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_]

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

ha! this is going on a bit long eh!!!!

how about a dedicated transformer? or would that be over the top.......

 

[telectrix]

ha! this is going on a bit long eh!!!!

how about a dedicated transformer? or would that be over the top.......

but could the top of the shed stand the weight? have to get a structural suit to analyse the situation, especially if somebody has drilled a hole in a roof timber

 

[ezzzekiel]

providing all holes are within the zones i cant see a problem myself

 

[jaresquire]

As long as the holes are filled with conduit..

 

[telectrix]

As long as the holes are filled with conduit..

leave em for 10 minutes, they'll get filled with itchy poo fibreglass

 

[Deleted member 26818]

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

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?

I don't know why people need to make sarky comments?
The question's not stupid, just the answers so far.
Anyway to answer the question:
The OP wants to minimize inconvenience, by not having to traipse back to the house everytime something he does in the shed, trips the RCD.
At present the installation doesn't comply with Section 314 Division of Installation.

 

[Dave_]

I don't know why people need to make sarky comments?
The question's not stupid, just the answers so far.
Anyway to answer the question:
The OP wants to minimize inconvenience, by not having to traipse back to the house everytime something he does in the shed, trips the RCD.
At present the installation doesn't comply with Section 314 Division of Installation.

Are you saying im making sarky comments? you've totally lost me. Im not. Im just having a laugh and a joke like everyone else

What exactly is he planning to do in the shed? put plugs in now and again with a n-e link?

section 314 - what exactly?

 

[Deleted member 26818]

I was refering to the comments made by other contributers.
I have no idea what the OP intends doing in their shed.
Section 314 of BS7671, which relates to division of installations.
To quote:
"Every installation shall be divided into circuits, as neccessary, to:
(i) avoid hazards and minimize inconvenience in the event of a fault
(ii) facilitate safe inspection, testing and maintenance (see also Section 537)
(iii) take account of danger that may arise from the failure of a single circuit such as a lighting circuit
(iv) reduce the possibility of unwanted tripping of RCDs due to excessive protective conductor currents produced by equipment in normal operation
(v) mitigate the effects of electromagnetic interferences (EMI)
(vi) prevent the indirect energizing of a circuit intended to be isolated."
Relying on the RCD at the house will not to my mind comply with parts i, iii and iv, especially as that RCD also provides protection for all the circuits in the house.

 

[Dave_]

I was refering to the comments made by other contributers.
I have no idea what the OP intends doing in their shed.
Section 314 of BS7671, which relates to division of installations.
To quote:
"Every installation shall be divided into circuits, as neccessary, to:
(i) avoid hazards and minimize inconvenience in the event of a fault
(ii) facilitate safe inspection, testing and maintenance (see also Section 537)
(iii) take account of danger that may arise from the failure of a single circuit such as a lighting circuit
(iv) reduce the possibility of unwanted tripping of RCDs due to excessive protective conductor currents produced by equipment in normal operation
(v) mitigate the effects of electromagnetic interferences (EMI)
(vi) prevent the indirect energizing of a circuit intended to be isolated."
Relying on the RCD at the house will not to my mind comply with parts i, iii and iv, especially as that RCD also provides protection for all the circuits in the house.

1) i) Its not really much more of an inconvenience than when your in the house if your in the shed when it trips.....
2) iii) This is more aimed at things like stairwell lighting, like for example complying with what the fire officer would tell you. I dont see what some circuits in a shed have to do with it....
3) iiii) unless he is planning on putting around 10 PC's in the shed i dont see a problem

And as i keep saying, if the install is sound then there is no reason for it to trip the RCD

 

[telectrix]

Sorry dave, got to disagree with you there. If i were in the shed and the whole house tripped in the middle of the night, pitch dark everywhere, i would call that not just an inconvenience but a potential danger. I might fall over the dog. Agree with spin.

 

[Dave_]

I can totally see your point but i'm still thinking about the fact he doesnt want to spend money. The first reg in that group maybe relevant but its open for discussion and certainly not black and white. You certainly wouldn't design an installation like that which is generally what section 3 gets used for. but im going by if its an existing installation....

Just out of interest though, what are you doing in the shed in the middle of the night?

 

[Dave_]

You could put an emergency fitting in the shed and maybe another by the CU?

 

[Deleted member 26818]

1) i) Its not really much more of an inconvenience than when your in the house if your in the shed when it trips.....
2) iii) This is more aimed at things like stairwell lighting, like for example complying with what the fire officer would tell you. I dont see what some circuits in a shed have to do with it....
3) iiii) unless he is planning on putting around 10 PC's in the shed i dont see a problem

And as i keep saying, if the install is sound then there is no reason for it to trip the RCD

1) The requirement is to minimise inconvenience.
To my mind, it's a no brainer that placing the RCD in the shed rather than at the house minimises inconvenience.
2) No, this requires you to consider whether there could be danger from the failure of a single circuit, the eaxample of a lighting circuit is just an example.
If you consider that no danger will arise then fine, although you obviously have considerd that it may arise by suggesting the use of EM light fittings.
Does that however take account of the danger that someone could be in the kitchen removing something from a hot oven just as the lights go out because a circuit in the shed has caused the RCD to trip.
3) it is not that there may be 10 PCs in the shed that needs considering, it may be that there are 9 PCs in the house and just the one in the shed. PCs are not the only items of equipment that have earth leakage in normal operation.
RCDs are not required because the installation may be unsound, they are required for if there is a fault. That fault does not neccessarily have to be with the perfectly sound installation, it could be a faulty appliance or item of equipment.

 

[SimpleSimon]

You could put an emergency fitting in the shed and maybe another by the CU?

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

 

[IQ Electrical]

He completed the shed installation 89 posts ago in less time than it took to read this thread.