When electrical cable (normal FT&E) is laid between joists, can it
rest on the ceiling plasterboard or ought it to be clipped to the
joist sides with Tower-type clips?

TIA

"jim_in_sussex" wrote in message
m...
When electrical cable (normal FT&E) is laid between joists, can it
rest on the ceiling plasterboard or ought it to be clipped to the
joist sides with Tower-type clips?

Surely if you wanted to do that you would have to lift every board along the
route!

In message , Ric
writes

"jim_in_sussex" wrote in message
om...
When electrical cable (normal FT&E) is laid between joists, can it
rest on the ceiling plasterboard or ought it to be clipped to the
joist sides with Tower-type clips?

Surely if you wanted to do that you would have to lift every board along the
route!

maybe it's in the loft?
--
Chris French, Leeds

"chris French" wrote in message
...
In message , Ric
writes

"jim_in_sussex" wrote in message
. com...
When electrical cable (normal FT&E) is laid between joists, can it
rest on the ceiling plasterboard or ought it to be clipped to the
joist sides with Tower-type clips?

Surely if you wanted to do that you would have to lift every board along
the
route!

maybe it's in the loft?

Maybe the loft is converted?

In article ,
chris French wrote:
Surely if you wanted to do that you would have to lift every board
along the route!

maybe it's in the loft?

Not floor joists, then. Unless it's boarded over. Then there's a hole in
the bucket, dear Lisa...

--
*He's not dead - he's electroencephalographically challenged

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

"Dave Plowman (News)" wrote in message ...
In article ,
chris French wrote:
Surely if you wanted to do that you would have to lift every board
along the route!

maybe it's in the loft?

Not floor joists, then. Unless it's boarded over. Then there's a hole in
the bucket, dear Lisa...


sorry if question sounds stupid, but it is something that's always had
a question mark over it in my mind.

a. to clarify please add 'or ceiling' before joists

b. if it is legit to just rest cable on the (ordinary) plasterboard,
which IEE regs installation method is this?

also ISTM that there must be some danger of the plaster board being
punctured by various sharp objects like nails.


just going over things carefully to make sure there's no glaring
exceptions before Part P bites...


TIA

In message ,
(jim_in_sussex) wrote:

"Dave Plowman (News)" wrote in message ...
In article ,
chris French wrote:
Surely if you wanted to do that you would have to lift every board
along the route!

maybe it's in the loft?

Not floor joists, then. Unless it's boarded over. Then there's a hole in
the bucket, dear Lisa...


sorry if question sounds stupid, but it is something that's always had
a question mark over it in my mind.

a. to clarify please add 'or ceiling' before joists


As you may have guessed it is almost always impractical to clip along a
joist, of whatever sort. Leaving the cable unclipped can also make it
easier to replace at some point in the future.

b. if it is legit to just rest cable on the (ordinary) plasterboard,
which IEE regs installation method is this?


Method 1 (free air, basically) BUT beware of bunching - grouping - where
several cables run together, particularly if they run together through
holes in joists. Better, in my mind, several small holes with one or two
cables in each than one large hole with many. Of course if we *are*
talking about the attic then we may be talking about Method 15 where the
cable is resting on the plasterboard ceiling (a "thermally conductive
surface" - see notes to Method 4) but otherwise covered with insulation.

also ISTM that there must be some danger of the plaster board being
punctured by various sharp objects like nails.


Possibly, though most people don't tend to hang much from their ceilings
other than lights which are usually already there. If a cable is loose
though, and reasonably free to move, there is every chance that a nail
(or screw, or drillbit) pushing through the plasterboard will simply
push the cable out of the way. If the drill bit is followed by one of
the expanding-type plasterboard fixings then there is a small chance the
cable could be trapped I suppose...


just going over things carefully to make sure there's no glaring
exceptions before Part P bites...


Hwyl!

M.

--
Martin Angove: http://www.tridwr.demon.co.uk/
Two free issues: http://www.livtech.co.uk/ Living With Technology
.... If there was a nuclear bombing, would I be alive to care?

jim_in_sussex wrote:

a. to clarify please add 'or ceiling' before joists

You'd think that'd send the pedants back into their box, but once they
have a hold... ;-)

b. if it is legit to just rest cable on the (ordinary) plasterboard,
which IEE regs installation method is this?

Kinda-depends what's resting on the plasterboard! If it's the common
case of the ground-floor-ceiling/upper-floor-floor void we're talking
about, there's usually no insulation, and this is pretty much our mate
Reference Method 1, Clipped Direct. If you're laying in a loft, you
should either derate by 50% compared to Reference Method 1 (for the
lighting cables which typically run there, the 1mmsq with a 6A MCB meets
this derating, by no coincidence at all ;-), or indeed go through the
extra bother of running them clipped towards the top of the joists so
that the effect of any insulation (which may not be laid at the moment,
but which reg 523-04 enjoins us to anticipate - the OSG suggests that
Reg's wording refers to cable "in a space to which thermal insulation is
likely to be applied".

also ISTM that there must be some danger of the plaster board being
punctured by various sharp objects like nails.

Pretty damn unlikely, really - once the PB is in place, nailed up to the
joists, you're not going see many nails going up through it! And even
when it's being installed, the nails/screws go up into the joist, unless
you miss. Walls - yes, picture hooks/shelf-fixings and the like go into
them, hence the practice of: no cables except in 6-in-wide Zones
vertically & horizontally from visible lectrickle fittings, and in the
upper and side (but not bottom) corners of the room, or mechanically
protected, or at least 2inches deep. But few householders nail shelves
and pictures to their ceilings. (Mirrors, maybe, in the bedrooms of
those with particular lifestyles: but the straight-laced engineers who
draft the Regs and write Guides to 'em seem to consider that a minoruty
interest!)

HTH - Stefek

Stefek Zaba wrote in message ...
jim_in_sussex wrote:

snip

b. if it is legit to just rest cable on the (ordinary) plasterboard,
which IEE regs installation method is this?

Kinda-depends what's resting on the plasterboard! If it's the common
case of the ground-floor-ceiling/upper-floor-floor void we're talking
about, there's usually no insulation, and this is pretty much our mate
Reference Method 1, Clipped Direct.

snip

HTH - Stefek

Yes thanks, but it's the words 'clipped direct' that throw me.
Loosely resting on plasterboard seems a long way from being clipped
every 9 inches to a timber joist.

I had the impression that one reason for clipped direct having a good
current rating was that holding the cable firmly against timber gave
you a reasonable heat sink (possible surrounding insulation being
ignored or assumed not present for the purpose of this discussion).
But I suppose resting on cold p'board might be as good.

Still slightly puzzled, but thanks all the same.

Yes thanks, but it's the words 'clipped direct' that throw me.
Loosely resting on plasterboard seems a long way from being clipped
every 9 inches to a timber joist.

I had the impression that one reason for clipped direct having a good
current rating was that holding the cable firmly against timber gave
you a reasonable heat sink (possible surrounding insulation being
ignored or assumed not present for the purpose of this discussion).
But I suppose resting on cold p'board might be as good.

Still slightly puzzled, but thanks all the same.

Well, Reference Method 1 isn't that specific about just what it is
you're clipped to - joist, plaster, whatever. So you have to assume that
in drawing up the tables, our friends at the IEE will have taken a
pretty poor-case assumption - e.g. clipped to wood, whose thermal
conductivity is pretty ****-poor, and whose specific heat is pretty low.
So there's not that much contribution to cooling from the clipped-to
side. Indeed, ratings for Reference Method 13 - Free Air - and its
kissing-cousing, Reference Method 11 - On Perforated Cable Tray - are a
little higher than the "standard" Reference Method 1: so (according to
one widely-applicable table (6E1) reproduced in the OSG) ratings for 1,
1.5, 2.5, and 4mmsq are 15,19.5,27, and 36A under RefMeth 1, while for
RefMeth11-or-13 they jump massively to 17,22,30, and 40A - an "uprating"
of a little over 10%. So using RefMeth1 figures for cable which is in
practice "resting loosely on cold p'board" gives you a slight
underestimate of current-carrying capacity; but allows for those parts
of the cable run where you do choose to clip. And it's RefMeth1 for
which figures are most widely quoted...

Frankly, for lighting and ring circuits in ordinary domestic
circumstances, it's pretty hard to route cable in such a way as to make
it overheat - just about the only situation is if you run 2.5mmsq under
loft insulation for a substantial length (1m+, though the Regs say 0.5m
is the point at which you must derate to 50% of RefMeth1). Things get
trickier with bigger cables carrying heftier currents (showers
especially, cookers to a degree), and caution is smarter than assuming
things'll be OK...

HTH - Stefek

also ISTM that there must be some danger of the plaster board being
punctured by various sharp objects like nails.

They're probably less likely to be damaged by such an event than if they
were clipped, so had something to push against.

Certainly my understanding is that loose laid is perfectly acceptable. It is
certainly pretty universal!

Christian.

jim_in_sussex wrote:

Yes thanks, but it's the words 'clipped direct' that throw me.
Loosely resting on plasterboard seems a long way from being clipped
every 9 inches to a timber joist.

The full description of Reference Method 1 (clipped direct) in Appendix
4 of BS 7671 is "sheathed cables clipped direct to or lying on a
non-metallic surface."

But I suppose resting on cold p'board might be as good.

You suppose correctly.

Returning to the original question, the 50mm separation requirement only
applies where a cable passes through a timber joist. At other points
along the run the requirement is only that it "shall be run in such a
position that it is not liable to be damaged by contact with the floor
or the ceiling or their fixings" - see Reg. 522-06-05.

--
Andy