Random "flashing" fixtures

[theatre4jc]

I'm in an ETC house with sensor racks, Emphasis server system with an Insight 3 and Unision house panels. I have just under 800 dimmers. This problem has been there since day 1 (6 years ago). ETC has been out multiple times to look into the issue and keep saying it's something that we refuse to accept as the answer. I'll explain that in a bit. I've only been at this place for 2 months and am just now getting to where I can start tracking down issues. So for what's going on:

Our house fixtures over the balcony are a combination of S4 Parnels and in the ceiling can lights. This is only an issue with the house fixtures and only presents itself during services. We cannot replicate the problem during the week. Since I cannot replicate the issue I cannot determine if it also occurs with the Unison system. At random points the random lights will begin to flash on and off. The Sensor rack reads an error on the dimmer. We will either replace to power cube or swap out the module with a known working module and that will stop the issue.

Now here is where it gets fun. I can put the module or cube from the flashing dimmer into another slot on dimmer circuit that we know works without issue and the dimmer never fails. So it's actually not a dimmer module issue. The ETC guy that came out (before I got here) said that the reason is because the house fixtures over the balcony are the farthest from the racks. I don't think this is the reason because I have another room, controlled by sensor racks in the same AC room that is about 150' farther away and it has no issues. I have 6 (I think) sensor racks and all issues are out of just one of them. I have not looked to see if it is a bad leg of power but I think the issue is something in the rack. Not simply because the house fixtures are so far away. The circuits running the S4 Parnels have 3, 575W units, and the recessed can lights we use have only 3 per as well. Do not know the wattage off the top of my head but I think it's safe to assume they are less than 600W. I don't think it's from overloading.

Before I purchase another round of power cubes I want to try and figure out what is actually causing this issue and why I cannot replicate it. Also why it's not always the same fixtures having issues. Since I can put the dimmer modules into another rack and they work fine I'm assuming they aren't the issue as well.

Comments, ideas on what the issue could be?

 

[BillESC]

I'd check to see if all of your racks are set to the same data rate.

 

[epimetheus]

What size are the dimmers for these circuits? What gauge is the wire that feeds these circuits? What is the circuit length from the dimmers to the first fixture and to the last? Have you currect clamped a circuit at 100% to check the current? I'm wondering if the load wattage plus the resistive losses in the wire are overloading the dimmers.

 

[waynehoskins]

Have you tried swapping (with appropriate readjusting) CEMs between the Bad Rack and a Good Rack?

 

[David Ashton]

I'd have a serious look at the neutral cabling and connections to this rack.

 

[Slitterst]

Is it consistently the same slot/s in the rack? If so, are the problematic slots on the same power phase? If the input power dips to low, that could cause the rack to disable those dimmers to protect them. You'd see this more often during a performance/service because you'll have more of a load on the entire system.

Also, check to make sure no HVAC or other building systems are sharing your rack power. This is something else that you won't notice during the week since the HVAC is probably not running as heavily when there are no bodies in the seats.

Is it the whole rack? Could the rack be shutting because of a faulty airflow sensor?

You've mentioned swapping out dimmer modules, but have you tried changing out the CEM?

One final thought, shut the rack down and make sure all the circuit connections in the rack are tight. A loose set screw could cause just enough arc to register as an overload or overheated dimmer. The action of slamming in a new module could be firming up that connection which is why changing modules appears to solve the problem.