Maximum distance for 16 mm mains tails?

This Q & A is one of thousands posted in our Technical Expertise area, and answered by our Voltimum Experts.

Question: 

In a new installation, I found 16 mm mains tails have been installed at a length of approx 12 meters between the meter cubicle and the consumer unit, they are protected by a 100 amp supply authority cut-out. Is this cable run too long?Should the tails be a minimum of 25mm?

Answer:

BS 7671 permits the electricity distributors cut-out fuse to be used as a means of overcurrent and fault protection in compliance with 433.3.1 (iii) and 434.3 (iv) providing the electricity distributor agrees. Although most electricity distributors will agree to their cut-out being used the typical maximum length of meter tails is 2 or 3 meters.

Generally installed meter tails are 25mm. A smaller diameter such as 16mm would be permitted providing the cut-out fuse is sized in accordance with section 433.1.1 of BS 7671, where the rated current of the protective device does not exceed the current carrying capacity of the meter tails.

NICEIC Technical Team