What is AC and DC voltage rating of switches

Alan0354

Super Member
As title, I am looking at sliding and rotating switch, what is the difference between ACV and DCV rating. They are not the same number.
 
Another thing to consider, is if your switch is going to be operated under load, or not. If you're thinking about something like a triode/pentode switch, I can't think about any reasonably priced switch which can do this with the power on. On the other hand, if you switch it only when the amp is off, then there is no arc, and thus the switch can be used well over its usual ratings for DC. In this case you only have to worry about insulation breakdown voltage, and not contact ratings. Gadget is absolutely right, a DC arc is hard to break, while an AC arc breaks itself at every zero crossing.
 
AC has a zero volt crossing, so the arc is much easier to break. DC never crosses zero, so the voltage that a switch will break reliably is far lower.
I know this is true, but have always wondered if there was set "ratio" between ratings AC vs. DC. In other words, if you know the AC voltage/current rating, can you calculate the DC rating, or vice versa? Or, is it not that simple?
 
I know this is true, but have always wondered if there was set "ratio" between ratings AC vs. DC. In other words, if you know the AC voltage/current rating, can you calculate the DC rating, or vice versa? Or, is it not that simple?

It isn't that simple, basically if it has no DC rating, find a switch which does, and if it has only a DC rating, it's fine to use on AC too. The two factors at play are insulation breakdown, and arc extinguishing.
 
There is something to do with the speed of the switch action too. I don't think its just an X% of AC = DC deal.
 
So the bottom line is look mainly at the DC rating.

The reason why I asked this is because I am looking for a PCB mount SP3T switch for choosing between Triode, UL and penthode mode by connecting the screen to plate, UL tape of OPT and to +350V respectively. The best I found is this one:

https://www.digikey.com/scripts/DkSearch/dksus.dll?Detail&itemSeq=244579932&uq=636469000785895511

It is not easy to find a switch that can withstand high voltage. This one is rated 125V for AC and DC. You think this is good enough? All the voltage is within 125VDC, the arm is plastic, so the whole switch can be float up.
 
So the bottom line is look mainly at the DC rating.

The reason why I asked this is because I am looking for a PCB mount SP3T switch for choosing between Triode, UL and penthode mode by connecting the screen to plate, UL tape of OPT and to +350V respectively. The best I found is this one:

https://www.digikey.com/scripts/DkSearch/dksus.dll?Detail&itemSeq=244579932&uq=636469000785895511

It is not easy to find a switch that can withstand high voltage. This one is rated 125V for AC and DC. You think this is good enough? All the voltage is within 125VDC, the arm is plastic, so the whole switch can be float up.

The key here is don't use it when the amp is on, then the ratings relax a lot. Can't get an arc if you don't actually throw the switch. Also, the DC voltage between the plate, screen, and UL taps is minimal, and current only screen current.

I can't see which one you picked, it comes up as a generic search
 
That's what I think, but even if you switch when the amp is on, it's within 125V......from 425 to 350V is only 75V.

You click the link, you can get the datasheet. also, if you scroll down in the digikey page, they tell you..
 
On my end that link doesn't bring up the product, maybe it's stored on your computer somehow.

I think a standard switch will work for a DIY amp though.
 
That's what I think, but even if you switch when the amp is on, it's within 125V......from 425 to 350V is only 75V.

You click the link, you can get the datasheet. also, if you scroll down in the digikey page, they tell you..

The thing that is not within 125V is the switch operator, Alan.
 
On my end that link doesn't bring up the product, maybe it's stored on your computer somehow.

I think a standard switch will work for a DIY amp though.
Strange!!

This is the manufacturer part number: R10307RN02Q

i googled and it worked.
 
The thing that is not within 125V is the switch operator, Alan.
Yes, all 4 contacts are between 425 and 350V, but the shaft is plastic, if I don't put any ground around the switch, the switch only see 75V. All it shouldn't hurt me if I touch the shaft.
 
Yes, all 4 contacts are between 425 and 350V, but the shaft is plastic, if I don't put any ground around the switch, the switch only see 75V. All it shouldn't hurt me if I touch the shaft.

Rating is 250VAC with a dielectric strength of 1000VRMS. Put a plastic knob on if and call it a day, switch only wirh amp off, Looks like a fine choice.
 

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ha ha, that's the only choice, I spent like 2 hours looking for a switch, from Digikey, Mouser, Newark and google.
 
I should work okay.

It is about, as previously posted, the switch's ability to "break" the circuit and that is more difficult with DC than AC.

General information.

Note the difference in the current carrying rating for AC and DC. When the switch is carrying the higher current the arc will be stronger and since it may last longer for a DC current, (no zero crossing to quench the arc) greater damage due to arcing will maybe done to the switch contacts.

upload_2017-11-22_0-32-12.png

I should be safe in terms of electrical shock.
 
Did you see in the datasheet on page 2 where it says, "No common terminal is present. Switching function is provided by movable contacts shorting adjacent pairs of stationary contacts."

If I understand that correctly, then you can't do what you want using just 3 positions.
 
Did you see in the datasheet on page 2 where it says, "No common terminal is present. Switching function is provided by movable contacts shorting adjacent pairs of stationary contacts."

If I understand that correctly, then you can't do what you want using just 3 positions.
I don't know what you are talking about. This is page 2, it specified "break before make"

R10307RN02Q page 2.JPG

It should be absolutely save to use this.
 
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