Control/Dimming Dimmer Wiring

[marcusianl]

During the renovation at our school's theatre this past year we received a new Sensor+ Dimmer rack. However, when wiring our FOH catwalk, they didn't run new Dimmer lines, they just ran new cable through the existing ones, so we only have 6 Dimmers on our catwalk (although we have 18 instruments and 24 outlets). Is there any way to increase the number of controllable dimmers without running more cable? I saw something on ETC's website about a Dimmer Splitter. Would that do the job?

-Marcus

 

[pdk]

It depends on what kind of fixtures you have and what your budget is. Dimmer doubling basically splits the power coming out of the dimmer into two independent 77V circuits. As far as I remember, dimmer doubling works only with ETC fixtures and you have to switch the fixtures to be doubled to a special 550W/77V HPL lamp and a special kind of twistlock connector in addition to buying the dimmer doubler itself. So basically yes, it can work in some cases and is cheaper than running new cable, but depends a lot on your exact setup. It only works on US supplies (115V 60hz) as I recall, so that might limit it as well. But generally, if running more cable is not an option because of cost or the space, then dimmer doubling can work.

 

[Footer]

Its called dimmer doubling. Essentially, you put 77v lamps in the lights (must be S4). You then attach a multiplex two-fer to the lights, and plug it in. The dimmer has to be told that it is multiplexed. You can two-fer off a multiplex as well.

Now... that being said... I hate dimmer doubling. I can not tell you how many channel checks I did in college after a 300-400 instrument hang and here "pop, pop" with 77v blowing in lights hooked up to 120v. If its not organized well, it can become a real headache real fast. It is however much cheaper then running new dimmer lines.

 

[derekleffew]

...and is cheaper than running new cable, ...

...It is however much cheaper then running new dimmer lines.

Disagree with the above as it depends on the circumstances. If the dimmers already exist or a less than fully-populated rack, and space available in the conduit, dimmer doublers would cost more, when one figures the cost of the lamps, connectors, DimmerDoubler, and the forever hassle of patching, non-standard lamp, etc.

#12 (or #10) THHN is inexpensive and I'd rather pay the labor once to pull it than for the rest of the dimming system's life (10-30 years?) deal with dimmer doubling.

 

[JD]

Have to agree with Derek. There are limits to the number of runs you can pull through a given conduit size, but even having additional conduit installed may be cheaper. Pipe is cheap, and unless they have to go through a block wall, they can simply duplicate the current bends and path taken. Depending on the school and the turnover, newbies would have to have DD explained to them, otherwise the consumption of lamps may go through the roof.

 

[marcusianl]

We are running on S4's and it's a pretty simple setup (only about 50 instruments hanging currently) but I'd like to be able to avoid the hassle and paperwork of requesting new lamps, different connectors, and the doublers, so maybe I'll ask about wiring new dimmers. Would it be a horrible idea to run the cable along a wall without being in an actual wire tube? The way our space is set up we could potentially run cable through a hallway into our FOH catwalk. It would probably be about a 200 foot run, maybe a bit more.

 

[jmabray]

You would be in violation of your electrical code not running it in EMT (Empty Metal tube) AKA Conduit. Theatres get away with running extension cables from one outlet to power a fixture because it is a temporary set up. When you get into running circuits like you are talking about, you are moving from temporary to permanent and it must be done according to code.

 

[marcusianl]

Figured as much. I highly doubt we'd be able to get the school to contract someone out to run the wiring seeing as the work order for the renovation that just happened was placed in 1992. Gotta love bureaucracy :/ For now I guess we'll just have to deal with it. Thanks for the help everyone

 

[derekleffew]

Weren't you the one asking what to buy given a windfall of a few thousand dollars? While not as glamorous as moving lights, investing in infrastructure is always good. I'm guessing adding six more dimming circuits could be right around $1500-$2500.

I realize there may be politics and procedures involved. In some cases it may be possible to buy equipment, but not improvements to the building, or the reverse.

 

[marcusianl]

Yes, I am the same person, and that's exactly my dilemma Derek. My administrators don't know that being able to control my lights in sets of 2 or even 1 as opposed to 4+ is far more important than new toys to play with, and seeing as I'm only a student I can't exactly tell them they're wrong. They respect that I'm one of the few people in the school who know how to run things, but I still have to bow to their authority. They honestly believe that the renovation we got this year transformed the space into some magical world where anything is possible, all you need are the fixtures. While the renovation did a whole lot of good (we had about 3 working dimmers and one working mic) it wasn't the best we could've hoped for considering how long the wait was. Anyways, I'll talk to my Director/Department head and see if the Admins would let more infrastructure work fly, but I doubt it. They want to see pretty things, not efficient things.

 

[STEVETERRY]

Disagree with the above as it depends on the circumstances. If the dimmers already exist or a less than fully-populated rack, and space available in the conduit, dimmer doublers would cost more, when one figures the cost of the lamps, connectors, DimmerDoubler, and the forever hassle of patching, non-standard lamp, etc.

#12 (or #10) THHN is inexpensive and I'd rather pay the labor once to pull it than for the rest of the dimming system's life (10-30 years?) deal with dimmer doubling.

I am somewhat confused by this thread. Dimmer doubling gives you 2X the number of controllable circuits with no impact on the infrastructure--just the cost of the dimmer doubling twofers. The cost of those twofers is trivial compared to more dimmers and more circuits in conduit.

The stated problem can be solved most efficiently by the addition of dimmer doubling twofers and moving to 77 volt HPL fixtures.

As to the "pop, pop, pop" post in this thread, if the wrong connectors are used on 77V fixtures it is both a Code violation and a design flaw in the system. This falls into the "really dumb" category. In a properly designed system (like nearly every Broadway show, for instance) it will not be possible to apply 120V to a 77V fixture.

Dimmer doubling gives you twice the number of controlled circuits for a given number of dimmers and branch circuits. This sounds like the ticket in this application.

ST

 

[Footer]

As to the "pop, pop, pop" post in this thread, if the wrong connectors are used on 77V fixtures it is both a Code violation and a design flaw in the system. This falls into the "really dumb" category. In a properly designed system (like nearly every Broadway show, for instance) it will not be possible to apply 120V to a 77V fixture.

Yep, they had the famous stagepin to twist adapters on all the the dimmer doublers. I never liked in that way, it drove me up the wall.

 

[SteveB]

During the renovation at our school's theatre this past year we received a new Sensor+ Dimmer rack. However, when wiring our FOH catwalk, they didn't run new Dimmer lines, they just ran new cable through the existing ones, so we only have 6 Dimmers on our catwalk (although we have 18 instruments and 24 outlets). Is there any way to increase the number of controllable dimmers without running more cable? I saw something on ETC's website about a Dimmer Splitter. Would that do the job?

-Marcus

A non-traditional approach. Since the school is willing to purchase gear, as opposed to paying for an electrician, (with a note that while I like the Dimmer Double option, I hate the complexity in an in-house system, where stuff moves around. I also think that getting an electrician to add additional circuits, assuming the rack has spares, is the best option), possibly do the following:

1) Convert the FOH Catwalk 6 dimmers/3 Sensor modules to Sensor direct circuit breaker modules. Now all 6 circuits on the catwalk are constant power @ 20 amps, single phase.

2) Purchase 3 - Lex Products Anaconda 6x800w dimmer packs. Power the packs via the constant power outlets. Ea. dimmer handles 800 watts, which is sufficient to handle a 575w Source 4 (but not a 750w, if continuous load factors are met). Each pack requires 2 - 20 amp feeds, single phase. This would give you 18 x 800 watt dimmers at the position, for the 18 existing units.

3) Run your own DMX to the packs.

Dimming & Control: Anaconda 6 Channel 800 W Stage Pin Dimmer | Lex Products

Steve B.

 

[derekleffew]

...so we only have 6 Dimmers on our catwalk (although we have 18 instruments and 24 outlets). ...

...Dimmer doubling gives you twice the number of controlled circuits for a given number of dimmers and branch circuits. This sounds like the ticket in this application.

It sounds as though there are four outlets per dimmer. What happens if a 115V lamp is plugged into an outlet that has been designated as DD? What happens if two DDs are plugged into the same dimmer via two outlets? There seems to be confusion as to whether twofers can be used with DDs, and if two 550W 77V lamps per side is acceptable. Do the dimmer numbers become nA and nB or n and n+256? L5-15 twofers and cable as well as stage pin twofers and cable. Two types of lamps. No possibility of going to a 750W lamp.

I like SteveB's solution, and was going to propose something similar, but feel it also is too complex for a high school situation.

 

[marcusianl]

Just clarifying:

1. There are no code violations in running open DMX cable, correct?
2. Our S4's are 750w (at least they read 750 on the barrel. I've never worked with 575w's but I always presumed that the 750 indicated 750w)
3. Where would one obtain circuit breaker modules for the Sensor? Would our supplier have them?

 

[MNicolai]

Just clarifying:

1. There are no code violations in running open DMX cable, correct?
2. Our S4's are 750w (at least they read 750 on the barrel. I've never worked with 575w's but I always presumed that the 750 indicated 750w)
3. Where would one obtain circuit breaker modules for the Sensor? Would our supplier have them?

Though AHJ (see glossary) will take precedence, DMX can probably be run open because it's low voltage. However, there are sometimes specific ways you have to run the cabling. If you look above the plenum ceilings in places, in many cases you'd find ethernet and all sorts of low voltage data/control cables that would just be sitting above the ceiling. However, firefighters started noticed when they would enter these buildings that as soon as the ceiling burnt up, the cables would drop and become an obstacle to them. As such, now in many places it's required that these low voltage cables not in conduits be secured in some manner, be it in a basket or harness of some form. This may or many not be applicable to you, but understand that just because it doesn't have to be in a conduit, doesn't then mean you can run it however you'd like. Also, you will not be able to run it in existing line voltage conduits; if put in a conduit it would need to be run in an individual conduit containing only low voltage wiring.

Any Source Four rated for 750w, may also use 575w and 375w lamps. Also, they can use 77v 550w lamps with dimmer doubling. The only difference is in the lamp, not the fixture. If you want your fixtures to be less bright, or you can't afford to use as much power, then you would lamp down to lower wattages. Also, 575w lamps burn through deep, saturated gels far slower than 750w lamps, and they do not burn gobos as quickly as well. Likewise, if all of your Source Fours are using 575w lamps and you some of them to be brighter, you would put a 750w lamp in. Most modern Source Fours are rated to 750w, but PAR MCM's (metal cold mirrors) and Source Four Juniors are only rated to 575w, and some older Source Four products may contain lamp bases that are only rated to 575w, as that is how they were originally designed. The upgrade for those fixtures is simply a new lamp assembly.

Obtaining parts or products for your Sensor racks shouldn't be too difficult. Your dealers can probably hook you up. ETC is a well-known manufacturer, and though dealers may not keep extra modules sitting on a shelf on site, many will have easy access to them that you could order the parts you need through them. However, I do not understand what you mean by "circuit breaker" modules. ETC makes many different products for their dimmer racks that use circuit breakers. If you're referring to a Constant-Circuit module (ex. CC20 = constant-on circuit @ 20amps), then that is a module that will simply always remain active at line voltage.

Another reason to consider dimmer doubling though is if the fixtures on your catwalk typically remain there. I know a couple theatres that have their entire catwalks on dimmer doublers because they never have to worry about mixing their 77v and 120v lamps and fixtures up as the fixtures on their catwalk almost always remain there. Dimmer doubling is actually a very simple and relatively inexpensive option if the fixtures on your catwalk are often static and wouldn't move to 120v positions regularly. As such though, I wouldn't recommend only a partial-upgrade. If you are going to purchase dimmer doublers, get them for each and every circuit on your catwalk. If you have a mix of 120v and 77v fixtures up there, then there will be mistakes made in using the appropriate lamps at their respective voltages.

 

[JD]

Just a quick note about Dimmer Doubling:
This works because the positive half of the AC waveform acts as one channel, and the negative half acts as another. The "splitters" at the lights contain diodes, so depending on the polarity of the diode, your light either sees the positive side (channel "A") or the negative side (channel "B".) As the lamps (77v) are "effectively" seeing 1/2 the RMS (thus 77 volts) their current draw for a given wattage is double. As long as the load is balanced (equal A fixtures and B fixtures) your dimmer capacity remains the same. You should not run 2k of "A" fixtures on a 2k dimmer as your current draw would be 2x rated load on that half of the wave, and 0x rated load on the other half. Even the SSRs internally contain two SCRs and this would stress the one allocated to that half of the waveform. (Probably enough of a safety factor, but still not a good idea.)

As for plugging in a conventional 110 volt fixture without an adapter, the result would be that channel A would operate the lamp from 0 to 50%. Channel B would also operate the lamp from 0 to 50%. Operating both channels together would operate the lamp 0 to 100%. Although odd, no damage would be done.

 

[KeeperoftheKeys]

Just to quickly add to that:
Since Dimmer Doubling works the way it does it is no problem to plug in two doulers in paralel, as long as the total load does not exceed the max load of the dimmer.
Plugging a doubler into a doubler would be utterly pointless and lead to nothing.
Also the doubling is supposed to happen near the fixtures, so a outlet should not be doubled (ie the doubling is not supposed to happen at the rack), I don't remember why this is but it is not recommended to have long cable runs 'behind' the doubler...

 

[derekleffew]

... As long as the load is balanced (equal A fixtures and B fixtures) your dimmer capacity remains the same. You should not run 2k of "A" fixtures on a 2k dimmer as your current draw would be 2x rated load on that half of the wave, and 0x rated load on the other half. Even the SSRs internally contain two SCRs and this would stress the one allocated to that half of the waveform. (Probably enough of a safety factor, but still not a good idea.) ...

So I must have an equal number of fixtures on each side? Must I also run them at the same level (which would seem to negate the DD)? What if a lamp burns out, I now have an unbalanced situation--must I stop the show while I relamp it?

 

[KeeperoftheKeys]

The dimmer 'understands' that the signal is going to be duplexed and as such it will be varying the degree of chopping for each 'side' of the sine wave on it's own, so you can run each side at an individual level and I don't think that the load needs to be balanced either, you just have to make sure you don't exceed the max load of the dimmer.