Tails from meter to CU - pretty long...

[1shortcircuit]

For those onlookers coming from the Electrical Trainee courses, I would just like to say that I too came into the trade this way and took the batterings on the forum that came with it.

It does get better after time when people read your posts and realise that maybe you know what you're doing or when a newer victim comes onto the scene. :devilish:

If you don't have thick skin you will need to grow some pretty sharpish. Sift through the posts that are helping you and ignore the ones that do not, members soon move on once they realise that you're not biting

Good Luck:thumbsup

 

[Strima]

This thread is making me chuckle... :lol:

Ed, work out your maximum demand and go from there. No pint over engineering it as it will only hit you in the pocket. The OSG has a handy section but I'm sure us Electrical Trainee's will be happy to answer any questions...

I'm not a fan of T&E tails either but like it or love it they're out there and we'll see them for many years to come. If cost isn't too much of an issue I like to use SWA as it terminates tidily.

 

[Jonny66]

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cheers jonny, i thought 25mm was regs minimum for meter tails consumer's side, seen this in OSG am i wrong?

OSG is what it says, a guide. Better to calculate as it saves money and lets face it thats what its all about.

 

[ed-ectrician]

Hi ed-ectrician

Agreed I dont like T&E sub-mains with their small cpcs...
Your volt drop calc should be 1.8volts not 1.8amps.....and should be calculated using your max demand.

IMO I would stick a 60amp metal clad switch fuse in next to the existing isolator and run your sub-main in 3core armored 16mm2. Needs switch fuse as tails > 3m.

Jonny66 - Are you referring to reg 434.2.1? the reason I ask is because if I am (HYPOTHETICALLY!) not reducing CSA of cable, (i.e doing it with 25mm tails - for argument's sake) then i wouldnt have to put a switch fuse in but if i assessed max demand and then found that i could get away with 16mm cable tails i would need a fuse as i am reducing the csa of the cable. Yes?!

 

[Jonny66]

No mate, not referring to BS7671, but ESQCR/ local DNO requirement of not using their cutout fuse for meter tails >3m.
Sorry fella, got the day off, had a few glasses of wine listening to a bit of Amy whinehouse and .......
Loads of threads on here to help you, just look up sub-main and switch fuse.

Also if you use a metal clad switch fuse it becomes nice and easy to terminate SWA cable and at load side you could use a metal clad box before CU....

 

[Jonny66]

Sorry fella, you do need to use a switch fuse due to the length of your sub-main again >3m. You can spend all day on the phone if you like to check with DNO, but its standard practice or should be. Nothing to do with reducing csa of cable.

 

[Paul.M]

@ Ed. The beginning is a very good to start. Have a look at all your loads in your flat and find out your demand (with or without diversity depending on cooker etc) and what are you pulling?

Then work out what size tails (and what type of cable) is suited to the installation method and what up front isolation switch/rcd is needed. What type of earthing arrangement is it? What size earth is needed to achieve disconnection times?


Some times its just a process to ask all the questions from the beginning to understand the full picture. Good luck ed, at least your putting an effort in to your education.

 

[telectrix]

best answer so far was jonny66 post. you need a switch fuse as your tails are > 3m, so fit a 60 A or 63A MCB then 16mm to CU.

 

[Jonny66]

Little Eddy Baby, or if you prefer Sir Edward or Eddy, or Ed, tis but as easy as putting in a switch fuse and some armored cable. If your rich beyond all comprehension, and have no intelligence at all then base your calculations on the OSGs maximum demand calcs. You say your talking about a flat so your max demand imho will probably be no more than around the 30/40amp mark on a bad day, if your lucky or unlucky depending on how you look at it, clamp the tails and see, or add all the breakers and times by 0.4 for a worse case ect. Bet your only pulling 30 amps, ok you might have a 10kw shower and Im a prat but hey ho. 25mm too big I bet, 16mm too big I bet, 10mm might be good enough...........do your calcs fella, its quite rewarding when you do it yourself and hey ho you've designed your submain.....good luck

 

[Jonny66]

Cant see a thanks button Telectrix, so thankyou