Explain what cosφ and L/R mean, and how they are used for the rated load?


Explain the rated load for a relay in the product catalog: What do cosφ and L/R mean, and what are the numerical background of cosφ = 0.4 and L/R = 7 ms used for the rated load?



These indicate the inductive AC or DC loads. The AC load is cosφ and the DC load is L/R.



Inductive load

  • Meaning of inductive load
    The inductive AC load is represented by cosφ, and the inductive DC load is represented by L/R. Both represent the current delay relative to the voltage of the inductive load. It appears in phase for AC and in time for DC.

  • Background of cosφ=0.4 and L/R=7 ms
    The values are set referring to JIS C5442 “Test methods of low power electromagnetic relays for industrial control circuits.”

    • AC cosφ = 0.4: For AC electromagnetic contactor/AC solenoid operation
    • DC L/R = 7 ms: For DC relay operation


Quick tips

The AC power factor and DC time constant are set based on the electromagnetic relay. If the listed level does not correspond to the load of the customer, test with the actual equipment.
For power relays, refer to the “Durability curve” data listed in the product catalog. If you need data that is not listed in the product catalog, please contact us.


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Relays | Digi-Key Electronics

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