where in the regs does it say 16mm Tails are ok?

[HappyHippyDad]

I have my sceme assessor coming today so am just brushing up on all the regs with regards the job he will be looking at.

Does anyone know where in the regs it says that 16mm tails are ok with a cut out fuse of 60A?

Thanks all :smile5:

 

[telectrix]

just basic knowledge here. the CCC of 16mm is approx. 87A. protected by a 60A fuse, then Iz > In, so compliance is achieved.

 

[Octopus]

If you are referrring to an existing installation, and you know that the DNO fuse is 60A there is NO REQUIREMENT to fit 25mm tails.

Simply look up the cable requirements for 60A and you'll see that 16mm is OK.

The point being is that neither the OSG or BGB state 25mm tails are required - but because the OSG shows 25mm in the pickies, people think its a reg.

If its a new build or rewire you could be in deep poo poo as the DNO's do recommend 25mm..... that said I'm not sure that the assessor will even comment.

 

[HappyHippyDad]

Thanks both of you. Thought it might be written in black and white, but you're quite right, it should be more than enough to point the assessor towards the current carrying capacities of 16mm.

No, it not a new build Murdoch :sweatdrop:

 

[7029 dave]

All as above, I would just add if say you fitted a new cu 100amp dp switch, the "assessor" might want you to put 25mm tails in to match cu max demand, weather it be 60amp or 100amp cutout.

 

[Octopus]

All as above, I would just add if say you fitted a new cu 100amp dp switch, the "assessor" might want you to put 25mm tails in to match cu max demand, weather it be 60amp or 100amp cutout.

You mean make up another reg thats not in BS 7671?

 

[brman]

All as above, I would just add if say you fitted a new cu 100amp dp switch, the "assessor" might want you to put 25mm tails in to match cu max demand, weather it be 60amp or 100amp cutout.

if an assessor tried that one on me he would get a good arguement! There is no connection between the rating of the main switch and the maximum demand.........

 

[Geoffsd]

Table 4D1A

 

[Geoffsd]

All as above, I would just add if say you fitted a new cu 100amp dp switch, the "assessor" might want you to put 25mm tails in to match cu max demand, weather it be 60amp or 100amp cutout.

How does that work?

 

[cadspark]

Engineer in my DNO area Scottish Power said they only fit 80 amp fuses as the meters are rated at 80 amps so still ok on 16mm tails.

 

[CrazyScozzese]

Mr M, Hope you are well. Long time no see.

I think this is what you are thinking of, despite the rambings:

16mm2 tails with a 100a cut out are ok if the MD of the installation(div & load inc) does not exceed the ccc of the tails. 434.5.2 must be met. easy peasy lemon squeezy.

cr.ed.

 

[Darkwood]

I fitted a domestic DB recently with 10mm tails and was within BS7671 .... Ill let you newbies ponder that one ...... (Dont spoil my fun! @ the Regular experienced members) :thinking2:

 

[plugsandsparks]

Its funny how there is all this excitement about meter tails yet when doing stuff in comm/ industrial its just straight forward cable calcs and you fit what is necessary.

 

[jamesBoater]

Single shower circuit with RCD/MCB possibly?

I fitted a domestic DB recently with 10mm tails and was within BS7671 .... Ill let you newbies ponder that one ...... (Dont spoil my fun! @ the Regular experienced members) :thinking2:

 

[Darkwood]

Near enough if the upfront devices i.e. the overload protection of the circuit(s) limits the max demand on the tails then the tails may be reduced.

2way DB with a 40amp and a 10amp mcb's will not demand more than 50amp under normal conditions so no need to tail with 16mm or 25mm
If spare ways exist then you shouldn't be practicing this method its for situations where design load has already een set and can't be added to.