16mm meter tails, do they always need upgrading

[chopper]

just a quick question folks, when changing a mains do u have to upgrade the tails to 25mm and earth to 16mm, at the min there is 16mm tails live and nutral and neutral and the main earth is 10mm,<br>it is a tncs system and the ze is 0.16, gas and water are also bonded with 10mm,<br>do they need upgrading its only supplying a old wylex 4 way board at min<br>cheers in advance for an info

 

[telectrix]

what rating is the DNO fuse? if it's over 80A you should upgrade tails to 25mm. and 16mm earth. gas and water bonding are good at 10mm.

 

[chopper]

60a fuse , would this mean the ok

 

[GLENNSPARK]

Post 2 mate....what do you think?....:shades_smile:

 

[tonyjones]

According to OSG minimum L & N tail size is 25mm or whatever DNO requires. I always use 25mm to be safe. Main earth conductor should be 16mm for TN-S and TN-C-S. 10mm to gas & water bonds. Hope this helps.

 

[fredrico]

If the cut out is a 60amp fuse, then 16mm tails are fine, ive always thought.

 

[telectrix]

agree^^^

 

[GaryM]

Single core 70 degree C insulated cables, non armoured, with or without sheath....

10mm rated at 65A
16mm rated at 87A
25mm rated at 114A

All based on installation method C, no option for in free air but conductors in free air generally dissipate heat better so method C would be conservative.

 

[malcolmsanford]

According to OSG minimum L & N tail size is 25mm or whatever DNO requires. I always use 25mm to be safe. Main earth conductor should be 16mm for TN-S and TN-C-S. 10mm to gas & water bonds. Hope this helps.

Are you sure the earth conductors should be 16mm for these systems?

 

[telectrix]

another myth, malcolm. based on the premise, if we fit 16mm, we can't go wrong.

 

[Rockingit]

Surely; whether or not we think the maths and cables calcs are right or wrong doesn't matter, it's 16mm/25mm as instructed in the OSG, so that's what we have to do, right??

The fact that it's only a 16mm concentric coming into the place........

 

[telectrix]

OSG. fig.2.2........... main earthing conductor shown as 16mm. agreed, but same diagram also shows DNO fuse of 100A. and no mention of L/N tail size.

 

[GaryM]

On Site Guide, yes, that's guide!
We are allowed to think for ourselves too!

 

[Rockingit]

I do vaguely remember one of the Dave & Tony films where TC works out the maths based on having gone round the place turning everything on then clamping the tails and declaring them fine at 16mm/10mm. But, with the rise of the 5 week DI, would we want them trying to make these judgement calls? Is it not actually better to perpetuate the myth just to prevent accidents happening through lack of knowledge.

 

[malcolmsanford]

Surely; whether or not we think the maths and cables calcs are right or wrong doesn't matter, it's 16mm/25mm as instructed in the OSG, so that's what we have to do, right??

The fact that it's only a 16mm concentric coming into the place........

No what we have to do is be guided by the regulations and as designers either adhere to the regulations or have a pretty good argument as to why we don't

The OSG is a guide to the regs, in a lot of cases a good guide but they are not the regs. They often quote a relevant regulation but in the case of tails it only quotes regulation 514.3 when advising about the 25mm size and that regs is just for conductor identification and as always it is the distributor that as the final word