Electrical junction box

An electrical junction box for a vehicle provides electrical connection to electrical connectors, fuses and relays. Upper and lower case parts (11,12) of a casing contain a base circuit (13), a fuse circuit (14) and a relay circuit (15). The base circuit (13) has first bus bars (16) and insulation layers (17) stacked together. The first bus bars connect to electrical connectors in use. The fuse circuit (14) has a substrate (21) which is discrete from the base circuit (16), and second bus bars (20) providing connection to fuses in use. The relay circuit (15) has a substrate (31), which is discrete from said base circuit (16), and third bus bars (30) providing connection to relays in use. The second bus bars (20) and the third bus bars (30) are joined to the first bus bars (16) by welding. A compact construction which is easily modified is obtained.