Mounting lights above breakfast bar – to steel beam?

Hennymore

We're looking to mount three pendant lights above our breakfast bar.

Each light is about 1.5 kg and the base attaches by two screws about 80 mm apart. We'd mount the lights about 450 mm apart.

The breakfast bar is placed between the kitchen and a conservatory extension, so there are (according to plans left by previous owner) two boxed-in steel beams running parallel with the bar.

I drilled a hole along the length-wise centre line of that ceiling box, where we'd like one of the lights to go. 50 mm of plasterboard and then hit red-painted steel. Tried drilling holes about 40 mm off the centre line to either side – same thing.

I have a few questions:

- Could I mount the lights just to 50 mm of plasterboard and expect them to stay up? Googling did not give clear answers.

- Could I attach them to the steel beam – if so, what's a good way of doing that? Some sort of self-driving screw that can go into steel?

- I have considered drilling more holes off the centre line, to see if I can find a spot between the two steel beams that's not so far off the centre that it looks bad, and then use one molly bolt on that side and perhaps just going into plasterboard with the other plug + screw. Could that work? Measuring + guesswork suggests that there should be 25-80 mm between this beam and the next one.

Once we figure out how to mount them, the next step is figuring out how to get the cables there. I suspect we couldn't fish them through from the back to the centre of the box, since the cables for the old light are on the conservatory side of a beam, and the bottom-side plasterboard is right up against the bottom of the beams. From measuring I don't think there's space above the beams either. I guess our options would be either to cut channels in the plasterboard, running it along there (on straight lines, of course, so the run is predictable for any future work) and then plaster it over, or just to run them along the outside and make it a feature. Any thoughts about that?

grumbler

Hennymore said:

- Could I mount the lights just to 50 mm of plasterboard and expect them to stay up?

With proper plasterboard fiixings you can. 1.5kg isn't too heavy for this. However, plasterboard can't be 50mm. You have to find out what's between it and the steel.

- Could I attach them to the steel beam – if so, what's a good way of doing that? Some sort of self-driving screw that can go into steel?

Personally, I'd cut threads with a tap, say, 4mm.

Once we figure out how to mount them, the next step is figuring out how to get the cables there. I suspect we couldn't fish them through from the back to the centre of the box, since the cables for the old light are on the conservatory side of a beam, and the bottom-side plasterboard is right up against the bottom of the beams. From measuring I don't think there's space above the beams either. I guess our options would be either to cut channels in the plasterboard, running it along there (on straight lines, of course, so the run is predictable for any future work) and then plaster it over, or just to run them along the outside and make it a feature. Any thoughts about that?

Difficult to say, but most likely it's I-beam with empty space on sides. If so, this space can be the easiest way.

FreeBear

grumbler said: Personally, I'd cut threads with a tap, say, 4mm.

I'd go for M5 or M6 - A better selection of screw lengths. One might struggle to find a long series tap with enough length to go through 50mm of PB/insulation and 10-12mm of steel at a reasonable price.

I would be wary of suspending a 1.5Kg load from plasterboard - Have seen a strip light coming down on someone's head before now. Not pretty, and made a right mess.

Hennymore

With proper plasterboard fiixings you can. 1.5kg isn't too heavy for this. However, plasterboard can't be 50mm. You have to find out what's between it and the steel.

Thank you! It's hard to tell through the small drilled holes (and I couldn't get a good photo), and I don't know this stuff well, but it's something dense and white anyway. I can see a line where either two sheets of plasterboard meet, or perhaps there is plasterboard up against the beam and the rest is skimmed plaster on top? There is a larger hole to the side where the cables for the old light fitting come out, and there it looks like it might be plaster over plasterboard, to my untrained eye.

The innermost stuff seems perhaps slightly more grey and the outermost stuff slightly more white. It's right up against the metal with no space between, anyway, and the depth of the metal seems to be very close to 50 mm exactly.

Personally, I'd cut threads with a tap, say, 4mm.

So this would consist of first using a "tap" to make threads in the beam, then screwing into it? I'll do some YouTube research – much appreciated

FreeBear, thanks to you as well. I'll make sure to get something with the right screw length.

And thanks for the warning about it coming down on someone's head. These lights are small but rather dense (concrete or concrete-like) and at least one would be above where our cats tend to hang out, so very much want to avoid that…

Hennymore

Difficult to say, but most likely it's I-beam with empty space on sides. If so, this space can be the easiest way.

Hm, not sure I understand which space you're thinking of here. There is some space to the side (the conservatory-side face of the box) between that side and a beam, but we'd want to mount the lights towards the centre of the box, which is on the other side of this beam. Since the plasterboard/whatever is right up against the beam on the bottom, there's no space there. So any space would need to be either above or on the ends (where it goes into the walls) but that would probably require some fairly big holes to find and fish the cable through, if it exists at all.

Ganga

What is above the ceiling ? is it possible to access the beams and the wiring from above.

Hennymore

Ganga said:

What is above the ceiling ? is it possible to access the beams and the wiring from above.

Tiled bathrooms I'm afraid

grumbler

Hennymore said:

Difficult to say, but most likely it's I-beam with empty space on sides. If so, this space can be the easiest way.

Hm, not sure I understand which space you're thinking of here. There is some space to the side (the conservatory-side face of the box) between that side and a beam, but we'd want to mount the lights towards the centre of the box, which is on the other side of this beam. Since the plasterboard/whatever is right up against the beam on the bottom, there's no space there. So any space would need to be either above or on the ends (where it goes into the walls) but that would probably require some fairly big holes to find and fish the cable through, if it exists at all.

I was wrong. The space that I thought was empty is in fact likely to have lots of pieces of wood inside.

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BillTrac

those pieces of wood are purely for the fitting of plasterboard etc. they're usually just a tight-fit and not secured to the RSJ at all. 
If the light fitting positions line up with the timbers then a hole drilled through would enable the light fixings to be screwed directly into the timbers. I'd rather the lights were held by these than just by plasterboard. Especially underneath bathrooms.
And of course, the other option is to drill and tap into the beam. Just take it slowly.   

Hennymore

Thank you again. You're saying the pieces of wood are likely to protrude on the sides of the beams, for fastening the bottom-side plasterboard, and we could possibly attach the lights to there?

We've looked into tapping a little. Also found self-tapping screws like https://www.screwfix.com/p/easydrive-carbon-steel-self-drilling-screws-5-5-x-75mm-100-pack/44476 – also considering that (probably with a pilot hole).

clive0510

I Would ask a electrician and have it done properly.