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hiace_drifter wrote: ↑Sat Jun 04, 2022 3:25 pmWould enlarging (orange crescent) go horribly wrong?

Just because you don't want it to, you can bet that it will go wrong.

If you really want to try, go ahead, but you may want to get an odd board, drill a pilot hole in it, poke it up into the ceiling, screw it down (From below) so it is partly above the hole, then you can use that to keep your hole cutter centred to where you want it.

Someone-Else wrote: ↑Sat Jun 04, 2022 7:56 pm

hiace_drifter wrote: ↑Sat Jun 04, 2022 3:25 pmWould enlarging (orange crescent) go horribly wrong?

Just because you don't want it to, you can bet that it will go wrong.

If you really want to try, go ahead, but you may want to get an odd board, drill a pilot hole in it, poke it up into the ceiling, screw it down (From below) so it is partly above the hole, then you can use that to keep your hole cutter centred to where you want it.

Good idea, I'll try that.

I noticed in the bathroom (7 downlights in there too) the lights are fed by white flexible stranded twin and earth. I was expecting it to be the grey solid core stuff. Is that ok? I can easily change it as there's loft above and the wiring is laying on top of the insulation.

Pictures always help.

Someone-Else wrote: ↑Sun Jun 05, 2022 10:02 am Pictures always help.

Indeed, sorry, was up a ladder!

The cable to the downlights in the bathroom looks like this:

Someone-Else wrote: ↑Sat Jun 04, 2022 7:56 pm

hiace_drifter wrote: ↑Sat Jun 04, 2022 3:25 pmWould enlarging (orange crescent) go horribly wrong?

Just because you don't want it to, you can bet that it will go wrong.

If you really want to try, go ahead, but you may want to get an odd board, drill a pilot hole in it, poke it up into the ceiling, screw it down (From below) so it is partly above the hole, then you can use that to keep your hole cutter centred to where you want it.

Well I'm pleased to say the job went very well (thanks to everyone for the help). I did indeed use a strip of wood in the cavity, screwed from below. I used various paper templates to make sure the new circle was in the correct location. I have a small amount of filling to do, but a small price to pay.

The wooden strips also acted as a back stop so the hole saw didn't go up into the cavity. In retrospect I will use that method again for enlarging holes rather than nested hole saws.

Glad it went well, my own lighting project has also gone well. I have said how I hate GU10 bulbs, but just fitted 5. Think now up to 12 in the house in ceiling lamps for general lighting, 4 are smart type.

However must admit using more power to the pendent lights they replaced, but also likely more light as well.

hiace_drifter wrote: ↑Mon Jun 06, 2022 7:25 am Indeed, sorry, was up a ladder!

The cable to the downlights in the bathroom looks like this:

That cable is flex. Flex is not meant to be used for fixed wiring, also I will guess your protective device for lighting is rated at 6A (Quite common, no problem with that) however most folk will use 0.5mm flex as it is cheap and common, the down side is that 0.5mm flex is only rated at 3A

I would not start to panic now, but if the flex is used in abundance I would put it down on the next on the jobs to do list, at the top to change it to 1mm twin and earth (Which is rated for 10A)

Someone-Else wrote: ↑Sat Jun 04, 2022 7:56 pm Just because you don't want it to, you can bet that it will go wrong.

If you really want to try, go ahead, but you may want to get an odd board, drill a pilot hole in it, poke it up into the ceiling, screw it down (From below) so it is partly above the hole, then you can use that to keep your hole cutter centred to where you want it.

hiace_drifter wrote: ↑Mon Jun 06, 2022 7:28 am Well I'm pleased to say the job went very well (thanks to everyone for the help). I did indeed use a strip of wood in the cavity, screwed from below.

The wooden strips also acted as a back stop so the hole saw didn't go up into the cavity. In retrospect I will use that method again for enlarging holes rather than nested hole saws.

Happy to have helped

Someone-Else wrote: ↑Mon Jun 06, 2022 12:57 pm

hiace_drifter wrote: ↑Mon Jun 06, 2022 7:25 am Indeed, sorry, was up a ladder!

The cable to the downlights in the bathroom looks like this:

That cable is flex. Flex is not meant to be used for fixed wiring, also I will guess your protective device for lighting is rated at 6A (Quite common, no problem with that) however most folk will use 0.5mm flex as it is cheap and common, the down side is that 0.5mm flex is only rated at 3A

I would not start to panic now, but if the flex is used in abundance I would put it down on the next on the jobs to do list, at the top to change it to 1mm twin and earth (Which is rated for 10A)

I'm about to buy some twin and earth to replace the flex. Can I use thicker than 1mm (so I've got it ready for other jobs that need thicker) or should it be 1mm specifically?

Twin and earth goes in sizes 1mm, 1.5mm, 2.5mm, 4mm, 6mm and 10mm (Not that you need the last 4)
The problem you will have is that in some of the lights (In this case) you will have to use 2 cables (1 in and 1 out) 2 x 1mm cable will easily fit, 2 x 2.5 cables will probably not fit as that is not what the light was designed for.

In general
You can use a bigger cable than required (NEVER SMALLER) but it can and usually does cause grief and confusion later on (Although not apparent now)

It will save time and grief if as always you do the job properly in the first place.

50m of 1mm twin and earth is less than £30 from screwfix

Someone-Else wrote: ↑Sat Oct 01, 2022 10:01 am Twin and earth goes in sizes 1mm, 1.5mm, 2.5mm, 4mm, 6mm and 10mm (Not that you need the last 4)
The problem you will have is that in some of the lights (In this case) you will have to use 2 cables (1 in and 1 out) 2 x 1mm cable will easily fit, 2 x 2.5 cables will probably not fit as that is not what the light was designed for.

In general
You can use a bigger cable than required (NEVER SMALLER) but it can and usually does cause grief and confusion later on (Although not apparent now)

It will save time and grief if as always you do the job properly in the first place.

50m of 1mm twin and earth is less than £30 from screwfix

Ok, thank you. 10m bought.

Someone-Else wrote: ↑Mon Jun 06, 2022 12:57 pm Flex is not meant to be used for fixed wiring

Why? I would agree flex costs more than twin and earth, and the current rating is for it being air cooled, so a flex rated at 13 amp when used in a wall may have a lower current rating, and there is a problem with strands getting into screws so a poor termination unless ferrules are used, but in the main flex can be used instead of twin and earth, but twin and earth can't be used instead of flex, wiring a mobile home would always use flex, as the building can flex.

1 mm² twin and earth does not have a single rating, depending on installation method 1 mm² twin and earth can be 8 to 16 amp depending on installation reference method.

If you look at table 4F3 click on this link it does say 1 mm² is 10 amp, but then as you continue down it gives de-rating factors, and what you would need to work out is what temperature it will get to when concealed in something which does not allow free air passage, so under a carpet it needs de-rating, it is easier to use the twin and earth tables and installation methods for flex than to work it all out.

But there is nothing to stop flex being used instead of twin and earth other than the price, and use of ferrules if the terminals require it.

hiace_drifter wrote: ↑Sat Jun 04, 2022 3:25 pm The problem is the ones that need moving are part of a set of 6. If I move them to new locations they will be very uneven (red circles). If I enlarge the holes, but off centre, they will still be out but only by a small amount. Would enlarging (orange crescent) go horribly wrong?

Try it in a piece of plasterboard before the ceiling , but it’s rather poor to begin with, so so typical of a rushed poor job