Let there be two lights

Canal Boat - - Back Cabin: - TONY REPLIES… TREVORW1, CB’s

QThe bed­room of our boat has two 12v spot­lights con­nected to a two-gang switch. Both lights are wired to one switch and I would like to have them work­ing in­de­pen­dently, how­ever, a new switch would be needed. Will a ‘nor­mal’ 240v switch from my lo­cal DIY shop work with a 12v sys­tem?



Mains (230v AC) switches usu­ally give no prob­lems on 12v DC light­ing cir­cuits, but no one can guar­an­tee that will be so in ev­ery case. When any switch is opened, a spark tries to jump be­tween the two open­ing con­tacts. On a DC cir­cuit, the spark will keep go­ing un­til the gap is too large for 12 volts to push a spark through ionised air. On AC mains, the cur­rent turns it­self off ev­ery 100th of a sec­ond so the spark stops quickly. This means the con­tacts on AC switches are usu­ally smaller than on DC switches and DC switches could use ad­di­tional means to deal with the spark. This is not nor­mally an is­sue with re­sis­tive loads such as fil­a­ment light bulbs, but it is a prob­lem with in­duc­tive loads such as mo­tors and other items with coils in them. There might be a longer-term prob­lem with 12-volt LED bulbs that have built-in elec­tron­ics. So, usu­ally, a mains switch will work for DC lights but there is al­ways a chance that it could fail be­fore a DC switch.

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