2 TP submains fed from a single switchfuse.

[Click-Sure]

Could do with opinions from the pros on this one.

DNO supply 200A TP+N (TNCS) feeds:
100A Three Phase switchfuse feeds:
Existing Main DB.

I intend to use the same switchfuse to feed a new DB in the workshop, ideally I would fit an additional switchfuse but there isn't room, also considering providing a single point of isolation for the premesis.
The existing switchfuse will provide adequate protection to each submain (along with a single point of isolation) and I do not expect maximum demand to come anywhere close to it's rating.
Operationally I don't foresee the need to be able to isolate either of the distribution boards seperately.

Your thoughts if you would please.

 

[ban-all-sheds]

Sounds OK. How will it be wired? 2nd set of conductors into the switchfuse (can it safely accommodate that?), or service connector blocks?

If space is a problem, could you replace the switchfuse with an enclosure with MCBs? You say "ideally I would fit an additional switchfuse but ... also considering providing a single point of isolation" so I'm not sure if you would prefer the new DB to be on it's own fuse or not.

What's your PFC, and what are the highest rated downstream breakers? Could you change the fuses to breakers, or would lack of discrimination scupper that?

 

[Click-Sure]

Thanks for your input b-a-s.
The switchfuse is a considerably sized Crabtree 200A unit, (hence my issue with space) fitted with 100A fuses, plenty of room in the splitter box above, bolted connections so I'll be dusting my big crimpers off next week for sure!
Aside from any discrimination issues I try to avoid MCBs on submains in the tool and plant hire environment, the big 110v transformers tend to upset them!
PFC is a bit lower than expected for such a sizable supply from the nearby very lightly loaded TX, 2.1kA there or thereabouts.

 

[RF Lighting]

I can’t see an issue with it assuming you’ve done your calculations and the combined loads are ≤100A per phase.

I’d also prefer to avoid sub mains fed from MCBs where possible.