capacitors across switches?

[coppercone2]

The art of electronics says you should put a capacitor across a mains switch to reduce arcing (x rated).

Has anyone seen this done before? I am guessing a capacitive short over the switch contacts.

[BravoV]

A cap (+resistor) across the switch form a snubber that suppresses arc and prolong relay contact life -> Keysight AppNote : Maximizing the Relay Life Span

[coppercone2]

have you ever seen this used for a mains switch?

here is a good document found as arc supression

https://www.illinoiscapacitor.com/pdf/Papers/spark_suppression.pdf

does anyone have the master document
1965 [4] C.C. Bates, Contact Arc Suppression of Electromechanical Relays,

[T3sl4co1l]

Consider the RLC network formed by the mains inductance (~250uH typically), load (much more, ~mH to H for transformers), and whatever capacitance is around (mostly the load, low ~nF for transformers?).  The load current at the instant of turn-off, and the mains voltage at the instant of turn-on, sets the initial condition for what follows when the switch changes state.

To dampen either event, an R||L in series (switch closing, dI/dt limiting and current damping), or an R+C in parallel (switch opening, dV/dt limiting and voltage damping) can be used.

And since we're considering the source-load system as its RLC equivalent (for short time scales), the value of R, L and C required to provide this damping are easily derived.

Tim

[coppercone2]

http://www.academia.edu/23402750/Power_Contact_Arc_Suppression_An_Investigation_into_the_Relative_Effectiveness_of_Snubbers_vs._an_Engineered_Electronic_Power_Contact_Arc_Suppressor

[vk6zgo]

The art of electronics says you should put a capacitor across a mains switch to reduce arcing (x rated).

Has anyone seen this done before? I am guessing a capacitive short over the switch contacts.

Probably a good idea, as far as arcing is concerned, but remember ac is not near as prone to this as DC.

In any case, I think any Electrical licensing authority in the World would have a fit, no matter how it is rated.
If that capacitor fails, you then have a Mains switch which cannot be turned off, but still looks like it is off.

[coppercone2]

2 mains switches then,one never used

[Zero999]

The switch on a device shall not be used as a form of isolation, so I don't see how it can be a safety issue. If there's a concern, then how about just using a Y-rated capacitor?

Another reason to put a capacitor across a switch is to provide a surge through the switch when it's closed, in circuits where the the current is below the switch's wetting current.

[coppercone2]

as an oxide breaker/hammer polish. thats interesting

but a switch does slow a fire down so if you have a electrical fire you can turn it off and have more time to get a extinguisher or throw it out etc if it starts to smoke.

like if its blockaded or the wire is in a wiring run and its not a IEC for some reason

a switch has to be better then a soft start solid state relay though

[Synthtech]

In my business I see them across switches in old Yamaha equipment that uses a single pole mains switch when set up for 100 Volts. The identical piece of equipment in the 240V setup version does not have the snubber capacitor, I assume that’s because is only half the current through the switch at the higher voltage so less damage to the switch as it closes and opens. 

[coppercone2]

if you want to test a switch life time, what is a reasonable switching frequency to use that wont accelerate wear?

[BravoV]

if you want to test a switch life time, what is a reasonable switching frequency to use that wont accelerate wear?

Assuming you're interested on the contact's life, not an expert though, there is a Japanese's standard for contact reliability called (JIS C4530 Allen Bradley Circuit), and I read it from Omron's specification for their relay product about this matter.

Click here and scroll down to the section called -> Maximum Switching Capacity

Also sample few Omron's relay datasheets that has comparable current capacity as your switch to get reasonable comparison or ball park number, as most include the details of relay contact reliability specification and the statistics.