capacitors across switches? - Page 1
Forum section: electronics / projects

author: coppercone2
author_rank: Super Contributor
timestamp: December 27, 2018, 03:32:44 am
content: 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.

author: BravoV
author_rank: Super Contributor
timestamp: December 27, 2018, 04:26:08 am
content: A cap (+resistor) across the switch form a snubber that suppresses arc and prolong relay contact life ->Keysight AppNote : Maximizing the Relay Life Span

author: coppercone2
author_rank: Super Contributor
timestamp: December 27, 2018, 06:55:22 am
content: have you ever seen this used for a mains switch?here is a good document found as arc supressionhttps://www.illinoiscapacitor.com/pdf/Papers/spark_suppression.pdfdoes anyone have the master document1965  C.C. Bates, Contact Arc Suppression of Electromechanical Relays,

author: T3sl4co1l
author_rank: Super Contributor
timestamp: December 27, 2018, 07:31:34 am
content: 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

author: coppercone2
author_rank: Super Contributor
timestamp: December 27, 2018, 07:56:01 am
content: 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

author: vk6zgo
author_rank: Super Contributor
timestamp: December 27, 2018, 11:55:34 am
content: Quote from: coppercone2 on December 27, 2018, 03:32:44 amProbably 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.

author: coppercone2
author_rank: Super Contributor
timestamp: December 27, 2018, 12:01:16 pm
content: 2 mains switches then,one never used

author: Zero999
author_rank: Super Contributor
timestamp: December 27, 2018, 12:03:20 pm
content: 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.

author: coppercone2
author_rank: Super Contributor
timestamp: December 27, 2018, 12:04:52 pm
content: as an oxide breaker/hammer polish. thats interestingbut 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 reasona switch has to be better then a soft start solid state relay though

author: Synthtech
author_rank: Regular Contributor
timestamp: December 27, 2018, 12:09:56 pm
content: 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.

author: coppercone2
author_rank: Super Contributor
timestamp: December 27, 2018, 12:12:52 pm
content: if you want to test a switch life time, what is a reasonable switching frequency to use that wont accelerate wear?

author: BravoV
author_rank: Super Contributor
timestamp: December 27, 2018, 12:58:46 pm
content: Quote from: coppercone2 on December 27, 2018, 12:12:52 pmAssuming 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 hereand scroll down to the section called -> Maximum Switching CapacityAlso 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.