Ckt Bkr is Tripping: Feeder for 40 HP Elevator.

[sspeare]

DESCRIPTION OF CIRCUIT:
Elevator motor is 40 HP, 208 Volt/3-phase. Motor FLA from NEC Table is 114 Amps. Breaker sizing: 114 FLA x 2.5 = 285 Amps, round up to 300 Amp. Circuit Breaker #1 is in the Main Dist Panel "MDP". CB #1 is a 300 Amp thermal magnetic breaker, as follows: Siemens JD Frame, model number JXD63B300. CB #2 is inside the elevator machine room. CB #2 serves as the NEC-required disconnect and OCP device. CB #2 is enclosed, and is exactly the same rating and model as CB #1. The cable between CB #1 and CB #2 is copper: 3-#2/0 phase conductors with 1-#4 equipment ground.

THE PROBLEM:
What I'm hearing from the field is: "the breaker is tripping." I have not managed to find out which breaker, or if it's both breakers. The electrician says the instantaneous trips are factory-set at the minimum. The electrician is asking me "how high" to set the adjustable instantaneous trips for these 2 breakers in series. I'm telling him to check for faults first.

QUESTIONS:
1) Am I in trouble because these breakers in series are "fighting" each other with their instantaneous trips?

2) Should I replace the CB in the machine room with a fusible switch?

3) Assuming we can't locate a fault, what can be done?

 

[sspeare]

WoodrowJWeen - that is an excellent suggestion indeed. This is my fault ....... I never shared with this Forum what type of building the elevator serves. It is a small apartment building. The sprinkler system is designed per NFPA 13R, which does not require a sprinkler head in the top of the elevator shaft. NFPA 13R does not require a sprinkler head anywhere in the shaft. NFPA 13R does not even require a spkr head in the Machine Room. I have no auxiliary contacts or devices that could trip the breaker based on a control signal. Some of my jobs (NFPA 13) DO require a spkr heads in the top/elev shaft and in the pit, so I'll remember your suggestions if I have problems on those jobs. Thank you for contributing, I appreciate it.

 

[kenojoe]

Have you considered connecting an analyzer or chart recorder to the circuit to find out what is actually going on? I have also used an "amprobe" in the past with the peak hold setting to help troubleshoot similar problems.

Calculations are great but I also like to find out what the actual measurements are.

 

[sspeare]

Yes, chart recording will have to be the next step. Otherwise, we're just guessing and theorizing. The electrician increased the instantaneous trip, and now everybody is "watching to see what happens." If we have any more problems I will ask the owner to have the electrician implement your suggestion. Otherwise, it will just drift along, and eventually the electrician will say it is a "design problem, blah, blah ..." So, you're suggestion is welcome. I'm stuck right now until something else happens. Thanks again.