Electrical switches

[Robert Johans]

I am less than satisfied with the quality and aesthetics of typical 12VDC switches — both those for automotive use as well as RV.

Are there any good looking light switches (and cover plates) available anywhere that will function properly and safely with 12VDC power?

Here are a couple examples of the look I'm going for...

[cpaharley2008]

I have always liked the idea of illuminated switches, telling one when it is "On" visually.

[Byron Kinnaman]

Any house light switches will work just fine for 12 Volt DC. I would stay away from lighted switches since the light will draw power from the battery.

[Robert Johans]

So, to follow up, there is no "electrical" argument against using 120VAC-designed switches for 12VDC applications?

[David Tilston]

AC and DC are different applications. AC switches have the advantage of the current crossing zero. This makes interrupting the current much easier. DC is much more difficult to interrupt.

If it is not rated for DC, it is not legal to use.

This is not to say that it would not work, just not to the rating of the switch. If you try to use a 20 A AC switch to turn off 2 A DC, there would probably not be a problem. But at 20 A DC, the current may continue to flow as an arc inside the switch. This may end in a melted switch, and a fire. Not likely, but possible.

[Jon Vermilye]

I agree with Dave. Here is an PDF that might be useful: AC vs DC Switching.

[Robert Johans]

Well, after yet more research on the subject, I too found the article posted by Jon. However, I found another more recent post somewhat contradicting it... Which of course has me scratching my head. (See "Switch_Ratings.pdf")


Nevertheless, I would prefer to install a "legal" switch option that is rated properly for DC applications. I just found this by Leviton (see "LevitonLo-Volt_AC-DC.pdf").

If I understand this correctly, these Leviton switches should be okay to use for overhead LED lighting applications. Right?

[Byron Kinnaman]

Originally Posted by David Tilston

AC and DC are different applications. AC switches have the advantage of the current crossing zero. This makes interrupting the current much easier. DC is much more difficult to interrupt.

If it is not rated for DC, it is not legal to use.

This is not to say that it would not work, just not to the rating of the switch. If you try to use a 20 A AC switch to turn off 2 A DC, there would probably not be a problem. But at 20 A DC, the current may continue to flow as an arc inside the switch. This may end in a melted switch, and a fire. Not likely, but possible.

Switches are rated by peak voltages, a 120 Volt AC switch is designed so that it voltage is which it will arc is well above peak voltage, with in this case is 1.4 x 120.
As far as zero crossing, zero crossing does occur in AC voltages, but a mechanical switch isn't going to always switch as zero crossing, any more than it will always switch a peak voltage. MYTH.

Current rating is determined by the size of the contacts, AC or DC matters not. A 20 amp contact is a 20 amp contact no matter the voltage.

I know the myths are because you read it on the internet.

The two PDF files linked to are concerning going from a low voltage switch to a higher voltage circuit. Going that direction is a problem, going from a higher rated switch to a lower voltage is not a problem.

[Robert Johans]

Or, what about this? Would this pass muster?

[Byron Kinnaman]

Originally Posted by Robert Johans

Or, what about this? Would this pass muster?

The chart and information is about going from a low voltage (28 Volt DC) to a higher (220 Volt AC). That direction I would never do. A 12, 24, 28 volt DC switch is likely to arc when off and used in a 120 or 220 volt AC circuit. For one thing AC voltages have a peak voltage of 1.4 times the listed or RMS voltage (120 Volt AC is an RMS voltaage) so they have to be designed to not arc at those high voltages as compared to 12 Volt DC. The biggest magic between AC and DC is DC Voltages are not changing. AC voltages are constantly changing therefore the DC equivalent is what is used and known as RMS (Root Mean Squared) voltage. I could go into much more detail but I think to answer your questions, a 120 Volt AC switch will work just fine in DC applications. As an electronic engineer I done it many many times and been part of a design team designing switches.

[Robert Johans]

Thanks very much, Byron.

However, can you say it is "legal" to use standard 120VAC switch in 12VDC applications?

What about landscape or architectural "low-voltage" switches? If a switch is "DC-rated" (though designated for 24VDC) is it safe for our trailer applications, especially for controlling a few LED light fixtures?

[Steve Outlaw]

These are the switches that I have chosen to be used in our new 22 foot Oliver that is under construction in Hohenwald, TN. We are using both illuminated and non-illuminated switches. The illuminated ones will be used in places where whatever they control might not be immediately evident, i.e. outside lights, cabinet lights and any other interior spaces that might get closed up with the lights inside still on such as the closet or the custom storage areas they are building under each bed as well as in the basement. I am not concerned about the current draw of the LED’s on the switch. The illuminated switches are SPST. The non-illuminated ones are SPDT, although they will primarily be used as simple on/off switches, the use of these provides the capability of using them as 3-ways in places that require that feature.

Non-Illuminated: http://www.delcity.net/store/Single-&-Double-Pole-Euro!style-Rocker-Switches/p_796737
Item # 7700302: This switch is rated up to 16A at 12VDC.
Drawing: http://www.delcity.net/images/linedrawings/7700302.pdf

LED-Illuminated:
http://www.delcity.net/store/LED-Illuminated-Single-Pole-Euro!Style-Rocker-Switches/p_796736
Item # 7700400: This switch is rated up to 20A at 12VDC.
Drawing: http://www.delcity.net/images/linedrawings/7700400.pdf

Each switch features a unique drainage system frame design to funnel water away from internal switch components.

[Jon Vermilye]

I'm not an engineer, but I can speak (well, type) from experience. I built a device using 10 amp, 240v AC rated relays for an effect in a theatrical production. Worked great at 120v AC. Later used the device on a parade float powering 5 amps worth of 12v DC lamps, and had many relay failures. Contacts welded together. I'd stick with following AC & DC current ratings...

On Edit -
After reviewing Byron's post I'll still stick with paying attention to DC switch ratings, particularly if they are lower than the AC rating, but I will agree with him that you are probably safe using a household switch at 12V. The lowest rated household switch is rated at 15 amps, and your lighting loads in a trailer are well under that. In fact, if you switch to LED lighting, you are probably under an amp.

Also, the number of make/breaks is often a switch specification - the device I built ran marquee chase lights; in 5 minutes it probably opened & closed contacts more times than you would in the life of your trailer!

One last point - do look at the switch specifications, particularly if you are going to punch a hole in the trailer that fits the switch. You don't want to end up having to patch things if the new switch isn't up to the job...

[Byron Kinnaman]

Originally Posted by Robert Johans

Thanks very much, Byron.

However, can you say it is "legal" to use standard 120VAC switch in 12VDC applications?

What about landscape or architectural "low-voltage" switches? If a switch is "DC-rated" (though designated for 24VDC) is it safe for our trailer applications, especially for controlling a few LED light fixtures?

Simple answer YES, to both questions, provided you pay attention to the current ratings.

[steve dunham]

Electrical switches are UL compliant when they are installed and operated according to their UL listing.

[cpaharley2008]

I wonder Robert, will Nest Caravans be a member of RVIA?

[Byron Kinnaman]

Originally Posted by steve dunham

Electrical switches are UL compliant when they are installed and operated according to their UL listing.

UL is a private company, not a government listing company unlike the CSA which is a Canadian government.

[Byron Kinnaman]

I purchased an environmental chamber and had it installed. It required an electrical inspection before I could use it. The local government inspector came out looked over the chamber, while he was at it I pointed out the UL sticker on the computer that controlled the chamber. Since it was built in that was good enough for him and he signed it off. The chamber had purchased the computer complete with UL sticker but did all the rest of wiring themselves.
UL doesn't have much meaning.

[Glenn Baglo]

Maybe the inspector hadn't had lunch yet.

baglo

[Byron Kinnaman]

Originally Posted by Glenn Baglo

Maybe the inspector hadn't had lunch yet.

baglo

Maybe, I don't remember what time of day he came out.
This pretty common according the chamber manufacturer. I could have paid an extra $1500 to have the whole chamber UL certified before delivery. The recommended not because my experience is common.