wood beams and electrics

[Vass]

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

[Tim S]

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

[Vass]

1961 Semi - 8 x 2 joists

-- Vass

[Vass]

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

[Rick]

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

Rick

[John Rumm]

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.

[Brian]

I have never been in a house that doesn't have sections cut out of the tops of beams! They had been wired when the 15th edition regs were about. All done by professionals! It doesn't do any harm unless you go wild and hack away half the beam.

[Alan]

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.

[John Rumm]

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.

[Lobster]

These things are just the job for protecting cables in notches (top or bottom of joists):

David

[Douglas de Lacey]

Brace and bit?

Douglas de Lacey

[John Rumm]

no, me neither!

Plumbers and CH fitters tend to do far worse the electricians as well it seems ;-)

It is one of those things that probably does not matter in most cases if you are sensible. So think where you are in the span of long beams and avoid the high stress sections, only notch in the centre of floor boards so there is less chance of the board being nailed back through the wires etc. Ceilings are a bit more dodgy since you less expect wires just under the surface there.

[Cicero]

================= See here for the general idea:

currently have a right angle drill attachment for about £8-00.

Cic.

[John Rumm]

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!

[Cicero]

======================== Screwfix do these:

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.

[John Rumm]

these:

They will fit an electric drill as well as the conventional brace. >

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

[Mike Barnes]

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.

[Cicero]

=============== 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.

[Vass]

thanks for all advice

[John Rumm]

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!)