Circuit Breaker Wiring Diagram - When considering cable ratings care needs to taken as this is not as straight forward as it may seem. For example, if you check the manufacturers current rating for 1.5 twin and earth cable (suitable for most lighting circuits in a domestic environment) it will state that it is around 20 amps, but this value would only apply if the cable was in free air (as it can cool easily).. The next item you will notice on a VW wiring schematic is a number size assigned to every wire. The number wire size varies from 0.5 to 6.0. This refers to a European sizing.