Pass electric cable through ceiling joist

[dubman]

Hi I'm installing a plasterboard ceiling in a porch and I want to pass the cable through a joist to feed the bulb.

This cable is twin & earth with external diameter of approx 7 mm and the joist in approx 35 mm thick. My question is what size hole should I drill through the joist so I can pass the cable through to the ceiling rose? I'm assuming these joist holes should always be big enough so that the cable doesn't overheat?

One other thing: the Rose has a pole for connecting an earth cable - is it usual or recommended to earth a ceiling rose? Thank you.

 

[Des 56]

Hi I'm installing a plasterboard ceiling in a porch and I want to pass the cable through a joist to feed the bulb.
Accepted

This cable is twin & earth with external diameter of approx 7 mm and the joist in approx 35 mm thick.
Cables core sizes are measured usually as 1.0mm or 1.5mm with 1.0mm cpc.the outer insulation can have varying thicknesses

My question is what size hole should I drill through the joist so I can pass the cable through to the ceiling rose?
I'm assuming these joist holes should always be big enough so that the cable doesn't overheat?
Heat dissipation through the hole is not an issue,cable size with regard to overloading is an issue
Cable sizes can be determined by various factors including insulation coverings, length, cross sectional area, type of material,and other factors
It is important that the cable is rcd protected if it is buried less than 50mm in the ceiling unless it has adequate mechanical protection

One other thing: the Rose has a pole for connecting an earth cable - is it usual or recommended to earth a ceiling rose? Thank you.[/QUOTE
Yes,also tests should be carried out to ensure that the cpc is actually continueous and the fault path within maximum limits for the type of protective device in order to acheive correct dis connection times

 

[dubman]

Thanks for the quick reply. Ok in this case the cable is 1,5 mm twin & earth, and the total exterior diameter is approx 7mm. So do you think a hole of say 9mm diameter would be ok, just so the cable passes through easily? Since as you say overheating wouldn't be an issue.

Another option would be NOT to pass the cable through the joist, but in this case the ceiling rose would be screwed into only the 12mm plaster board (using rawl plugs of course)

 

[Doomed]

When drilling holes in joists there are areas where you are not supposed to drill, such as near the middle of the length of the joist or near the ends.

 

[Hawk81]

Thanks for the quick reply. Ok in this case the cable is 1,5 mm twin & earth, and the total exterior diameter is approx 7mm. So do you think a hole of say 9mm diameter would be ok, just so the cable passes through easily? Since as you say overheating wouldn't be an issue.

Another option would be NOT to pass the cable through the joist, but in this case the ceiling rose would be screwed into only the 12mm plaster board (using rawl plugs of course)

rawl plus into plaster board???? I would use plaster board fixing screws. Made for the job.

 

[Des 56]

Puss the cable through the baton as you stated and secure the fitting,fix another baton if necesary to do sol
Take care not to screw or nail the cable

If you are using a class (meta) lightl fitting,ensure you make the earth connection and that it is actually an earth,if it is plastic.then it remains there unused but ready for possible future use

 

[JUD]

Thanks for the quick reply. Ok in this case the cable is 1,5 mm twin & earth, and the total exterior diameter is approx 7mm. So do you think a hole of say 9mm diameter would be ok, just so the cable passes through easily? Since as you say overheating wouldn't be an issue.

Any holes should be drilled in an area between 25% and 40% of the span of the joist.

The diameter of the hole should not be more than 25% of the height of the joist and must be 50mm from the top/bottom.

Example

If your joist has a span of 3m and a height of 150mm, your hole should be in an area between 0.75m (3m x 0.25) and 1.2m (3m x 0.4) with a diameter no more than 37.5mm (150mm x 0.25), making sure that the top and bottom of the hole are at least 50mm from the top and bottom of the joist.


If it's a hole for just one cable just drill it big enough for the cable to pass through easily without damaging it.

 

[dubman]

actually strictly speaking I suppose it's not a joist. It's boards running under the joists, like you might use to get the ceiling more level, or a bit lower. These boards are about 35 mm in thickness and 80 mm in width, and the plaster board is nailed into them. So in this case I am drilling the hole about 2 cm from the edge of one board, so as to be able to screw the rose through the plaster and into the wood. At the same time keeping the rose almost in ther centre of the ceiling. So I assume those regulations / distances etc about holes in joists don't apply in this case?