Jam Protection

As per ANSI C 37.2, Device Function No. 51 is "Time Delayed Overcurrent Relay" and No. 50 is "Instantaneous Overcurrent Relay". Even though it is incorrect to number 50 for Jam Protection or Locked Rotor Protection, one might assume that jammed rotor condition results in a very high current of the order of 6 to 8 times the rated motor current. Thus, it could be assumed to be instantaneous overcurrent protection and thus numbered 50.

Usually, Jam protection is for use at some level BELOW the Locked Rotor Amp setting, more as a means of protection MECHANICAL components faster than the overload protection will. Think of it like an electronic shear pin (if you know what a shear pin is). Typical settings are 200% or 300% of FLC, but the range of adjustment will usually be between 50% and 600% of motor FLC, just with a time delay during startup to avoid nuisance tripping from Starting Current. But because it is still an "instantaneous current" value that is selected, people often use the IEEE number 50, and then notate it as "Jam protection" because there is no other IEEE number separately for that.

In ETAP, Whats the difference in selecting the trip elements "50 Jam" & "instantaneous" trip element (under the Overload function) & then also select the trip element "50 instantaneous" (under the overcurrent function) as the feature of a multifunction relay....compared to when i just select one of those 3 trip elements ("50 Jam", "Instantaneous" or "50 Instantaneous" ?