Consumer unit feeding another consumer unit via Main switch

tidytech · Feb 24, 2024

Can a domestic consumer unit feed another consumer unit, via the Main Switch. Details are:

domestic property with 100A single phase supply, TN-C-S
incoming supply to Main Switch on DBU1
Output from the DBU1 Main Switch, also outputs two two wires, that connect to the input of another consumer unit DBU2, which is right next to DBU1
A earth conductor from DBU1 links to DBU2.

Is this within the regulations of BS7671?

MDJ · Mar 12, 2024

tidytech said:
Can a domestic consumer unit feed another consumer unit, via the Main Switch. Details are:

domestic property with 100A single phase supply, TN-C-S

incoming supply to Main Switch on DBU1

Output from the DBU1 Main Switch, also outputs two two wires, that connect to the input of another consumer unit DBU2, which is right next to DBU1

A earth conductor from DBU1 links to DBU2.

Is this within the regulations of BS7671?

are you saying the mains supply loops both boards or goes to one board then the second is fed from the first?

James · Mar 12, 2024

Is there a possibility of overloading the main switch?

tidytech · Mar 12, 2024

Sorry for the crude diagram, it looks like this. Seems they jammed another wire into the input L and N of the main switch on CCU1, that link to the CCU2 main switch inputs

[ElectriciansForums.net] Consumer unit feeding another consumer unit via Main switch

James · Mar 12, 2024

Although it would be more normal to use some Henley blocks to split the supply.
It is down to your experience to determine if the cables or terminals are overloaded in there current arrangement.

MDJ · Mar 12, 2024

tidytech said:
Sorry for the crude diagram, it looks like this. Seems they jammed another wire into the input L and N of the main switch on CCU1, that link to the CCU2 main switch inputs

View attachment 113846

although that is a rough job it is the sort of thing I have seen many times, and in theory it is no different than 2 boards connected to a RDL block, personally I would fit a switch before the boards, whether it is up to regs these days I am not sure, hopefully some of the domestic guys will chip in and help out, personally, although crap I doubt it is dangerous

Rockingit · Mar 13, 2024

Strictly speaking it doesn’t adhere to BS7671 because you are required to have ONE single point of isolation for an installation.

James · Mar 13, 2024

Rockingit said:
Strictly speaking it doesn’t adhere to BS7671 because you are required to have ONE single point of isolation for an installation.

Unless there is a main isolator between the meter and the 1st DB.

Rockingit · Mar 13, 2024

James said:
Unless there is a main isolator between the meter and the 1st DB.

Well, yes, but then that becomes that point, and so on. This is Ch 46 area if I recall.

tidytech · Mar 13, 2024

462 excerpt below. The incoming supply is via a electrical plant room to the block of flat, each flat has a standard DNO cutout fuse but no isolator on consumers tails. A SWA feeds up from the plant room to the apartment and then into CCU1 main switch. So is 462.1 complied because CCU1 and CCU2 each have a main switch, albeit they are linked via their inputs?

Code:

462 ISOLATION
462.1 Each electrical installation shall have provisions for isolation from each supply.
462.1 .201 A main linked switch or linked circuit-breaker shall be provided as near as practicable to the origin of every installation as a means of switching the supply on load and as a means of isolation.
A main switch intended for operation both live conductors of a single-phase