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.
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.
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.
*Growing old is inevitable, growing up is optional *
Dave Plowman email@example.com London SW 12
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.
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
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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.
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 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
| *mains (in permitted zone in corner or horiz from accessory)
| ****SKT****SKT TELE DATA
| & &
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
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..
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