17th edition
- Thread starter jmr
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AFAIK, concealed cables that are not buried at least 50mm below the surface of the plaster must be mechanically protected, otherwise they must be RCD protected.
Its probably going to mean the demise of the bog standard split load board and more dual split load boards (which just as much of a bodge, there is much debate as to weather they conform to regs).
The best option in my opinion is to use RCBO's across the board, problem being the vastly increased cost, well for the time being at least once demand pushes the price down.
Its probably going to mean the demise of the bog standard split load board and more dual split load boards (which just as much of a bodge, there is much debate as to weather they conform to regs).
The best option in my opinion is to use RCBO's across the board, problem being the vastly increased cost, well for the time being at least once demand pushes the price down.
Afaict using cables with an earthed metal layer is also an acceptable way of protecting non-rcd circuits though for some unexplained reason split con has been removed from the list of acceptable cables for this.
and theese requirements only apply if there is not an instructed person responsible for keeping an eye on the installation. Exact interpretation of that particular reg is not entirely clear at the moment.
While rcbos are better than a split load they aren't much better. A single faulty appliance can still take out all the sockets on an entire floor. Unfortunately doing a rewire in MICC with all RCD protection at the point of use is rather expennsive.
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Out of interest how would people interpret this requirement regarding submains? I'm in the situation where my consumer unit is remote from the incoming service head. Currently there is a 60A switchfuse next to the service head, then normal meter tails running down the wall and under the suspended floor to the consumer unit. I'm toying with the idea of replacing/uprating the submain to 25mm² (in preparation for a supply upgrade to 100A) as part of some other work. Originally I was planning on using split concentric, but to comply with 17th edition it seems as though the only sensible way of doing it is with SWA (and the thought of wrestling with 25mm² SWA isn't appealing!). Protection of meter tails / submains seems to me to be a bit of puzzler with the 17th edition..
If you think about what you are doing then it’s not that complicated. The purpose of the regs is to ensure that if a cable buried in wall gets accidentally punctured a protective device will operate - either the circuit over current device or an earth leakage device.
522.6.6 Gives you 5 options to comply.
(i) You could use SWA, however, because it’s backed with a 60amp fuse and your intension is to up-grade to 100amps I don’t see SWA as an option. If the cable was punctured then the person could end up with flash burns.
(ii) Same as above
(iii) Same as above
(iv) IMO, in your case mechanically protecting the cable(s) sufficient to prevent penetration of the cable(s) by nails, screws and the like is the best option.
(v) Not an option because you would need an RCD which you can’t use on a sub-main and still comply with 314
522.6.6 Gives you 5 options to comply.
(i) You could use SWA, however, because it’s backed with a 60amp fuse and your intension is to up-grade to 100amps I don’t see SWA as an option. If the cable was punctured then the person could end up with flash burns.
(ii) Same as above
(iii) Same as above
(iv) IMO, in your case mechanically protecting the cable(s) sufficient to prevent penetration of the cable(s) by nails, screws and the like is the best option.
(v) Not an option because you would need an RCD which you can’t use on a sub-main and still comply with 314
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My shiny new red book is at work at the moment so I'll look at the detail a bit more in the morning. My field is in industrial electrics so domestic meter tails aren't really in my day to day operations!
My thinking in considering SWA was that the mechanical protection was in effect integral to the cable - I hadn't considered the possibility of flash burns. My first plan was to use split concentric for ease of installation until I read that this was not 'permitted'. Running normal tails in steel conduit or trunking may turn out to be the best option. I'm also wondering whether I could get away with running normal tails (or split concentric) on the surface rather than burying them, and then taking them below the floor joists so that they ended up deeper than 50mm below the boards. The tails would be concealed by the kitchen cupboards so asthetics wouldn't be a problem, but it still doesn't feel like the best way of doing it to me...
My thinking in considering SWA was that the mechanical protection was in effect integral to the cable - I hadn't considered the possibility of flash burns. My first plan was to use split concentric for ease of installation until I read that this was not 'permitted'. Running normal tails in steel conduit or trunking may turn out to be the best option. I'm also wondering whether I could get away with running normal tails (or split concentric) on the surface rather than burying them, and then taking them below the floor joists so that they ended up deeper than 50mm below the boards. The tails would be concealed by the kitchen cupboards so asthetics wouldn't be a problem, but it still doesn't feel like the best way of doing it to me...
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I'm probably going to go with normal 25mm tails as described above, but am still intrigued about the use of SWA. Looking in the big red book at 522.6.6 (i), the first cable listed as being permissable is one to BS 5467, which is surely XLPE SWA?
SWA does meet 522.6.6 (i) however, as the designer, meeting the regs is one of many consideration.
I did say "IMO" because although you can use SWA on its own, personally, I would never bury a 100amp submain in wall within domestic premises without mechanical protection.
There's a big difference between putting a nail/screw through a cable that's backed with a 32amp device and one that's backed with a 100amp device.
I did say "IMO" because although you can use SWA on its own, personally, I would never bury a 100amp submain in wall within domestic premises without mechanical protection.
There's a big difference between putting a nail/screw through a cable that's backed with a 32amp device and one that's backed with a 100amp device.
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