wood beams and electrics

Can I cut out channels for cable on the underside of a beam (i.e. in the ceiling downstairs) for wiring purposes? or can you only cut out sections on the top of the beam? Weakening the beam is my worry ta
--
Vass



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On Wed, 04 Jan 2006 08:57:17 +0000, Vass wrote:

In the case of regular joists:
Hole through the centre neutral axis are preferred as these have little effect on the strength.
The top is in max compression and the bottom is in max tension so notching out top or bottom does weaken the beam.
Having said that, the beam *may* be so over specified as to not care. Distance from the end of the beam is a factor too.
The real downside with this is tendency to put nails through cables later, which is another reason why the centre is preferred.
Is it a joist (8x2, 4x2 etc) or a big heavy beam a la period cottage that you have?
Tim
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1961 Semi - 8 x 2 joists -- Vass
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Tim S wrote:

These things are just the job for protecting cables in notches (top or bottom of joists): <http://www.screwfix.com/app/sfd/cat/pro.jsp?cId 1228&tsh294&id0038>
David
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On Wed, 4 Jan 2006 08:57:17 -0000, "Vass"

Only in the top, and only in certan zones, and certan max sizes, according to my book on building regs.
Rick
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Vass wrote:

yes, but best you don't

not ideal there either! ;-)

There are two issues to factor here: structural integrity of the beam, and safety of the wiring.
The preferred solution is to drill through the middle of the beam since this has least impact on it structurally, and also keeps the wires well out of reach of damage. Even then there are guidelines in the building regs about the maximum size of hole, and also where in the span it is best placed (span/4 at each end being best IIRC).
Electrically, if you place wires into a ceiling notched into the bottom of a joist, they are out of the expected "zones" for wiring runs and not at sufficient depth (50mm) to be protected. Hence they will need additional mechanical protection to make sure they can't be screwed or nailed into. The same issues need to be considered if the wires are supported directly below a floor covering.
--
Cheers,

John.

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OK great thanks for the advice, but not having seen a right angled drill how do I get a hole in the centre with joists just 12 inches apart (approx)? ta
--
Vass



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I find that a long (12" long or more) spade bit works well for this, allowing you to drill at an angle with just the shaft of the bit rubbing on the adjacent beam while drilling, keeping the drill itself out of the way. You'll end up with angled holes however.
An alternative is to hire a R/A drill and use a short spade bit or hole cutter.
Alan.
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Vass wrote:

Hacksaw the end off a spade bit - leaving enough shank such that when inserted into a drill there is about a joists thickness left sticking out. Obviously opt for a short drill as well. I find a spade bit in my 18V cordless combi just fits between 3" wide joists on 400mm spacings. A small corded power drill will also probably fit - the bottom of the range elcheapo shed specials without any gearbox etc are often quite short.
Failing that you can get a right angle drilling adaptor for under 20. These are not ideal however and best avoided if you can find another way of doing it.
--
Cheers,

John.

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John Rumm wrote:

Brace and bit?
Douglas de Lacey
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Douglas de Lacey wrote:

Can work, but these tend to be quite long, so you either have to drill your hole at an angle (less of a problem with wires but a pain for pipes), or sometimes you may get lucky and find the offset bit of the brace lines up with the next joist and you can get a half rotation out of it!
--
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John.

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pipes),
lines
=======================Screwfix do these: http://www.screwfix.com/app/sfd/cat/pro.jsp?cId 0195&tss211&id082
They will fit an electric drill as well as the conventional brace.
There used to be a brace similar to a socket set ratchet which was excellent for getting into tight spaces. Unfortunately, it appears to have disappeared from the market. Maybe somebody will know if they're still available.
Cic.
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Cicero wrote:

Still a bit long at 4" though... and you can't cut them down like one of these:
http://www.screwfix.com/app/sfd/cat/pro.jsp?cId 0195&tsu084&id901

You might find if they have a hex end that an ordinary socket will fit.
--
Cheers,

John.

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==============They do have a hex end and they do fit a in a small socket. As far as cutting a spade bit to length is concerned, you couldn't cut it much shorter (if at all) than the auger bit so there's no real difference between the two. However as another poster points out the auger bit can be rather fierce in a power drill so it pays to use the slowest practical speed.
Cic.
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Cicero wrote:

You can cut a spade to have only 2" projecting from the end of the drill if required - not sure you could do that with an auger.
(also less sure I would want to go trashing a good auger bit in the first place!)
--
Cheers,

John.

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first
====================My 25mm (95mm long) auger bit (Screwfix) projects 2.75" (70mm) from the drill chuck. Cutting a 25mm spade bit to the shortest feasible length would leave a minimum projection of 2.625" (67mm) - a difference of only 1/8" (3mm).
Lengths are proportionately less for smaller sizes of auger / spade bits, so there's not much to be gained by cutting a spade bit.
Cic.
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In uk.d-i-y, Cicero wrote:

If you use one of those in an electric drill, be *very* careful. It can screw itself down a hole faster than a ferret after a rabbit.
--
Mike Barnes

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John Rumm wrote:

You'll be wanting a joist brace... e.g. http://www.antiquetools.co.uk/1291.html
--
Andy

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Andy Wade wrote:

Nice looking bit of kit....
Don't fancy the price much though!
--
Cheers,

John.

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<snip>

lawson-his.co.uk/scripts/details.php?cat=Rotary%20Drills&product'147
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