front driveway.

Now I could plug in two appliances. Lets say both draw up to 13A before
their individual plug fuses pops. Thats a total load of 26A which is on
a 32A rated 2.5mm ring main.

A cable that if surface wired on in masonry actually has a 27A
capacity... however that's not the point. For the purposes of design, a
double socket is rated at 20A total load. In reality some will do better
than that, but many will not like it if you actually stick two 13A long
term loads on. Chances are the socket will suffer long before the cable.

Now doing 26A continuously on a single 2.5mm2 spur cable between the
ring main and double socket I was not comfortable with, let alone a
potential up to 32A flowing in the case of a dead L-N short.

Some will argue that you can get even more load on it since a 13A BS1361
fuse will carry 20A before blowing... armed with some multi way
extension leads you could have the socket in a molten mess in very short
order ;-) In reality it never happens since actually getting long term
loads (i.e. those that are not intermittent due to usage patterns, or
due to the actions of thermostats etc) is actually quite difficult (a
couple of 3kW fan heaters to warm the garden perhaps?).

Along the same line of thought it is also worth remembering that a 32A
circuit breaker does not trip at 33A. In fact you need 1.45 x nominal
current to ensure they trip, and 5x normal current to insure they trip
"instantly" (i.e. when clearing fault currents)

Have a look at the response curve of a 32A type B MCB:

http://wiki.diyfaq.org.uk/images/d/d...e-MCBTypeB.png

Switch isolators come rated as 20A or 45A. So 20A is less than 26A that
the double gang socket could be going up to. So I went to 45A rating for
the switch neon isolator.

No harm in doing that, except that you pay more for the switch, and the
socket etc is not really up to the job of matching the performance of
the switch.

So I put a 45A rated neon switch on the 2.5mm2 ring main and reasoned
that as current flows both ways round the ring, that 5.0mm2 is the same
as 2 x 2.5mm2. So I opted to run the spur cable as 4.0mm2 from the 45
amp isolator to the double gang socket. Now I am then comfortable with
up to 26A flowing continuously on this 4.0mm cable from isolator to
double gang socket.

Indeed. although normally if one were proposing to have very heavy loads
on sockets in this way, they would ideally be better in the ring and not
on a spur.

For your actual application, I would be entirely comfortable with a
single 2.5mm^2 cable and a double (IP 56) socket on the end.

I fully appreciate the above scenario is highly improbable and that I
have probably over-engineered my circuit but hopefully at least a sparky
can't find fault with my reasoning!

There is nothing dangerous about what you propose, although its over
egging things a tad. Lots of design effort over the years has gone into
make sure that these things work well in reality, and while there are
theoretical weaknesses in the designs of unfused spurs, they prove time
and again in practice to be very robust and reliable.


--
Cheers,

John.

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

On 18/02/2013 21:14, John Rumm wrote:

Some will argue that you can get even more load on it since a 13A BS1361
fuse

Sorry typo, BS1362 - 1361 are mains incomer fuses!


--
Cheers,

John.

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

On Monday, February 18, 2013 6:18:39 PM UTC, Stephen H wrote:

I did actually sit down and think this through from a good design point
of view...
As stated, there is a 2.5mm2 ring main with a 32A RCBO.
I was not worried about L-E or N-E shorts as there is the 30mA RCD part
in the RCBO that takes care of that.
However, I had two scenarios to think about regarding my outside sockets.
I wanted to put a single external socket in the front porch.
So that meant a single 2.5mm2 spur T&E cable from the 32A ring main in
the garage to a single socket in the front porch via a bedroom.
Given that the max current available on the ring main would be 32A
before the consumer unit's 32A RCBO opens and that the maximum

32A is what it'll pass indefinitely. Real life trip current is far higher

in-service non-fault conditions continuous current would be 13A at the
porch socket, (limited by the 13A or less fuse in the plug of whatever
appliance plugged in)

fuses don't limit current at all. A 13A fuse can pass around 20A for a long time


I had thought about what could happen if there was a dead L-N short on
the single 2.5mm T&E cable running between the ring main and the single
gang socket.

PSCC is anywhere upto 6,000A. Whatever PSCC actually is it'll normally trip the 32A mcb first. If its north of the mcb's breaking capacity it'll take out the incomer fuse instead.

Obviously this single 2.5mm cable is capable of taking a 13A current
continuously between the ring main and the single socket via the spur
cable, I felt uncomfortable with it potentially carrying up to 32A
before RCBO opens in case of a L-N short on the spur cable.

It would carry anything upto 6kA. Its not a problem for the very short time involved.

Thus, I put a 13A fused switched neon faceplate at the point where the
spur is connected to the ring main in the garage to protect the spur.

no point

The other scenario was the double gang socket on the front driveway.
Now I could plug in two appliances. Lets say both draw up to 13A before
their individual plug fuses pops. Thats a total load of 26A which is on
a 32A rated 2.5mm ring main.
Now doing 26A continuously on a single 2.5mm2 spur cable between the
ring main and double socket I was not comfortable with, let alone a

its within the 27A cable rating. But what real life loads would draw 26A continuous?

potential up to 32A flowing in the case of a dead L-N short.

more like thousands of amps

Switch isolators come rated as 20A or 45A. So 20A is less than 26A that
the double gang socket could be going up to. So I went to 45A rating for
the switch neon isolator.

no need. 20A's enough for a double socket.

So I put a 45A rated neon switch on the 2.5mm2 ring main and reasoned
that as current flows both ways round the ring, that 5.0mm2 is the same
as 2 x 2.5mm2. So I opted to run the spur cable as 4.0mm2 from the 45
amp isolator to the double gang socket.

no need

Now I am then comfortable with
up to 26A flowing continuously on this 4.0mm cable from isolator to
double gang socket.
I fully appreciate the above scenario is highly improbable and that I
have probably over-engineered my circuit but hopefully at least a sparky
can't find fault with my reasoning!
Stephen.




NT

On 18/02/2013 21:21, John Rumm wrote:
On 18/02/2013 21:14, John Rumm wrote:

Some will argue that you can get even more load on it since a 13A BS1361
fuse

Sorry typo, BS1362 - 1361 are mains incomer fuses!




Incidentally. There has been a thought about ring mains that has
bothered me for some time.

in a perfect world, you have a continuous live loop and a continuous
neutral loop on a 32A MCB ring main, from teh CU to all the sockets and
then back to the CU.

What if you had a break in the cable between the CU and the last socket?
This converts the ring main to a radial circuit.

Lets assume the ring main is then loaded to its full capacity of 32A.

This would mean that *ALL* the current would be flowing along one route
between the CU and the first socket (assuming multiple appliances
plugged in a various points around the radial.

Can a single 2.5mm2 T&E really sustain a 32A continuous load?

Also as I understand it, you should only have a 20A mcb on a radial
circuit wired in 2.5mm T&E. if you complete the radial into a ring, then
the MCB can be changed to a 32A MCB.

John Rumm writes:

On 18/02/2013 18:18, Stephen H wrote:
On 16/02/2013 20:00, John Rumm wrote:

(In reality a 20A plate switch and a single 2.5mm T&E would have been
adequate (i.e. in effect creating a switched unfused spur)).

I did actually sit down and think this through from a good design point
of view...

As stated, there is a 2.5mm2 ring main with a 32A RCBO.

snip

Ah, right I see the line of thought you are following. In fact you are
over worrying since this exact scenario has already been thought about
in the design of unfused spurs...

snip

There is nothing dangerous about what you propose, although its over
egging things a tad. Lots of design effort over the years has gone
into make sure that these things work well in reality, and while there
are theoretical weaknesses in the designs of unfused spurs, they prove
time and again in practice to be very robust and reliable.

I'm pinning this reply in my newsreader as I've never seen it explained
so clearly before. Perhaps this Q&A is also worth sticking on the Wiki
somewhere?

Alex

--
Swish - Easy SFTP for Windows Explorer (http://www.swish-sftp.org)

On 19/02/2013 00:41, Stephen H wrote:
On 18/02/2013 21:21, John Rumm wrote:
On 18/02/2013 21:14, John Rumm wrote:

Some will argue that you can get even more load on it since a 13A BS1361
fuse

Sorry typo, BS1362 - 1361 are mains incomer fuses!




Incidentally. There has been a thought about ring mains that has
bothered me for some time.

in a perfect world, you have a continuous live loop and a continuous
neutral loop on a 32A MCB ring main, from teh CU to all the sockets and
then back to the CU.

What if you had a break in the cable between the CU and the last socket?
This converts the ring main to a radial circuit.

Indeed it does...

In reality you could have a break anywhere - and would then get a pair
of radials.

However each circuit topology has strengths and weaknesses. There are
several types of faults (high resistance connections being the most
common, followed by disconnected conductors, and finally disconnected
cables). Each will have different effects.

The options are covered in some detail he

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

Lets assume the ring main is then loaded to its full capacity of 32A.

This would mean that *ALL* the current would be flowing along one route
between the CU and the first socket (assuming multiple appliances
plugged in a various points around the radial.

Can a single 2.5mm2 T&E really sustain a 32A continuous load?

Depends on the circumstances and how quick it can shed heat. It also
very much depends on how long you can keep that load on for. Rings
typically serve general purpose use sockets, which form a diverse load.

Also as I understand it, you should only have a 20A mcb on a radial
circuit wired in 2.5mm T&E.

Yup

if you complete the radial into a ring, then
the MCB can be changed to a 32A MCB.

Obviously.

--
Cheers,

John.

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

On 19/02/2013 00:44, Alexander Lamaison wrote:
John Rumm writes:

On 18/02/2013 18:18, Stephen H wrote:
On 16/02/2013 20:00, John Rumm wrote:

(In reality a 20A plate switch and a single 2.5mm T&E would have been
adequate (i.e. in effect creating a switched unfused spur)).

I did actually sit down and think this through from a good design point
of view...

As stated, there is a 2.5mm2 ring main with a 32A RCBO.

snip

Ah, right I see the line of thought you are following. In fact you are
over worrying since this exact scenario has already been thought about
in the design of unfused spurs...

snip

There is nothing dangerous about what you propose, although its over
egging things a tad. Lots of design effort over the years has gone
into make sure that these things work well in reality, and while there
are theoretical weaknesses in the designs of unfused spurs, they prove
time and again in practice to be very robust and reliable.

I'm pinning this reply in my newsreader as I've never seen it explained
so clearly before. Perhaps this Q&A is also worth sticking on the Wiki
somewhere?

Well to be fair this has been discussed a few times in the past, so I
have had practice ;-))

I think most of it ought to be in the wiki... although if you find a bit
missing feel free to either highlight what, or for that matter add it
yourself (drop me an email if you want a wiki account) ;-)

Fault and overload currents are discussed here (and in other places):

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

The effects on different circuit types along with that of other common
fault conditions is discussed he

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

The responses of fuses and MCBs he

http://wiki.diyfaq.org.uk/index.php?title=Fuse
http://wiki.diyfaq.org.uk/index.php?title=MCB



--
Cheers,

John.

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