Just wanted to check that I was reading the OSG correctly!

If I use Reference method A (i.e. enclosed in conduit in insulated wall)
then 2.5mm flat T+E cable will be sufficient for a ring circuit.

Presumably I cannot put 2 cables in the conduit (i.e. to and from the
socket) as this will derate the circuit under 20A and I would need to
increase the size of the cable.

The alternative is to ensure that the cable is touching the inner
surface of the plasterboard and that the two cables do not run in close
proximity to each other.

Cheers

Martin
--
Martin Carroll

"Martin Carroll" wrote in message
...
Just wanted to check that I was reading the OSG correctly!

If I use Reference method A (i.e. enclosed in conduit in insulated wall)
then 2.5mm flat T+E cable will be sufficient for a ring circuit.

Presumably I cannot put 2 cables in the conduit (i.e. to and from the
socket) as this will derate the circuit under 20A and I would need to
increase the size of the cable.

The alternative is to ensure that the cable is touching the inner
surface of the plasterboard and that the two cables do not run in close
proximity to each other.

You can't do that unless the cable is protected or you have 2" plasterboard.

In article , dennis@home
writes


"Martin Carroll" wrote in message
...
Just wanted to check that I was reading the OSG correctly!

If I use Reference method A (i.e. enclosed in conduit in insulated wall)
then 2.5mm flat T+E cable will be sufficient for a ring circuit.

Presumably I cannot put 2 cables in the conduit (i.e. to and from the
socket) as this will derate the circuit under 20A and I would need to
increase the size of the cable.

The alternative is to ensure that the cable is touching the inner
surface of the plasterboard and that the two cables do not run in close
proximity to each other.

You can't do that unless the cable is protected or you have 2" plasterboard.

Or the cable run is in the zone horizontally/vertically to the socket.
--
Martin Carroll

"Martin Carroll" wrote in message
...
In article , dennis@home
writes


"Martin Carroll" wrote in message
...
Just wanted to check that I was reading the OSG correctly!

If I use Reference method A (i.e. enclosed in conduit in insulated wall)
then 2.5mm flat T+E cable will be sufficient for a ring circuit.

Presumably I cannot put 2 cables in the conduit (i.e. to and from the
socket) as this will derate the circuit under 20A and I would need to
increase the size of the cable.

The alternative is to ensure that the cable is touching the inner
surface of the plasterboard and that the two cables do not run in close
proximity to each other.

You can't do that unless the cable is protected or you have 2"
plasterboard.

Or the cable run is in the zone horizontally/vertically to the socket.

That doesn't satisfy the new regs AFAIK

In article , dennis@home
writes


"Martin Carroll" wrote in message
...
In article , dennis@home
writes


"Martin Carroll" wrote in message
...
Just wanted to check that I was reading the OSG correctly!

If I use Reference method A (i.e. enclosed in conduit in insulated wall)
then 2.5mm flat T+E cable will be sufficient for a ring circuit.

Presumably I cannot put 2 cables in the conduit (i.e. to and from the
socket) as this will derate the circuit under 20A and I would need to
increase the size of the cable.

The alternative is to ensure that the cable is touching the inner
surface of the plasterboard and that the two cables do not run in close
proximity to each other.

You can't do that unless the cable is protected or you have 2"
plasterboard.

Or the cable run is in the zone horizontally/vertically to the socket.

That doesn't satisfy the new regs AFAIK

Why not? AIUI as long as a cable runs in a line horizontally or
vertically to an accessory or within 150mm of top of wall or angle
formed by two walls.

Martin
--
Martin Carroll

Martin Carroll wrote:

Why not? AIUI as long as a cable runs in a line horizontally or
vertically to an accessory or within 150mm of top of wall or angle
formed by two walls.

Used to be, now 17th edition requires either

cable is buried more than 50mm

or

cable is not buried at all

or

conductors are fully enclosed by an earth (e.g. T&E within earthed metal
capping, or a cable such as SWA, or BS8436 cable with foil screen, or
pyro etc)

or

protected by 30mA RCD or RCBO

or

something else I missed?

In fact, one PC may be
enough to trip a 30mA RCD because of the feedback to earth from the
switching PSU. Try it, though.




Must be a really duff PC to be leaking that much!.....
--
Tony Sayer

In article ,
BigWallop wrote:
To comply with the 30mA RCD ruling, you won't be able to run a fan
heater or anything else of that nature on the final ring.

Eh? The type of element normally used in fan heaters isn't associated with
earth leakage which might cause an RCD to trip.

In fact, one PC may be enough to trip a 30mA RCD because of the
feedback to earth from the switching PSU. Try it, though.

The value of 'feedback' to earth is such that many SMPS can be used on one
RCD - far more than likely in a domestic environment. The effect is
additive. You might well have problems in an office, though, with lots of
them.

--
*Keep honking...I'm reloading.

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

Dave Plowman (News) wrote:

The value of 'feedback' to earth is such that many SMPS can be used on one
RCD - far more than likely in a domestic environment. The effect is
additive. You might well have problems in an office, though, with lots of
them.

Indeed, I think the amount of leakage from such things is often
overstated. I must have at least a dozen SMPS in this room alone, and
there are two other socket circuits on the RCD that serves this circuit
as well. In addition I can still stick at least another 15mA leakage
into the thing with my RCD tester and not trip it. (under test it trips
in 26ms at 30mA leakage)

--
Cheers,

John.

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

In article ,
John Rumm wrote:
Dave Plowman (News) wrote:

The value of 'feedback' to earth is such that many SMPS can be used on
one RCD - far more than likely in a domestic environment. The effect
is additive. You might well have problems in an office, though, with
lots of them.

Indeed, I think the amount of leakage from such things is often
overstated. I must have at least a dozen SMPS in this room alone, and
there are two other socket circuits on the RCD that serves this circuit
as well. In addition I can still stick at least another 15mA leakage
into the thing with my RCD tester and not trip it. (under test it trips
in 26ms at 30mA leakage)

The figures have been pointed out elsewhere - it's effectively the thick
end of 10 watts needed to trip an RCD. That is a lot of heat to dissipate
unnecessarily from a power supply which would add to its cost. And such
high current resistors ain't cheap compared to what's used - as well as
bulky.

--
*I speak fluent patriarchy but it's not my mother tongue

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

Dave Plowman (News) coughed up some electrons that declared:

The figures have been pointed out elsewhere - it's effectively the thick
end of 10 watts needed to trip an RCD. That is a lot of heat to dissipate
unnecessarily from a power supply which would add to its cost. And such
high current resistors ain't cheap compared to what's used - as well as
bulky.


Shouldn't that be "10VA" - the leakage might be largely reactive, and
probably will with things that employ mains conditioning filters.

Just a thought.

Cheers

Tim

"BigWallop" wrote in message
om...


To comply with the 30mA RCD ruling, you won't be able to run a fan heater
or
anything else of that nature on the final ring. In fact, one PC may be
enough to trip a 30mA RCD because of the feedback to earth from the
switching PSU. Try it, though.

I recommend you get the appliance tested.
No PC or fan heater or fridge or anything else I have has every tripped a 30
ma rcd and I don't see why they should.

In article ,
Tim S wrote:
Dave Plowman (News) coughed up some electrons that declared:

The figures have been pointed out elsewhere - it's effectively the
thick end of 10 watts needed to trip an RCD. That is a lot of heat to
dissipate unnecessarily from a power supply which would add to its
cost. And such high current resistors ain't cheap compared to what's
used - as well as bulky.


Shouldn't that be "10VA" - the leakage might be largely reactive, and
probably will with things that employ mains conditioning filters.

There are all sorts of ways - but many SMPS do use just simple resistors.

Just a thought.

--
*Never underestimate the power of very stupid people in large groups *

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

BigWallop wrote:

To comply with the 30mA RCD ruling, you won't be able to run a fan heater or
anything else of that nature on the final ring. In fact, one PC may be
enough to trip a 30mA RCD because of the feedback to earth from the
switching PSU. Try it, though.

Rubbish. My whole house is on a 30mA RCD. I wouldn't do it like that if
I were rewiring, but it is there and it doesn't give me nuisance trips.

Pete

On Nov 17, 11:19*pm, "BigWallop"
wrote:
"Martin Carroll" wrote in message

...



In article , Andy Burns
writes
Martin Carroll wrote:

Why not? *AIUI as long as a cable runs in a line horizontally or
vertically to an accessory or within 150mm of top of wall or angle
formed by two walls.

Used to be, now 17th edition requires either

cable is buried more than 50mm

or

cable is not buried at all

or

conductors are fully enclosed by an earth (e.g. T&E within earthed metal
capping, or a cable such as SWA, or BS8436 cable with foil screen, or
pyro etc)

or

protected by 30mA RCD or RCBO

or

something else I missed?

In the 17th Edition OSG, (page 60)

A cable installed in a wall or partition must:

i * *be at least 50mm from surface
ii * have earthed armouring.....
iii *be enclosed in earthed steel conduit....
iv * be provided with mechanical protection......
v * *be installed either horizontally.........

In domestic and similar installations, cables not installed as per i,
ii, iii or iv but complying with v shall be protected by 30mA RCD.

So as long as there is an RCD in CU protecting the circuit cable can be
unprotected in the "safe" zones.

Cheers

Martin

To comply with the 30mA RCD ruling, you won't be able to run a fan heater or
anything else of that nature on the final ring. *In fact, one PC may be
enough to trip a 30mA RCD because of the feedback to earth from the
switching PSU. *Try it, though.

First it was burning transformers with 10% overload, now SMPSs that
will trip 30mA RCDs.

What next?

MBQ