Pilot Duty Rating

Mark J Strawcutter

I'm looking for the definition/meaning of the "pilot duty" rating of relays and the like.

Mark

Mike T., Swampeast MO

Public info from Rockwell

Question:
For relay contacts, why is there sometimes a difference in Rated Thermal Current and the Thermal Continuous Current Test from the NEMA Contact Ratings Designation for Pilot Duty Ratings?

Answer:
For example, we can review the Electrical Ratings on the 700-HA relays:

The 10A thermal current is both an IEC and UL rating. The 10A rating for UL is termed "general purpose" which is a slightly inductive load. The B300 rating is termed "pilot duty" which means it is for a specific highly inductive load. UL / NEMA define the B300 thermal current as 5A and this does not change even if the product can support a higher thermal current. All of the A-B relays have a general purpose rating and most have a pilot duty rating. This means that a 700-HA for example has a thermal rating of 10A and is also capable of switching inductive loads as described by B300.

Unknown

Pilot Duty

In simple terms it defines for some switching contacts on controls their diversity of voltage applications.

Example: A series 40 120 volt control such as a P404 pressuretrol used on many older steam systems can be used for 120 volts, 24 volts and millivolts. They are often called Dual Rated Controls, they may have a rating that says PILOT DUTY 2 a at 25 VAC; 0.25 A at .25 to 12 VDC this would mean a control could be used on 24 volts and also millivolts (750 millivolts is 3/4 of a volt DC).