incandescent lamps used on such systems are thicker and therefore mechanically more rugged than those of 240 V lamps. North America This three-wire single phase system is common in North America for residential and light commercial applications. Circuit breaker panels typically have two live (hot) wires, and a neutral, connected at one point to the grounded center tap of a local transformer. Usually, one of the live wires is black and the other one red; the neutral wire is always white. Single pole circuit breakers feed 120 volt circuits from one of the 120 volt buses within the panel, or two-pole circuit breakers feed 240 volt circuits from both buses. 120 V circuits are the most common, and used to power NEMA 1 and NEMA 5 outlets, and most residential and light commercial direct-wired lighting circuits. 240 V circuits are used for high-demand applications, such as air conditioners, space heaters, electric stoves, electric clothes dryers, water heaters, and electric vehicle charge points. These use NEMA 10 or NEMA 14 outlets that are deliberately incompatible with the 120 V outlets. Wiring regulations govern the application of split-phase circuits. Since the neutral (return) conductor is not protected by a fuse or circuit breaker, a neutral wire can be shared only by two circuits fed from opposite lines of the supply system. Two circuits from opposing lines may share a neutral if both breakers are connected by a bar so that both trip simultaneously ( NEC 210.4), this prevents 120 V from feeding across 240 V circuits. Railways In Sweden split-phase electric power is also used on some railways. The center tap is grounded, one pole is fed with an overhead wire section, while the other wire is used for another section. Amtrak's 60 Hz traction power system in the Northeast Corridor between New York and Boston also uses split-phase power distribution. Two separate wires are run along the track, the contact wire for the locomotive and an electrically separate feeder wire. Each wire is fed with 25 kV with respect to ground, with 50 kV between them. Autotransformers along the track balance the loads between the contact and feeder wires, reducing resistive losses. In the UK Network Rail are using autotransformers on all new 50 Hz electrification, and (as of 2014) are converting many old booster transformer installations to autotransformers, to reduce energy losses and exported electromagnetic interference, both of which increase