My House Rewire (Current progress and some questions!)

[HDRW]

4. We are about to install an upstairs ring, the problem lies in the cable routing. the holes in the joists that the previous circuit used (radial circuit) aren't between 25 and 40% of the beam length. Would it be okay to use these holes are will the council ask me to drill holes in the correct place? I figure having two holes is worse than having one!

The hole-placement is nothing to do with electricity - it's the reduction in strength of the joists that's as stake. If there are holes there already, even if they're in the wrong place, I can assure you that drilling new ones won't make the joists stronger!

If there are holes you can use, use them. If not, drill the new ones in the right areas of the woodwork.

Cheers,

Howard

 

[lorraine]

Hi

Yes thats what I thought, if you drill another hole you reduce the second moment of area some more which is not a good thing. I was just worried about the building regs guy coming and telling me off.

I think the joist can be modelled as a simply supported beam with two reactions at either end and then a point load in the middle. Suggesting that around the 25% area is where the bending moment is 0.

Lorraine

 

[andy]

the joists have already been weakened by the exisint holes. now, do you use those holes, meaning it stays at how strong it is now, or drill more holes weakening it even more. i would just use the old holes

 

[ban-all-sheds]

He wasn't particularly familiar with electrics

Don't let him touch them, then....