Switch Ratings

[cdeerinck]

Can someone answer this for me please?

If a switch that is rated for 4 amps at 125 volts, is that the same as rated for 40 amps at 12.5 volts?

If not, how could you determine what it would be rated at?

[YellowJacket RV9]

In general, the current rating will not change - it is current that creates heat. That is why some people advocate for 28V electrical systems in airplanes, as the lower currents allow the use of smaller (lighter) wiring. It is also important to be sure you are looking at DC current ratings, not AC. And definitely use an aviation-type switch, not something from home depot.

Chris

[Mich48041]

Switches used in DC applications should be snap action to minimize arcing. Arc suppression diodes should be installed across inductive loads such as relay and contactor coils. Because DC current does not drop to zero like AC does, switches used for DC need to be derated. So the current rating will not increase from 4 to 40. A switch that is loaded above its rating will not immediately self destruct. But its life expectancy will be shortened. For instance, if a switch that is rated for 10,000 cycles at 4 amps is used in an 8 amp circuit, it might only last for 3,000 cycles. The actual lifespan can only be determined by testing. Most switch manufactures have those test results but might not publish them.

[vlittle]

http://www.bandc.aero/pdfs/Switch_Ratings.pdf

[gasman]

I have used quality AC switches in DC applications that were switched 20 to 40 times per day, five days a week, for over 18 years without a single failure.

The switches were purchased from Grainger and used on my Propane truck. I have no problem using them on my RV.

[cdeerinck]

Thanks to all of you for the replies. I particularly found the B&C document very useful. It turns out the switch I had would have worked initially, but likely have failed during the first year.

It was going to supply the electronic ignition coil packs.

I did a search, and located a much more appropriate switch that is rated for more than required.

You might have saved me an engine out failure, so again thank you!