# how stuff works (dimmer racks)



## itie (Dec 24, 2009)

hello CB,

so i got my high to open up the door for me into the dimmer room (no one in the fine arts department has the key). i have been in here before i just don't understand how it works. so i took some pics and want to ask you guys. from what i have read all i know is that each fixture goes to a dimmer. since our school is on a 1 to 1 patch im guessing that fixture 5 goes to dimmer 5. i would like to know more about how the dimmer rack works and what this blue box is. one last question why do the dimmers skip around in the rack? wouldn't it be easier to put them in order.

thank you
giovanni 
oh yeah our school opened 4 years ago so everything is about 4 to 5 years old.


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## Les (Dec 24, 2009)

Seems like I _may_ have been proven wrong on this, but as I understood it, the dimmers skip around to balance the loads. Someone please correct me if I'm wrong. 

The blue box looks to be a type of transfer switch for the houselights. Either that or an architectural control similar to the ETC Unison system.

In a 1:1 patch, yes, channel 1 = dimmer 1. When you are looking at those modules in the rack, remember that each one contains two independent dimmers.


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## MaxS (Dec 24, 2009)

Les said:


> Seems like I _may_ have been proven wrong on this, but as I understood it, the dimmers skip around to balance the loads. Someone please correct me if I'm wrong.



Yes, this is correct. The circuits are jumbled around in order to alleviate imbalance between phases. If you were to (please don't) remove all of the dimmers in the rack you'd most likely see 3 large, copper plates labeled A, B, and C along the left side, going top to bottom. These busbars are HOT, and supply power to the dimmers that clip into them. By rearranging circuits, it is more likely that phases will be balanced around the theatre. Usually dimmers 1 and 2 will be at the top of the Ø1 supply, 3 and 4 at the top of Ø2, and 5 and 6 at the top of Ø3.

To the OP: As far as the technology behind dimming, a good discussion took place in this thread a few weeks ago.


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## itie (Dec 24, 2009)

ok thank you for the quick replies. i skimmed through that post a couple of weeks ago, it seem to me that it was more on the dimmer themselves. i am wondering more about how to operate the whole rack. like is there anything that needs to be maintained periodically, or if there is a problem what should look for. and about our house lights, to my understanding they go through the dimmers. i can control them on the light board and they have there own dimmer number. 

thank you 
giovanni


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## sstolnack (Dec 24, 2009)

I think possible for the houselights to be in normal dimmers as well as going through an architectural system like Unison. Your setup looks similar to my highschool, and we do have a box thing (it's black, not blue) that has our Unison system control panel thing. What does the little screen thing say on the blue box? You could try searching any brand names (does it say Levitron?) and see if they have any products that look like that.


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## Studio (Dec 24, 2009)

Les said:


> The blue box looks to be a type of transfer switch for the houselights. Either that or an architectural control similar to the ETC Unison system.



The Gray box next to the blue one with 3 buttons and three lights looks more like an emergency transfer, the blue box could be a lighting control system the box says leviton and is a a-2000® Cabinet

a-2000 Cabinets > Dimming Panels > Dimmers (commercial) > Commercial Lighting > All Leviton Products from Leviton Electrical and Electronic Products


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## SteveB (Dec 24, 2009)

itie said:


> hello CB,
> 
> so i got my high to open up the door for me into the dimmer room (no one in the fine arts department has the key). i have been in here before i just don't understand how it works. so i took some pics and want to ask you guys. from what i have read all i know is that each fixture goes to a dimmer. since our school is on a 1 to 1 patch im guessing that fixture 5 goes to dimmer 5. i would like to know more about how the dimmer rack works and what this blue box is. one last question why do the dimmers skip around in the rack? wouldn't it be easier to put them in order.



The blue box is a Leviton a-2000 architectural dimming cabinet, probably 24 dimmers, probably the house lights. It's sometimes cheaper to use architectural dimmers rather then stage dimmers in an application such as this. One common reason is it's typical in many situations for permanently wired house lights to be on 15 amp/1800w branch circuits. There are a lot of inexpensive dimmers designed for architectural use in that load size. Stage dimmers are at minimum usually sized as 20amp/2400 watt dimmers or larger (breaker/choke/solid-state-switching-relay/internal wiring). When stage dimmers (ETC Sensor, Strand, Brand X, or the ones show) are used for 15amp loads, the only thing that changes is the individual circuit breaker(s) on the module, which will be sized down to 15 amps to match load and wire sizes. Thus there's a bit of a cost penalty using a dimmer otherwise rated at 20 amps, in a 15 amp application. 

a-2000 Cabinets > Dimming Panels > Dimmers (commercial) > Commercial Lighting > All Leviton Products from Leviton Electrical and Electronic Products

The reason stage dimming racks have dimmers skipping around in terms of location in the rack - I.E. why they are not in sequential order, top to bottom, is as others have stated, to distribute the dimmers evenely across the 3 power feeds (3 phase). With a standard circuit breaker panel, the a-2000 is a typical industrial design, the power gets to the individual circuit breakers via internal copper buss bars that are sized for the maximum load of the panel. A (commercial) circuit breaker panel has typically 3 phases/feeds of power and these buss bars sit next to each other laterally in the panel, behind the breakers. Having them side-by-side takes up more room laterally, but requires less depth, which is useful for standard building distribution where the closet/room the breaker panel sits in HAS to have a 30" wide door, thus there's often plenty of room side to side, but possibly less depth.

High density dimmer racks have the buss bars spaced vertically, with A phase in the upper third of the rack, B phase in the middle, and C phase in the lower third. The racks are deeper to allow room for all the feed and load wiring inside, with the dimmers and control electronics module mounted in the front of the rack for easy access. The racks are taller to cram in as many dimmers vertically as possible taking up as much height as a room can offer. The racks take up less room side-to-side to allow more dimmer racks to sit adjacent to each other. The dimmers in the 1.8kw and 2.4kw sizes are mounted in pairs on a module, thus you get dimmer 1&2 (phase A) on the very top, 3&4 (phase B) somewhere in the upper middle, and 5&6 (phases C) in the lower, etc... splitting up this way helps balance the load across all 3 phases. 6kw and 12kw dimmers are on individual modules and take up the same slot as a paired 1.8 or 2.4, or a 12kw can take up 2 vertical slots. 

Your 2 racks look like Colortran iSeries racks, with 192 dimmers 96 ea on 48 modules), probably 2.4kw each.

Steve B


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## derekleffew (Dec 24, 2009)

itie said:


> ...i am wondering more about how to operate the whole rack. like is there anything that needs to be maintained periodically, or if there is a problem what should look for. ...


See the information at Welcome to iseriese.com - help for the production lighting professional!, specifically the information on page 35 of the iSeries Installation and Maintenance Manual.pdf. I'm not suggesting a HS student attempt this himself, but bringing the need for maintenance to the appropriate person along with an offer to assist may get results. The best thing you can do for your dimmers is keep them clean and cool.


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## DuckJordan (Dec 25, 2009)

What i am concerned with is why a fine arts teacher does not have a key to this room... in an older theater especially with colortran systems i have found that they like to over heat and get filled with dust... even though colortran is not as touchy as some other systems, i have gone through a few shows where the lighting system has gone berserk. this required us to do a hard shutdown and restart of the system with "emergency" stage lights plugged into standard edisons. its a huge warning sign to me that the only ones in your building who have knowledge to run these lies within the custodial staff.


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## starksk (Dec 25, 2009)

derekleffew said:


> See the information at Welcome to iseriese.com - help for the production lighting professional!, specifically the information on page 35 of the iSeries Installation and Maintenance Manual.pdf. I'm not suggesting a HS student attempt this himself, but bringing the need for maintenance to the appropriate person along with an offer to assist may get results. The best thing you can do for your dimmers is keep them clean and cool.



*Especially page 35!* Even if you can't find a maintenance staff member to power down the rack to clean the interior of the rack, cleaning the filters on the doors will still go a long way to improving the life and health of your dimming system. (And from the looks of the picture, they could use a good cleaning!)


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## Footer (Dec 25, 2009)

Having the houselights in your dimmer rack is actually a good thing. If you are in a HS enviorment where the houselights are on 12 hours a day, that means your rack fans are also on 12 hours a day. That brings in a lot more dust and causes you to clean your rack more often. 

If the room is sealed off, your maintenance cycle is much less involved then if your rack is onstage. Keep your filters clean. You can do that yourself. If you stay on top of that, you won't have to take the rack apart all that often. 

You can check on the dust status by* first turning off the two breakers* of one of the dimmers and pulling it out. If you see it caked with dust, might be time to do some cleaning. Put the dimmer back and turn the breakers back on after the dimmer is completely seated. Call the shop that installed the rack to give you a hand with the cleaning if it needs it. I would pull "samples" from around the rack, one at a time, to check the dust situation whenever you clean the filters. 

If it looks like this... time to clean...


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## starksk (Dec 25, 2009)

Footer said:


> You can check on the dust status by* first turning off the two breakers* of one of the dimmers and pulling it out. If you see it caked with dust, might be time to do some cleaning. Put the dimmer back and turn the breakers back on after the dimmer is completely seated. Call the shop that installed the rack to give you a hand with the cleaning if it needs it. I would pull "samples" from around the rack, one at a time, to check the dust situation whenever you clean the filters.



I would still recommend powering off the rack due to the arc flash potential. (This is manditory if you are following NFPA 70E, unless you are wearing proper protection.)


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## photoatdv (Dec 26, 2009)

I haven't read the manual, but I thought the sensors were hot-swapable. In fact aren't those the ones that the CEM's can be hot-swaped? Pardon me of I'm being crazy.

If the breaker is powered off and therefore under no load, how would there be a potential for arc? My understanding is it results from a large current being broken...


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## Sony (Dec 26, 2009)

photoatdv said:


> I haven't read the manual, but I thought the sensors were hot-swapable. In fact aren't those the ones that the CEM's can be hot-swaped? Pardon me of I'm being crazy.
> 
> If the breaker is powered off and therefore under no load, how would there be a potential for arc? My understanding is it results from a large current being broken...



Yes they are hot-swappable, however you should NEVER hot-swap a module unless absolutely necessary. (i.e. under show conditions where you cannot turn the rack off) It is always better and safer to completely power down the rack when swapping modules. So yes you are correct, at least with ETC Sensor and Strand CD-80 Supervisor racks. I cannot vouch for any other rack as those are the only types I've used on a regular basis.

When cleaning your rack it is ALWAYS, *NO EXCEPTIONS*, required that you COMPLETELY power the rack down. Because when you remove multiple modules you expose the copper bus plates, which carry enough current to most likely kill everyone in your dimmer room just due to the arc flash should anything come into contact with an energized plate.


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## starksk (Dec 26, 2009)

photoatdv said:


> If the breaker is powered off and therefore under no load, how would there be a potential for arc? My understanding is it results from a large current being broken...



The potential exists where the module connects to the energized phase bar.


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## derekleffew (Dec 26, 2009)

Sony said:


> ...So yes you are correct, at least with ETC Sensor and Strand CD-80 Supervisor racks. I cannot vouch for any other rack as those are the only types I've used on a regular basis. ...


Colortran ENR and iSeries are remarkably similar to Sensor in design, for good reason.


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## itie (Dec 27, 2009)

thank you guys for all the info. im going to read the manual twice before doing anything. but there is no one at my school who knows anything about theatre lighting the maintenance staff comes to me when there is a simple problem with the lights (like the need to change a lamp). so i will clean the filter in the doors first then try powering down the rack and remove one module to check the dust behind them. i assume that there will be plenty of dust because they haven't been cleaned since they were installed 5 years ago. do you guys recommend keeping the doors closed because like i said we don't the key to the room, then the doors on the rack are on a pressure lock but the school doesn't have the key to the lock i think county maintenance staff has them cause they were in there on day and left them open. next time i got that door open i asked the head of the custodial staff if he had the key to them and he said he didn't. 

now we have some channels that are not working and if i plug the fixture into another channel they work do you think it could be from the dust?

thank you
Giovanni


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## mstaylor (Dec 27, 2009)

Maybe, but the thing to do is to clean everything, then test it. If the dimmer still doesn't work, swap it into another slot and see if the problem travels with the dimmer or if it just that slot. Once you find out which it is then you can contact your supplier for repair. 
MAKE SURE YOU ARE NOT ALONE WHEN WORKING ON DIMMERS.


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## itie (Dec 27, 2009)

yeah i was planning on having the head of the custodial staff there cause i dont want them to think that a broke when it was not working all ready. plus once they see the condition they are in maybe he will get the school to call a pro company to clean them. one can wish 

thank you 
giovanni


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## DuckJordan (Dec 27, 2009)

the head custodian should have a universal key to the building that key should open the door it doesn't make sense to me to have a person who isn't often in the building to have the only key to the door. if that is the case talk to your principal at the school and tell him the need to have someone on site at most times to be able to open that door if not have the key on the drama depart heads keys. the worst thing that can happen is during a show your lights go out and its a breaker on the dimmer pack that you can't get to because the school thinks its unsafe to let responsible adults have the key to get to the room.

That being said, i would point him to this thread if he has any concerns or questions regarding letting someone in the building have the key and it may be over him that doesn't want the key in the hands of a teacher but its a very useful thing instead of having to call someone to get down to the theater in the middle of a show to reset a dimmer pack.


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## kicknargel (Dec 28, 2009)

And when we say "power down the rack"--there should be a service disconnect in a separate box with a large frankenstein handle that cuts power to the rack. Definitely have a building engineer do it--wouldn't want to accidentally shut down a wing of the school!


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## Anonymous067 (Dec 28, 2009)

kicknargel said:


> And when we say "power down the rack"--there should be a service disconnect in a separate box with a large frankenstein handle that cuts power to the rack. Definitely have a building engineer do it--wouldn't want to accidentally shut down a wing of the school!



That wouldn't put you on the good side of the staff in terms of getting another staff member a key to the dimmer room if you're dropping power to the school. Also-I've always been told to let custodians deal with breakers (for liability reasons...).


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