coughed up some electrons that declared:

On 22 Aug,
Tim S wrote:

One cable in each half of a newly divided conduit run, not 2 cables in
one conduit.

Unless things have changed,whenn using steel conduit all cores of an AC
circuit should run within the same conduit to cancel out the magnetic
field to prevent eddy currents in the steelwork.


You're right about the eddy currents, which is why I would be forced to use
32mm steel for me meter tails (11mm outside diameter for double insulated
tails, not quite fit in 25mm).

But methinks you may have missed the context:

Cable != wire, conduit = plastic oval, not steel (that'll be the other
branch of this thread thread I'm wittering in, re meter tails)

and this is what I meant:

=== is oval conduit, on a ring or radial socket circuit:
Conduit contains exactly 1 twin+earth cable

Socket ==================================== Socket
^^^
Sink new box here to get

Socket ============== Socket ============== Socket

One cable, each half. It's probably not going to ever be necessary if one
installs enough sockets to start with, but, well...

The original point was, that if you do this, you don't get enough spare
cable to terminate to the new middle socket. But with oval (any) conduit
you do get to pull new bits in.

Never mind, it was a silly point anyway. :-O

Cheers

Tim

coughed up some electrons that declared:


I was under the impression that it /was/ for meter tails buried in a wall,
and thus needing more protection than plastic would give. Perhaps I got my
threads crossed.


This thread's rather gone off on several tangents. We've got oval conduit,
meter tails and general wall chasing. The only thing that's not here is
Dribble, he's busy marvelling at ALDI plumbing tools

;-

On Fri, 22 Aug 2008 22:16:10 +0100, wrote:

On 22 Aug,
Tim S wrote:

You're right about the eddy currents, which is why I would be forced to use
32mm steel for me meter tails (11mm outside diameter for double insulated
tails, not quite fit in 25mm).

But methinks you may have missed the context:

Cable != wire, conduit = plastic oval, not steel (that'll be the other
branch of this thread thread I'm wittering in, re meter tails)

I was under the impression that it /was/ for meter tails buried in a wall,
and thus needing more protection than plastic would give. Perhaps I got my
threads crossed.

Somehow I had the idea that it was verboten to bury meter tails in a
wall - they obviously can pass through a wall however, as they do
here. The meter is 'outside' in a Permali box and the CU's inboard of
it.

--
Frank Erskine

Tim S wrote:
coughed up some electrons that declared:

On 22 Aug,
Tim S wrote:

One cable in each half of a newly divided conduit run, not 2 cables in
one conduit.
Unless things have changed,whenn using steel conduit all cores of an AC
circuit should run within the same conduit to cancel out the magnetic
field to prevent eddy currents in the steelwork.


You're right about the eddy currents, which is why I would be forced to use
32mm steel for me meter tails (11mm outside diameter for double insulated
tails, not quite fit in 25mm).

In my ignorance, what would be the outcome of getting eddy currents in
my steelwork?

David

In article ,
Lobster wrote:
You're right about the eddy currents, which is why I would be forced
to use 32mm steel for me meter tails (11mm outside diameter for double
insulated tails, not quite fit in 25mm).

In my ignorance, what would be the outcome of getting eddy currents in
my steelwork?

I've only seen it once where there were two steel conduits feeding a
multiple switch plate which included neons as tell tales, and a 'tidy'
sparks had run all the feeds down one conduit and returns down the other.
The conduit got hot. So it is wasting electricity at best.

--
*A closed mouth gathers no feet.

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

Lobster coughed up some electrons that declared:

Tim S wrote:
coughed up some electrons that declared:

On 22 Aug,
Tim S wrote:

One cable in each half of a newly divided conduit run, not 2 cables in
one conduit.
Unless things have changed,whenn using steel conduit all cores of an AC
circuit should run within the same conduit to cancel out the magnetic
field to prevent eddy currents in the steelwork.


You're right about the eddy currents, which is why I would be forced to
use 32mm steel for me meter tails (11mm outside diameter for double
insulated tails, not quite fit in 25mm).

In my ignorance, what would be the outcome of getting eddy currents in
my steelwork?

David

As you know, current down a wire produces a magnetic field and AC makes for
alternating magnetic field.

Alternating magnetic field and induce current in conductors, and the effect
is *much* stronger if magnetic (eg ferrous) materials are involved.

Normally, none of this is a problem if all phases and the return neutral of
a circuit are contained together because the sum of the magnetic field is
zero. So for single phase, L+N should always run through the same aperture
in any ferrous enclosure, including pipe. This includes entry holes in
equipment too, though the issue can be mitigated by cutting a thin slot
between two adjacent holes and using them.

The final effect of strong alternating magnetic fields is induced
alternating current in the steel pipe or whatever, which working against
the resistance of the material produces, as someone else said, heat.

Cheers
Tim

Dave Plowman (News) wrote:

The conduit got hot. So it is wasting electricity at best.

It adds unwanted impedance in the circuit increases voltage drop. It
can interfere with motor starting, especially for motors which have to
start on load and will stall if there is insufficient starting torque.
Where line and CPC paths are separated in this way the earth fault loop
impedance could become too high to ensure that overcurrent protective
devices operate to clear an earth fault, leading to a serious fire risk.

So it's a complete and utter no-no.

--
Andy

dennis@home coughed up some electrons that declared:



"Tim S" wrote in message
...


Unfortunately, there isn't an "over the door" as such - the soffits are
more
or less level with the top. I'll see if there's any clearance above the
soffit boards (they need to come off anyway). Might be able to notch out
their supports a bit. Worth a look.

I was just going to suggest taking the soffits off.
The rafters/trusses shouldn't be structural at that point (assuming there
are no joint plates) so you can drill quite large holes to thread SWA
through.
You can probably just run it in the attic without cutting anything.
If so fix it to the underside of the roof so it doesn't get covered by
insulation, then you don't have to de-rate.

Good news for me. Done a bit more investigation. Upon making a hole in the
soffitts, I can see the inner leaf of the wall. It stands about a foot
higher than the outer leaf and seems clear of obstructions on the
cavity-side face.

I think I've found the place to clip either cable or conduit.

I could probably argue that I could run tails without mechanical protection
as they would be 50mm from the face of the wall (that's wall, not leaf).
Technically they are not in the cavity either, they are over it.

But I would probably use protection anyway, though steel trunking would also
be viable.

So, I can manage a fused switch in a 2nd meter box, conduit, trunking or SWA
to CU. Or fused switch above picture rail, tails straight in through the
back. Conduit would require 2 90 bends, so use fittings.

Well, down to a couple of sensible arrangements now. And either would work.

Cheers for all the ideas etc.

Tim

PS

Don't forget it's 8kg SDS+ and core drills day at ALDI today!