Electrics and Wiring Questions

[HEJL]

Hey CB,

You have been really helpful on a previous post, so I thought I'd pitch this one out there as well. I've got some meetings with designers, ME's and engineers coming up, and I like to go into meetings with a basic understanding of the topic at hand. It leads to more fruitful discussion and less frustration on both sides. I will not be installing this myself, and final plans will be made by certified electricians.

THE PREMISE:

We're building a small rental theater, blackbox, new construction. Pipe Grid, 18' high, no catwalk. Floor plan of whole room is ~30' x 40'.

We're a small operation, so figure 8 Source4s and 12 Fresnels to start with. Also figure companies will bring in their own equipment, but we're working with independent local companies, so probably not anything elaborate.

I'm looking at 100 amps, 240v single-phase power dedicated to lighting.

QUESTIONS:

Is there anything in what I wrote that glaringly does not make sense?

Do you think that'll be enough power to get the job done?

Can single phase handle the job or should we look to upgrade to 3-phase? What is the advantage of 3-phase power when it comes to lighting? (It is also very expensive to make this upgrade.) (Also, to save you the typing, I do know roughly the technical difference between single and 3-phase, just not the advantages for lights.)

If we have single phase power and the option for the circuit to be either 120v or 240v, should we go with one 240v 100A circuit, or two 120v 100A circuits? I am under the impression that in the US, when you ask the city for 240v (to run a washing machine, etc.), they combine two single-phase circuits with some power loss due to the electricity frequencies being out of sequence. Is what I just said nonsense? If it is sensical, wouldn't it be more efficient to have two 120v's instead of one < 240v?

I'm looking to install some dimmer racks. Does anyone have recommendations on what kind would be suitable for a space our size? I'd like to get about 40 channels, 600W. Does this sound sufficient?

Thanks, as always, for your expertise.

-HEJL

 

[JD]

Wow, where to start....
Single phase will give you 2/3rds the power of three phase at any given ampacity simply because there are two hots as compared to three. Other than that, there are no disadvantages to single phase power.
The 120/240 volt question does not come into play. You will have two 100 amp legs coming from a 100 amp two pole common trip breaker. Both legs will measure 120 volts to neutral and that is what your lighting equipment will be using. Between the two hot legs, there is 240 volts, but that is a non factor unless there is a specific piece of equipment that requires 240 volts. (Doubtful.)

With the 20% de-rate rule, you will have a continuous running capacity of 19,200 watts on single phase power. (80 x 2 x 120) This does not limit the amount or rating of the dimmers, it simply limits the fixture inventory that can be handled if you were to turn everything on at the same time. (Note- the de-rating has to do with the characteristics of the breaker, not any loss.)

Most common dimmer channel rating is 2.4Kw (20 amps) Dimmers are often used that are smaller (1.2kw) but outside of shoebox dimmers, 600 watts is not too common.
The most logical dimmer layout would be 24 channels at 1.2kw. This would be giving you a dimmer per circuit. Most fixtures are 550 watts or 750 watts. Even assuming you were running (24) 750 watt fixtures, your current draw would be below 80 amps per leg.

These are just some general guidelines, there are exceptions, but it is a good starting point.

 

[porkchop]

I'm no linesman, but when you're talking about 208V single phase in entertainment (what I assume you are getting at by saying 240V) you're usually talking about two different phases of 120V power. I would talk to an electrical installer or consultant and see if the 3rd leg is really that prohibitively expensive. You may not need the power now, but especially if you're dealing with other company's equipment you need to be prepared for anything, and 3 phase power distribution is pretty normal in my experience. I can't imagine a fixture you would use in that space that would need three phases, but you certainly couldn't run any of my distros on the power connection you're talking about.

As far as the dimmer racks go look at your math again. 600W x 40 circuits is 24kW or a total of 200A assuming 120V power. That alone would require two 100A services (assuming you don't go for 3 phase power) and I am unsure if you can even wire a dimmer rack like that in a manor that is more cost effective than the more traditional 3 phase configuration.

In a space that size I could certainly see having some built in lighting and a 100A 3-phase company switch as a reasonable amount of power, but that would probably require a 3-phase 200A power run to the facility which it sounds like you might really have to work hard to get. I think it would be worth it, especially if you're already anticipating dealing with other companies equipment, but people that have to answer questions about money don't always see things the way I do.

There's my 2 cents

 

[JD]

I'm no linesman, but when you're talking about 208V single phase in entertainment (what I assume you are getting at by saying 240V) you're usually talking about two different phases of 120V power

He might want to get that metered before the meeting. If it is 208, then he does have three phase service and the cost of bringing that to the stage would be worth it. On the other hand, if it comes up as 240 volts, then he truly has single phase service and the building service would have to be changed which is a lot more money.

 

[JChenault]

Well - Let's walk through this and do some analysis. I will attempt to show you my steps so you can tweak it to fit what really makes sense for you.

I'm addressing the issue of power here. Getting power wrong is one of the hardest things to fix.


First of all - let's pick a stage / audience arrangement that is moderately difficult to light. The space is 30 x 40 feet. Let's put in a thrust stage with audience on three sides. Three rows of audience is about 9 to 10 feet - so the acting area I need to light is about 20x20 feet.

Now how many areas will I need? If I plan for three areas accross, each area is about 7 feet which for a grid at 20 feet seems about right. If I tried to do it with two areas, we would be at a 10 foot area which seems too big. I would be willing to go to around 8 feet, but more than that, with the lights as close as they will be to your actors faces, you would get some extreme angle changes as someone walked from area to area. You might be able to do it with 6 areas ( three wide, and two deep). It is usually better to have an odd number of areas since the center of the area is usually just a bit warmer, and directors like to put actors in the center. For now let's assume 9 areas.

How many fixtures per area. A good basic plot would have three lights for faces, and a couple of down lights ( or some kind of color mixing downlight). Let's assume we use some kind of 575 watt elipsoidal for the area lights, and 500w fresnels for downlights. So each area will need 3x575 watts + 2x500 watts for a total of 2725 watts. Times 9 gets you to 24,525 watts. But wait - there is more.

But there's more than basic area lighting. You will likely need / want some specials in your show. Let's assume 6 specials at 525 watts for an additional 3150 watts. At some point you will want to light a cyc along the back. Let's assume the cyc is 25 feet wide lit with top and bottom cyc units. Say RGB 500 Watt units every 6 feet. This adds another 12000 watts.

Let's do the math. So a quick back of the envelope calculation gives me 24,525 + 3,150 + 12,000 watts of lighting. For a total ( assuming all conventional units here ) of 39,675 watts. W= V*A so we will need 39675/120 Amps of service - or about 330 Amps.

And we have not talked about house lights yet. - so I would argue that, if you want to be safe, you should pull a minimum of 240V / 200 amp service - OR 3 phase 150 amp service.

Note - be sure that your HVAC guy sees these numbers - you will need to air condition the place with this much heat in the air.


Now you did not ask about LED units. If you consider that approach the power requirements drop quickly, but the fixture costs go up.

Have fun.

 

[Aman121]

Yeah Id be a little leery of only 100 amp service to an all conventional rig, it adds up quick. 200 amp 240 volt service will give you allot more power to play with and the ability to fire up more instruments at once. On the other hand if your going all or partially led, 100 amp service to a load of constant on outlets around the space and a small rack for houselighting and a few stage channels could work.

 

[Esoteric]

I would be VERY leery of 100A of service, even for a space that small. If you want 40 channels I would start with a 300A 3 phase service and work up from there. When we install Unison racks with 24 20A dimmers we start with a 150A 3 phase service and work up from there (we prefer to install it with a 200A 3 phase breaker). The biggest mistake we see, and where we make a ton of money is by doing electrical retrofits where too little power was initially pulled. We did a blog over a dimmer rack remodel we did where lack of power pushed the project price up 20% over what the cost would have been had there been sufficient power. We also just had a project for a new theater die on the vine because they promised city officials (and only saved money for) too small of an electrical service that would not meet their needs.

Take the electrical needs you think you will need and add about 20%.

Also, hire a theater planning and electrical professional. It may seem redundant, but 95% of architects, electrical companies, and engineers know nothing about the lighting needs of a theater. Get someone who does.

Like others have said LED brings your power requirements down, but takes your per unit cost up by 2x-3x.

 

[DavidNorth]

For the number of fixtures you are running, the 100A per phase feed is fine. However, if you EVER think you will expand, now is the time to put in double what you are asking for.

Also remember that 14AWG wire is the smallest you can pull per circuit and that 600W dimmers do not cost a quarter of what 2400W dimmers cost. In fact, in an installation rack, they are nearly the same. So decide early on what the maximum load might be that you would ever place on a single dimmer because that will determine your dimmer size and wire size.

So I think you have two decisions: what is your max load per dimmer and do you ever want to expand the system in the future. I would suggest that if your inventory is never going to change and you do not see expanding, them your 100A feed is fine and you should consider 1200W dimmers. If you plan to double the inventory, double the feed.

David

 

[HEJL]

>>>This does not limit the amount or rating of the dimmers, it simply limits the fixture inventory that can be handled if you were to turn everything on at the same time. (Note- the de-rating has to do with the characteristics of the breaker, not any loss.)

>>>The most logical dimmer layout would be 24 channels at 1.2kw. This would be giving you a dimmer per circuit.

Thanks, that was excellently helpful. If I may ask a question or two further to clarify some of what you said:
1. I will plan for 80% of what my on-paper power allotment is.
2. Would it be wise to plan based on the assumption that all lights will be turned on at some time, as a way of ensuring we will be under our maximum load? It sounds sketchy to me to assume plan that "as long as no one turns all the lights on at once, this will work". But correct me if that's how it's done.
2b. Actually, I think I get what you're saying - 24 channels of 1.2kw, as long as they were all 750w lights would keep us under 80% of on-paper allotment. So when you figure lights, you figure total load as well as per-circuit load. Fascinating.
3. I'm not completely sure of dimmer terminology. The dimmer's I've worked with were backpack style, hanging from the poles, with multiple channels in each dimmer "pack". When you say "a dimmer per circuit" do you mean each 1.2kw circuit is its own channel, so all the lights on it brighten and fade together? If this is the case... I wonder if 24 channels is enough. That sounds like an design fight for specials on the board, even if we 2-fer the wash lights and end up with 14 channels used by in-house lights, leaving 10 open for rented lights and specials. Does one 2-fer front lights in plays? Just musing that we may need to go up to 250A or 300A on the total service.
4. Great to know that single-phase is good for lights. I doubt we'll need 240v power as well.

Thanks again.

 

[DavidNorth]

Thanks, that was excellently helpful. If I may ask a question or two further to clarify some of what you said:
1. I will plan for 80% of what my on-paper power allotment is.
2. Would it be wise to plan based on the assumption that all lights will be turned on at some time, as a way of ensuring we will be under our maximum load? It sounds sketchy to me to assume plan that "as long as no one turns all the lights on at once, this will work". But correct me if that's how it's done.
2b. Actually, I think I get what you're saying - 24 channels of 1.2kw, as long as they were all 750w lights would keep us under 80% of on-paper allotment. So when you figure lights, you figure total load as well as per-circuit load. Fascinating.
3. I'm not completely sure of dimmer terminology. The dimmer's I've worked with were backpack style, hanging from the poles, with multiple channels in each dimmer "pack". When you say "a dimmer per circuit" do you mean each 1.2kw circuit is its own channel, so all the lights on it brighten and fade together? If this is the case... I wonder if 24 channels is enough. That sounds like an design fight for specials on the board, even if we 2-fer the wash lights and end up with 14 channels used by in-house lights, leaving 10 open for rented lights and specials. Does one 2-fer front lights in plays? Just musing that we may need to go up to 250A or 300A on the total service.
4. Great to know that single-phase is good for lights. I doubt we'll need 240v power as well.

Thanks again.

2. Yes, plan for all of your fixture inventory to be on at full, but not all of your dimmers. You may have more dimmers than fixtures and/or you may have more dimmer capacity [unused wattage in each dimmer] that you do not need to account for. However, if you think you will add more fixtures in the future, account for them as well. So you currently are thinking about 20 fixtures at let's say 600W. If you think you will double that for some shows, then your total load is 100A. Use the 80% derating and you have 125A per phase, bi-phase or 120/240.

3. There are shoebox dimmers that have 600W to 1200W ratings [typically] and the fixtures plug right into them. There are also rack-type dimmers in which conduit and wiring runs from their mounting location in a room elswhere up to circuit boxes with outlets in them. Typically the later are wired "dimmer per circuit" so that each outlet in the space is wired back to a dimmer in a cabinet. Rack dimmers are more expensive and typically more robust and more easily serviced. Shoebox dimmers can go most anywhere, are hard to get to, but are easily and cheaply purchased. For your application, a larger number of shoebox dimmers may give you more flexibility for the cost. Do note that you are limited by both their per dimmer wattage [600W or 1200W] and their max rating per the dimmer pack [could be 1800W, check carefully]. Does that make sense?

If you choose an installation rack of dimmers, you have one large feed and then lost of circuit wiring out to outlet boxes. For shoebox dimmers, the feed must then go to a breaker panel to knock down the currrent to 20A per outlet and then you have to run conduit to single outlets. Either will cost money so make sure to add together the cost of both the dimmers and the installation for your venue. Each venue is different.

THere should be no reason for 240V, however, some electricians will call 120V bi-phase power either 240V or 120/240V. If you say 120 bi-phase or 120/240, it will be clear. If bi-phase is there, use it. If three phase is there, recalculate your needs and use it. Do not convert from three phase to bi-phase. I'm sure you already know that.

David

 

[derekleffew]

#2. See Dimmer feeds--How much power is enough? - ControlBooth , and

See also 2011 NEC 520.53(H)(1):

The supply cords or cable (and connector assembly) shave have current ratings not less than the total load connected to the switchboards and shall be protected by overcurrent devices.

Bolding mine. Note it says nothing about possible potential load or nameplate rating. Perhaps even more on point, NEC 2011 520.27(C):

Supply capacity. For the purpose of calculating supply capacity to switchboards, it shall be permissible to consider the maximum load that the switchboard is intended to supply in a given installation, provided that the following apply: ...

Again, bolding mine.

as well as this thread: http://www.controlbooth.com/forums/lighting-electrics/29039-how-much-power-3-sensor-sr48-racks.html regarding requirements for houselight circuits.

#2b. 24x1.2kW is the nameplate rating. As explained above, in most cases, NEC allows you to instead size the supply based on demand: 24x750W. Fascinating, yes, as well as confusing.

#3. See DPC. Usually theatre circuits are 20A, each fed by a 2.4kW dimmer. The backpack dimmers with which you are familiar are more often called shoebox dimmer s: four dimmers/circuits at 600-1000W each, although the total limit on the pack is 1800-2400W.

#4. If you're going to install a dimmer rack, you'll need three-phase power. If 3Ø 120/208V power is not present, which is not unusual in commercial/residential and non-industrial buildings, will probably cost a minimum of $10K to install. The term single phase is ambiguous, which is why we have taken to using the terms split-phase and bi-phase.
So you're looking at using dimmer pack s rather than racks, which can either be portable or permanently installed. Just as well, as you won't find a dimmer rack with 600W dimmers, even 1.2s are rare. Note that shoebox dimmers can never be permanently installed. Once you start requiring the running of conduit, the labor costs can easily exceed the cost of the dimming system.

I second the suggestion above to engage the services of a professional consultant; even for a small project such as this, it's money well spent.

EDIT: Posted simultaneously with Mr. North.

 

[TimMiller]

Just to clarify, we do have several discussions of 3 phase vs single phase power and their associated voltages but I will sum it up for you and give you a few things to think about. Single phase power (120/240v) is 2 120v legs that are 180 degrees out of phase with each other so when you meter between both 120v legs you get 240v. There isn't any single magic wire that carries 240. When you call for 100 amps of single phase you are getting 2 hot legs of 120v each breakered at 100 amps so you have 200 amps total, but you can only pull upto 80% of that load without risking your breaker tripping. 3 phase 120/208 (you do not want 120/240v 3 phase power, also called 3 phase hi-leg delta) what you will get is 3 legs of 120v power but when you meter between any 2 legs you will get 208v. Which is common in most performance venues. So with 3 100a legs you have the total potential of 300a keeping in mind the 80% factor. Also you need to factor in all of your other requirements such as are you going to have a scene shop with lots of large power tools? How about dressing rooms? Hair dryers and such pull a lot of current when you get several going. Also will your space have some type of kitchen? Also how about your air handlers? Your actors, audience, and equipment generate a lot of heat. 3 phase motors are a lot more reliable and energy effecient than their single phase counter parts. Also keep in mind the sound guys will probably need at least another 100 amps of dedicated power. Lights pull a lot o power very quickly especially when you start adding up.

 

[noderaser]

General clarification note/peeve: 120 VAC is the standard phase-neutral voltage of both three-phase and single-phase systems for most of North America. 208 VAC is the phase-phase voltage of a standard three-phase wye system, common for commercial and many industrial applications in the United States and Canada. 240 VAC is the leg-leg voltage of a "split" or single phase system, which is derived from a single-phase transformer. Both legs from a single phase system are "in phase" with each other, not 180 degrees as some people claim; the increased voltage by connecting a load between both legs is achieved because you are connected across more windings on the secondary side of the transformer, not because of a vectorial sum in a polyphase system. Basically, North American single-phase 120/240 V transformers are similar to the 240 V secondary transformers found in places like Europe, but the "halved" voltage is made available by adding a center tap to the secondary windings of the transfomer. A Euro 240 V transformer would be connected with one side of the winding grounded, the other supplying the "hot" line conductor.

Note that there are some true "two phase" systems in existence, and there are systems such as the various deltas that provide voltages other than those listed above. In that case, it's best to get a capable electrician/electrical engineer involved because the voltages in these systems fluctuate, which is not desirable in dimming systems. Also, the difference between split-phase and three phase is a pedantic note when dealing with most dimmers, since the actual loads are connected line-neutral, not line-line. Most racks are field modifiable to select between split-phase or three-phase distribution, either splitting the rack into thirds or half for phase/leg input as appropriate.

 

[DELO72]

Let's assume we use some kind of 575 watt elipsoidal for the area lights, and 500w fresnels for downlights.

Bah! Put 575W BTH lamps in your fresnels! 35% more lumens, Higher color temp. Same look, CCT, and output to your 575W Elipsoidals!

And thus ends my marketing pitch for the best **** Med Prefocus base lamp on the market. And I'm not ONLY saying that because I invented it... okay, maybe I am. But it's still true. Anyone with 6" fresnels NOT using a BTH should have their head examined. Or ask me for a sample so they can see why I say this first hand.

 

[JD]

Just one quick clarification on "Shoebox" dimmers:
If you can, don't use them! They are handy, but there are so many "If this, don't that" exceptions, that it can get confusing. If you do want to use them, here are the top things to be aware of:

1) Most do not have UL ratings so watch out.
2) Most are rated at 10 amps per channel which may imply 1.2kw, but treat them as 600 watts as there is not much headroom on the triacs.
3) Most have either 12/3 (20 amp) or 14/3 (15 amp) line cords on them which limit the total pack wattage.
4) Most have a 15 amp U ground plug (Standard Edison) which limit the pack further to 15 amps.
5) Some have a 10 amp pack connector, which limits the pack to 10 amps!

There are a few good ones out there, but if at all possible, as said above, stick with Rack dimmers.

Price out 1.2kw and 2.4kw racks. As said above, nothing wrong with using 2.4kw as electrical loading is based on the lights plugged into the racks. (2.4Kw is more-or-less the universal standard unless you have some real big loads!)

One other thing. Minimum branch wiring is #12 and minimum extension rating is 12/3 S type cable, so you don't really save any wiring costs with the 1.2Kw dimmers.

 

[DELO72]

That's a very good point. Assuming you will be buying/renting Dimmer racks, you will want the space to be spec'd with Three-phase power for those dimmers. So DEFINITELY not 120V, single-phase. Whether you have hard-wired permanent 20AMP dimmers, or rental dimmer packs, most will be 3-phase and need feeder cable for the hookup. Your dimmers will send out 120V single phase to the fixtures, but the dimmers themselves in most cases will want to be powered by three-phase 208V.

 

[JD]

Forgot about the "road show" part!
Google "Company Switch." There are a lot of them out there and prices are all all over the place. Again, Three phase if possible, but if you are "stuck" with single phase, so be it. A company switch is basically a disconnect box that outputs to Cam-lok connectors. Your own racks could also be set up with these, unplugged and moved to a secure location when you have outside shows in.

One footnote: Make sure your switch is equipped with series E1016 Cam Loks. Although these are rated at 400 amps, which you will likely never draw, it is the size/style found on almost all rental equipment and traveling road shows. So, even if the breaker is only 100 amps, use the E1016 connectors.

 

[cbrandt]

Could I get a quick clarification? Is there an NEC regulation against installing single phase dimmers? Quite a few are easily configured to run single phase. There have been a couple of statements in this thread saying that you must have three phase to install a dimmer rack. While I can agree that it would be preferred, is it required?

 

[JD]

Could I get a quick clarification? Is there an NEC regulation against installing single phase dimmers? Quite a few are easily configured to run single phase. There have been a couple of statements in this thread saying that you must have three phase to install a dimmer rack. While I can agree that it would be preferred, is it required?

No.

That being said, almost all rental gear and road shows are going to show up wired and looking for three phase. If this were just an in-house system, single phase power would not be a problem.

 

[Esoteric]

No.

That being said, almost all rental gear and road shows are going to show up wired and looking for three phase. If this were just an in-house system, single phase power would not be a problem.

Yeah, we have installed dimmer racks on single phase power before.

But in 15+ years I have never seen a road rack in a single phase configuration. If you are going to have road shows coming through you NEED a 3 phase disconnect. In most of the roadhouses we do we install 2-4 (or more) of them, at least 1 on the upstage wall and one on the proscenium wall.