circuits not requiring an rcd
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circuits not requiring an rcd

by jasont82 » Thu Jul 24, 2008 9:16 pm

hi there

was just wondering with the new 17th edition regs stating cicrcuits to be used by an ordinary person must be on rcd (or something along those lines), what does that leave out? does this only apply to sockets? Can someone explain it for me? I know lights should be on rcd and so should sockets unless labeled for specific equipment. and also bathroom circuits including showers are to be protected. what about ovens, boilers and smoke detectors?

reason i ask is that i have looked at a crabtree dual rcd consumer unit. i cant see how you would not put something on rcd. the unit is set up with main switch rcd1 then 7 spots for breakers, then rcd2 and another six spots. the buzz bar is a clip in system so you cant alter it, or can you?
i would have though smoke detectors at least would be unprotected by an rcd.


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by TheDoctor4 » Fri Jul 25, 2008 9:43 am

Hi There

Have you had a look at the DIY project on 17th edition: This may be of some help to you.


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by kbrownie » Fri Jul 25, 2008 12:56 pm

Basically all circuits that are buried into walls should be protected by RCD's. That includes Cookers, ovens, boilers.
A socket can be specified and needs to be indentified and labelled for the use of deisignated equipment (ideally something like your freezer. for examaple a RCD trips and disconnects all appliances on that circuit, if the freezer is not on that circuit any food inside will not start to thaw out) as freezer, pcs and fridges all leak to earth these are the type of equipment that would suit circuits without RCD protection. To prevent nuisances tripping.
RCDs are used in earth fault protection and will detect a change in the ballance between line/live and neutral currents and if these currents are unballanced within a range of appox 30ma (normally about 25ma) as recommended in domestic installs the RCD will trip.


by ericmark » Fri Jul 25, 2008 1:07 pm

The rules on RCD’s look at a number of reasons which they should be fitted.
1) All sockets under 20 amp and all electrics in a bathroom.
2) Wires buried at less than 50mm and not protected.
3) Fire.
4) Earth loop impedance.
First two are 30ma and this is maybe be over simplified and there are also rules as to splitting supplies which have resulted in multi RCD’s being fitted in most cases.
Since to fitting of consumer units also comes within Part P it is unlikely any DIY work would be worth while by time LABC charges are taken into account.

You ask what it leaves out and in the main either surface wiring or one of the permitted cables would need to be used i.e. Flexishield. Using this type of wiring sockets marked for the use of a specific item i.e. Fridge/Freezer, Cooker, Immersion heater, Smoke detectors will not need RCD. Lights with exception of bathroom will not need an RCD.

The main problem is most houses have cables buried in walls which do not comply with BS 5467, BS 6346. BS 6724, BS 7846, BS EN 60702-1 or BS 8436 so although the smoke detector does not require an RCD the wiring feeding it does, and also safety circuits can’t use same RCD as sockets etc so a RCBO would be required.

Most BS 8436 also complies with FP200 so fire protection circuits with BS 8436 cable would make sense. As yet the BS 8436 has not really caught on so not so easy to source but I am sure that will change soon.

Remember I have not included all factors like earth loop impedance for example but anyone fitting a consumer unit would need to fill in the installation certificate and should know all of this anyway. A copy of the certificate will be found I think page 23 of Part P document a link to that will be found in Projects section.

Many consumer units now have three neutral bars two for use with RCD’s and one for RCBO’s used on smoke alarms and the like or where cable to BS 5467, BS 6346. BS 6724, BS 7846, BS EN 60702-1 or BS 8436 is used.

Yours Eric

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by Cerberus » Mon Jan 05, 2009 11:23 am

[quote="ericmark"]so although the smoke detector does not require an RCD the wiring feeding it does, and also safety circuits can’t use same RCD as sockets etc so a RCBO would be required.

Just been reading through the forum as it came up in a google search i had just done and i came across this thread which caught my eye, according to the NICEIC's Technical Manual & Helpline (I'm an NICEIC QS for a large testing and inspecting company) this info is incorrect, They recently told me when i enquired about this a few weeks ago that if the smoke detector has a battery backup (and most of them do) then its fine to use a 30mA RCD to protect that circuit in a domestic dwelling...


by ericmark » Mon Jan 05, 2009 6:17 pm

Thank you Cerberus since that post which was only just after the regulations came in that has been talked about and yes makes sense.
Any new wire I would use Ali-tube cable anyway to smoke alarms well I say that not had to yet and not tried buying or using Ali-tube cable but I would use in my house anything to reduce RF.
The problem with smoke alarms is where interconnected and I have not fitted any in years and completely out of touch on what the battery back up covers.
There are so many rules on RCD use now. One question which has been raised is where the consumer unit is not accessible by wheel chair users and it would cause danger to them if plunged into darkness or ended up eating food which had partly defrosted was the danger fitting an RCD greater than danger not fitting one?
If my father died I think since my mother is in that position I would pay out the £350 for an auto resetting type.
Under the 17th Edition there is provision for omitting overload devices where if they trip is causes danger not seen same on RCD though?
And if using Auto Resetting type would I need two?

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