Extending an existing installation and 17th Series Regs

[Andrew May]

As far as I can make out section 522.6.7 of the 17th series wiring regulations requires that cables run in the safe zones less than 50mm deep be protected by a 30mA RCD where those cables are not mechanically protected - i.e. normal wiring.

This would appear to make it impossible to extend any existing installation that has a fusebox for circuit protection without a lot of additional work. Even something as simple as a spur would need to use armoured cable or metal conduit.

Is this interpretation correct?

Andrew

[newshound]

Wouldn't simple metal channel capping be sufficient?

[Tim W]

newshound wibbled on Saturday 02 January 2010 11:15

Technically, no. Metal conduit would though.

But for tweaking an existing installation, I would just do it personally and keep it to the 16th, assuming the OP doesn't care about certification or building control...

[ARWadsworth]

That is about the most sensible answer I have ever read.

When my parents rehung a bedroom door whilst decorating a few weeks ago I did just that when I changed the position of the lightswitch to fit with the way the door now opens.

Adam

[js.b1]

Options are... #1 - As stated :-) #2 - Extension supplied by 1-gang RCD protected 13A fused spur. Can not recall the price, =A315-22, check backbox depth required. #3 - BS8436 cable, which is about =A31.50-2.00 per metre, 100m reels as TLC do not carry it.

Impractical options #4 - Armoured cable is out unless glands are left exposed for inspection & testing. #5 - Metal conduit is out for domestic once you start involving many corners. #6 - MICC/MICS is a possibility, but expensive, needs tools, IR 1kV test-gear. #7 - Steel sufficient to prevent penetration by nail (conduit is 2mm CDS).

BS8436 is the replacement for #4-7 and frankly "about time" re domestic usage. Note it has I think a 12x bend radius so nothing like FTE which is much more co-operative. FP200 is not BS8436 re i) nail test ii) FP insulation when BS8436 specifies GP8 hence no FP200 can be both FP and GP8 iii) the foil on most BS8436 I've seen is more substantial than FP200 probably re nail test.

It is a pity that TLC QVS TradingDepot DiscountElectrical Screwfix do not carry BS8436 in cut-length, even if that means multiples of 25m (keeps it simple re 3 reels on the rollers and investment of =A3400-550).

[Andrew Gabriel]

Someone at work got same advice from their BCO, when they asked a month or so back (and that was for an extension which will be cert'ed, although I think it's quite small).

[alexander.keys1]

Is BS8436 another name for 'HDX', a circular screened fixed-wiring cable available from electrical wholesalers? I've not had a chance to use any yet, but it seems to be a good alternative to 2&E for some jobs.

[Andrew May]

Thanks all. Keeping to the 16th means that I will be doing what I had planned before reading all the regs and since the consumer unit will be replaced at some point in the not to distant future should do.

It was a requirement that I had not come across before and have not seen discussed. It does seem to be a bit of a gift for the pros though. To the little old lady who wants a new socket fitted 'sorry luv, it's the regs - gonna have to fit a new fuse box as well'. And how do handymen like TMH fare when requested to make small changes that would require a new consumer unit which comes under Part P?

Andrew

[baldelectrician]

A couple of points

'doing it to the 16th Regs' will probably require a RCD for sockets. The general rule was ';sockets reasonably expected to supply equipment outdoors'. As a rule of thumb we usually put RCD's on all socket circuits

Another point the 17th Edition requires all socket circuits (in domestic situations) to have RCD protection, so if it is a socket circuit then RCD is the game

My obvious question has to be- why would you not want RCD protection on your socket circuits. i can understand not putting a fridge on a RCD on it's own circuit, but standard sockets

[Andrew Gabriel]

Usually taken to be ground floor sockets, unless there are sockets explicitly provided outdoors for the purpose.

Likewise, except as noted below.

My normal rule for 16th ed circuits was one non-RCD protected ring (or radial, depending) containing the fridge, freezer, central heating and any other frost protection, life support (e.g. fish tank heaters/filters, but with their own local RCD), and possibly any non-portable appliances with metal sheathed mineral insulated heating elements which are allowed high leakage when cold (during PAT test). So this covers items which you don't want sharing an RCD with anything else, and which don't merit dedicated RCDs on safety grounds themselves. Sockets on this circuit not to be easily accessible for other purposes, and labelled as such.

[Andrew May]

No objection to RCDs whatsoever it's just the current consumer unit uses wired fuses and I need to add a couple of new sockets. I don't want to replace the consumer unit with RCDs as that gets into serious Part P work and will be done in any case at some point in the future - probably as part of a complete rewire.

Andrew