Alternating current is the type of electricity we get from the mains in houses and workshops. On the Irish national grid, electrical flow alternates 50 times per second (50 Hz).

Mains voltage in Ireland is approximately 220V ac, and this is often written as 220V ~, with the tilde symbol (~) being used to represent ac. 

Also, position sensors on electronically managed engines (such as the crankshaft speed/position sensor) produce ac, but at much lower voltages. For example, on the Perkins 1100 series engines, under cranking, the crankshaft sensor produces about 0.4V ac.

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