Joist hole cutting

[a1topdog]

I need to cut some holes in my joists for rewire and have the following questions:

1) - What size holes should I cut and how many wires is it safe to feed through them. (I'm doing both ring main and lighting circuits)

2) - Where abouts in the joist is safe to drill so not to weaken the joist?

3) If I have to drill several holes in the same joist how far should I space them apart?

3) - I can't use a wood cutting bit in my drill as the space between the joists is too narrow. Will I be OK with a hole cutting fixing? (I'm guessing they are shorter)

Many thanks

 

[IanDB]

What size holes should I cut and how many wires is it safe to feed through them.

The hole size should be such that you still have 50mm of joist above and below your hole - work out your maximum hole size. Obviously the smaller the hole the less the joist is weakened. Cables shouldn't be forced though holes so if it looks tight drill another hole at least 3 diameters distance from the first one.

If you follow the above then you don't have to worry about where you're drilling holes.

I can't use a wood cutting bit in my drill as the space between the joists is too narrow.

That's a pain. Have you considered a right angled drill attachment? If you're doing a lot of holes it would be worth the investment.

 

[Damocles]

Also keep holes away from the ends of the joists. The 50mm deep rule is to prevent nails etc being driven into the cables. There must be another rule about the amount of wood you can remove but I dont remember exactly what it is. Spreading cables in smaller holes may be better than bunching everything in a bigger one, but depends on circumstances, access etc.

 

[ban-all-sheds]

All those questions are answered in the OSG. Why don't you have a copy?

 

[a1topdog]

I have no idea what the OSG is.

 

[breezer]

On Site Guide you can get one here

 

[a1topdog]

Thanks - I'll read the book and forget about using the forum

 

[ban-all-sheds]

I have no idea what the OSG is.

No way should you be attempting a rewire then....

 

[a1topdog]

No way should you be attempting a rewire then....

I beg to differ - there are other publications available that quote the latest standards and regs - the one I had read just didn't give me enough info various hole sizes.

You will say I read the wrong book - which may be the case. Now I know about the OSG I will read it.

I'm sure your answer of "read the OSG" would apply to most questions asked on this forum. If someone asks how to fix their car would you just reply saying "go and read the manual"?

 

[breezer]

. If someone asks how to fix their car would you just reply saying "go and read the manual"?

you would be surprised the number of people that come on this forum (not just uk electics) that ask "silly questions" only because they didn't read the manual

 

[ban-all-sheds]

I'm sure your answer of "read the OSG" would apply to most questions asked on this forum. If someone asks how to fix their car would you just reply saying "go and read the manual"?

No I wouldn't, that's CPW's job, but you'd already had the answer from someone else, so you didn't need me to repeat it - I was just trying to highlight the value of the OSG.

Yes there are other books (with insufficient info in this case it seems ), so maybe it was a bit OTT to say you shouldn't be rewiring without the OSG, but it is pretty good, and comes straight from the horses mouth. I recently also bought the Amicus guides, on recommendations - haven't spent much time using them, but at first glance I don't like them as much.

 

[Damocles]

But from time to time sparks do post complaints about the OSG, that they don't agree with it. But it is straight from the horses mouth.