Bonding in the cu

Yes.

 

Yes that's ok Col, I see it done that way quite often in flats etc. There might be some questions from some as to whether the 16mm core is big enough to serve as an earthing and a bonding conductor but I don't see a problem (and i'd do it!) Could you earth the armour at both ends just to "give it a bit more"?

 

Hi Sen,
Isn't this no difference to what happens in a lot of installations; where the gas and water bonds are connected to the consumer units earthing bar and then the main earth (16mm) takes it all down to the suppliers head?
Not trying to be pedantic mate just trying to get it clear in my own mind as this came up in college once.

Hi Col,
Wont you need another method of over current protection due to:

Going beyond the suppliers usual 3 metre rule
Is the service fuse 100A? 16mm is rated less than this.

 

Hi Fats, yes that's why I mentioned it, as you say it's quite usual to have the bonding on the earth bar in the c/unit but in this case there's a sub-main so all the fault current has to go through that conductor too. I think it might be more of an issue on tncs systems?
As for the over current protection i'd guess that Col might fit a 60 amp switch-fuse.

 

Hi Sen,
Yes, i recall the tutor saying although there are guides for the main earth CSA which in essence is relevant to the supply - the operator can install larger on TNCS due to network currents (being connected to neutral at several places i guess)

 

Nope it's not a myth at all, just not understood.

 

A lot of people have this strange idea, that the cut out fuse is there to protect the installation.
It's not, it's there to protect the distributor's equipment.
As far as BS7671 is concerned, unless the distributor agrees that their fuse will protect the installation, there is no protection for the tails.
The Regs deal with this via Regs 433.2.2 and 434.2.1.

 

Like I said, not understood.
They apply wherever there is a reduction in current-carrying capacity, for what ever reason.
Yes they do apply to Spurs, but exclusively.
As for a link to what the DNO specify, how would I have one?
I have no idea which DNO supplies the area you intend to carry out the work in.
Some DNO's limit the length to 2m, some 3m, others have no limits.
That aside, Ido know that any DNO has a statutory obligation to provide a connection to an installation which satisfies the requirements of BS7671.
As long as your installation complies with BS7671 (ie, your tails are no longer than 3m) you should be fine.

 

the 3M rule isn't a myth the recommended limits and required limits depending on supplier are between 2 - 4m so 3m is an average

http://www.meteroperators.org.uk/faqs




http://www.westernpower.co.uk/docs/connections/New-Supply-Guide.aspx



https://library.ukpowernetworks.co....S+08-0129+Underground+Services+up+to+100A.pdf

 

There you have it.
2m and 25 mm according to the DNO.
3m and appropriately sized, according to BS7671.

 

I think you could have it as long as you like after the fused switch (subject to volt-drop) Col.

 

To sum up the furthest you can go from the suppliers cut out is 3 meters unless you fit a KMF (or other fused switch) within that 3 meter limit... once you have a fuse in place within 3 meters from the suppliers you can run as far as you want to..

the furthest from the suppliers cut out to a board or switch fuse is 3M

 

I'm saying, do it as per BS7671.
What exactly do you believe installing an isolator at the start of a run would achieve?
The distance between the cut out and the meter does not matter, as it is outside of the scope of BS7671. Not your responsibility, nothing to do with you.
BS7671 starts where the installation starts.
So you measure 3m of cable, wack it in the meter and at the other end you stick either your CU or perhaps a switched fuse.

 

Not saying just an isolator Spin, a switched fuse, which in effect IS an isolator incorporating a fuse!