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[Don Lomonaco CFCRC]

If they trip that fast, that suggests to me that something fairly drastic is wrong.  Are you sure you don't have a couple 750w bulbs on those circuits?  Check the tightness of screws in the dimmer panel, measure the voltage in your facility to make sure you aren't running too far above nominal - both at the dimmer and at the fixture if possible, and verify that all bulbs are 575w 120v.

Now I'm not so sure these lamps are 120v.  Here's a pic.  When I search for replacements I see them listed as 115v. The model number on the bulb is HPL575X-C.

[TJ (Tom) Cornish]

Now I'm not so sure these lamps are 120v.  Here's a pic.  When I search for replacements I see them listed as 115v. The model number on the bulb is HPL575X-C.

That can be confusing.  Here is a 120V long-life bulb:
http://bulbman.com/stage-studio-c-1_284_293/hpl575120x-p-405.html

[Cailen Waddell]

There are several versions of hpl 575s.   The ones we are concerned about are the 575-115x and the 575-120x.  Generally etc dimmers show about a 3 to 4% drop in output at 100% so if your incoming voltage is 120, use a 115 lamp, if it's 125, use a 120.  The x btw indicates a reduced output long life lamp.  2000 hours versus 300 I think.

[Don Lomonaco CFCRC]

Ok.  With some further testing I have these results.  I think we're close to getting to the bottom of this.

Circuit 1-4 lamps running will trip in 1:26.
Circuit 4-4 lamps running will trip in 0:33.
Circuit 3-4 lamps running will occasionally trip (time cannot be determined).
Circuit 9-4 lamps running will trip in 0:42.

Circuit 10-3 lamps running because 1 is burned out will not trip.
Circuit 2-3 lamps running because 1 is burned out will not trip.
Circuit 11-2 lamps running because 2 are burned out will not trip.
Circuit 12-3 lamps running because 1 is burned out will not trip.
Circuit 5-3 lamps running because 1 is burned out will not trip.

I've swapped out some modules from the circuits used to control the spots and the same banks of par cans trip regardless of the module.

[Cailen Waddell]

Don I don't think a unison rack will show voltages, like an etc dimmer rack does, but the advantage is a unison rack has an 8 year warranty....  Anyway, I would guess that you have low voltage.  You have a 2300w load, at 115v that is 20 amps.

2 options - ask an electrician to check your voltage, see if you are getting low voltage from the poco.  Otherwise, if you can't change your voltage, relamp with the 375w lamps. 

[TJ (Tom) Cornish]

Don I don't think a unison rack will show voltages, like an etc dimmer rack does, but the advantage is a unison rack has an 8 year warranty....  Anyway, I would guess that you have low voltage.  You have a 2300w load, at 115v that is 20 amps.

2 options - ask an electrician to check your voltage, see if you are getting low voltage from the poco.  Otherwise, if you can't change your voltage, relamp with the 375w lamps.

Low voltage in this case would be a good thing. I suspect he has high voltage.

[Don Lomonaco CFCRC]

Low voltage in this case would be a good thing. I suspect he has high voltage.

I'm checking wall outlets in the building while I arrange a lift in place and obtain a twofer to take measurements at the light source.  Verdict so far:  each outlet is reading 124.7 or 124.8 volts ac.

[Cailen Waddell]

Low voltage in this case would be a good thing. I suspect he has high voltage.

It may be the end of a long day for me so I may not be thinking of this clearly, but a light bulb is a constant wattage or resistance, therefore if the voltage goes down, the current goes up, causing the breaker to trip, if the voltage is high, the current is lower, allowing the bulb to blow but not trip the breaker....

[TJ (Tom) Cornish]

It may be the end of a long day for me so I may not be thinking of this clearly, but a light bulb is a constant wattage or resistance, therefore if the voltage goes down, the current goes up, causing the breaker to trip, if the voltage is high, the current is lower, allowing the bulb to blow but not trip the breaker....

Nope. A lightbulb is a simple device - as the voltage goes up, the current goes up too. A filament's resistance is not linear, but more voltage always means more current, and less voltage means less current.

Induction motors work the way you are describing to some degree.

[TJ (Tom) Cornish]

I'm checking wall outlets in the building while I arrange a lift in place and obtain a twofer to take measurements at the light source.  Verdict so far:  each outlet is reading 124.7 or 124.8 volts ac.

that's on the high side, and could be problematic with 115V bulbs.

[ProSoundWeb Community]