In a total re-wire situation, is it acceptable to form the ring using only junction boxes and then spur of these to the individual sockets ?
am going to replace my two cartridge type consumer units with a single split load mcb type.
NO. junction boxes can only be used where they are accessable for servicing. why if your totaly rewiring would you want to use junction boxes?
loz
I believe so, provided that it can be proved that voltage drop, earth loop impedence and cable capacity is not exceeded at any point. This may require you to do some calculations, rather than relying on the total cable length tables in the On Site Guide. Is this a drop down from ceiling because of concrete floor scenario?
An alternative is to run a radial circuit instead of a ring. Then you can run cable in any configuration you like, although you'll need 6mm or 4mm cable (depending on installation method and circuit length).
Consider using a non-split load consumer unit and using RCBOs for any circuit that would have been on the RCD side. It'll be more expensive, but a better solution.
Christian.
Well, if the junction boxes are to be inaccessible, there are other alternative methods of connecting cables than screw terminals.
The most common reason is when installing in a house with a concrete floor. This usually entails drop cables from the ceiling. Some installers might prefer to drop only one cable instead of two.
In particular, with many sockets (as suggested by the latest regs) you could very quickly run into the ring main cable length limits. This might make it easier to run as a radial with drop cables from junction boxes, as the electrical length from any particular socket outlet back to the consumer unit will be massively shorter, enabling a greater number of sockets to be installed and a lower voltage drop and earth loop impedence.
Christian.
Not sure, but one thing to note is that JBs must be accessible after the finish of the job.
If the walls are solid, I'd say that chasing down from the ceiling to every socket would be more work than other ways. If the walls are dry lined in such a way as to make access behind them easy, then I can't see why you'd want to effectively spur each socket.
Which other ways?
Because if you allow 4m of cable for each drop from the ceiling void (can't bury in the floor and shouldn't just run buried horizontal) then you can't get many sockets before the ring length exceeds what is permitted, particularly if you follow modern guidance as to the number of sockets that should be installed.
Christian.
On a related point. I was reading the Collins DIY manual, the older 1993 version. On earthing it says all pipes in a bathroom, even if no electrical appliances in there, must have an earth clip on them near the taps and an earth wire daisy chaining from one to the other and back to the earth point at the meter. It also says a metal bath must be on this earth chain, and if there is no earth lug on the bath then drilling into the bath feet should be done to secure an earthing point. I assume this is the IEE 15th . Is that the case in the 16th?
I know that earthing is not required for plastic pipes. Also with mixed plastic and copper pipe what is the way to go with the 16th? Or can this earth chain be eliminated by having the odd plastic fitting in the copper pipework?
All my pipes are hidden. My query is hypthetical. Nevertheless I intend to upgrade to the IEE 16th as far as I can go and bathroom earthing is one point.
Buried horizontally is allowed by the regulations surely!?
Then AIUI, no bonding is required. Supplementary bonding is about making sure everything metal that you could touch in the room is at the same potential to every other bit, or alternatively, is totally isolated from everything else, including earth.
If the pipe is entirely unable to be touched (i.e. is behind panelling that needs at the least a tool to open) then it doesn't need bonding.
Christian.
It is looked down upon as it isn't quite as safe as vertical runs (the exception being kitchen worktop sockets). Also, it can be difficult to maintain around fiddly bits where there are no accessories on that particular bit of wall. I suspect with the increased number of sockets that need to be installed, combined with the increased height of sockets and more use of concrete floors, that horizontal runs will get more popular, though.
Christian.
"Christian McArdle" wrote | >Buried horizontally is allowed by the regulations surely!? | It is looked down upon as it isn't quite as safe as vertical runs | (the exception being kitchen worktop sockets). Also, it can be | difficult to maintain around fiddly bits where there are no | accessories on that particular bit of wall. I suspect with the | increased number of sockets that need to be installed, combined | with the increased height of sockets and more use of concrete | floors, that horizontal runs will get more popular, though.
Horizontal runs should be in the permitted zone from accessory to accessory, and especially with the trend/requirement to mount sockets higher they should be well above skirting level.
My objection is that it then makes it difficult to mount any other accessory (phone, data, speaker outlet etc) so that it lines up wiht the mains sockets. However if the mains is brought down in the corner and then horizontal to the socket near the corner, the low-voltage can line up in the middle of the walls eg
corner | | *mains (in permitted zone in corner or horiz from accessory) | * | * | * | * | * | * | ****SKT****SKT TELE DATA | & & | &&&&&&&&&&&&&&&&&&&&&&&&&&&&&&& | ----------------------------------------- /////////////////////////////////////////
Owain
I'm involved in a property (small flat) where the power ciruit is just one big spur with junction boxes under the floor boards. I was considering making into a ring main by running a cable back from the last socket to the CU. Would under floorboard junction boxes count as being accessible? There is a hatch in a cupboard to get under floor..
I'm not an expert on the regs by any means, but that would seem reasonable to me. Inaccessible to me means plastered over, etc.
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