agricultural building

[Pat Tester]

Assistance please anyone with a reg book (can't find mine, may have to empty van in morning)
supply is TT
from meter into 4 pole RCD is it 300mA ? this is supplying via two fused switch in swa two separate fuse boards one single phase one three phase

Question all socket outlets on 30mA but should other circuits be on 100mA delay rcd to provide discrimination ?

many thanks

 

[Engineer54]

The main supply is correct according to BS 7671, but in my opinion should be an S type, as discrimination cannot be assured between standard 300mA and 30mA RCD's. Only a time delay can assure discrimination... All circuits on a TT system should be RCD protected at 30mA, not just sockets.

 

[Richard Burns]

I thought that for a TT system that all circuits had to have RCD protection to ensure disconnection in case of a fault. However I thought there was no requirement for the RCD to be 30mA.
30mA RCD's are used as additional protection for socket outlets and areas of increased risk.
This is why you can have an upfront 100mA time delay RCD and then have 30mA RCD's for the appropriate circuits needing additional protection.
Or is the 30mA for all final circuits?

 

[Engineer54]

I thought that for a TT system that all circuits had to have RCD protection to ensure disconnection in case of a fault. However I thought there was no requirement for the RCD to be 30mA.
30mA RCD's are used as additional protection for socket outlets and areas of increased risk.
This is why you can have an upfront 100mA time delay RCD and then have 30mA RCD's for the appropriate circuits needing additional protection.
Or is the 30mA for all final circuits?

Maybe with the older Reg editions but i think you'll find that all circuits on a TT system require 30mA RCD protection now, and should really be all DP protection as well. 100mA up front RCD's don't as far as i'm aware comply anymore, even if 30mA units are provided with socket outlets (no discrimination)... But it still certainly makes sense to install an S type 100 or 300mA RCD up front, as a backup for failing circuit RCD's.

 

[Pat Tester]

found my book, the current one is red correct ? as job is non domestic it says 30mA on socket circuits up to 32A, circuits with socket outlets above 32A at 100mA all other circuits on 300mA

would a 30mA not provide discrimination with a 300mA ? or should I use a time delay version.
I guess 30mA rcbo s is the best option but would this be considered overkill ?

 

[telectrix]

it's green regs. book now, mate. and regs. 411.5 and 705.411.1 apply. if using RCD for fault protection then it depends on the Zs value of the circuit/s. e.g. 1667 for a 30mA, 167 for a 300mA.

 

[Pat Tester]

thanks i'll have another look in the van, found a brown one !

 

[telectrix]

you sure that's not a green one gone rusty with disuse?

 

[Pat Tester]

defo have both, still wondering about green version have found OSG in green

 

[Guest111]

As others have said,a time delayed unit is better top end then your 30Ma downstream,otherwise it is perfectly possible that the main unit will trip and take the lot down instead of a local device.depending on what they have on the farm this may not only be inconvenient but could be dangerous.

 

[Engineer54]

I wouldn't use a 300mA RCD on lighting or for other final domestic/farm type circuits on a TN system, so i certainly wouldn't use them on a TT installation, especially those that are following BS7671 regarding Ra values!! lol!!

30mA will discriminate with a 300mA RCD on a gradual/slowly increasing earth fault, but will not discriminate on higher sudden faults. Only a time delay on the upstream RCD will assure discrimination in both situations.

 

[Pat Tester]

Many thanks for assistance. time delay RCD on order

 

[GLENNSPARK]

found my book, the current one is red correct ? as job is non domestic it says 30mA on socket circuits up to 32A, circuits with socket outlets above 32A at 100mA all other circuits on 300mA

would a 30mA not provide discrimination with a 300mA ? or should I use a time delay version.
I guess 30mA rcbo s is the best option but would this be considered overkill ?

bloody hell where you been?

 

[JD6400]

The main supply is correct according to BS 7671, but in my opinion should be an S type, as discrimination cannot be assured between standard 300mA and 30mA RCD's. Only a time delay can assure discrimination... All circuits on a TT system should be RCD protected at 30mA, not just sockets.

Hello Engineer54
Although I could not agree more with all circuits going on a 30mA , even 10mA on certain circuits in a agricultural installation and personally speck to this standard .
I am not aware of any reg to back this up ?
I have not yet looked in my old red sixteenth reg's book , but I am pretty sure that I have never seen one in there either .
As you know we are heavily agriculturally based in our work load , so to be honest you have me a little concerned that I am unaware of this one , even if I do unwittingly follow it anyway !

 

[Engineer54]

As you know we are heavily agriculturally based in our work load , so to be honest you have me a little concerned that I am unaware of this one , even if I do unwittingly follow it anyway

Even more reason to have all circuits protected by 30mA RCD's.

I'm not a design and wire by numbers man. I know what i'd be happy leaving behind me when the job was finished, especially on an agricultural installation, where the need for safety should be heightened, but unfortunately, that's rarely the case!!

 

[spark 68]

Here you go from GN7

 

[Engineer54]

Well that answers a few questions on why agricultural installations are or tend to be less than satisfactory. As i say i wouldn't leave lighting and other non socket outlet circuits sitting on a remote or even a local 300mA RCD on a TN system, let alone a TT system....

 

[spark 68]

That needs to be considered with other regs though E54, the wiring containment is meant to be suitable for the environment, which to all intents and purposes means steel conduit in the animal sheds for example

 

[Engineer54]

That needs to be considered with other regs though E54, the wiring containment is meant to be suitable for the environment, which to all intents and purposes means steel conduit in the animal sheds for example

So what about the standard 300mA RCD's at the main distribution panel?? Potential discrimination problems with every building on the diagram. Nope, i think i'll stick to my own system set-up, that layout distribution diagram is just pants!! lol!!

 

[spark 68]

I agree with you btw, BS7671 is the minimum standard.

I added another file in the above post, and the notes say not exceeding certain mA ratings.