Sub main advice please

Octopus · Oct 18, 2018

mossep said:
You could put a Henley block in and split the tails like you suggested, but there should be 1 point of isolation for the whole installation,

Really ............ reg number please?

mossep · Oct 18, 2018

MDJ said:
Isolator? you will need an OCPD for the circuit, why 16mm2? did you calculate the load required? I bet that is overkill, also why a joint in a new cable run? have you got test equipment? there are plenty of other answers needed to the questions already asked to be fair.

I would imagine the joint is because it easy to terminate an SWA in an external adaptable box, and then run T+E internally to the fuse board. Not that uncommon really, aesthetically it might even look better on the outside wall as you'll struggle to put a neat bend in a 16mm SWA as it goes through the wall. Assuming its been done right what problems do you see with having a joint?

mossep · Oct 18, 2018

Murdoch said:
Really ............ reg number please?

462.1.201

Baddegg · Oct 18, 2018

What book is that in mossep?

'mr2'gd4u · Oct 18, 2018

davesparks said:
Why an isolator? It needs an OCPD not just a switch.

Nah... I was going to suggest a 10a light switch!! Lol

mossep · Oct 18, 2018

This book

[ElectriciansForums.net] Sub main advice please

mossep · Oct 18, 2018

View attachment 44956

'mr2'gd4u · Oct 18, 2018

Baddegg said:
What book is that in mossep?

Bbb p121

Baddegg · Oct 18, 2018

'mr2'gd4u said:
Bbb p121

Thanks, wasn’t taking the pi$$ I’m still on the byb and couldn’t find it...

mossep · Oct 18, 2018

Its in the BYB too, not sure what page though but probably a similar reg number.

Spoon · Oct 18, 2018

mossep said:
Its in the BYB too, not sure what page though but probably a similar reg number.

537.1.4 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 by ordinary persons, e.g. of a household or similar installation, shall interrupt both live conductors of a single-phase supply.

BYB page 154

MDJ · Oct 18, 2018

Nothing wrong with a Joint if it is done right, and if there is no other way, I don't think the job has been planned properly at all, a 16mm2 armoured and 16mm2 t&e for a very small out building with one ring a heating mat and a couple of lights, plus direct connection to an isolator and no OCPD is of concern, I appreciate the OP is very inexperienced and such should answer questions aimed at him by the other guys on here, I have seen him post since these questions and not answer. Has he concidered RCD protection for example, what type of earthing arrangement, is it notifable work? a lot to take in for a very basic job, hopefully he will start again and let us all into his thoughts so we can try to help properly. By the way that Bob the Builder book isn't great, I have the set, that story is one of the worse ones

mossep · Oct 18, 2018

Its might not be great, but it helped me build my loft extension!

Baddegg · Oct 18, 2018

Spoon said:
537.1.4 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 by ordinary persons, e.g. of a household or similar installation, shall interrupt both live conductors of a single-phase supply.

BYB page 154

Thanks spoon I’ll be in there later.

Baddegg · Oct 18, 2018

mossep said:
Its in the BYB too, not sure what page though but probably a similar reg number.

Thanks mossep

'mr2'gd4u · Oct 18, 2018

Baddegg said:
Thanks, wasn’t taking the pi$$ I’m still on the byb and couldn’t find it...

Its OK.. I still haven't booked my 18th exam. Don't think I'm gonna get a place before Jan either

.

Octopus · Oct 18, 2018

Spoon said:
537.1.4 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 by ordinary persons, e.g. of a household or similar installation, shall interrupt both live conductors of a single-phase supply.

BYB page 154

Which is open to interpretation ... A main switch per fuseboard and per switch fuse could serve to provide the necessary isolation.

If not hundreds of thousands of properties could be deemed dangerous

mossep · Oct 18, 2018

Murdoch said:
Which is open to interpretation ... A main switch per fuseboard and per switch fuse could serve to provide the necessary isolation.

If not hundreds of thousands of properties could be deemed dangerous

I don't think it would mean properties would be dangerous, just poorly designed.

Would you have the same opinion if you went into the mains room of a large factory and had to shut off the power in an emergency, and instead of having a single main isolation switch, you had a series of 15 randomly placed switch fuses and fuse boards? BS 7671 applies to all setups after all.

DPG · Oct 18, 2018

Not quite the same thing though is it. Two consumer units next to each other do not really create an isolation problem. Certainly not one which means it is essential to install a separate isolator next to them anyway.

Matthew · Oct 18, 2018

MDJ - thanks for your reply. To clarify intent. Split incoming mains and install a CU house side that will feed 16mm to outbuilding. CU in outbuildings supplying one RFC one lighting circuit and 15m2 of UFH and two electric Velux. The reason for T&E into SWA was picked up in a post - for aesthetics as conduit into box outside looks better than trying to get 16mm SWA out and down a wall. Does this answer Qs or have i missed something? Thanks so far all. I was going to install a mains isolated while i was there as currently not one

mossep · Oct 18, 2018

I picked an example at the other end of the spectrum on purpose to be honest. The regulation doesn't say how many fuse board there needs to be before you need an isolator to turn it all off, it just says that every installation needs one at the origin.

Nigel · Oct 18, 2018

bigspark17 said:
Youve changed your tune haha

Exactly what I was thinking.

Octopus · Oct 18, 2018

Spoon said:
537.1.4 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 by ordinary persons, e.g. of a household or similar installation, shall interrupt both live conductors of a single-phase supply.

BYB page 154

In such a case where there are 2 boards or more, you could argue that 537.1.6 would then apply ................... (BYB p 154)

Wilko · Oct 18, 2018

Murdoch said:
In such a case where there are 2 boards or more, you could argue that 537.1.6 would then apply ................... (BYB p 154)

Can you believe they've deleted 537.1.6 from BBB. I think we will have the same label at 514.15.1 and perhaps 537.2.7 (new) which says isolators to be clearly identified.

Octopus

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