Light switches

[o b clathers]

Hi All

 

Is it acceptable to use a normal household 240v light switch for 12v (provided it covers the necessary amperage) ? - there`s obviously a MUCH greater choice than one can buy thru` chandlers and the like

 

Sorry if this has been covered before - I`ve hunted thru` the forum and can`t seem to find anything on the subject

 

Thanks

 

Richard

[John Orentas]

Hi Richard.

 

Domestic light switches are perfectly adequate for your boat, they are normally rated at 5 amps or so. The only problem you may encounter is the physical size of the terminals, as we tend to use thicker conductors that in domestic use try to find a type with big enough apertures for the wires and find a way of wiring the lights in such a way that you do not need to get more than one wire into a single terminal.

Edited November 7, 2005 by John Orentas

[Keeping Up]

 

Is it acceptable to use a normal household 240v light switch for 12v (provided it covers the necessary amperage) ? - there`s obviously a MUCH greater choice than one can buy thru` chandlers and the like

 

Yes it is acceptable, but you need to be generous with the current rating. If a switch is rated at 5 Amps for 240vac it will NOT reliably switch 5 Amps of 12 volt DC. The problem is caused mainly by sparking at the contacts when switching off. I can't remember the correct de-rating factor, hopefully someone else here will know, but at a guess I'd say at least 3:1 for lighting (and a good deal more for inductive loads such as motors etc) - so my guess is that a 5 Amp switch would be suitable for a light of up to 20 watts.

[John Orentas]

Yes it is acceptable, but you need to be generous with the current rating. If a switch is rated at 5 Amps for 240vac it will NOT reliably switch 5 Amps of 12 volt DC. The problem is caused mainly by sparking at the contacts when switching off. I can't remember the correct de-rating factor, hopefully someone else here will know, but at a guess I'd say at least 3:1 for lighting (and a good deal more for inductive loads such as motors etc) - so my guess is that a 5 Amp switch would be suitable for a light of up to 20 watts.

 

 

Allan.

 

There isn't a formal de-rating factor it is a function of the air gap and contact speed. These days the dual specifications seem to be disappearing from such products. A normal lighting circuit being a non inductive load the difference can be disregarded.

[Keeping Up]

Allan.

 

There isn't a formal de-rating factor it is a function of the air gap and contact speed. These days the dual specifications seem to be disappearing from such products. A normal lighting circuit being a non inductive load the difference can be disregarded.

Thanks John, I guess my info is somewhat out-of-date. I guess that's what happens when you retire.

[Maffi]

........................The problem is caused mainly by sparking at the contacts when switching off.

 

So is it not possible to put a capacitor across the contactst to absorb the spark?

 

(notice I did not say slap a capacitor across the contacts)

[David Schweizer]

So is it not possible to put a capacitor across the contactst to absorb the spark?

 

(notice I did not say slap a capacitor across the contacts)

From experience I would suggest that Normal domestic switches are fine. I recently changed all mine onnthe boat (for cosmetic reasons) and they had been in service for over twenty years. Some of them are now operating (240 volt) lighting in my workshop at home.