Channel Stuck?

[Charc]

Brett, he will have the building manager there conducting the work, he says.

When I did the stuff with my dimmers I had 3 maintenance guys with me... then again it was the rally point for discussing in detail the various issues in the theater.

 

[porkchop]

Ok so after making it red and underlining it I decided to do what I do best...numbers.

Pic 2 shows 17 Modules. I'm going to assume that they are 2.5k W dimmers (I would say the most common rating, but by no means the only one). That means that you have 17 x 2500W going into the rack. Thats 42,500 Watts possible, thats something on the order of that amount of power going through a low power overhead line.

Just one dimmer (if its in fact 2.5k W) would have 120 V and 20.83 Amps (2500W/120V). Now if I had to make an approximation of the amount of power it would take to kill a person, I'd say something like 1 Amp at 120V. Yah that's A LOT less than 20.83 Amps.

In one last point, every modern dimmer rack that I've dealt with has 2 dimmers per module. If thats the case then you have the potential for doubt the power going into the rack.

Now do you understand why we're really touchy about you playing around inside the rack, and why the company has very specific protocols for powering down your dimmer rack so that it can be worked on?

 

[Charc]

Ok so after making it red and underlining it I decided to do what I do best...numbers.
Pic 2 shows 17 Modules. I'm going to assume that they are 2.5k W dimmers (I would say the most common rating, but by no means the only one). That means that you have 17 x 2500W going into the rack. Thats 42,500 Watts possible, thats something on the order of that amount of power going through a low power overhead line.
Just one dimmer (if its in fact 2.5k W) would have 120 V and 20.83 Amps (2500W/120V). Now if I had to make an approximation of the amount of power it would take to kill a person, I'd say something like 1 Amp at 120V. Yah that's A LOT less than 20.83 Amps.
In one last point, every modern dimmer rack that I've dealt with has 2 dimmers per module. If thats the case then you have the potential for doubt the power going into the rack.
Now do you understand why we're really touchy about you playing around inside the rack, and why the company has very specific protocols for powering down your dimmer rack so that it can be worked on?

I note 17 modules with 4 breakers per module. I believe the most common dimmer is 2.4kW. We may be looking at a lot more power if that is ((17x4)2.4kW)=A ; but I don't know if those numbers are correct, just making random guesses.

 

[porkchop]

My point is that as previously mentioned the building manager may or may not know any more about the system that our new friend Sync. That in mind even if the building manager knows about electricity and it's dangers. He/She maybe not realize exactly what goes into a dimmer rack. I'm not saying you have to LOTO to clean a dimmer rack. I'm just saying make sure you have a talk with someone that has a good idea (keywords) exactly whats going on so you can stay safe.

EDIT: maybe 2.4k is right, it doesn't really matter. The point was to give round numbers to show why dimmer racks need to be respected.

 

[Charc]

My point is that as previously mentioned the building manager may or may not know any more about the system that our new friend Sync. That in mind even if the building manager knows about electricity and it's dangers. He/She maybe not realize exactly what goes into a dimmer rack. I'm not saying you have to LOTO to clean a dimmer rack. I'm just saying make sure you have a talk with someone that has a good idea (keywords) exactly whats going on so you can stay safe.

Oh, I'm in agreement. But presumably the building manager will be handling the power... if they can't handle it... then why are the building manager? Oh well, they won't be for much longer...

 

[porkchop]

Oh, I'm in agreement. But presumably the building manager will be handling the power... if they can't handle it... then why are the building manager? Oh well, they won't be for much longer...

True, but if the building manager doesn't understand the power involved there could be things that are overlooked because "that isn't really important until you get to something with more power." Think about it as far as a High school goes most things use significantly less power thats what the building manager will be used to working with.

EDIT: And that "Oh well" situation isn't going to be a good one.

 

[Synchronize]

Guys, you have to understand here, I'm no idiot. I'm the kid that gets nervous about putting a new male end on an extention cord and then plugging it in. I'm not the kid that says, "OOOOO pretty shiny copper... lets touch it." The Building Manager is getting all of the original paperwork on the system, including wiering schematics. I am also going to contact Lehigh and get the proper method of doing this. I am most likely only going to handle the modules until after they have been removed by the Building Manager. Believe me when I say I'm not going to "play" around in the dimmer rack. Electricity scares the LIVING POOP (since nice filters wern't in place for the other word) out of me. I'm no fool.

But just to let you know, I do appreciate all of your concern.

 

[porkchop]

That's what I wanted to hear, basically I know in high school I would have just turned off the breaker and had at it, and if that had happened odds are good I wouldn't be here.

 

[derekleffew]

Ok so after making it red and underlining it I decided to do what I do best...numbers...

Sorry, but that point is arguable.

Pic 2 shows 17 Modules. I'm going to assume that they are 2.5k W dimmers (I would say the most common rating, but by no means the only one). ...

2.5Kw dimmers exist only in countries that have 220-240VAC power. The standard in this country is the 20A, 2.4Kw dimmer, usually in dual modules.

Just one dimmer (if its in fact 2.5k W) would have 120 V and 20.83 Amps (2500W/120V).

Dimmers are rated by their circuit breaker, and you'd be hard-pressed to find a 20.83A breaker. The OP has 17 Quad modules, which I suspect are 10A, as 20A quad modules are rather rare (Kliegl and EC come to mind). This would yield a total theoretical load of (17*4*10)=680A. The NEC allows "undersizing" of incoming feeder, as not every dimmer will ever be loaded to full capacity, and the disconnect switch looks to be of 120/208VAC 3Ø Wye-connected 4W+G, 200A size.

...Now if I had to make an approximation of the amount of power it would take to kill a person, I'd say something like 1 Amp at 120V. Yah that's A LOT less than 20.83 Amps...

From here: A low-voltage (110 to 220 V), 50 or 60-Hz AC current travelling through the chest for a fraction of a second may induce ventricular fibrillation at currents as low as 60mA.
That's 0.06 amperes, about as much as a 120V, 7 watt night-light.

Yes, electricity is dangerous and can kill, but should be treated with caution and respect, not fear. Just like a loaded gun.

The question remains as to whether a minor or non-staff member should be working around any electrical circuits, even plugging in an extension cord. That's for each venue/school district and their insurance carriers and lawyers to decide.

 

[gafftaper]

That's what I wanted to hear, basically I know in high school I would have just turned off the breaker and had at it, and if that had happened odds are good I wouldn't be here.

Amen Brother! Preach it!

 

[porkchop]

ok derek you beat me, but my point still stands. I didn't do much research for my numbers cause I knew that they were so big that rough estimates would illustrate my point. 2.4k is apparently the US standard, thats an oversite but still close enough to get the point across, your point about undersizing of breakers is interesting but in the realm of understanding if there's enough power in a dimmer module to kill you, the more the marrier but you'll still be fried in the end. And yes if a relitively small current passes directly trough the heart is can be lethal but I figured that 1 Amp was an easy to comprehend estimate that covered most any way that power could pass through the body, and it is still an order of magnitude lower than your estimated 10A per dimmer. Basically if I had really wanted to give exact number I would have looked harder. Yes maybe I should have done that , but I was really just trying to give a little more perspective than
HUGE AMOUNTS OF ELECTRICITY!!!!!!.

EDIT: I do like your loaded gun simile it's very true. There are amazing things that can be done if we take our respect of electricity and put if plus knowledge to good use

 

[TimMiller]

I'm always the one to jump head first into a dimmer rack. Yet I have accumliated knowlege from ETC and Strand, and have been working on dimmers since i was about 14. I'll work on a dimmer any day over a strobe. Dimmers as long as you lock out tag out are very safe. (lock out tag out is a practice in which you turn off the disconnect, lock it with a padlock, then tag it so it says Do not energize equipment, or do not turn on). You do have to be aware commonly you have more than one disconnect running to dimmer racks. So even though you powered off one rack there may be another one still powered up. Also they sometimes do some really strange stuff to add on non dim circuits.

Being over cautious is good. Studies have shown that the well seasoned electricans get shocked more than the younger ones, due to they become too comfortable around electricity. Honestly i have gotten shocked a few times, but it is normally in the shop when repairing moving lights and strobes due to caps not discharging. I know i have said this before on here, but never assume anything. I have never been shocked repairing a dimmer rack.

Turn off the main disconect, then turn off the breakers on the dimmers. Then remove the modules. For a very detailed rack cleaning like yours needs, after you remove all of the modules look around and find all the fans. out of safety pratice DO NOT TOUCH THE BUSS BARS IN THE BACK OF THE RACK. If you must touch them be sure to verify with a meter that they are truely off. Then blow out all the fans. Don't let the aircompressor make the fans spin or you will be putting extra wear and tear on the fans, and when you make them spin the fans actually work as a generator and back feed the circuit board in the processor module. After blowing out the fans i give them a spin by hand to make sure they spin freely. If they catch, bind, spin very little or dont even spin at all they need to be replaced. You can usually get new fans from electronic stores or industrial supply houses. You are best off bringing in the old fan so they can match it for you, or just get one from your local theatrical dealer.

Disassembling your first dimmer will be a great learning experience and a good practice of electrical safety. Just remember never assume anything is actually off. I will PM you my cell number incase you need it

 

[church]

The message to have a qualified person do this is absolutely correct, not only does the lock out tagout procedure need to be followed but just turning off the main breaker switch for a complete dimming system can be dangerous and is considered as working on a live circuit even when the breaker box is enclosed.

This is because you may have an arc flash hazard issue depending on the voltage, current and the supply but theatre installations tend to have large power supply capability.

This is one reason why switchgear is suppossed to be in a locked room. operating breaker switches can and often does require the electrician to wear a fire resistant clothing ranging from pants and shirt (and underwear up to special nomex suits and helmets. There are special techniques required for this to minimise injury should a flash occur.

Our electricians regularly have to put on their suits when changing fuses etc.

I know this is probably not what you want to hear or read for that matter but the shocks you get from working on an instrument on a bench are a completely different situation to what can happen when you start operating three phase switchgear handling large currents etc fed from high voltage transformers. You don't get second chances with this stuff.

I know we have all operated switchgear without thinking about this but thousands of people are injured every year in the US and Canada by these types of incident. FYI the temperature of the flash is usually 35,000F with noise levels of 125dB and a shock wave of 125 psi. The flash boundary can be anything from a few inches up to 8 feet and more. You need an engineer to analyse the specific situation, the flash hazard is suppossed to be identified on all recent switch gear installations. BTW wearing the PPE doesn't mean you will not be injured it is inteneded to limit injury to recoverable second degree burns.

So it is quite likely that the Building Manager does not have this knowledge or training because they are not supposed to be operating Switchgear.

 

[Synchronize]

Its done. We cleaned it and it didn't solve the ghosting. Any other ideas as to what in the module could cause the problem? Is there a specific part that we could order from the manufacturer that can be installed in the module.

The first time the channel is turned on it will turn off if the dimmer swich is pushed down quickly it will turn off. After that it only backs down to about 40% and wont come down any more.

 

[icewolf08]

I have been holding off on posting in this thread because of a couple things. Mostly I was trying to compose some thoughts.

First off, I know that we preach safety, but most modular dimmer racks are designed such that cleaning them can be done safely and with relative ease. I know that at the moment for this thread it is a moot point (given that the cleaning has occurred before my posting), but given some of the things that have come up in this thread about cleaning dimmer racks it makes it sound like on one should be cleaning their own racks. I have seen dimmer rack disasters (luckily only resulting in damaged tools), but only when people have done stupid things.

Now, as for solving your ghosting problems, you should try swapping the position of the affected module with a working one. If the problem follows the module (i.e. some other channel than the one you said was a problem now has the problem) then you know that the module needs replacing. If the problem stays with the same output then chances are the rack controller has an issue.

Here is a quick why this works: The modules are essentially dumb, they don't know what number they are or what they turn on and off. The rack controller takes the information from the console or architectural controllers and tells the dimmer in a given slot to turn on or off. Dimmers are controlled by their position in the rack. To wrap this up, it means that you can take the first module and swap it with the fourth and it won't change what comes on when you bring up a channel on the console.

The other thing that is worth checking (though I don't know if it is even possible with your gear) is to see if you have a dimmer profile set up for that particular dimmer either in the board or in the rack controller.

 

[Synchronize]

Yeah, after all of your warnings, I was quite unimpressed with the "HUGE AMOUNTS OF ELECTRICITY" and the implied amount of danger. I'm pretty sure that there was more danger of getting my ID sucked into the shop vac and strangling me. I'll try switching the modules in the next couple weeks. Spring break started and I'm leaving for a cruise on Saturday. XD

 

[TimMiller]

have fun. You may have a bad fader on your console also.

 

[gafftaper]

Yeah, after all of your warnings, I was quite unimpressed with the "HUGE AMOUNTS OF ELECTRICITY" and the implied amount of danger. I'm pretty sure that there was more danger of getting my ID sucked into the shop vac and strangling me. I'll try switching the modules in the next couple weeks.

I told you early on in this discussion that you won't be all that impressed when you see it done. Done safely and properly, it's not a big deal but done casually without knowing what you are doing... and let's be honest when we started this thread you didn't know what a dimmer rack was... it's VERY dangerous. Now that you guys know what you are doing swap modules. if the problem follows the module. Lock out, tag out and take the bad module to the nearest theater dealer for repair.

 

[Synchronize]

have fun. You may have a bad fader on your console also.

We considered that too, so we tried it on the wall controler. Same thing, it only backed down to about 40%.

 

[Synchronize]

Lock out, tag out and take the bad module to the nearest theater dealer for repair.

That would be very hard to do considering that it is an auditeria and the cafe (or house) lights are controled by that dimmer rack as well. If we lock out then the cafateria will have no lights, and I'm quite sure that the administration won't be too fond of that. Is it safe enough to remove the module then turn the power back on with a missing module, lock the dimmer rack, then lock the booth?