Fault studies: chillers and other motors

[VUGear]

When modeling 480V distribution systems, do you folks represent large chillers as motors or as non-motor loads? We use the SKM products and we've been told to put in chillers under the 80% miscellaneous category, because chillers wouldn't contribute to fault current.

Also, what's considered the size threshold for when a motor significantly contributes to fault current? Occasionally we have to run a fault study of an existing facility and need to collect all the connected motor info, and some people ignore anything below 5hp as insignificant from a fault current standpoint, but others use 25hp as their break point.

 

[cadpoint]

You are right on however:

You need to know what the type of controller is for the chillers that's will be in front of the motor, the hit will be there at the controller not at the motor that is downline from the controller for your calculations.

Isn't the the mimimun thress hold based on your fee ?

Put it this way if you counting five's everytime someone else is counting the 100's or 1000's, where's that put your calculation

 

[ron]

We typically draw the line at cord connected motors. Everything else gets included.
If the chiller starter can function as an across the line starter (even a solid state starter with a bypass), then it too gets modeled as a motor.

 

[VUGear]

If the chiller starter can function as an across the line starter (even a solid state starter with a bypass), then it too gets modeled as a motor.

Sure, but my main concern is not so much the starting current, but fault current contribution; does a typical centrifugal chiller provide little or no fault current due to quickly slowing down upon loss of power?