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Michael, you have missed some essential points.

1. The new tails (heading towards the garage) MUST pass through a current limiting device. RCDs do not limit the current.
So a switch/fuse is needed at that point (I think I detailed this in this thread about 6 months ago. I CBA to read all the way back).
The fuse needs to be appropriate for the SWA.

2. A time delay RCD (or any RCD) is NOT necessary at the house end.
 
Michael, you have missed some essential points.

1. The new tails (heading towards the garage) MUST pass through a current limiting device. RCDs do not limit the current.
So a switch/fuse is needed at that point (I think I detailed this in this thread about 6 months ago. I CBA to read all the way back).
The fuse needs to be appropriate for the SWA.

2. A time delay RCD (or any RCD) is NOT necessary at the house end.

Absolutely agree about switch fuse, schoolboy error.

I agree time delay "might" not be necessary, but it gives another level of protection I think is worth the extra small cost.
 
Dave, unsurprisingly you are correct. Had time to check my understanding this morning. Obvious when you take time to think about it.

So best solution would be pull tails from house CU into service block. Then new tails into house CU and new RCD enclosure with time delay RCD. Then SWA to garage CU with RCD.
Cheap simples and best soloution. Any fault in garage will only trip garage RCD, with SWA cable also protected by time delay RCD.

Why the time delay RCD?
 
I agree time delay "might" not be necessary, but it gives another level of protection I think is worth the extra small cost.

Level of protection against what? It does not provide shock protection and the fuse is more than adequate for fault protection.
 
No, please do start as this thread has improved my knowledge which has got to be a good thing. And hopefully for others.

Agreed time delay RCD does not provide shock protection, but it does still provide earth leakage protection. So I'm still thinking it's a good thing ?
 
No, please do start as this thread has improved my knowledge which has got to be a good thing. And hopefully for others.

Agreed time delay RCD does not provide shock protection, but it does still provide earth leakage protection. So I'm still thinking it's a good thing ?

Why does it need earth leakage protection?
 
So that begs the question; what use does a time delayed RCD have?
We know it must be used for RCD's in series.

Time delayed RCDs are used to achieve discrimination where the upstream device is providing fault protection because the required EFLI for the mcb or fuse cannot be met. For example TT systems where you can rarely achieve a low enough Ra to allow mcbs or fuses to operate in the required time.
 
As a s type max allowed tripping time is 500ms and 130ms min tripping time then I wouldn't particularly use it where you need a disconnect time of 0.2 seconds for final circuits upto 32 amps(depending on rcd tripping time when tested) 100ma standard device would be used for fault protection only.
Where a s type is useful is protecting tails entering a metal enclosure and distribution/circuits above 32amps which have generally a 1 second disconnect time and discrimination against downstream rcds.
For a TT system
 

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