time delay setting of branch feeder
time delay setting of branch feeder
(OP)
I am doing a relay setting for a plant. I found that the settings for MCC feeders should be set at short time delay and long delay without any instantanneous settings. Otherwise it would be hard to corrdinate with down stream circuit breakers. Is is a common pratice here in North America?






RE: time delay setting of branch feeder
RE: time delay setting of branch feeder
Arc-flash levels will be higher than on instantaneous trip, as mentioned. But if short time delay is kept at minimum, the downstream arc energy is generally not too high.
RE: time delay setting of branch feeder
This does not help the arc flash level at the motor control centers or otehr loads.
What you have found is very common in low votlage equipment.
RE: time delay setting of branch feeder
One note - Switchboards built to UL 891 standards (most common in the U.S.), instantaneous trip function is required. Only ANSI design power circuit breakers in ANSI standard switchgear may be configured without instantaneous trip.
RE: time delay setting of branch feeder
RE: time delay setting of branch feeder
It is also possible to get UL 891 devices where the instantaneous is a high current override that does not show in the adjustable settings of the breaker, but needs to be included in the trip curves. Typically these will be used where the maximum fault current is well below the override value.
RE: time delay setting of branch feeder
Thanks
RE: time delay setting of branch feeder
Look at page 3 of the following website.
http
RE: time delay setting of branch feeder
I agree. Setting the inst. pickup above the available fault current is the only way to assure coordination of devices with insta. trip at high fault current. Instantaneous override sometimes confuses people (even those sell circuit breakers) into thinking there is no instantaneous trip function because there is no dial to adjust.
RE: time delay setting of branch feeder
RE: time delay setting of branch feeder