Meter tails over 3 meters

haptism · Jun 4, 2018

Hello, anyone know when the regs recommending a switch fuse for meter tails greater than 3m long was introduced ? On older installations (about 20 years ago) was a switch fuse required on tails over 3m ?

Thanks

kenny7askew · Jun 4, 2018

if there is not much in it i wouldn't worry too much about it,i have a"slightly out of calibration tape measure" that comes in handy for things like that

buzzlightyear · Jun 4, 2018

haptism said:
Think I will give the DNO a call

computer says 3mtr max .

Deleted member 26818 · Jun 5, 2018

haptism said:
433.2.2 concerns devices for protection against overload, however the next one (433.3.1 [iii]) concerns omission of devices for protection against overload, and says a device can be omitted "where the suppliers fuse affords protection to the part of the installation between the origin and the main distribution point of the installation where overload protection is provided" (The CU in this case). So that rules that out. Looks like it is the DNO rules regarding tail length

Only if the DNO agrees their fuse can be used.

johnduffell · Jun 5, 2018

I thought it was so the dno can guarantee the load is removed before pulling the fuse to isolate. If the trails go round the house then Henley blocked to an outbuilding or two they won't have a clue how to safely isolate.
I once calculated the clearance time of a 100a fuse on a 0.8 ohm efli (tn s) and off hand I've a feeling it was not quick enough, which would imply if it's bs7671 the 3m rule for omission of fault protection would apply.
Never mind the protection on the incoming supply, that's more than 3m long!

Dave OCD · Jun 5, 2018

Distribution rules and regs are very different , in street lighting it was common for a 16mm concentric service cable to be jointed straight off a 95mm or larger main. Quite legitimately though !