Hello Braintrust, encountered a strange breaker issue over the past few days I'd love some opinions on as I continue to research the answer..
I've inherited an annual installation that runs for multiple hours each night during the month of February. This is my first year dealing with it, though it has happened in the same arrangement and setup at this venue for multiple years now.
The installation is ~45,000 watts of parcans powered by a portable dimmer rack. Math Suggests this draws ~375 amps total, or in a balanced world 125 amps/leg. The dimmer rack is (and has been) powered by a 100amp 3phase company switch. Did the setup as per usual, and amp-clamped the legs at ~140, 145, and 80 amps (the installation fades continuously, so the power varies--but the highest legs remained above 100 amps.) If this was a brief spike I could see the breaker not catching it, but this runs for hours above the breaker spec without tripping. It's a union company switch with a 100amp 3-pole breaker protected upstream by a 100-amp 3 pole breaker, so even with a bad breaker in the company switch itself I'd think that the breaker upstream would trip.
Now, obviously this is not good (tm), and power has been redirected/rerouted/rebalanced to fit within what the breaker should trip at, but I'm concerned that it worked fine for as long as it did. I'm also concerned that there are another dozen or so company switches in the building that are the same model and protected in a similar fashion.
I suppose my questions for the brain trust are as follows:
1) As far as I can tell, the breaker in the company switch is not indicated as rated for continuous duty, and I can almost guarantee the breaker feeding it isn't. How do two breakers not fail when loaded so far over their duty rating for much longer than the 80% rule should allow..?
2) Suggests on safe ways of testing the remaining company switches in the building short of rolling around enough watts of light to trip them?
3) War stories related to similar experiences? (I'm looking at you, @RonHebbard )
Thanks in advance--will be looping in electrical engineer and local electricians as well, but wanted to inquire here as well.
I've inherited an annual installation that runs for multiple hours each night during the month of February. This is my first year dealing with it, though it has happened in the same arrangement and setup at this venue for multiple years now.
The installation is ~45,000 watts of parcans powered by a portable dimmer rack. Math Suggests this draws ~375 amps total, or in a balanced world 125 amps/leg. The dimmer rack is (and has been) powered by a 100amp 3phase company switch. Did the setup as per usual, and amp-clamped the legs at ~140, 145, and 80 amps (the installation fades continuously, so the power varies--but the highest legs remained above 100 amps.) If this was a brief spike I could see the breaker not catching it, but this runs for hours above the breaker spec without tripping. It's a union company switch with a 100amp 3-pole breaker protected upstream by a 100-amp 3 pole breaker, so even with a bad breaker in the company switch itself I'd think that the breaker upstream would trip.
Now, obviously this is not good (tm), and power has been redirected/rerouted/rebalanced to fit within what the breaker should trip at, but I'm concerned that it worked fine for as long as it did. I'm also concerned that there are another dozen or so company switches in the building that are the same model and protected in a similar fashion.
I suppose my questions for the brain trust are as follows:
1) As far as I can tell, the breaker in the company switch is not indicated as rated for continuous duty, and I can almost guarantee the breaker feeding it isn't. How do two breakers not fail when loaded so far over their duty rating for much longer than the 80% rule should allow..?
2) Suggests on safe ways of testing the remaining company switches in the building short of rolling around enough watts of light to trip them?
3) War stories related to similar experiences? (I'm looking at you, @RonHebbard )
Thanks in advance--will be looping in electrical engineer and local electricians as well, but wanted to inquire here as well.