Sub main advice please

[Matthew]

First post!!!

Very newly qualified so please bare that in mind!!

Recently converted a garage alongside a builder friend. Garage/living annex now has been wired with RFC one lighting circuit. Havent installed yrt but electric underfloor heating and towel radiator (small shower room)
Now what are your thoughts and please explain so i can learn!
I have run 16mm cable from house to garage but nothing connected. I was going to Henley block incoming tails to feed a new CU at house end and new CU garage end. OR could I/ what is stopping me connecting 16mm to current house CU thus preventing installing a new CU off split tails?
Thoughts gratefully recieved

 

['mr2'gd4u]

That's sounds fine, you could send straight to current cu but depends what you already have in your cu. My pref. Would be to fit to new supply like you said. If its more than 3m from supply to cu I'd fit an isolator at the Henley.

 

['mr2'gd4u]

Also the usual.. "get an electrician in to do it/check test and insp." there... I said it lol

 

[Matthew]

Thanks - i am newly qualified but not registered with CPS so will be third party tested/inspected - just after peoples advice and experience

 

[Wilko]

Hi Matthew and Welcome.
Your 16mm cable - what is it, how long is it, how is it installed, how will it be protected? Bonding?

 

[Octopus]

What has your schemes technical support line suggested?

 

[Matthew]

Thanks - 16mm T&E clipped direct to 1st floor joist then SWA trenched to garage all in all approx 15m. Will be earthed via current earth block at CU

 

[Matthew]

Not contacted Tech Support as wanted ither peoples opinions and experience

 

[mhar]

16mm implies either a substantial load or a long length to allow for volt drop.
A 50A mcb in your house consumer unit to protect the cable will not really give any discrimination from the mcbs in your garage cu so the answer is usually to use a fuse, something like a 63A in a switch fuse isolator.
Do your cable calcs really dictate a 16mm supply? Maximum demand is usually significantly less than how the OSG advises how to calculate it. For some (high integrity) cus you may be able to get a fuse holder instead of an mcb and fit a 40A fuse. Do a search on here for 'maximum demand', real life experience is likely to be an eye opener.
I would suggest that a non rcd protected swa from the origin connected into a small rcd/rcbo board is what you would be looking for

 

[Pete999]

What has your schemes technical support line suggested?

The OP doesn't seem to have left any information in his profile, in which case it is very difficult to see what experience, qualifications or any Scheme membership he has.

 

[Pete999]

Thanks - i am newly qualified but not registered with CPS so will be third party tested/inspected - just after peoples advice and experience

Thanks Matthew.

 

[Wilko]

Thanks - 16mm T&E clipped direct to 1st floor joist then SWA trenched to garage all in all approx 15m. Will be earthed via current earth block at CU

Hi - not meaning to sound funny, but as a learning opportunity perhaps have a cup of tea and a read of Reg 522.6 section in relation to how you've run your cable. See if anything stands out .

 

[Matthew]

Cable is more than 50mm from top and bottom.

 

[Pete999]

Cable is more than 50mm from top and bottom.

From top and bottom of what Matthew?

 

[davesparks]

That's sounds fine, you could send straight to current cu but depends what you already have in your cu. My pref. Would be to fit to new supply like you said. If its more than 3m from supply to cu I'd fit an isolator at the Henley.

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

 

[davesparks]

Thanks - 16mm T&E clipped direct to 1st floor joist then SWA trenched to garage all in all approx 15m. Will be earthed via current earth block at CU

Make your mind up, is it T&E or SWA? Surely you haven’t installed a such a short new circuit with a joint in it?

 

[Matthew]

Thanks to all the people who posted with helpful - non-judgemental advice, one of the reasons most of us use forums like this.

 

[telectrix]

i'd be concerned about bonding, esp. if it's PME. that cpc in the T/E will not be large enough to comply.needs 3 core SWA for the whole run.

 

[leep82]

Thanks - i am newly qualified but not registered with CPS so will be third party tested/inspected - just after peoples advice and experience

You dont need to be registered with a scheme to be able to carry out notifiable work. Im not, so i contacted my LABC. They requested copies of all my certificates to see i was competant and then put me on their list of registered electricians. Whenever i carry out notifiable work i have to apply for a building notice certificate from them, this costs £80 regardless of size of job. Long term it would probably be more beneficial for me to be part of a scheme but for now its how i get by.

 

[Spoon]

I have just read this thread. (Comp likes to play up on site site). The OP has been given some good points but looks like he has not acknowledged them.
Text is a funny thing and can be interpreted different ways.

 

[westward10]

Okay I have removed and tidied up some of the posts. Can we try and be respectful to one another and keep the thread on track. Thank you.

 

[mossep]

Hi

Depending on your installation method you could get away with a 63A MCB in the existing board if it has space, assuming your Zs at the new board is fine. You might get discrimination issues, but it’s hardly a critical installation that will cause life threatening issue if it does happen - you will have to have a think about that and any issues it may cause. Someone else mentioned fitting a fuse carrier rather than an MCB, thats a good idea if you can.

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, so you might create more work doing it that way. In my experience, the majority of domestic customers want a cheap job rather than a well specced job.

Your 16mm T+E should be fine with regards to earthing, presuming its not being used as a bonding conductor. If it is being used as a bonding conductor then it will need to be sized appropriately. Is there services in the new area that need bonding, or are they supplied by plastic pipework?

 

[bigspark17]

Okay I have removed and tidied up some of the posts. Can we try and be respectful to one another and keep the thread on track. Thank you.

Youve changed your tune haha

 

[Matthew]

Mossepp - thank you for your detailed reply. My preference would be to split mains and add an isolator so will price up both methods! As for bonding - no - the new installation in entirely plastic pipe.

 

[MDJ]

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.

 

[Octopus]

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]

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]

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

462.1.201

 

[Baddegg]

What book is that in mossep?

 

['mr2'gd4u]

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

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

 

[mossep]

This book

 

[mossep]

View attachment 44956

 

['mr2'gd4u]

What book is that in mossep?

Bbb p121

 

[Baddegg]

Bbb p121

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

 

[mossep]

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

 

[Spoon]

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]

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]

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

 

[Baddegg]

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]

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

Thanks mossep

 

['mr2'gd4u]

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]

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]

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]

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]

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]

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]

Youve changed your tune haha

Exactly what I was thinking.

 

[Octopus]

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]

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.