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,

 

[pushrod]

There is already confusion.
If we were to alter an existing non-RCD protected RFC, by simply changing an existing single socket to a double, would there be any requirement to provide RCD protection, and where would that protection be required to be placed?
As it stands if the socket is intended to be used for a specific item or items of equipment then there is no requirement for RCD protection. However if the socket was intended for general use there would be a requirement for RCD protection. This could be achieved by either the use of an RCD socket or by placing the RCD at the origin of the circuit.
If however you believe that the circuit requires protection, then the RCD would have to be at the origin of the circuit.
Simple enough if the CU can accept an RCBO, not so simple if the CU can't.
Before you know it, you are looking at a board change and all the attendant inspecting and testing; completely unesseccary as at most all that is required is the installation of an RCD socket.

You digress.

Aah well, you can lead a horse to water... as the saying goes. I'm afraid i won't reply to this thread again. As i think Ezzzekiel said earlier "you can be the boss". Well done

 

[Deleted member 26818]

I don't believe that I have digressed.
I have attempted to show that an erroneous belief that all circuits are required to have RCD protection can lead to costly uneccessary work.
A great deal of Local Athority housing uses earthed conduit, and often alterations and additions have used surface trunking.
There are also many converted properties where internal insulation has been applied to external walls enatailing that existing wiring is now at a depth greater than 50mm.
There are many instances where uneccessary RCD protection has been provided, often resulting in non-compliance with other Regulations.
To my mind, if we start with the premise that not all circuits require RCD protection, we will have a better understanding of when and where protection is actually required.
However as you say, you can lead a horse to water...

 

[SimpleSimon]

Or if you use SWA than you can omit RCD at the board for the distribution cable as it's mechanically protected and surface mount your sockets in conduit.

 

[Deleted member 26818]

Exactly.

 

[Dave_]

A circuit is an assembly of equipment supplied from and protected from overcurrent by one protective device. This would include cables and sockets. Ordinary twin and earth (which must make up 95%+ of domestic cabling) that is either not surface mounted or deeper than 50mm or mechanically protected/protected by earthed metallic covering
will require rcd protection regardless of location. Reg 411.3.3 specifically talks about rcds for additional protection.

I couldnt agree more.

411.3.3 this is one of the most well known new regs to conform with BS7671:2008

Sockets generally need RCD protection and in this case definitely. Unless you want to wire the shed in metal conduit!!!

 

[Deleted member 26818]

How exactly does metal conduit affect Regulatiom 411.3.3?

 

[Geordie Spark]

Hello everyone!!

I'm a (very) new member here, and would first of all like to tell you how much I am enjoying this excellent forum - particularly this thread because at some time soon I have to wire-up two garages - both at the bottom of gardens and one of them is to a house with a TT system, so thanks to all of you for your very usefull comments.

 

[ezzzekiel]

welcome along geordie (most threads dont usually go this way

 

[malcolmsanford]

welcome along geordie (most threads dont usually go this way

Unless alistair Campbell is in residence

 

[Dave_]

oops 522.6.6, 522.6.7 .......wasnt actually looking in the book....!

 

[antimatter]

Sorry but I'm lost on this one.


Is the answer 4?

That made me laugh

 

[Deleted member 26818]

oops 522.6.6, 522.6.7 .......wasnt actually looking in the book....!

I thought that those Regs. only applied to cables concealed in walls?
How do you conceal cables in the wall of a shed?

 

[ezzzekiel]

arghhhhhhhhhhhhhh somebody shoot me please!!!

 

[Dave_]

arghhhhhhhhhhhhhh somebody shoot me please!!!

I do agree..! im just debating a few points.....

Shed Installation Disconnection time?

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,
​

Where does the current install not comply? its rcd protected etc.... understand you may need to TT the shed and keep it seperate depending on whats its made of etc.... I dont see why you need to do anything.... can some enlighten me on what im missing?

 

[telectrix]

feel like using semtex on the shed-- or myself.