Control/Dimming Strand CD 80 Control Problem - Post Explosion...

[Murphy913]

This morning I shut off of the dimmer modules and pulled it out. As I did so it exploded and sent sparks everywhere. I tripped the breaker that it was connected to in the process. I shut everything down and put wires caps on the now bad channel that exploded. I reset the breaker the turned the control board back one. I tried one channel which should have just turned on one light but instead every light that was connected to the system would flicker on and off in a random order. This happens with every channel that I turn on.


Ideas? Its not a power issue because the lights works. In my mind it has to be a control issue. I checked all of the cables to the board and the rack. Everything is set right, or so it looks. No burns marks anywhere. I am not sure if the ramp cards are fine or not. That is where I get stuck.

 

[TimMiller]

What exactly did you pull out? Dimmer module, ramp card, power supply? Are you sure the breakers were off? I would be hesitant to re-energize the rack without a full electrical evaluation. Also Was it a 2.4k dimmer or something much bigger such as a 12k which I could see happening if you were to pull it while it is fully loaded. The new SOP (standard operating procedures) to pulling dimmer modules is to LOTO (lock out tag out) power feeding the rack to prevent something like this from happening. Also if it is a portable rack than like with any portable rack you need to reseat all of the dimmer modules before powering up.

 

[mstaylor]

It sounds like it could be a couple of things. You may have burnt the buss bar affecting the processor. You may have interrupted the dimmers causing them to be reset. You may have burnt an entire phase. I rarely use Strand so I will leave it to guys with more experience but because lights come on doesn't mean it isn't a power problem.

 

[DrPinto]

Almost sounds like either a bus bar was loose and grounded out when you pulled the dimmer or something else was loose and contacted a hot with either a ground or neutral. That's why when you pull dimmers you're supposed to power down the rack. If it was spectacular enough to cause an explosion and trip the main breaker, you should lock out the main breaker and have a qualified electrician look at it. Don't mess with it!!!

 

[JD]

Welcome to the wonderful world (and often lethal) of of arc flash. One of three things may have occurred:
1) Molten metal has ended up somewhere it shouldn't have.
2) Voltages were back-sent on data lines.
3) You created your own mini-EMP and damaged the controller.

You may simply need a software reboot, but the system needs to be shut down and inspected. Arc-flash can leave behind carbon traces which are now conductive and may subsequently cause a fire or other damage.

Read:
Implementing an Arc Flash Compliance Program

view:
http://www.youtube.com/watch?v=W6Im7PLduwc#t=01m10s

Helpful tech hint: the #t=01m10s at the end of the link, starts the video 1 minute and 10 seconds in

 

[MNicolai]

JD and the others are right. You need to get this looked at by an electrician and possibly an install tech trained on the Strand gear.

There is a difference between killing the energy to a dimmer and killing the power to a module. When you turn off the circuit breaker on a module, that stops electricity from flowing through the dimmer and out to your circuits. What it does not kill is the power coming into the module from the buss bars in the rack. You really should be killing power the entire rack before you remove any modules -- not just the circuit breakers on the modules being removed.

I would call Strand @ 1.214.647.7880 and get their initial reaction. Then take whatever advice they give to you, which will probably include having a service tech look at your racks in person. It's possible the service tech would be qualified enough to deem the rack safe, but you really should get a certified electrician to look at your rack before anyone else does.

Until it passes an inspection, I'd leave that rack powered down via a LOTO procedure until it can be professionally serviced.

 

[Murphy913]

I pulled out the dimmer module. When I pulled the module out the breakers were on, as I have always done this. It was a 2.4k dimmer.

 

[Murphy913]

I have left the system alone today, no new news as to what happened exactly. I talked to my local Strand tech and had our electrician on site come out and look at it. THey all suggested ramp cards but I took them all out and they look fine. Is there a way to test ramp cards without having them in the rack?

Second, we have a show in two weeks. No dimmers=no lights. Is there a portable dimmer system that I can wire into to use our lights and board? Assuming this rack is dead...

 

[MNicolai]

I'm sure you and thousands of others have done that before without problem. The problem is that one in every x-thousand of times something may go wrong.

I used to do the same thing with ETC Sensor racks and sometimes still do, but ETC tells everyone because of arc-flash concerns that they should power down the racks first.

I know a lot of people who used to and still do hot-swap modules, but how acceptable that practice is throughout the industry is changing, albeit slowly. There almost always will not be a problem, but as you've learned it is possible for something to go wrong.

You're fortunate though that the only thing damaged is the rack. Arc flashes, when they aren't lethal, are perfectly capable of blowing your arm up or permanently disfiguring you. It's the kind of injury you can spend months in a hospital recovering from.

 

[BGW]

If you insist on hot-swapping, always always ALWAYS make sure the breaker is off, even if the channel is at zero. Rupturing under load is absolute hell on module connectors- it often leaves them pitted with carbon buildup. This in turn adds resistance to the connection and prevents tight, solid contact. Sketchy connections at the rack ask for a fire.

Not to mention arcing leaving behind conductive deposits, as mentioned above.

 

[zmb]

So why can't a system be designed that would cut power by using a small switch and relay to disconnect the connections in the module?

 

[BGW]

So why can't a system be designed that would cut power by using a small switch and relay to disconnect the connections in the module?

You mean shut off the mating terminals inside the rack? I think it would just add a lot of complexity and points of failure. Turning off the breakers on a module stops all current flow (well in our racks at least- I don't know for sure about racks that use modules with on-board control circuitry), preventing any arcing between contacts.

If everything was in perfect condition, hot swapping in a responsible manner wouldn't really be an issue. The problem lies in the things you can't see- like maybe one of the buss bars is loose and the pull of removing the module will bring it into contact with the metal frame of the rack. Very unlikely, but like MNicolai said, there's always that chance that something WILL go wrong. Is it potentially worth someone's life to save a minute or two when moving modules around? I don't think so.

 

[chausman]

I think I remember seeing that Sensor dimmers are hot swappable, but it isn't a good idea. Too many ways it can go wrong to try when it's not needed.


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[carmellights]

I think I remember seeing that Sensor dimmers are hot swappable, but it isn't a good idea. Too many ways it can go wrong to try when it's not needed.


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if this is a CD 80 rack with the ramp card cage at bottom - here's a couple thoughts:

1 - always shut down main power before removing and inserting individual modules because....it's a good practice on any rack ( 32 years of field repair...and not bit yet ) but also because in my experience turning these racks on originally, the field load wiring can easily get pinched between the dimmer module and the rack receptacles.
2 - if you ever trip a mains it probably shouldn't be brought back on without a very careful inspection and a lot of static testing by a service tech ( with a licensed electrician standing by to make any corrections ) mains breakers do not trip easily - when they do, something has gone badly wrong and safety should become your main cioncern.
3 - if these are old ramp cards, it is pretty likely that quite a few or atleast some have gotten whacked. a couple service people still work on those cards I believe, but my best advice is to look at a Johnson Systems retrofit kit ( or Strand...but they cost a bit more I think. )
4 - Mainly i would LOTO it, and pull all modules, have electrican inspect load wires and neutrals, tighten all wiring ( feeder torque ) , do a static phase to phase, phase to ground, ground to Nuetral test. with everything out of the rack, power up and have electrican do power tests.

my hunch is if you can get it back up, that once you get to the ramp cards they will be whacked. do a retrofit. single rack should be no more than 8 K.

C

 

[phenry]

To answer some questions that were scattered in this thread:
I know it is general practice to just shut off the module breakers and pull a module, but it does leave a potentially dangerous margin of error. You may go your entire career in theater without having a problem doing this, but it only takes once to regret it.
I would not necessarily expect an arc flash to damage a processor… unless the voltage path went down the communication pins for some reason, then I would expect it.
I know of no way to test ramp cards outside of a complete processor or special test rig built from a processor.
I would contact as there is a time crunch, I would contact century lighting. They are expert at repairing ramp cards and usually keep spares. (201-791-7000).
The Johnson retrofit is not actually cheaper (anymore). And a final note on that, the Johnson kit voids the ul listing of the rack, the C21 retrofit will not.