I have a 3000-amp 480-volt bolted pressure switch with GFI set at 1200-amp that has shut a 3 story office/retail building down twice in the last 2 years. (building is 5 years old) The original electricians that built the building claim the GFI relay was properly set and calibrated, but were surprised to hear the trip time was set at instantaneous (maybe some else moved it?) It has since been moved up.
During the last event, when the main was switched back on, a 120-volt breaker to the elevator shunt circuit was found tripped as well as a 120-volt breaker to the battery back-up telcom room which also has a small fan on it. I have dismissed those two as a result of power restoration rather than a cause because any ground fault from those breakers would have returned to their respective transformers and not be seen by the 480-volt main.
I am suspecting either improperly set and/or calibrated equipment or possibly an improper G-N bond in one of the downstream 480-volt panels. I will throw a meter around the main bonding jumper looking for amperage to try to determine that.
Any other suggestions on what to look for? What else could cause intermittent tripping other than an improper bond, faulty rely/pickup equipment, or poor settings?
I guess the other place to look might be the 480-volt elevator that the shunt circuit was feeding, but I am not familiar enough with the specifics of those controls to speculate on how those could relate and give the results found.
What other kinds of things have some of you found to be the culprit in a situation like this?
How likely is it that the trip time setting was responsible?
Last edited by Jps1006; 09/06/07 11:48 AM. Reason: added building age in()
