AC wall switch work on 12V DC?

[Kevin Warnock]

I don't know the answer, but the nice people at BackWooodsSolar.com have told me to never use a house type wall switch with DC, period. I had a long talk with them about this, because the nice Decor designer wall switches just look so much like home, and I want my bus to look like home. He knew of no safe way to use an AC house switch with DC. That website specializes in off grid solar living, so they probably know something. I'm not saying they do, or that this is the right answer... but I thought I should chime in with this point of view.

I just want to switch 24 volt DC fluorescent fixtures, and these don't take much power when running. But he said these fixtures can take 10+ amps on starting and I think he said they can take even more when the bulbs or ballast fail, but I can't recall for sure, as the conversation was months ago. He said the danger is a fire danger from the arching inside the switch. I don't see why I the circuit breaker wouldn't trip before a fire could start. But what do those fancy arc detecting circuit breakers do? Would I need one of them? Do they come in DC rated versions? I do have DC rated normal circuit breakers for the bus conversion.

I decided against using the AC wall switches because I just couldn't evaluate the risks to my satisfaction, and I don't want to burn down my bus.

[JackConrad]

No data or theory to back this up, just what has worked for us. We used standard house type 120 volt wall switched in our conversion to control interior 12 volt lighting (single throw & 3 way). 10 years and no switch failures so far. We were careful to limit the draw on these circuit to no more than 8-10 amps. Just our real world experience, YMMV.  Jack

[junkman42]

Boogie, I did not say that cheap home wall switches would not work!  And I should have said that resistance in a switch might have a different effect when being used in a  low voltage high current circuit, but you are right.  Just curious as an EE is it possible that the switch manufactures do not know what They are doing or are They just ripping Us off?  Why is it that dual rated switches have a much lower current rating for DC than There AC current rating?  In the overall scheme of things it does not matter and I am sure that some people will tell Us that cheap extension cords are just fine for wiring Our coaches.  There are also those that believe home wiring products are far superior to Marine and Aircraft products.  Run what You brung and if it works for You great.  I warned all that I could not use a keyboard properly!  Regards John

[Len Silva]

In reality, there is little risk.  The worse that can happen is that the switch will fail, most likely in the open position.  There is very little difference in operation when the switch closes, it is on open that you get more arcing than with AC.

I wouldn't worry about it if you keep the load under 10 amps and use good quality commercial rated switches, not the 79 cents ones at HD.

[usbusin]

I'm with Jack Conrad, 16 years in the bus and 8+ years in the truck-conversion and no problems on house-type light switches. 

I had all "designer" type switches, but in confined areas I would always bump into the switch and turn on the light!  So, in the hallway I replaced them with the standard type house switch.

YMMV

[Nusa]

Ya, you can usually "get away" with using AC switches on low voltage DC loads of the same current rating, for resistive loads. The original poster was asking about using the switch for an inductive load, which is MUCH harsher duty for a switch (which is why often find horsepower ratings on switches in addition to current ratings).

Switch failure can be either in the OFF (contacts dirty/burned) or ON (contacts permanently welded) positions. Fail-ON is more likely with DC than AC, and a strong indicator you've exceeded the DC capacity of that switch. So always consider what the switch controls. What happens if it fails to turn off, and you didn't notice?

[RJ]

All -

Just sort of a "dumb" question here, but would using an AC wall switch on DC be a problem if all it was switching on/off was a relay?

Regardless of whether it's an inductive or resistive item being switched, the relay would carry the load, not the switch itself.

I would think in that situation that an AC switch would be fine. . .

Or am I missing something?  (Other than making a circuit more complex than it may need to be, that is.)

FWIW. . .

[Nusa]

A relay coil is an inductive load. But if an appropriate relay is selected, it's likely a small enough load to not be a problem for an 15A AC switch.

[dtcerrato]

We have a common 110 vac house switch in the bus master bedroom at the rear door to operate an outside entry 12 vdc light for 38 years now with no issue...

[sixtyseven]

Hey Bob,  since Dan is bringing this post back from the dead, I would like to know if you used the house switch and if it has held up for 9 years ?