splittting the tails

[soulman]

i need to split the tails to add an additional consumer to run a radial socket circuit & lighting circuit. will it be ok to provide this consumer unit with tails 4mm or 6mm

Cheers

 

[steptoe]

whats the loading?

could be a 63A radial and 10kW of lighting!

 

[soulman]

sorry steptoe, just 4 sockets 2 smokes 2 lights.

 

[ADS]

i need to split the tails to add an additional consumer to run a radial socket circuit & lighting circuit. will it be ok to provide this consumer unit with tails 4mm or 6mm Cheers

Is there a reason you don't want to supply the second board with 25mm tails? Or am I missing something?

 

[steptoe]

so, 20A radial, and 6A lighting?

thats 26A max demand,

what size tails do you think?

BTW, Ive never ever used 4mm tails, do they exist?

only ever used 6, 10, 16+

---------- Post Auto-Merged 22nd February 2012 at 00:00 ---------- Previous post was made 21st February 2012 at 23:59 ----------

Is there a reason you don't want to supply the second board with 25mm tails?

small board? and shear size of cables trying to terminate them maybe?

 

[soulman]

i know 6 will be fine but wasn't sure if it would have to be 25mm tails, as you have to take 25mm to the main ccu

cheers

p.s this board will only ever serve these circuits

 

[ADS]

small board? and shear size of cables trying to terminate them maybe?

Is overcurrent protection not coming from the service fuse if he's splitting the tails - so 6mm tails on a 80A/100A fuse.

 

[steptoe]

as you have to take 25mm to the main ccu

you dont as it happens,

but thats another story,

you may find it hard to get anything smaller than 16mm over the counter though,

but 6mm would be more than adequate,

as an aside, and its only my personal preference, keep all your earths the same size,

ie, if your largest earth is 16mm, then make the earth to all your CUs 16mm, not including MEBs or supplementaries of course.

---------- Post Auto-Merged at 00:07 ---------- Previous post was made at 00:06 ----------

Is overcurrent protection not coming from the service fuse if he's splitting the tails - so 6mm tails on a 80A/100A fuse.

no, not over a short distance, they can be fused at either end,

this is one of the reasons (apparently) that the DNO has a max distance/length of tails permitted.

 

[ADS]

keep all your earths the same size,ie, if your largest earth is 16mm, then make the earth to all your CUs 16mm, not including MEBs or supplementaries of course.

So you're going to run 6mm Line & Neutral - because it could be hard to terminate 25s..........but you're going to run a 16mm earth?

 

[soulman]

cheers steptoe have always used 25mm tails when splitting tails into another consumer unit regardless of loading, just thinking is it really necessary as i could get away with much smaller. and i couldn't find a reg to say you cant.

Cheers

 

[ADS]

no, not over a short distance, they can be fused at either end,

this is one of the reasons (apparently) that the DNO has a max distance/length of tails permitted.

The OP might insist that the CU will only ever serve the circuits he has suggested - but the fact is, it's possible for 6mm tails to be overloaded with the setup he describes.

Different, of course, if he runs them through a suitably rated, switch-fuse first.

 

[soulman]

See you point ads cheers will probably stick to 25mm.

Cheers

 

[sellers]

I can't see how the 6mm could be overloaded with only a 20a and 6a mcb?

 

[ADS]

Tell me something, Soulman (and Sellers ) - If you turned up to inspect and test a property and there was a 2/4 way CU fed by 6mm tails and a 16mm 'earthing conductor', protected by a 80A cut-out.................would you pass the installation??

Because that's what you're asking if you can do..................take away the 'existing' tails, and that's what you'll have.

 

[Apache]

So you're going to run 6mm Line & Neutral - because it could be hard to terminate 25s..........but you're going to run a 16mm earth?

No - he's going to bang a rod in.

 

[sellers]

There could be a nail in the cut out? Can't assume its an 80A

With a 2way CU with a 6A and 20A MCB giving a max possible of 26A being drawn, a 6mm with 40A+ currenty carrying capacity is more than ample, so no overload protection is required.

The only problem may be with the fault protection, weather 6mm is enough to carry the potential fault levels.

 

[ADS]

Hi Sellers,

I've clicked the 'like' button for your post - because I know what you are suggesting and the 'regs' you are using...........but can you answer this, then:

If you ask the DNO to upgrade the service fuse from a 60A to an 80A, they will change the tails from 16mm to 25mm - now, they'll do this regardless of whether you have a 2-way, 4-way or 16-way CU attached to the end of them, and regardless of what rating of MCBs you have in the CU........why?

If the cut-out was only providing 'fault protection' to the tails, then you could leave the 16mm tails in, but, obviously it's providing 'overload' protection as well.

 

[sellers]

correct me if I am wrong, but the fault current on your 25mm tails in the CU would be near enough the same as the fault current say on a 1mm twin supplying a spur right next to the CU.

 

[ADS]

correct me if I am wrong, but the fault current on your 25mm tails in the CU would be near enough the same as the fault current say on a 1mm twin supplying a spur right next to the CU.

Yes, but that 1mm twin wouldn't be coming off a henley block connected directly to the tails - it would be connected to a suitably rated MCB, that would trip first.

 

[Apache]

If you ask the DNO to upgrade the service fuse from a 60A to an 80A, they will change the tails from 16mm to 25mm - now, they'll do this regardless of whether you have a 2-way, 4-way or 16-way CU attached to the end of them, and regardless of what rating of MCBs you have in the CU........why?

Are you sure? When we moved in to our house we had 16mm tails on a 80A fuse (verified). I thought the tails belonged to the homeowner, not the DNO. Mine were upgraded when we got the CU changed.