The rating of the cable is important too - a 2.5mm core mains lead is required on most UK caravan sites to satisfy IEE regulations [1]; rated to either 20 or 25 Amps (depending on the insulation and grade of copper).

What are the types and sizes of wire?

White sheathing indicates NM cable with 14-gauge conductors. Yellow sheathing indicates NM cable with 12-gauge conductors .NM Cable14-gauge (15-amp circuits)12-gauge (20-amp circuits)10-gauge (30-amp circuits)8-gauge (40-amp circuits)6-gauge (55-amp circuits)2 Feb 2021

What are the sizes of Armoured cable?

3 Core Armoured SWA - 1.5mm - 2.5mm - 4mm - 6mm - 10mm - 16mm - 25mm. Branches stock lengths up to 1,000 mtrs in some sizes. Application: Designed for use in mains supply electricity. These cables are provided with mechanical protection are therefore suitable for external use and direct burial.

How much current can a 3 1 2 Core 100 mm wire carry?

Answer: Normal current which a 3-1/2 core 95 sq.mm PVC insulated un-armoured copper conductor can carry is 210 Amps and for Al conductor it will be 165 A.

Can I use 2.5 mm cable for lighting?

2.5mm should be fine so long as the breaker is <= 10a. In fact its actually quite a good idea as it will help with volt drop. Personally I would say that he must have some other reason for insisting on this as no spark in his right mind would get busted up over the cable size being too big.