Why oh why 25mm meter tails?

[GLENNSPARK]

That's it in a nutshell for me. With the proviso that as long as you have the knowledge (or the professionalism to want and gain the knowledge) as to why what you're fitting isn't strictly necessary then it's OK.

A similar situation IMHO to the "it must be RCD protected, and if it is all's well in the world". I've been to quote on a couple of jobs in the last few weeks where the customer has been told "It must have an RCD" or "You need a new CU" when neither is true. I just can't make up my mind if it's an excess of greed, or a shortage of knowledge driving them to tell customers such things.

well any work we do (my boss n i) that requires additional protection by means of RCD....we just fit a garage board...fed either from a spare way in the existing c/u.......or henley...either way you dont need to be fitting a complete new c/u as firstly you will need to inspect and then test the whole install again...( a can of worms)....and secondly only work you do needs to comply with the current edition of BS7671.....

 

[Edd]

I havent read all the posts!! but when I did my 16th edition and test and connect course years ago I was told that even though you may have a 60/80 Amp head at the time, the DNO may upgrade their service to 100 amp, therefore its prudent to fit 25mm tails.

 

[GLENNSPARK]

I havent read all the posts!! but when I did my 16th edition and test and connect course years ago I was told that even though you may have a 60/80 Amp head at the time, the DNO may upgrade their service to 100 amp, therefore its prudent to fit 25mm tails.

and if you do your diversity calcs for the CU?.....100% of the highest load then 40% of the rest combined?..probably wont be 100A....and dont forget you can clamp it n all....bet you dont get anyware near 80A never mind 100A....

 

[Edd]

Totaly agree Glennspark, if you do get near 100A in a domestic setting I would hate to see what the quaterly bill was!!! and 25mm just dont bend as easy as 16mm and im sure the design of most the domestic stuff aint designed for 25mm, all the main switches seem to destort and argue.. but nothing a hammer cant fix "I will get that tail in"

 

[1shortcircuit]

well any work we do (my boss n i) that requires additional protection by means of RCD....we just fit a garage board...fed either from a spare way in the existing c/u.......or henley...either way you dont need to be fitting a complete new c/u as firstly you will need to inspect and then test the whole install again...( a can of worms)....and secondly only work you do needs to comply with the current edition of BS7671.....

I recently had to do work on a shower circuit and was going to do a two way wylex with main switch and 40A RCBO. Instead though, I discussed with the client and agreed to fit a 5 way board. My reasoning was that at any point in the future they could have an individual circuit tested and dropped in AND protected with a 30mA RCBO. If there was any fault finding to be done then there would be no interuption to their installation.

 

[Tuttle]

I've wondered about this as well. I've got a CU change coming up in a house with 16mm tails. I am tempted to just fit 25mm tails from the meter to the CU because it's a no brainer, it's not that much hassle and is probably the safest option from a part P assessment point of view, even if it is not really necessary from an electrical point of view, but the only thing that puts me off this approach is DNO seals on the meter connections. How do most sparks deal with that?

 

[GLENNSPARK]

well you can always replace tails but how about showing your assessor how you do diversity calcs...for current using equipment/connected loads as well as C/Us.....that would be good wouldn`t it....

 

[1shortcircuit]

well you can always replace tails but how about showing your assessor how you do diversity calcs...for current using equipment/connected loads as well as C/Us.....that would be good wouldn`t it....

I preferred the look of the brand new 25mm tails in the CU I had fitted but wait... Nice new sparkly seals too... Now how does that work?

 

[GLENNSPARK]

I preferred the look of the brand new 25mm tails in the CU I had fitted but wait... Nice new sparkly seals too... Now how does that work?

well if your refering to what i think you are short...then thanks for the reminder mate..lol....

 

[flukey]

but the only thing that puts me off this approach is DNO seals on the meter connections. How do most sparks deal with that?

do the maths and leave the 16mm in if ok.

if dno want to come along at a later date and up to 100A fuse thats their look out just make sure you comply with your work and leave them meter seals alone!!

 

[flukey]

I've been to quote on a couple of jobs in the last few weeks where the customer has been told "It must have an RCD" or "You need a new CU" when neither is true. I just can't make up my mind if it's an excess of greed, or a shortage of knowledge driving them to tell customers such things.

i take it your quoting for surface mount in trunking then?? perhaps others are chasing in properly??

 

[Tuttle]

well you can always replace tails but how about showing your assessor how you do diversity calcs...for current using equipment/connected loads as well as C/Us.....that would be good wouldn`t it....

Yeah, I suppose, as long as he is not of the opinion that tails should always be upgraded to 25mm.

For meter tails the OSG says: "the minimum cable size should be 25mm. The distributor may specify the maximum length and the minimum cross-sectional area". It doesn't say anything about sizing the tails according to the maximum demand. I'm not saying that you're wrong, I'm just saying that I think that I would have a hard time justifying why I ignored what it said in the OSG if it came up in an assessment.

 

[Tuttle]

The other thought I had was if the distributors tails between cut-out and meter are 16mm then perhaps I could assume that their minimum csa couldn't be any larger than 16mm.

 

[GLENNSPARK]

The other thought I had was if the distributors tails between cut-out and meter are 16mm then perhaps I could assume that their minimum csa couldn't be any larger than 16mm.

distributers tails are DNO property..so you wouldn`t worry about those anyway......unless they were damaged..then you pick up the phone.....

 

[jase]

distributers tails are DNO property..so you wouldn`t worry about those anyway......unless they were damaged..then you pick up the phone.....

and which tails are not their property then? the ones coming from the meter to the fuseboard? the meter you are not spose to touch cos that is also their property and it has a seal on it? so i essence we really shouldnt worry about changing any tails cos they are all sealed up and the DNO's :confused5:

 

[topquark]

and which tails are not their property then? the ones coming from the meter to the fuseboard? the meter you are not spose to touch cos that is also their property and it has a seal on it? so i essence we really shouldnt worry about changing any tails cos they are all sealed up and the DNO's :confused5:

Where the tails run from meter to CU/DB is not normally sealed, just a removable cover plate.

 

[flukey]

Where the tails run from meter to CU/DB is not normally sealed, just a removable cover plate.

with a seal on it lol

if meter is sealed and tails need changing this is where mr henley comes in

 

[Tuttle]

distributers tails are DNO property..so you wouldn`t worry about those anyway......unless they were damaged..then you pick up the phone.....

Ok, I know that, what I was trying to say was perhaps I could assume that the distributor's requirement for the csa of the tails on the consumers side of the meter would not exceed the csa of their own tails on their side of the meter, I just didn't explain myself very well. I'm guessing that the main fuse is probably only a 60A or 80A but I haven't checked yet.

Why do I feel like I am digging myself into a hole

 

[topquark]

with a seal on it lol

if meter is sealed and tails need changing this is where mr henley comes in

Not when I find them, not sure why that is.

 

[Tuttle]

When British Gas did some work around my house they sealed the Henley blocks as well!

For safety reasons I think as they are on the consumers side of the meter ... you'd have to be pretty daft to try and nick electric from there