Old farm sheds electrics.

[allyhme]

Good afternoon everyone

Bit of a long read here! Trying to give as much info as I can. There is 2 sheds with power and I’d like to add power to a 3rd.
Wondering what would be the best practice for installing a new consumer unit in an shed (shed 3) coming from a 32A breaker in an existing consumer unit (shed 2)
To start at the beginning, the main supply for the original consumer unit in shed 2 comes from a 32A breaker in a type B MCB board connected to the fuses/meter in shed 1 via a 100A breaker.
From the consumer unit in shed 2 there is a 32A breaker spare which I would run a 6mm SWA cable to the consumer unit in shed 3.

My question is that since there is an 80A/30mA AC type RCD in the consumer unit in shed 2, and a 63A/30mA A type RCD in the new consumer unit in shed 3, would it be best to fit an S Type RCD on the consumer unit in shed 2 to give some discrimination so that a fault in shed 3 wouldn’t also trip the consumer unit in shed 2?

The new consumer unit will have a double socket fitted to the 16A breaker and a few strip lights to the 6A breaker.

Appreciate any advice.

 

[Phoenix]

What is the earthing arrangement to the site?

 

[allyhme]

I’d need to go back and check this.
Assuming that the consumer unit in shed 2 is earthed correctly, could I run a cable from the spare breaker to the new consumer unit? Does the new unit need to be earthed separately?

 

[Fleeting]

I would be passing this over to an electrician.

 

[Murdoch]

Circuits not labelled. Not ideal

 

[binky]

So both boards have 30mA RCDs as main switches. Clearly not installed by a competent electrician, but that's not unusual on farms

 

[allyhme]

Hi Binky, that’s my question though, should it be a time delayed RCD in the first CU (shed 2) then a type A in the second CU (shed 3)?

 

[Fleeting]

What is the earthing system?

 

[John Burns]

So both boards have 30mA RCDs as main switches. Clearly not installed by a competent electrician, but that's not unusual on farms

But legal and works. The French have a main whole house RCBO where is doubles as a main switch. This one can be set to a max over-current of 15, 30 or 45A by the DNO. They are way ahead of us.

 

[John Burns]

I am confused about what is what here. What shed is the incomer in, etc?
A main MCB after the main fuse of 32A? What is the size of the main fuse?

 

[binky]

But legal and works.

But lacks discrimination of the RCDs, a requirement of BS7671. The only good thing about finding something like this is there's unlikely to be any wiring faults, otherwise the RCDs would be tripping on a regular basis, provided anyone has pressed the test buttons on a regular basis...

 

[UNG]

But legal and works. The French have a main whole house RCBO where is doubles as a main switch. This one can be set to a max over-current of 15, 30 or 45A by the DNO. They are way ahead of us.

What has selecting the over current level of an RCBO got to do with the leakage current discrimination of RCD's

 

[John Burns]

?

 

[UNG]

?

I'm struggling to decipher that reply

 

[Geoff1946]

I think the point was that the unit which limits current to the premises, which I believe is part of the French tariff setting system, is also a 500mA RCD, but you have to look closely at the photo to see that.
I was under the impression though that the French current limiting function in domestic premises was designed to shed large loads, such as heating, rather than cut off the whole supply. I maybe wrong here; would be interested to know.

 

[John Burns]

I think the point was that the unit which limits current to the premises, which I believe is part of the French tariff setting system, is also a 500mA RCD, but you have to look closely at the photo to see that.
I was under the impression though that the French current limiting function in domestic premises was designed to shed large loads, such as heating, rather than cut off the whole supply. I maybe wrong here; would be interested to know.

The French whole house RCBO cuts off when over-current, fault and earth leakage, with a long lag on over-current before cut off. They do have main blade fuses before the main RCBO. The newer units can have the max amps set remotely using a comms connection. The one shown is set on the unit to 15, 30, or 45A, sealed up when set. Load shedding is the responsibility of the home owner.

Simple units are available in the UK...

 

[Fleeting]

We aren't in France.

 

[binky]

The French whole house RCBO cuts off when over-current, fault and earth leakage, with a long lag on over-current before cut off. They do have main blade fuses before the main RCBO. The newer units can have the max amps set remotely using a comms connection. The one shown is set on the unit to 15, 30, or 45A, sealed up when set. Load shedding is the responsibility of the home owner.

Simple units are available in the UK...

the French pay for the size of leccy connection, so a 15A supply is cheaper than a 45A supply, can't rmember if they get alower rate oer kwH for a smaller supply.

 

[Fleeting]

Why on earth are we discussing France?

 

[John Burns]

Read back on the thread. Whole house over-current protection.