No RCD in sub main

[KeenPensioner]

Hi, as I've said I'm not an electrician but studying C&G in my own time and have worked as a mate.
I've just had a qualified sparky upgrade my CU to a split board 10 way dual RCD. He has run a 4mm2 cable (from a 40A MCB protected by one of the RCDs) to my hut and will be coming back to wire up a sub main for a radial with a couple of double sockets and a light circuit. He says he is fitting a sub board whose main switch will have no RCD (since the circuit is already protected by the RCD form the main board?) I don't understand that. Can someone help? BTW, I couldn't find the DIY section to post this.

 

[westward10]

No it is NYY-J commonly known as Hi-Tuff.

 

[KeenPensioner]

Just a big thank you to you all. I know "a little knowledge is a dangerous thing" and having a little knowledge would certainly apply to me, but I'm still learning and you guys help greatly.

 

[AJshep]

Either way Hi-tuff has not got an earthed metallic covering (like SWA) so it will need to be protected at source by an RCD like he has. Just not ideal its attached to the same RCD thats covering some of your house circuit's

 

[ipf]

Hi-Tuff is a good alternative to swa in some circumstances.
Question is, is the cable being run underground to the shed? If so, it's not an option, due to insufficient protection.
How old is the consumer unit? Is it possible to alter and feed via RCBO?

 

[KeenPensioner]

Hi-Tuff is a good alternative to swa in some circumstances.
Question is, is the cable being run underground to the shed? If so, it's not an option, due to insufficient protection.
How old is the consumer unit? Is it possible to alter and feed via RCBO?

Thanks for replying. The cable is cleated to joists through my shop store to the shed attached to the shop store. At no point is it underground. As in the OP, the consumer unit fitted by my sparky is a brand new Hager 10 way dual RCD

 

[ipf]

Thanks for replying. The cable is cleated to joists through my shop store to the shed attached to the shop store. At no point is it underground. As in the OP, the consumer unit fitted by my sparky is a brand new Hager 10 way dual RCD

OK, then.
As regards the Hager, I'm not positive, but would think it's possible to create a non RCD protected section. 20/32 amp RCBO should be fine.

 

[davesparks]

Either way Hi-tuff has not got an earthed metallic covering (like SWA) so it will need to be protected at source by an RCD like he has. Just not ideal its attached to the same RCD thats covering some of your house circuit's

That doesn't necessarily mean it needs to be protected by RCD.
This would only be required for the cable if it was chased in to a wall at less than 50mm deep, so if it is clipped direct as it appears then its not needed.

 

[AJshep]

That doesn't necessarily mean it needs to be protected by RCD.
This would only be required for the cable if it was chased in to a wall at less than 50mm deep, so if it is clipped direct as it appears then its not needed.

Agreed. For some reason I was under the impression it was buried.