Ball Field Lighting Breakers Trip

[augie47]

Contractor asked my opinion and I'll ask yours.
Ball field lighting:
400 amp fusible disconnect feeds (2) 200 amp MB single-phase 240 v panels with 30 amp branch circuits to various 1000w Metal-Halide Fixtures.
Both 200 amp breakers are tripping after 15 or 20 minutes of operation (no 30s tripped).
Measured load when the lights are first energized is approx 125 amps per phase (equal), Over time to load will increase to 147 amps per phase.
Most likely reason for the main breakers to trip is__________________ ?

 

[mgookin]

old age is my first guess. How old is the system?

Have you ever been measuring load as it trips?

Do they both trip at the same time?

 

[GoldDigger]

old age.

Most likely.
Also possibly high ambient temperature at panels or high breaker temp because of high resistance termination to breaker lugs or panel bus bar (less likely to affect two panels at the same time.)
High ambient is the most likely to affect both breakers equally, while simple old age might allow for more variation between the breakers. Termination problems are least likely to affect both panels equally.

 

[cowboyjwc]

old age is my first guess. How old is the system?

Have you ever been measuring load as it trips?

Do they both trip at the same time?

I'd go with old age too. Many parks and what not did not or do not install a contactor so they use the breaker as a switch for the lights.

 

[augie47]

I'd go with old age too. Many parks and what not did not or do not install a contactor so they use the breaker as a switch for the lights.

I'm not discounting the old age factor (I'm an EXPERT on that )
I did ask if they were using the 200 amp breakers as switches and supposedly they are using the 30's.
I did suggest a thermal scan.

 

[Volta]

Or poor connections at the 400 amp load-side of switch to the dual lugs.