regulation for 80amp fuse and 16mm meter tails

[topcat72]

Clarifiation please !

I have read somewhere, maybe in BS7671 or on a forum site regulation that states that 16mm meter tails can or should be used on supplies rated at 80amps or under and 25mm tails on supplies rated at 100amps.

I have scoured BS7671 and various forums but cannot find this regulation, have I seen this, does such a regulation exist ?

As the current carrying capacity of a 16mm meter tail Is 87amps it would make sense or is this just common practice

Thanks in advance

TC

 

[shanky887614]

Clarifiation please !

I have read somewhere, maybe in BS7671 or on a forum site regulation that states that 16mm meter tails can or should be used on supplies rated at 80amps or under and 25mm tails on supplies rated at 100amps.

I have scoured BS7671 and various forums but cannot find this regulation, have I seen this, does such a regulation exist ?

As the current carrying capacity of a 16mm meter tail Is 87amps it would make sense or is this just common practice

Thanks in advance

TC

follow the tables in bs7671 and you cant go wrong.

most people install 25mm simply because usually the fusecarier can only take a max 100amp fuse unless its replaced with a slow blow

 

[shanky887614]

Clarifiation please !

I have read somewhere, maybe in BS7671 or on a forum site regulation that states that 16mm meter tails can or should be used on supplies rated at 80amps or under and 25mm tails on supplies rated at 100amps.

I have scoured BS7671 and various forums but cannot find this regulation, have I seen this, does such a regulation exist ?

As the current carrying capacity of a 16mm meter tail Is 87amps it would make sense or is this just common practice

Thanks in advance

TC

the only info i have found atm in byb is 16mm copper and 25mm ali is the minimum p133

 

[davesparks]

Clarifiation please !

I have read somewhere, maybe in BS7671 or on a forum site regulation that states that 16mm meter tails can or should be used on supplies rated at 80amps or under and 25mm tails on supplies rated at 100amps.

I have scoured BS7671 and various forums but cannot find this regulation, have I seen this, does such a regulation exist ?

As the current carrying capacity of a 16mm meter tail Is 87amps it would make sense or is this just common practice

Thanks in advance

TC

The cable size should be calculated in the same way as all other cable sizes are, though it is safe not to worry about VD at that length.

 

[Farmelectrics]

personally id change them to 25mm but your right 16mm is ok for 80amp my tails in my house are 25mm but the dnos are 16mm so when they were changing my meter to one of these smart ones i ask him how come my tails have to be 25 and yours are 16 makes no sence he said we work to different reqs ha ha bull ****

 

[shanky887614]

personally id change them to 25mm but your right 16mm is ok for 80amp my tails in my house are 25mm but the dnos are 16mm so when they were changing my meter to one of these smart ones i ask him how come my tails have to be 25 and yours are 16 makes no sence he said we work to different reqs ha ha bull ****

not really, we work to bs7671. they dont, they work to a different guide book

 

[Farmelectrics]

yes i gather that shanky but we have to upgrade are tails and they dont dosent seem right to me

 

[cprfenom]

I agree that if we are being told to upgrade tails, then the meter installers should replace them too.

That said, changing tails should be based on the situation, including length, reference method and potential load.

 

[Darkwood]

CPR got it ... changing tails are subject to the same calcs and rules as any cable throughout an install and its this that denotes the size... the 25mm is a safeguard as we legally do not have access to the DNO cutout fuse rating and as in most domestic this is inside a 100amp rated carrier then we are to assume it for a max rated fuse.
If you have knowledge of a lower rated fuse then that can be used for your design and thus in your situe be 16mm.

 

[davesparks]

yes i gather that shanky but we have to upgrade are tails and they dont dosent seem right to me

Who says we 'have to' upgrade the tails?

 

[davesparks]

not really, we work to bs7671. they dont, they work to a different guide book

But any of their equipment which is in the consumers installation has to comply with 7671. It's in the ukpn paperwork I've got buried somewhere

 

[Farmelectrics]

bs7671 dave

 

[davesparks]

bs7671 dave

Whereabouts in there does it say that you must upgrade the tails?

 

[HappyHippyDad]

The Best Practise Guide for domestic consumer unit change (number 6) says on page 5 (note 4 I think) that you can keep the 16mm tails even if there is a 100A cut out fuse..... as long as it meets reg 434.5.2 (i.e K[SUP]2[/SUP]S[SUP]2[/SUP] is greater than I[SUP]2[/SUP]t) AND your max demand is less then the CCC of the 16mm tails.

 

[Dave OCD]

It's all a bit academic really when many incoming supplies are only 16mm anyway ?

 

[baldsparkies]

Where the majority of domestic installs are concerned the chances of overloading a 16mm 1 meter or less, set of supply tails is very unlikely.
These days its the modern showers that are probably the heaviest appliance loads followed by kitchen cooking equipment hobs and the like.
None of which are pulling current for long enough to cause issues.
The only time I have seen problems have been in commercial settings, and usually down to poor or loose connections.
Certainly helps to explain why in the real world you wont see many heat damaged 16mm tails even if they are paired with a 100 amp cut out fuse.

 

[Welchyboy1]

Ive always found this 25mm tails in free air a bit of a nonsense when even new DNO 100a supplies are normally in 16mm concentric cabling

i think the CCC is around 93A

 

[baldsparkies]

Another IMHO valid point is one of flexibility and practicality when working 25mm into a single screwed soft material clamping point.
Those not so sturdily manufactured plastic mains isolators can be very unforgiving and with plastic din mounts and often limited access space in some of these domestic c/u's. 16mm can often result in less mechanical strain and a superior clamp connection.
A good tight connection that's not subject to mechanical strain is as far as I am concerned more important when it comes to the possibility of heat or thermal damage to tails.
In real world scenario it doesn't take a lot to work a 25mm tails loose in those isolators compared to 16mm.
So your damned if you do and damned if you don't.
Oh well !! we can cover the problem up in metal enclosures soon so whoopie dee.

 

[davesparks]

Ive always found this 25mm tails in free air a bit of a nonsense when even new DNO 100a supplies are normally in 16mm concentric cabling

i think the CCC is around 93A

Not round here they aren't, it's 35mm al/cu concentric for all new supplies