what type RCD protection

[markthebuilder]

I have taken on some snagging work on a job where the original builder has since gone bump. the original Contract was to split a house into 2 flats which has been completed both flats occupied by my client and his x wife
Upstairs looks like a newish cu 8ft up on hall wall its on a tt but there is no rcd and tails look 10mm but maybe 16mm max
The downstairs has a new CU and is fitted to a new supply with earth provided so im guessing its pme it dosn't have an RCD either both flats have 4 circuits lights ring cooker heating cooker points have socket outlets.
I turned off the power to the upstairs but client has turned back on and said that its never had an RCD???
I'm going to try get upstairs flat converted to Pme as supply comes out of ground rather than from a pole. i don't think it will be a problem but then I'm a builder not a sparky.

In the meantime
I am thinking of fitting rcbos to cooker and sockets downstairs but not sure weather to fit rcbos to all circuits upstairs or just fit a 100ma rcd incomer

am I doing the best for my client or have you other suggestions
All pipework is plastic

 

[Adam_151]

Are there two service heads (and meters?), where are they? distances from CUs?

What make of CU are they? how many ways? and how many spare?



(PS. I won't be replying between 8am-5:30pm ... I'm one of those lucky people who work Sunday!)

 

[Big_Spark]

Mark, are you certain that the upstairs supply is a TT? If the downstairs has a new PME feed then it is possible this was linked off it, perhaps as a PME, but perhaps as a TN-S, in which case the earth would be provided by the sheath of the cable if an SWA or by an integral Earth if another type of cable.

Secondly, RCD's are required by BS7671 for TT supplies, but simply fitting any old RCD will cause problems further in time, and if you fit it, firstly I suspect your not Part P registered, and secondly, you would be legally responsible for for RCD.

The downstairs supply, being PME does not require an RCD, however if there are sockets that will feed outside equipment then these need to be RCD protected, the cheapest way would be to install a 30mA 32A RCBO on the ring main.

Personally, I would suggest you call in a spark, I presume that you know at least one, that way you ensure the job is done right and you pass over the legal responsibility to the spark in question..

 

[markthebuilder]

Adam and big s thanks for response .and further thoughts/advice welcomed
yes there are 2x service heads /meters The original one with home made seals is in the lobby and is 2ft from the CU which now only serves the upstairs flat .
Its defiantly TT and has 2 spare ways Its also the one I am most concerned about because if I fit a 30 ma incomer and it trips at night someone is going to have to come down 2 flights of stairs climb over various bikes coats etc set up step laders etc to reset
so is a 100ma better or rcbos * 4 the way forward .bering in mind im thinking of a fairly immediate solution and getting the supply converted in the dno ;s own time particlualy if Ze is 100+which around here is v=likley it should be posibel as supply comes out of ground and the new supply to ground floor flat is in an external box and has a MET.

thing about what you said Big S i;m wondering if some one may have linked the earh from old cu to earth rod aand then to met on new supply it would explain why some of the earth cabals run the way they do????
Anyway as said new meter for ground floor flat is in external box approx 5m away from original supply and then tails run 4m through box conduit to a Cu in bedroom nect to the lobby it has a couple of spare ways but I agree an rcbo on sockets should cover that

No i am not part p though in process of becoming regesterd with niceic as a DI so i will be contacting LBCO to establish his position
Client is going to need an eic to get conversion work signed off and had to pay fees for the conversion so hopefully lbco will be ameanabel.

From a liability point of my point of View I figured I need to treat it as a CU change as
a) from what I have seen I cant assume other circuits are sound and need to inspect and test as far as practicable.
make good practice for assessment anyway

 

[Big_Spark]

Mark, the Regs state that on a TT the RCD incomer should be a 30mA type rated for the installation, but also this should be a Type S (Time delayed)

Personally I think this too low, but it's what the Regs recommend.

It might be an easier option to see if the local DNO will convert the supplyt to a PME and thus erradicate the problem, failing that then the installation of a Type S 30mA suitably rated RCD is the only real option to ensure compliance.

 

[SparkyMarky]

Mark, the Regs state that on a TT the RCD incomer should be a 30mA type rated for the installation, but also this should be a Type S (Time delayed).

I thought it was ok to have a 100mA type S RCD as the main incomer on a TT system, providing that any socket outlets which could supply equipment outdoors were protected by a supplementary 30mA RCD?
(assuming that the RA I-delta-n calcs are ok of course)

 

[Big_Spark]

Marky, I think you may be correct on that, but I think the trip current is dependent on the resistance rating of the earth connection..but could be wrong on this.

To be honest whenever I have installed them, I always use a 100mA Type S and put sockets and similar circuits on RCBO's... One NICEIC inspector didn't like this and said it breached 7671..I never really chased it up..

 

[markthebuilder]

Cheers Big spark You had me a little worried for a while but its been good learning.
i've been trawling through regs forums OSG etc and my latest informed opinion is _
OSG page 20 "Where an RCD is fitted only because the earth loop impedance is to high-----The rated residual current should not be less than 100mA"
guidance note 1 Page 56 TT systems ---"all socket outlets have to be protected by RCD there is no specific limitation placed on the rated residual current "--except where supplying portable equipment as per 7671

So as no sockets likely to feed outside i would have gone for a TD 100ma RCD for whole board and possibly 30ma RCBO on kitchen sockets with there associated washing machines kettles etc. if NICEIC didn't like it I would refer him to OSG page 23 & guidance note 1 page 55

However I have contacted dno and seams I can get converted to pme for £40 in 6 -8 weeks so I now need a temp solution. further more
Client wants a socket in lobby so she can hoover her car out and would like to CU lower as she cant reach it of a chair.

Can I get a stand alone 100mA TD RCD in its own enclosure which I will fit next to meter. New 25mm Tails from it to CU 100A dp isolator. Extend wiring crimp&heatshrink 4 x circuits all in some conduit and then fit 30ma rcbos as required I'm thinking 1day to fit 1 day to test £400+mats & vat
Go back when new MET fitted and reclaim RCD and conect earth

Thanks for your comments /advice all

 

[Big_Spark]

Thanks for the OSG infor about the RCD..thought I was right but as I said, never had a real reason to follow it up..

Regards the socket, I would suggest a dedicated one for outside use that incorporates an RCD..however I would not get a cheap one, MEM, Crabtree or MK would be my recommendations. It does not need to be outdoor IP rated, just a standard unit..

DDA Regs do not apply to consumer units and I would be hesitant to lower a consumer unit so that a person in a wheel chair can reach it, unless it was protected by an enclosure. If she can reach it, so can children, and that has many dangers..