Junction box depth

I don't under stand the need to use junction boxes for a rewire? I assume you are using J804 maintenance-free ones?

Hi,

Yes, MF ones

It's a down light circuit, so no ceiling rose to loop through. I could loop at Light Switch box but is junction box not a cleaner way? 

I've seen this where the cieling joists are only thick enough to hold up the plasterboard. I think you are thinking that in future the home owner might want to board out the loft. I don't think they should even consider this without strengthening the joists and making them thicker to support the extra weight above, make this clear to them. So your boxes should be fine protruding above the existing.

Thanks, I actually hadn't thought about the loft boarding situation, although it has 300mm.of loft insulation, so would have to be on stilts anyway.

While on the subject and in regards to WHjohnsons comment, what are most peoples preferences these days to creating the loops.

Is the most common still at the ceiling rose (where pendants are fitted), or are most switching to looping at the switch now? Do many loop at Maintenance Free boxes, so only a. Single 2 cores cables drop to the switch and single 2 core off to the light point? (especially as most modern lights these days done have terminal to loop at them, so option 1 is dying out a bit) 

When changing a circuit to down lights, if a joint is required for the mains etc , even if it's an MF one i try to get the joint so that it can be pulled through one of the down light holes. There's no searching for it then if you note it on your paperwork.

Gary

I loop switch to switch so that a neutral is available at the switch. The more points of connection you have spread around under floors and in lofts, the higher the number of points of potential failure you are introducing, plus some accessories won't work with out a neutral at the switch position. For retrofitting downlights to an existing loop-in system I use wago boxs or J804s.

Yep, loop at the switch positions. That is sensible, and a neutral available if needed in the future. Perhaps a deeper box than usual at the light switch positions as well.

526.3. Are we allowed to use "maintenance free" junction boxes that float in mid air or sit on glass fibre loft insulation?

B.S. 5733 equipment?

526.3 (vi).

Z.

A lot depends on the exact situation, but my usual order of preference is: 1) large central joint box somewhere out of the way but accessible ideally with a spare core or two to each switch/light point (best future-proofing option for later centralised lighting controls), 2) loop in at the switch (naturally gives a N at the switch in compliance with 559.5.1.208 and puts more the more difficult/crowded connections where they're most accessible), 3) loop in at the light - for downlighters etc using something that's accessible when the fitting is removed - I've used 'clickflow' connectors before with success - they feel a bit flimsy but provide a loop terminal, sufficient wiring space and an easy means of unplugging the light for testing & fault-finding.

   - Andy.

If it is a rewire then N at the switch with as deep backbox as possible.

If it is existing wiring the I like to use the Hager J501 with down-lights. Especially if there are going to be more than two cables e.g. feed-in, feed-out, switch, local load, load to next fitting. They are not MF but can be easily accessed by removing the down-light. They are also smaller then J503 and J504 so easier to fit.