Pilot Duty: What is this contact rating?

October 2, 2018
Tech Tuesday

Choosing the right relay for your application should be much easier than flying an airplane! For my last blog post of this series “what is this contact rating,” I want to explain what the “pilot duty” rating is. With that, sit back, relax, and enjoy the flight! Oh, and make sure your seatback tables are in their upright and locked positions.

So, does a pilot duty rating have anything to do with flying a plane? No, not at all. However, like we trust a pilot of a plane to steer the aircraft safely through the skies, we also place trust in pilot duty relays that control electrical operations within a building.

What kinds of loads fall into the pilot duty rating? Inductive loads, which could include relay coils, contactor coils, or solenoids. That is why you will see an amount of “VA” for the pilot duty ratings, like a transformer or power supply would be rated. One may see a solenoid assigned a couple VA numbers: “in-rush VA” and “holding VA.” For sizing a relay to the pilot duty load, I would suggest going by the in-rush number (the larger number, typically) to cover all bases. However, it may be an even better idea to contact the manufacturer of that pilot duty load to see if they have a specific relay suggestion.

For example, you have a 120Vac solenoid that says, “Holding VA: 10VA” and “In-rush VA: 80VA.” I would say to go by the 80VA rating and find a relay with a 120ac pilot duty rating. Which RIB relay device would I suggest in this example? Since the RIBU1C does not have a 120Vac pilot duty rating, I suggest the RIB2401B relay. Though, the solenoid manufacturer may say that the RIBU1C relay would be enough. Just like getting a diagnosis from a doctor, it never hurts to get a second opinion, and I trust that a solenoid maker would know their solenoids.

Below, you may see the pilot duty ratings circled for the 10A, 20A, and 30A RIB relay devices that we manufacture.

I hope this final blog post of the “what is this contact rating” series helps to explain the pilot duty rating. As we know that the world is not perfect, not all inductive loads react the same way. This blog does not provide a comprehensive explanation. I advise to check with the manufacturer of the load as well as call the technical support here at Functional Devices to get the best suggestion for any of the controls projects you hope to complete. Tech support is standing by, and we’re happy to help the best we can!

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About the Author

Meet Samuel Klennert – you can call him Sam. He was born and raised amongst the farmland of Indiana, which included corn, soybeans, and sometimes wheat. Sam graduated from Purdue University with a Bachelors degree in Electrical and Computer Engineering Technology in 2015. He has a focus in analog circuitry and power electronics, but he’ll give software a try from time to time – just not that digital witchcraft!

Outside of work, Sam enjoys outdoor activities including (but not limited to) hiking, mountain biking (or just really-big-hill biking), and camping. Call Sam for tech support today – he’ll give his best effort to any task at hand!