Upgrades to fuse board supply

[Panda07]

Alright folks.
Just wantin to run something by you all. Have been in a property to wire a bathroom and do a fuse board upgrade. The existing fuse board is in a cupboard upstairs, connected to the cut out outside by a 16mm twin and earth and seperate 10mm cpc, approximately 12 metres of cable run. Im going to be leaving in the 16mm twin and just upgrading the 10mm to a 16mm seperate earth. My query is regarding protection of the 16mm twin feeding the fuse board. Im going to have to put in an isolator of some sorts but should this be an rcd? At this stage i cant see how the cable is run so have to assume at some point it will be less than 50mm from surface. If it should be an rcd would i be better with 100ma to avoid it nuisance tripping whole property?
Thanks in advance for any input

 

[DPG]

You cant use a 100mA RCD if a 30mA one is required.

12M is a fair old run. Has it not got a fused switch already then?

 

[Panda07]

You cant use a 100mA RCD if a 30mA one is required.

12M is a fair old run. Has it not got a fused switch already then?

No theres no fused switch in place already. Installation is untouched since it went in 40 years ago by look of things

 

[HappyHippyDad]

Alright folks.
Just wantin to run something by you all. Have been in a property to wire a bathroom and do a fuse board upgrade. The existing fuse board is in a cupboard upstairs, connected to the cut out outside by a 16mm twin and earth and seperate 10mm cpc, approximately 12 metres of cable run. Im going to be leaving in the 16mm twin and just upgrading the 10mm to a 16mm seperate earth. My query is regarding protection of the 16mm twin feeding the fuse board. Im going to have to put in an isolator of some sorts but should this be an rcd? At this stage i cant see how the cable is run so have to assume at some point it will be less than 50mm from surface. If it should be an rcd would i be better with 100ma to avoid it nuisance tripping whole property?
Thanks in advance for any input

Absolutely not Panda.
Just imagine those tails in the wall being drilled into without 30mA protection, the customer is going to easily get a lethal electric shock from 100mA.
However, I would also not be fitting a 30mA Main switch in the switched fuse as that would not meet the regs and be a right pain for the customer.
I would either use 16mm SWA instead of tails although SWA can be a right pain so I would also consider mechanical protection for the tails (see link below).

16mm Galvanised Cable Protectors Sheathing

16mm galvanised cable protector in 2m length. Durable steel sheathing for external wall cable protection. Corrosion-resistant and regulation-ready.

www.directchannel.uk.com

You could also try and fit a socket or similar in the same run as the tails on the wall as then the tails would be in an electrical zone, although that would not strictly be needed if you added mechanical protection.
Last option would be to run the tails in conduit out side the house and up to the first floor.
With all these options I would still tend to install a 100mA S type RCD as part of the switched fuse.

 

[radiohead]

As above, getting involved with the sub is going to be a can of worms. Providing additional protection to a buried cable by means of a 30ma RCD would be a breach of regulations. If you cannot install a new sub in surface wiring, or a flush cable with earthed steel protection, is just leaving it as it is and doing your fuseboard change without touching the sub an option?

 

[Panda07]

As above, getting involved with the sub is going to be a can of worms. Providing additional protection to a buried cable by means of a 30ma RCD would be a breach of regulations. If you cannot install a new sub in surface wiring, or a flush cable with earthed steel protection, is just leaving it as it is and doing your fuseboard change without touching the sub an option?

Id love to just leave as is but dont think thats an option. I get the impression the customer thinks im at it when i approched the subject. I think at the very least im going to have to get a 16mm earth to the board from the cut out so if im going to that effort im as well trying to replace the whole supply with something armoured. Pain in the arse

 

[westward10]

Why the need for a 16mm cpc.

 

[Panda07]

Why the need for a 16mm cpc.

I thought you needed a 16mm earth with 16mm supply? Or have i missed something?

 

[westward10]

I assume main protective bonds are connected from the board and 10mm is likely to be large enough to support them. You will need circuit protection for the submain so this will effectively become a cpc.

 

[davesparks]

I thought you needed a 16mm earth with 16mm supply? Or have i missed something?

Yes, I think you may have missed the calculation of the required size of cpc using the adiabatic equation.