holes in joist

[chrisreid186]

hi guys

looking through electricians guide to building regs (small green book) pg 31 and
having trouble understanding :

' holes on centre line in a zone between 0.25 and 0.4 x span'

in regards to running cables in joists

could someone please explain in layman's terms

thanks in advance

 

[Mark_Burgess]

If the length of wood was 1000mm and you wanted to put several holes for cabling, basically measure and mark 250mm to 400mm away from one end of the wood (0.25 and 0.4 x span) and put the holes within this area.

 

[Johno]

If the joist is 3m long then 0.5 would be 1.5m

 

[chrisreid186]

cheers for the lightening response,

 

[Graeme Harrold]

Dont drill through the centre of the span basically.............(oh an a little bit either side), so for a 3m span, measuring fom one side, do not drill through the first half meter, then the next 0.7m can be drilled. The same is true from the other side......so you have an undrilled piece at each end, plus a bit in the middle.....

 

[Johno]

and don't drill a hole more than a quarter of the thickness of the joist

 

[Spudnik]

Dont forget you can get away with closer depending on hole size and joist thickness.

 

[Amp David]

Then along comes the other trades and blast the same joist full of noches and holes where ever they like.

 

[Spudnik]

Thats life im afraid!

 

[cbw]

Dont forget you can put notches closer to the edges than holes and use existing holes/notches

 

[Amp David]

Always use any existing holes anyway and lately have taken the same interest as the plumbers do over the position of new holes to be drilled.

Hate using notches, new or old, always end up putting a screw through the cable.

Before you mention it, 9 out of 10 jobs don't pay enough to start fitting steel plates to cover the notches.

 

[cbw]

I cannot possibly agree with that attitude!!!!

If plumbers want to drill lots of holes and then not put their pipes in, thats a different matter..................

 

[Amp David]

Hit the nail on the head there cbw

 

[DurhamSparky]

hehehehe!! never fitted a metal cover YET!!! and im in agreement with the above!! all my notches / holes already there!! bit like the meter seal always been broke!! CRAZY!!

 

[solo2771]

just had to redrill for tails as they were in notches touching floorboards with no protection.