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Switch contact ratings

Switch contact ratings

Switch contact ratings

Does anyone have some formulas for calculating switch contact ratings?  Something that would give me the breaking AC & DC voltage and current that the contacts would be expected to handle.

RE: Switch contact ratings

Need more information as to type of circuits are you switching?
Control circuits less than 5 amps or Power circuits greater than 5 amps.
What is the voltage level?
What is the circuit type ie resistive or inductive?

RE: Switch contact ratings

1. Normally, contacts have various shapes and various ratings at various voltages for various loads (resistive, capacitive, inductive).
2. There are some standards covering relay contact ratings in catalogs, such as Allen-Bradley, Square D, etc.
3. Theoretical approach to the contact rating can get fairly involved and it is rarely shown anywhere. When there were telephone exchanges using tens of millions of electromechanical relays, there was one book written on the relay contact theory and rating. That was a long time ago in England.
4. Visit
for more info.

RE: Switch contact ratings

The switches (including those used in relays) are used in Elevator Controls and the switches and circuits are varied and from a number of manufacturers.  The currents run from the milliamps to the 10’s of amps and the voltages from 12V to 240V AC or DC.  The circuit types are either resistive (input to a controller) or inductive (to actuate relays or motors).

The switches were designed in the 70’s and 80’s as direct replacement parts.  They were only rated as being equivalent to the OEM part (same size, gap, and material), but no specification was given as to voltage or current.  The OEM part normally did not have a rating (it was only designed to work in their product) and many are no longer made by the OEM (and they no longer have or will not release this information).

It would be nice to have a ballpark figure that I could give my customers, so they know how upgrades and modernization will effect their equipment.

Thanks for the web pages, I'll check them out.

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