Shed Installation Disconnection time?

[Just]

Hi I have a socket Radial off a 20A MCB and a lighting Radial off 6A MCB in a shed the board is fed by a 32amp MCB protected by an RCD on a TNCS syatem in the house. If I want the first point of fault ie the shed to trip first should I be using an RCBO for a TT system that trips under .2s? This would avoid both RCDs or the one in the house tripping first if I use an RCD 0.4s disconnection. I could change the type of RCD in the house but that protects a number of circuits. I have a 4 way CU so could either have a RCBO main switch, protect two MCBs with a different type RCD or fit two RCBOs. Too many options!
Thanks for your advice,

 

[Dave_]

Dave I love the enthusiasm but if the OP don't want alot of mess or money spent we might as well split the tails at the board!!
Anyway where is the b****y OP?! Feel like he's thrown a juicy bone into a pack of lions! Lol

yeah i certainly wouldnt make any money if i looked at every job like this

And spin i see your point i do, The RCD would be better in the house but i dont think its enough to not put it in the shed. If your in any RCD protected domestic install its arguably more dangerous if you have walk down a pitch black staircase if the RCD trips and the board is downstairs. Thats no different really from the inconvenience if your in the shed (providing its not 50 metres down the garden) The emergency lights would not be a bad idea in any domestic install and if you see my point they would help get over (i) and (iii)

 

[SimpleSimon]

yeah i certainly wouldnt make any money if i looked at every job like this

And spin i see your point i do, The RCD would be better in the house but i dont think its enough to not put it in the shed. If your in any RCD protected domestic install its arguably more dangerous if you have walk down a pitch black staircase if the RCD trips and the board is downstairs. Thats no different really from the inconvenience if your in the shed (providing its not 50 metres down the garden) The emergency lights would not be a bad idea in any domestic install and if you see my point they would help get over (i) and (iii)

True. But if in the shed is in metal conduit so mechanically protected and protected from the likes of rodents and animals what other situations could ensue to cause an RCD to trip, apart from nusciance tripping. (don't use that over active imagination of yours too much Dave.

 

[Dave_]

Where cables are installed in areas
inhabited by rodents, such as might be
found in a garage, the wiring system must
be capable of resisting damage caused by
gnawing (Regulation 522-10-01).

Plastic conduit would suffice

 

[SimpleSimon]

Where cables are installed in areas
inhabited by rodents, such as might be
found in a garage, the wiring system must
be capable of resisting damage caused by
gnawing (Regulation 522-10-01).

Plastic conduit would suffice

Yep, so no need to RCD at shed.

 

[ian.settle1]

Yep, so no need to RCD at shed.

But what about the possibility of a lawn mower being plugged into a socket ?

 

[malcolmsanford]

There does appear to be quite some confusion about the requirements in BS7671 for RCD protection.
The requirement in BS7671 is that socket-outlets intended for general use by ordinary persons and those for use with mobile equipment outdoors, must have RCD protection; the requirement is for the socket-outlets to be protected not the circuit.
Of course generally the easiest thing to do is to place an RCD at the origin of the circuit thereby protecting all the socket-outlets in one go. Another option would be to use individual RCD socket-outlets, which would be quite costly. However it is the installer's or client's choice, there is no requirement to protect the whole circuit.
In BS7671 the only reference to RCD protection for circuits, is where they are of special locations.

But what about the possibility of a lawn mower being plugged into a socket ?

There is always of course this way

 

[Dave_]

Its still being protected by an RCD at the origin. assuming its TNC-S and the shed is just a wooden shed it should comply......?

 

[SimpleSimon]

But what about the possibility of a lawn mower being plugged into a socket ?

RCD socket

 

[telectrix]

been more time devoted here to discussion than it would take to do the job. ( including a 2 hour lunch break)

 

[SimpleSimon]

been more time devoted here to discussion than it would take to do the job. ( including a 2 hour lunch break)

Hmm, there's a joke in here somewhere ......
How many Sparks does it take to put a shed supply in?

 

[Deleted member 26818]

Wait untill we start on whether the earth should be exported.

 

[antimatter]

The only thing we should be exporting is Great British products from our manufacturing industry to other countries and get the UK economy going again, so we can all get well paid job and earn lots of money!

 

[telectrix]

The only thing we should be exporting is Great British products from our manufacturing industry to other countries and get the UK economy going again, so we can all get well paid job and earn lots of money!

not the only thing. a few million immigrants exported would be a good idea.

 

[Dave_]

not the only thing. a few million immigrants exported would be a good idea.

I second that!!

 

[RogertheBodger]

After all that, if it was me, I'd just drag the house closer to the shed