I know this is going to sound wacky, along with being Pseudoscience, but sometimes you might just get lucky with a Ground Fault not activating the Trip on a GFPE Disconnecting Device (Main Circuit Breaker or BP Switch for 480Y/277V 3PH. 4W. Services of 1000A and greater).
Personal Experience case in point:
Back in the Days, when I actually worked hard (in the Field), there was a Large Commercial "Park", with 8 separate 120,000 sq. ft. Two-Floor Tilt-up Buildings (Occupancy B), of which We had T.I. Contracts with several Clients in several of these Buildings.
Each Building has a Four Thousand Amp 480Y/277V 3PH. 4W. Service, and each Service Disconnect included GFPE.
No Downstream GFPE was used, and the settings on all GFPE Trips were minimal delay, minimal time pickup, minimal threshold.
On One particular "Hellish" T.I., a crew of "MC Jockeys" known as "The Kings", were hired to install MC in the Steel Stud Office's Walls for each Tenant Space.
(BTW; "MC Jockeys" = something similar to "Romex Jockeys" or "Ropers"; in this case, a crew of Belligerent Beer-Fueled, normally fighting piece workers, whom are rocket fast at installing MC Cable, but have questionable Circuitry Make-Up Skills, and do not pay too much attention to details - such as Color of Wires being Terminated)
The Kings had completed Prewiring for Lighting (277V) and Receptacles (120V), and a separate (and competent) crew brought the Branch Circuits from the Suites to the Panelboards, where I Terminated the Circuitry.
After Devices & Fixtures were installed, I energized the Branch Circuits.
Beginning with the 120V Circuits, only found One Fault - a Drywall Screw penetration that occurred after we checked for Ground Faults via Ohm Meter (Cabinet Installers used long screws, missed the stud but hit the MC Cable).
When the Lighting Circuit Home runs were installed, they were also tested for Faults and Continuity. All was good at the time, several days prior to energizing Circuits.
So I throw the Breakers for the Suite Lighting Circuits.
All is OK, until I throw the Second to last Breaker - which trips-free as I throw the handle.
Lights dim out during the Fault, and I am stunned the Main did not trip!
Crew performs Troubleshooting on the Lighting Circuits, to locate this issue.
After extensive searching, the issue is discovered in a Light Fixture.
Switch Leg was connected directly to the EGC - and everyone feels this was a "King-Typical mistake".
Remaining Fixtures are checked, Circuitry checks out good, and Circuit Breaker is reset - no Trip issues. Same with final Breaker - no Trip.
Next morning, I go to turn on the Lighting, and this time the Second Breaker trips free!
Lighting dims, and once again I am stunned that the Main has not tripped!!!
Someone is sabotaging the Lighting Circuit! (turns out to be one of the Kings, disgruntled from an earlier intoxication issue).
The Troubleshooting crew must now verify all Circuitry before ANY Circuit Breaker is closed.
(read: major overhead headache, loss of productive labor, etc,)
I inform the Security Staff of the issues, which brings up the instance of "One of the 'Kings' was seen entering the Building yesterday, around 4:30PM" (we leave at 3:00PM, I leave maybe by 3:30PM at best - normally it will be 4:00PM).
So, eventually the T-Shooters finish up, and once again, the Lighting Circuits are energized.
This time, the Breakers are thrown by someone else; I was discussing installs with Two of my Crew Leads (Top Journeymen), when a familiar "Pop and Buzz" was heard, followed by darkness.
This time, the Main Tripped!!!
Strangest thing ever!!!
I had Two separate occasions, with no Trip.
The Troubleshooter was not so lucky;
first Device thrown - Bam! Down goes the entire Building!
Oh, forgot to mention the best part!
Of course, the P.M. of the complex has their Office at this Building, and - of course, One of the Staff has a Superiority Complex (AKA "I used to be an Electrical Engineer" kind of an Attitude), and is instantly on my Butt, due to this Outage issue. (read: "Nasty-Grams and Penalties A'-Coming).
I was able to relax this Person, and actually avoided all Nasty-Grams, and any Penalties from being issued!
Nevertheless, there is no legitimate reason (other than the Electro-Gods smiled happily upon me), why after Two consecutive Ground Faults, the GFPE Main did not trip for me, yet it did trip for the Journeyman!
Each instance was the same Fault condition: Switch Leg terminated directly to the EGC - via Wirenut - in a 2x4 Troffer.
Each was due to Sabotage performed by the same King, sneaking on the Job. (He was finally apprehended by a few of the more "Muscle-Enhanced" Journeymen on my crew, and dealt with as necessary; ultimately putting an end to the Ground Fault issues).
There is no Moral to this Story, and by no means am I hinting towards "sometimes it is OK to work on Hot Circuits".
Sometimes things just seem "Biased" towards a certain Person.
I have no idea what allowed for the Selective Coordination, then Non-Selective Coordination between the Two separate Devices!!! Believe me, I researched the heck out of this one!!!
--Scott (EE)
