Control/Dimming Balancing the 3Ø legs

[McCready00]

... for dimmers and 3phases circuits.

I'm at the point where I need to understand what is happening on this subject. I do understand the main concept of the thing but never did it by myself.

I just want to know how you guys are doing it. If you had some examples, that would be nice to.

I think it would be good for everyone to have a talk on it.

Thanks.

 

[len]

Are you talking about electrical loads on a dimmer, 3-phase electrical loads, loads on trussing, loads on pipes? You'll need to be more specific.

 

[McCready00]

oups yea sorry.. dimmer and 3-phase electrical loads

 

[icewolf08]

I think you still need to be more specific in your questions. What exactly do you want to know? Is there a specific scenario that you are looking at? Your current question is so broad it is hard to give a useful answer.

 

[len]

Well, if it's a big 48 or 96 channel dimmer rack like an ETC or Applied or Leprecon dimmer rack, you don't need to worry about it, as far as I know. Just bring in all 3 phases of power via feeder, then run multi-pin cables out to the fixtures and patch away. If you have camlocks at the wall/generator, and camlocks at the dimmer, even someone as uninformed as me can do it.

BTW, since this still is a discussion about electricity, etc., it may be a violation of the site's TOS, so feel free to edit/delete my comments as needed.

 

[JD]

Fundamentally, it is more of a patch issue as you are not talking about wiring the dimmers up, right?

Lets say you have 18 channels. Maybe 1-6 is on one phase, 7-12 is on the second phase, and 13-18 is on the third.

Balancing is just the math of the patch. You try to put the same total wattage on 1-6, 7-12, and 13-18.

Random example:
Ch 1 has 2kw on it, Ch 2 has 2kw on it, Ch 3 to 6 have no load.
Ch 7,8,9,10 each have a 1kw load, Ch 11 & 12 have no load.
Ch 13,14,15,16,17,18 each have a 750w load.
So, you load would be almost balanced. (4k, 4k, 4.5k)

There is some debate as to if any of this matters as long as you have proper feed to the rack. The only time it comes into play is if you are working with a restrictive supply, like a Gene on a portable show. The other problem is that unless you always operate all your dimmers at the same level (fat chance) it will never "actually" be balanced anyway. (The exception would be movers, which are always on anyway.)

 

[icewolf08]

Well, if it's a big 48 or 96 channel dimmer rack like an ETC or Applied or Leprecon dimmer rack, you don't need to worry about it, as far as I know. Just bring in all 3 phases of power via feeder, then run multi-pin cables out to the fixtures and patch away. If you have camlocks at the wall/generator, and camlocks at the dimmer, even someone as uninformed as me can do it.

Well, that isn't really true. Most (not all) INSTALLED racks are designed such that balancing loads across a three phase system is done "automatically." How? Look at an installed rack and usually you find that the dimmers don't go in numerical order. Take installed ETC Sensor dimmers for example. Dimmers 1 & 2 are on phase A, 3 & 4 on B, 5 & 6 on C, and so on. This is done because it is assumed that you may not use every circuit all the time, and every circuit may carry a different load. So by dividing up the dimmers as they do, they effectively "randomize" and somewhat balance the load (unless you only use dimmers 1,2,7,8,13,14, etc.).

On the other hand, most (not all) touring or portable racks are just wired in numerical order with the first third on one phase, the second third on phase B and the third on phase C. In this case, you want to try to balance your loads across the three phases, meaning you want to have as close to the same total wattage on each phase.

This is pretty oversimplified, but I think that the OP still needs to ask more pointed questions, the field is still too broad.

 

[derekleffew]

...On the other hand, most (not all) touring or portable racks are just wired in numerical order with the first third on one phase, the second third on phase B and the third on phase C.

Not quite. The most popular dimmer line in the world's touring racks are wired as follows:
ØA:1-8, ØB:9-16, ØC:17-24,
ØA:25-32, ØB:33-42, ØC:43-48.
Repeat the pattern for 72- and 96-way racks. Ever notice the dimmer holes are colored black, red, and blue in the pin patch bay? See attached.

ML PDs are usually (but not always) wired XY: 1-2, YZ 3-4, ZX 5-6. A common mistake is when electricians make all their spare circuits either 6, or 5&6, as very few PDs have patchable circuits, thus guaranteeing the blue phase will be "low". McCready00http://www.controlbooth.com/forums/members/mccready00.html, see this post regarding determining load of 208V moving lights.

Loads should be planned so that the lowest leg is no less than 75% of the highest leg. Obviously, one cannot balance incandescent loads for every cue, but one should avoid having all the frontlight on one leg, all the backlight on another, the cyc on the third, etc.; as well as a three color wash distributed as Leg A,B,C. Only the Master Electrician cares what the dimmer numbers are, so this falls squarely on his/her shoulders. It's much more critical in a portable situation, where one is dealing with feeder in open air and Main Circuit Breakers or Fuses of questionable age and reliability *cough*Hotel Ballrooms*cough*, than in a permanent installation, where one hopes a competant electrcial engineer has taken this into account for you.

 

[rmarston]

It's simple really isn't it - balance the lighting load between the available phases. Easier said than done. Just because you patch the plot evenly between the phases does not mean that anywhere in a given show the cueing will result in an even phase load. So - when patching a show some consideration has to be given to the show cueing.

 

[GoboGuy]

every once in a while i need to do a show somewhere that doesn't have enough power to fully load up the dimmers. I have to make sure that my cues don't pull more load than the house can supply and i have to balance the load across the legs.

there's one theatre in town, for example, that has a single phase 100amp service and I use a [email protected] ETC sensor rack. Ya gotta make sure that you don't go over 100amps on each leg of power (checking each of the cues). I use an amp meter and step through each cue and check all the legs. This method is also very common when using generators... you have to make sure that you balance the load so that you are using the generator as evenly across it's legs as you can... or it gets really cranky (pun intended)

in general you should always try to spread out your lamps across the legs, but sometimes designers don't let you know that they are going to use all of the 2k circuits on phase B and none on phase A. So, if you check each cue and test the legs, you can move your lamps around to different dimmers to balance it all out.

 

[TimMiller]

between the dimmer rack patch, and the console patch, you can balance your loads pretty evenly, and keep the designer/board op happy. Also having balanced legs, keeps your neutral - ground voltage down. I was at a place once where they were running all of their welders off of a single phase panel, but they had three phase service, the load kicked the one leg off so bad, that i was measuring about 40V between neutral and ground.