Electricity Question: Dimmer Feeds

[STEVETERRY]

OK, many things to respond to:

1. There is not much cost difference between a 2400W phase-control dimmer and a 1200W phase-control dimmer--and there never will be. That is why you have not seen 1200W dimmers appear in any significant quantity. Also, imagine a system of 1.2kW dimmers where just a few 2.4kW dimmers were needed. How and where do you deploy them in a way that makes sense? Sure, a 1200W sine wave dimmer costs a lot less than a 2400W sine wave dimmer--so power reduction makes sense in a sine wave environment. But, as we have seen, demand for sine wave dimmers in North America has been minimal. "Sine wave is the party that the dimmer manufacturers gave where nobody came".

2. I am still in favor of power de-rating at the highest possible level to assure the maximum current to any given dimmer rack. This avoids "cables from the balcony rail to the cyc".

3. It is clear that the smaller the system, the less opportunity for feeder de-rating. A single rack system might need less de-rating, but even 600A to a single rack is hard to justify when presented with the results of the load survey.

4. I still like the idea of saving money by rack-to-rack bussing rather than full-sized breakered feeds to each rack.

5. #14 AWG is allowed for 15A circuits.

6. NYC Code is now the same as NEC, except for a few amendments.

7. New sources for the future will draw less current. It's hard to justify excessive feeder sizes when you consider the additional cost of HVAC capacity.

8. Yes, we have known each other for more than 30 years. It means we're both just old farts.

ST

 

[STEVETERRY]

SteveB , STEVETERRY tells me I'm wrong all the time. It's something one becomes accustomed to--an acquired taste, if you will.

Truth be told, you're also right a lot of the time.

ST

 

[SteveB]

Yeah you totally lost me with that...

It's all about breaker de-rating. Circuit breakers that power incandescent lighting loads and that operate for more then 3 hours, need to be de-rated, so that you never see a load that is more then 80% of the capacity of the breaker. Now not all facilities are going to operate their incandescant lighting system for 3 consecutive hours, with all the circuits parked at 100%. But some times they do or come close, with TV and Film facilities being a typical example. And sometimes you get an odd European designer that wants a lot of white light and you sit in rehearsal all night in the same ****ed cue, and well you get the idea...

If you have a Sensor 48 module dimmer rack, with 96 dimmers @ 2400 watts per dimmer (and are in a US/Canadian facility with 120 volt line voltage), then you have a connected load of - 96x2400=230,400 watts, divided by the line voltage of 120 = 1920 total amps required to power every dimmer on at the same time. Since these systems are typically supplied with 3 phase power feeds, the amperage draw per phase is 640 amps (1/3 of the amperage total). That's what you need to keep the rack powered with every dimmer loaded full. When you account for de-rating of 20% you need to size up the main breaker accordingly, which is 800 amps per phase, which is why the buss bars in the back of the Sensor rack are rated at 800 amps and why the rack is rated at 800 amps per phase.

When you choose to not power the rack with an 800 amp, 3 pole breaker, a common occurance, you then start to deal with the potential for every dimmer not being able to be loaded to full, if you assume you use every dimmer. I would venture to say that the smaller the system, say 1 or 2 racks, the more likely that every dimmer gets used, where as with larger systems, say 4 racks or more, that many of the dimmers are occasional use only, though this a is huge assumption and is certainly not true in all instances, but mostly an observaton that facilities with multiple rack numbers often have a lot of spares located around the facility that are occasional useage only.

So lets say you install a 400 amp main breaker for a 96x2.4kw rack. De-rating the breaker 20% yeilds 320 amps per phase/960 total and if you then use every dimmer, you can only load a typical dimmer to 1200 watts/10 amps average. Which might just be fine if your entire inventory consists of 96 S4's @ 750 watts and you only load one fixture per dimmer.

The minute you start adding fixtures beyond 96, or you start using strip lights @2250 watts per circuit, you need now to start being aware of the main breaker limitation, which is something you don't have to pay as much attention to when the breaker rating is closer to the rack rating.

 

[derekleffew]

Here is a real-world example of how important knowledge of the loading and phasing of a dimmer rack can be.

Attached is a map of the power layout:
View attachment CorpShowPower2Map.pdf
Two hours before doors, in the midst of programming and client walk-throughs, we noticed the 100' 4/0 feeder getting warm.
Hot, actually, as in too hot to comfortably hold, along its entire length, but hotter nearer each end.
The black leg measured 405 amps, red was ~350, and blue was ~250.
Turns out the Production Electrician didn't know how the dimmer rack was phased.
Moving a multi, (12 lamps) from the black phase to the blue brought us into tolerable range, as the numbers on the map reflect.

Even though the dimmer rack was only powering 66 575W lamps, the distribution of those lamps across the phases became critical given that the same service was also powering 60+ moving lights. This was a party, and the conventional lights were being used to light decor, so one had to expect that all the lamps would be at Full the entire evening. As it turns out, the LD decided to run them at about 80%, which was a help.

 

[xander]

This thread turned into a very interesting conversation. Thanks to Steve B, Steve T, and Derek L for sharing their wealth of knowledge with us, shall we say, less worldly folks.

-Tim

 

[Footer]

Going back to the OP here and the DF50AF modules. I can only assume the DF50 module was made as a retrofit option for venues that have a large number of 6k dimmers and was never intended for use in a new install. I would also have to assume that they were not intended to FILL a 96 rack.

 

[sk8rsdad]

We have a relatively new install and have a single D50AF in the rack for our the overhead house lights (12x500W). I expect other venues may use D50AF's for similar loads.

 

[starksk]

Going back to the OP here and the DF50AF modules. I can only assume the DF50 module was made as a retrofit option for venues that have a large number of 6k dimmers and was never intended for use in a new install. I would also have to assume that they were not intended to FILL a 96 rack.

D50AF Modules are used in new installations every day. They can be used to fill an SR48/SR48+ rack. The catch being that they are single density (one dimmer per slot, not two), need to be installed by a certified technician if the rack wasn't preconfigured at the factory, and require the load wire to be sized appropriately. An install rack full of D50AF modules, while not overly common, has been installed in several venues.

And, yes, you can have a rack full of D100AF modules too. Those modules are 1/2 density (take up two slots for 1 dimmer) and also require special configuration of the rack as well as appropriately sized load wire(s).

 

[derekleffew]

Footer and sk8rsdad , it's D50 or D50AF. A DF50 is a hazer.

@ starksk, has ETC ever built a TR24 or TR48 with D50 modules? Did it have Socapex outputs and patching, or just 2P&G-60A direct outs? How about an SP6 with D100s?

 

[Sony]

Going back to the OP here and the DF50AF modules. I can only assume the DF50 module was made as a retrofit option for venues that have a large number of 6k dimmers and was never intended for use in a new install. I would also have to assume that they were not intended to FILL a 96 rack.

I know of several brand new installations that have D50AF modules, one of them is Newton North High School where I work, which was just completed this month, another I know of is Trinty Repertory Company. At NNHS the D50 modules are used exclusively for house lights, however at TRC we use the D50 modules to power 15" 5k Arri Tungsten Fresnels that are used in almost every production we do there.

Footer and sk8rsdad , it's D50 or D50AF. A DF50 is a hazer.

@ starksk, has ETC ever built a TR24 or TR48 with D50 modules? Did it have Socapex outputs and patching, or just 2P&G-60A direct outs? How about an SP6 with D100s?

I don't know about D100's but I know Trinity Repertory Company has a SP6 full of D50's which we use for powering the 5k Arri Fresnels in the smaller of the two theatre's. The upstairs theatre has dedicated D50's in the 4 SR48 racks, but the smaller theatre uses 3 TR48 racks and a SP6 for it's dimming needs.

 

[starksk]

@ starksk, has ETC ever built a TR24 or TR48 with D50 modules? Did it have Socapex outputs and patching, or just 2P&G-60A direct outs? How about an SP6 with D100s?

Yes. There have been several different configurations of touring racks built. The standard output method is the 2P&G-60A for 50A modules but there are other custom options available.

As for the SP6 with D100AF modules, it is a standard item with 2P&G connectors. (It is also available as a standard item for the SP12 size pack, and both sizes also have a standard part number for being fully populated with D50AF modules)