Garage Board - achieving discrimination?

[Taylortwocities]

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.

 

[Michaelwgroves]

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.

 

[Taylortwocities]

I think is worth the extra small cost

Time delay RCDs come in at £80+

Imo, bit more than a "small" cost! plus an enclosure.

 

[davesparks]

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?

 

[davesparks]

Re-reading the OP there is T&E for part of the run so it may need 30mA protection for that.

 

[davesparks]

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.

 

[Midwest]

Level of protection against what? It does not provide shock protection and the fuse is more than adequate for fault protection.

Don't you start, had a similar long debate, a while ago.

 

[Michaelwgroves]

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 ?

 

[davesparks]

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?

 

[Michaelwgroves]

If someone working in the garden accidentally hits it, it will trip early. Rather than not at all if it was an Earth fault?