Channelling cables in the plaster of ceilings

[Delboybully]

I have been doing some subbying work for an NICEIC approved sparks. He will channel out the plaster of ceilings to run new cables in.

For example, today there was on light in a ceiling in an corridor and we were removing this and replacing with 4 spotlights. So the spark said to take out the plaster under the joists and lay the cable in. I wasnt happy about this but its his job and his name on the cert.

I suggested that this wasnt a good idea and shouldnt be done. He said find me a reg to say you cant do it. So I have looked in the BYB, in particular 522.6.201 to 522.6.204. As the joists are not being notched or drilled there is no problem there. 522.6.202 and 522.6.203 are refering to cables buried in walls.

This leaves 522.6.201
the first line is in regard to the cable being run in such a position that it wont be damaged by contact with the floor or ceilings or fixings. This seems to me to be the only reg that outlaws the channeling of the ceiling. But if the ceiling is already installed the fixings wont damage the new cable.

I still think its bad practice to channel the ceilings but am getting a bit lost as to whether the regs allow it

 

[davesparks]

Is it compromising a fire barrier?

 

[telectrix]

had to do the same when fitting downlights with no access from above. personally i can't see why the ceilings should not have safe zones between fittings, just like walls.

 

[Delboybully]

had to do the same when fitting downlights with no access from above. personally i can't see why the ceilings should not have safe zones between fittings, just like walls.

I can see your point but at the moment they dont have safe zones in ceilings.

And what happens when someone puts some christmas decorations up and puts the drawing pin into the cables?

 

[davesparks]

i can see your point but at the moment they dont have safe zones in ceilings.

And what happens when someone puts some christmas decorations up and puts the drawing pin into the cables?

bzzzzzzzzzt bang!!

 

[Paul.M]

When stitching cables in ceilings you normally chisel or drill out a bit of the joist to have a bit of depth for the cable, 50mm from finished surface is the target.

 

[NDG Elecs]

I am not too fussed that safe zones do not exist in ceilings. Xmas decos would likely go around the edges adjacent to the wall. Other than that what else is likely to cause the ceiling to be drilled or drawing pins put in it... Ok, there are things like decorative kids canopies and funny bed pelmets I suppose.

To the OP, I would always preferably cut a narrow and say 20-30mm deep notch to put the cable in. I reckon a member of Joe Public would be more likely to put a nail through a switch drop, as only electricians seem to be aware of safe zones, which kinda defeats their purpose!

 

[davesparks]

When stitching cables in ceilings you normally chisel or drill out a bit of the joist to have a bit of depth for the cable, 50mm from finished surface is the target.

You are not permitted to cut in to the bottom surface of a joist according to part A

 

[Paul.M]

You are not permitted to cut in to the bottom surface of a joist according to part A

Really! Whoops my mentor 20 years ago did not mention that and I've been doing it ever since lol.

Ok the other way of doing it when you dont have any access from above is to:-

With a 78mm (or whatever reasonable size) hole saw, cut a hole a few inches before the joist. Now with a long 16mm or 20mm flat wood drill bit, drill a hole through the joist. Fish your cable from one ceiling hole to another. Keep the cut outs (biscuits), get a bit of wood, batten it across the hole and replace the biscuit. Leave it to the plaster to sort out or fill it in yourself using finishing plaster (takes a bit of practice btw). Sand it down if needed and paint, job done

 

[NDG Elecs]

You are not permitted to cut in to the bottom surface of a joist according to part A

Yep, and it makes sense when you think of how the loading from above will impart itself onto the joist below. In an old house with big 9x2" or whatever sized joists then I do not think a small notch would particularly lead to any future structural problems. I have seen many older joists cut to ribbons (usually by plumbers!) that are still holding strong. Not that it is best practise...

Worst I saw was some clever arse who decided to cut away three inches depth for 1000mm from two six inch deep joist so their shower tray would be flush with the floor above.

 

[Delboybully]

With a 78mm (or whatever reasonable size) hole saw, cut a hole a few inches before the joist. Now with a long 16mm or 20mm flat wood drill bit, drill a hole through the joist. Fish your cable from one ceiling hole to another. Keep the cut outs (biscuits), get a bit of wood, batten it across the hole and replace the biscuit. Leave it to the plaster to sort out or fill it in yourself using finishing plaster (takes a bit of practice btw). Sand it down if needed and paint, job done

This is what I do except I use a 100mm hole saw and use my angle drill. He complained that I had ruined the ceiling. The plasterers sorted it out. He also made a valid point that was how do you know you are drilling in the correct position on the span of the joist without seeing the whole length.

 

[davesparks]

This is what I do except I use a 100mm hole saw and use my angle drill. He complained that I had ruined the ceiling. The plasterers sorted it out. He also made a valid point that was how do you know you are drilling in the correct position on the span of the joist without seeing the whole length.

You don't know for absoloute certain, but you should be able to identify where the walls are and measure the distance between them. Bearing in mind the positions of the holes are measured on the span not the length. The span being the distance between supports.
If a joist or beam is supported at both ends and again in the middle then it is over two spans, not one.

 

[Delboybully]

You don't know for absoloute certain, but you should be able to identify where the walls are and measure the distance between them. Bearing in mind the positions of the holes are measured on the span not the length. The span being the distance between supports.
If a joist or beam is supported at both ends and again in the middle then it is over two spans, not one.

That interesting, I didnt know that.

What about those joists that get joined by overlapping mid way across a ceiling, does the same rule apply?

 

[Paul.M]

He also made a valid point that was how do you know you are drilling in the correct position on the span of the joist without seeing the whole length.

Easy, you use a stud finder or tap your knuckles on the ceiling. Hollow,,, hollow,,, hollow,,,, not hollow, that will be a joist!

To some customers this is rocket science!!!!

 

[davesparks]

That interesting, I didnt know that.

What about those joists that get joined by overlapping mid way across a ceiling, does the same rule apply?

Span is the distance between supports, if the rule was concerned with the length then it would say length.
It doesn't matter how many joints there are, the span is still the distance between supports. Not that I've ever seen a joist with a joint in it mid span? Are you sure about this?