Split load CU

Getting differing messages on what to protect (RCD) and what not...
What's the general view ?
Lighting ... NO
Ring Mains... YES
Install a (unprotected) separate socket for Fridge Freezer Yes or No ?
Cooker Outlet ..Yes or No ?
Gas Boiler ... Yes or No ?
Outside supply (unprotected) use individual plug-in RCD's for portable
tools. Yes or No
Install a CU with a 100mA main RCD and then
use 30mA RCBO's but all the CU's I've seen have 30mA main RCD's ... Is
this a real option ?
and finally: If you were doing a re-wire now would you connect the
bathroom lighting cct seperatly via a RCBO or is there danger that
this requirement in the 17th edition will not be ratified.
Reply to
ac1951
In article , ac1951 writes:
Unprotected. Can also feed boiler, alarm, any life support systems (e.g. tropical fish tank with a dedicated plug-in RCD).
Unprotected.
Unprotected.
Use an RCBO or separate hard-wired RCD from the unprotected side. (Individual plug-in RCD's wouldn't conform to regs.) I would also recommend an isolating switch for the outdoor circuit inside the house (which could be part of the RCD protection).
Install a CU with a 100mA main RCD and then
That option is only required if your earthing is via your own earth rod (TT system), rather than by an earthing terminal provided by the supply company (TN system).
There's no chance that what you describe will become the norm; RCBO's are too expensive and not available for many of the budget CU's often used in initial installs. I suspect it's most likely to be done with an FCU taking power from an RCD-protected ring circuit, which in effect replaces the fan isolator which becomes no longer necessary, so there's no cost increase.
Personally, I would not RCD protect the bathroom light at this time, but I do fit them out of reach. I might consider RCD protection if the lighting was in reach, such as makeup lights around a mirror.
Reply to
Andrew Gabriel
In article , snipped-for-privacy@cucumber.demon.co.uk (Andrew Gabriel) writes:
Just to add -- don't use a cooker switch with integral socket.
Reply to
Andrew Gabriel
I did a rewire recently, following the above scheme, and it was all checked over and approved by a sparks... however he mentioned that although he considered it barmy, he couldn't have approved it once the forthcoming 17th edn came in to force - I think the issue would have been over provision of the dedicated unprotected fridge/freezer socket?
Is that so? - presumably would be resolvable by hardwiring the freezer with an FCU?
David
Reply to
Lobster
I'm not so sure. Part of the reason for RCBO's expense will be the level of use. Once demand increases, price will drop.
Yup, agreed. Certainly to start with.
Reply to
dom
I suspect it's most likely to be done with an FCU taking power from an RCD-protected ring circuit, which ineffect replaces the fan isolator which becomes no longer necessary, so there's no cost increase.
Would you install the FCU inside or outside the Bathroom ?
Reply to
ac1951
In article , ac1951 writes:
Inside, in Zone 3 or further (and out of reach for normal use). If it's not inside the bathroom, it would need to be able to be locked in the off position, which not all FCU's are (check for a padlock hole in the opened fuse carrier).
Reply to
Andrew Gabriel
It is my intention when the new rules come in to use an RCD fused spur off the lighting ciruit for the bathroom lights. This is for a cost reasons. Most houses do not have the CU near the bathroom and the labour for installing one radial off an RCBO for one room would have to be passed on to the customer.
Adam
Reply to
ARWadsworth
I'd say there is no doubt at all that the 17th ed. will require 30 mA RCD protection for all bath/shower room circuits.
Apparently the published 17th ed. (BS 7671:2008, due in January, effective from 1st July) will contain many changes from this year's draft edition, and these point in the direction of increased RCD protection (some may choose to call it paranoia).
The REALLY BIG potential change (final decision said to be mid-November) concerns cables buried in walls at less than 50 mm depth. Here the requirement of the draft edition [522.6.6] is very similar to the 16th ed. in that such cables must comply with one of three options - i.e.:
- use of a cable type with an earthed metal covering (SWA, FP200, Earthshield (BS 8436), etc.) or;
- must be in earthed metal conduit or trunking (metal capping doesn't count), or;
- must be in the "safe zones".
For ordinary house wiring in T&E the safe zones option is of course the one used.
Now the draft 17th added proposed reg. 522.6.7 which allowed a get-out, i.e. if none of the three above options could be applied then 30 mA RCD protection could be used instead, which seemed quite sensible.
It now appears that all this will change, such that all power cables buried at less than 50 mm depth will require 30 mA RCD protection, _even_if_in_the_safe_zones_ unless one of the above special cable types, or metal conduit/trunking is used.
Should this turn out to be true then _all_circuits_ wired in T&E will need to be 30 mA RCD'd, unless buried to what is normally an impracticable depth. Non-RCD protected circuits will need special cable types. Perhaps individual circuit RCBOs will become the norm...
Reply to
Andy Wade
In article , Andy Champ writes:
Don't really want the cooker RCD protected, but you do want all worktop sockets RCD protected, where things like kettles are plugged in.
Reply to
Andrew Gabriel
In article , Andy Wade writes:
What's the justification for this? Or is it just knee jerk without any risk analysis to back it up?
Reply to
Andrew Gabriel
I guess it's that it will give supplementary direct contact protection for people, ignorant of the safe zones concept, drilling, nailing or screwing through live cables.
No idea. The makers of RCDs and the more expensive cable types will doubtless be pleased though...
Reply to
Andy Wade
Assuming you don't have a TT supply:
No RCD
RCD
No RCD
No RCD
If you are just talking about sockets for feeding appliances outside then RCD. If you are talking abut submain feeds to outbuildiongs then see:
Install a CU with a 100mA main RCD and then
Hmm, I suspect he did not quite know what he was on about. This sort of setup is only really required on TT systems, and then the main RCD would need to be a time delayed type so as to discriminate with the downstream RCBOs on current imbalance faults.
You can change the RCD in a CU if required for a different trip threshold one.
Can't see it changing in a big way now since the time for comments have passed and it will be issued soon.
Reply to
John Rumm
As long as it was clearly labelled that the socket was for Freezer use only then IIUC it ought to be fine.
Reply to
John Rumm
There is also a certain logical elegance there in that turning off the lighting circuit for that floor will also turn off the bathroom lights.
Reply to
John Rumm
Which by virtue of the switch drops would include lighting circuits as well. This would seem to have the same negative safety implications of the 15th edition "whole house RCD" all over again.
Reply to
John Rumm
RCBO Lobbyists, er oops, Manufacturers :-) Quite seriously, the major manufacturers do directly drive IEE BS EU committee standards. They target the committee members quite relentlessly with a very blatant sales agenda. Challenge and you get a new corner office: window seat. It is endemic within the EU "health & safety" crowd.
I am not surprised. I had expected "RCBO for every single final circuit" re IEE & Part P wording H&S-extremous. IEE will cite a) drilling-in-bathroom fatality re cable angle, or b) electrified spice rack, or c) other trades ignorant of zones.
Q - Does FP200 qualify as concentric, earthed metal covering?
I ask because whilst FP200 has a bare CPC in direct contact with a metal shield, the shield is merely electromagnetic shielding foil. Foil has substantially less fault current capability vs MICCs.
I am thinking of cable penetration by ubiquitous picture nail, small dia, contacting only an small area of foil & phase. A small partial circumference of wafer thin foil carries fault current. For RCD protection that is 30ma, for 30A Type-C MCB it is 300A. Adiabatic calculation for that bit of foil would be interesting. MICCS, SWA & FP400 are all be ok, but is FP200??
FP200 has a 6r bend radius, 57mm for 2.5mm 2-core-&-earth. Keeping within 6r bend radius is not easy re plaster depth or conduit box rear exit (I suspect most strip the sheath off).
Reply to
Dorothy Bradbury
Is it Belgium or Portugal that requires basically a semi-armoured domestic cable? There are no zones, either cables are at some silly-depth or are armoured.
France insulates the CPC, altho I wonder if in doing so they reduce the insulation thickness on Phase/N.
Each country seems to use historic "freak case" to drive standards, the IEE/UK/Part-P picking every worst case to drive each one of its standards in the end. Plus they can not even quote the facts correctly in doing so. A brilliant way of creating committee employment. The result is a camel - and people use cowboys vs electricians, even more so when electricians/corgi milk people by fake regs.
An important step in a formal risk management process is a cost benefit analysis. Now considering Part P, Brown, Govt in general, I suspect we should not expect any better.
Reply to
Dorothy Bradbury

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