I assumed, from the countersunk holes provided, that jb's are meant to be screwed to the side of a joist (in a loft). If so, I must be the only one in the south east doing so. All the ones I find are just laying loose on the plasterboard. Even on new builds.
What do the regs say about that?
Junction boxes should be secured to a joist. However some common sense is needed. If there are low voltage spot lights then you need a junction box for the transformer. I would prefer this JB not to be secured so that it can be pulled through the spotlight hole to allow the transformer to be changed without having to bugger about in a loft full of insulation.
Adam
If that were the case shouldn't all cables be clipped to a joist etc too? Fine on a new build but plainly impractible at rewire time. I would certainly secure a JB where it's always accessible - like say in a loft or cellar but wouldn't bother if it's inside a ceiling void etc.
I've never quite understood why low voltage transformers don't have loop through facilities - including ECC - given how often they're part of multiple lights.
On new builds you do not have any option but to clip the cables as there is no plasterboard when you do the first fix.
You can buy them. The ones I have tried were poorly designed. It was faster, cheaper and safer to use small JBs.
Adam
It occurs to me, that since there are no cable grips in a JB, it would be better to leave it & the cables loose. If someone pulls the cable through the ceiling e.g. to get at a transformer and the JB is fixed, a conductor could come adrift?
When I screw a box to a joist I usually clip the cable to the joist with a couple of clips to reduce the risk.
Terminals not properly tightened if this could happen.
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