Guidance on running cables through joists please

BrianHJR · Jun 16, 2020

Hi, I’m adding a heat detector into my existing smoke detector system.
The new detector will be inspected and commissioned by an electrician, but I’m fitting it to the ceiling and running the cables to save time taken by a professional (their suggestion as they are very busy).
This is already a good loop of cable left in between detectors for exactly this eventuality - I just need to get the cable from under the loose Floorboards in a cupboard and across the joists to be further into the centre of the room. The joists in the trafficked part of the room can be drilled at centre so they are fine, but in the cupboard it becomes a problem due to 22mm f&r pipes and a gas supply. So my question is can these cables be let into shallow slots in the tops of the joists, on the basis that the boards are loose and will not be screwed or nailed?
I can’t see any other way of getting the cables past these obstacles.
Photo added for clarity.
Thanks.

Andy78 · Jun 16, 2020

I think it best if you direct this question to the electrician as they will be signing the certificate for the work.

SJD · Jun 16, 2020

Looks to me like the joists already have huge notches courtesy of a plumber, and then additional timber added to the sides of the joists, possibly to support the floorboards, unless they are strengthening joists with notches that shouldn't be there.

littlespark · Jun 16, 2020

Looks like the original huge notches have been there for pipes that are no longer there.

If notching for cables, make them as small as possible, running along the centre of the floorboards (not to the side where a fixing screw might catch it) and cover with some form of mechanical protection. (tin plate still in use these days?)
Clip the cables in the notch so they don't suddenly spring up when you're laying the boards back down and get them squashed between joist and board

BrianHJR · Jun 16, 2020

littlespark said:
Looks like the original huge notches have been there for pipes that are no longer there.

If notching for cables, make them as small as possible, running along the centre of the floorboards (not to the side where a fixing screw might catch it) and cover with some form of mechanical protection. (tin plate still in use these days?)
Clip the cables in the notch so they don't suddenly spring up when you're laying the boards back down and get them squashed between joist and board

Thanks, yes the huge notches used to have pipes in but I removed them before the new combination boiler was fitted a couple of years ago.

I added the strengthening and bridging timber to augment the weakened timbers while giving a better bearing surface for for the floorboards.
They’re nailed/screwed and glued where possible.
I’m not planning to notch any more than is absolutely necessary. I’ve got an oscillating Bosch multicutter so can do it neatly

I now recall that I've seen the plates in the Screwfix catalogue - they’re called Protectaplates - I presume that I can use some bits of steel plate of a reasonable gauge?

Thanks for the advice.