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Jakob B.

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Joined
Feb 25, 2016
Location
San Diego, CA
Hi all!

I'm setting up our light plot from a university designer for our spring musical this year. I've had experience with our ION board, using conventionals as well as intelligent lighting (DMX). The problem I have when circuiting a plot, I'm not too sure how to figure out how many of an instrument I can two-fer or daisychain to one circuit. For example, we have 575w Source fours, Whats the limit number of lights that I can plug into a 20-amp circuit? We also have Altman SpectraCyc 100's, which require 100w of hot power. Am I correct in saying that a 20-amp circuit can supply 2400w? Would that theoretically supply 24 SpectraCycs?

Also, what happens if a circuit is "Overloaded"?

Thanks for your help!
 

DeadCheerios

Member
Joined
Dec 22, 2012
Location
Edmonton, AB
One of the first things you need to find out is does the designer need control of each individual Source 4? If so then you cannot two-fer them together.

In theory if you plug 24 of those spectras it should work however I would never recommend loading a circuit to the max.

If a circuit is overloaded it will not work as it will flip the breaker or blow a fuse.
 

microstar

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Joined
Jan 19, 2014
Location
Lawton, OK
Hi all!

I'm setting up our light plot from a university designer for our spring musical this year. I've had experience with our ION board, using conventionals as well as intelligent lighting (DMX). The problem I have when circuiting a plot, I'm not too sure how to figure out how many of an instrument I can two-fer or daisychain to one circuit. For example, we have 575w Source fours, Whats the limit number of lights that I can plug into a 20-amp circuit? We also have Altman SpectraCyc 100's, which require 100w of hot power. Am I correct in saying that a 20-amp circuit can supply 2400w? Would that theoretically supply 24 SpectraCycs?

Also, what happens if a circuit is "Overloaded"?

Thanks for your help!
How do you know its a 20 amp circuit to begin with? No offense, but if you are tasked with being the "master electrician" for the show, I would think any basic lighting course would have included W=VA. Also, Altman's spec sheet says a maximum of 20 Spectra Cyc 100's can be daisy-chained .
 

derekleffew

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Jakob B.

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Location
San Diego, CA
How do you know its a 20 amp circuit to begin with? No offense, but if you are tasked with being the "master electrician" for the show, I would think any basic lighting course would have included W=VA. Also, Altman's spec sheet says a maximum of 20 Spectra Cyc 100's can be daisy-chained .
Hi, sorry, forgot to mention that I'm in High School, and this show is at our campus, we don't offer any kind of lighting course, and my drama teacher wasn't too much help, hoping you guys could. I know it's 20amps because that is what our breakers in our sensor 3 dimmer rack are outputting, as well as the breakers in the breaker panel (for hot power).

I did some googling, and found that equation (W=VA) and thats how i concluded that a 120Volts times 20amps gives me 2400Watts per circuit. Did I do this correctly? And does this mean that as long as the combination of instruments on each circuit is well below that 2400w limit, I'm good?

And lastly, I did see that in the SpectraCyc Manual, it's why I said theoretically (we don't even own that many units). I'm just trying to grasp the idea of wattage and loads.
If there are any books, articles, videos, or readings that anyone knows of for a newbie, I'm more than happy to learn!
 

microstar

Well-Known Member
Joined
Jan 19, 2014
Location
Lawton, OK
Hi, sorry, forgot to mention that I'm in High School, and this show is at our campus, we don't offer any kind of lighting course, and my drama teacher wasn't too much help, hoping you guys could. I know it's 20amps because that is what our breakers in our sensor 3 dimmer rack are outputting, as well as the breakers in the breaker panel (for hot power).

I did some googling, and found that equation (W=VA) and thats how i concluded that a 120Volts times 20amps gives me 2400Watts per circuit. Did I do this correctly? And does this mean that as long as the combination of instruments on each circuit is well below that 2400w limit, I'm good?

And lastly, I did see that in the SpectraCyc Manual, it's why I said theoretically (we don't even own that many units). I'm just trying to grasp the idea of wattage and loads.
If there are any books, articles, videos, or readings that anyone knows of for a newbie, I'm more than happy to learn!
OK, good answers and nice job doing research on your own! When you said university designer I took it the wrong way.
 

BobHealey

Active Member
Joined
Aug 6, 2011
Location
Troy, NY
With LEDs and moving lights, the simple W=VA equation doesn't tell the full story. Because of how motors, transformers, and power supplies work on an electrical engineering level, for those you need to read the manuals and/or look at the fixture face plates to find out how much current they draw and/or how many you are allowed on one circuit. For example, I have some dimmable LED worklights with a rating of 90W. But the manufacturer says I can only use 3 on a 10 Amp/1200Watt dimmer unit.
 

Scenemaster60

Active Member
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Apr 17, 2013
Location
Minneapolis, MN
You CAN put up to four 575 watt instruments on a 20 amp circuit and will likely not have have any trouble.
However, there are two things that can happen here:
1. The inrush current of the cold lamps coming on can trip the breaker so you have to be careful how you bring a circuit that is fully loaded on. If you slam it from 0 to full in a 1 second fade you are more likely to trip the breaker than if you use a five second fade. Your results may vary, though.
2. When a circuit is loaded that close to max there will be more voltage drop meaning that the color temperature of the lamps will be lower at full.

I personally, try not to load a 20 amp circuit beyond 2000 watts. Technically speaking the National Electric Code says that you should not load a 20 amp circuit beyond 1920 watts for a continuous load. Now stage lighting is not a continuous load and the code allows us to load a 20 amp circuit up to 2400 watts for stage lighting use. You just need to be careful whenever you go over about 1800 watts on a circuit because the chance for things going wrong goes up in a hurry after that point.
 

RickR

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Joined
Sep 18, 2009
Location
Spokane, WA the great "Inland Northwest"
A key factor in your situation is mentioning the Sensor rack. It has breakers rated for the full 20A of continuous use. See http://www.etcconnect.com/uploadedFiles/Main_Site/Documents/Public/White_Papers/AN101-B_100__Cont_Load_4pg.pdf http://www.etcconnect.com/uploadedF...c/White_Papers/AN101-B_100__Cont_Load_4pg.pdf

The non-dim breakers are quite likely not rated this way. Inrush is a bit more complex, but slamming lights to full in 0 time is just painful anyway.http://www.etcconnect.com/uploadedF...c/White_Papers/AN101-B_100__Cont_Load_4pg.pdf
 
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Don't forget when powering your non-dim fixtures (LED units, any movers, etc.) the cables you use at the source end of your run (and this goes for your conventionals, too) are carrying the full load for the entire circuit - so all 2.4K goes through that first cable. You'll get a lot of voltage drop if the cable isn't up to snuff when it's loaded that much, and the further you go, the worse it gets. (This is another reason why manufacturers sometimes cap the number of fixtures on a string somewhere below what's theoretically possible.) Also, underpowering the non-dim circuits likely isn't healthy for power supplies' life cycles. It's a good idea to leave yourself some headroom.

Another thing to keep in mind is that while 20 amps at 120V gives you 2.4kW, quite a few places don't actually supply 120V - it's often closer to 110, depending on your location. Where I am (in Eastern Canada) it frequently varies between 117-ish and 122V, but I've seen 115V at a venue less than an hour's drive away (also Eastern Canada, but closer to the States, where they seem to prefer lower voltages). It's not a bad idea to meter your sources regularly.

To add to the confusion, LED units frequently self-refer to their combined LED engine output as their wattage, but like compact fluorescent bulbs, it's sometimes just the manufacturer's loose interpretation what of their light output would be, in a conventional lamp. So a 90W LED fixture could maybe have a similar output to a 90W bulb while drawing far more (or far less, depending on the internal power supply used) than a 90W lamp. And if the fixture has other functions, like pan and tilt motors, well, they use power, too. F'rinstance: The Martin Mac 350 Entour is a pretty basic LED moving head profile. Its source engine has 7 50W LEDs, so about 350W of equivalent output; but the fixture draws about 450W, or around 4 amps, at or about 120V.

Practically: Don't overload your circuits. Don't overload your cabling. You've got good dimmers, and good conventional fixtures - they aren't likely to be the weak spots in your system. The fixture's manuals are your friends. Adding cables is cheaper than replacing fixtures. Keep away from children. Shake well before using.
 

DeadCheerios

Member
Joined
Dec 22, 2012
Location
Edmonton, AB
Don't forget when powering your non-dim fixtures (LED units, any movers, etc.) the cables you use at the source end of your run (and this goes for your conventionals, too) are carrying the full load for the entire circuit - so all 2.4K goes through that first cable. You'll get a lot of voltage drop if the cable isn't up to snuff when it's loaded that much, and the further you go, the worse it gets. (This is another reason why manufacturers sometimes cap the number of fixtures on a string somewhere below what's theoretically possible.) Also, underpowering the non-dim circuits likely isn't healthy for power supplies' life cycles. It's a good idea to leave yourself some headroom.

Another thing to keep in mind is that while 20 amps at 120V gives you 2.4kW, quite a few places don't actually supply 120V - it's often closer to 110, depending on your location. Where I am (in Eastern Canada) it frequently varies between 117-ish and 122V, but I've seen 115V at a venue less than an hour's drive away (also Eastern Canada, but closer to the States, where they seem to prefer lower voltages). It's not a bad idea to meter your sources regularly.

To add to the confusion, LED units frequently self-refer to their combined LED engine output as their wattage, but like compact fluorescent bulbs, it's sometimes just the manufacturer's loose interpretation what of their light output would be, in a conventional lamp. So a 90W LED fixture could maybe have a similar output to a 90W bulb while drawing far more (or far less, depending on the internal power supply used) than a 90W lamp. And if the fixture has other functions, like pan and tilt motors, well, they use power, too. F'rinstance: The Martin Mac 350 Entour is a pretty basic LED moving head profile. Its source engine has 7 50W LEDs, so about 350W of equivalent output; but the fixture draws about 450W, or around 4 amps, at or about 120V.

Practically: Don't overload your circuits. Don't overload your cabling. You've got good dimmers, and good conventional fixtures - they aren't likely to be the weak spots in your system. The fixture's manuals are your friends. Adding cables is cheaper than replacing fixtures. Keep away from children. Shake well before using.
Good post.
For me I always use a 80% max load when doing calculations. That way even if the voltage drops as low as 110 I wont be screwed.
 

JChenault

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Joined
Jan 5, 2009
Location
seattle, wa USA
Another thing to keep in mind is that while 20 amps at 120V gives you 2.4kW, quite a few places don't actually supply 120V - it's often closer to 110, depending on your location. Where I am (in Eastern Canada) it frequently varies between 117-ish and 122V, but I've seen 115V at a venue less than an hour's drive away (also Eastern Canada, but closer to the States, where they seem to prefer lower voltages). It's not a bad idea to meter your sources regularly.

Practically: Don't overload your circuits. Don't overload your cabling. You've got good dimmers, and good conventional fixtures - they aren't likely to be the weak spots in your system. The fixture's manuals are your friends. Adding cables is cheaper than replacing fixtures. Keep away from children. Shake well before using.
You seem to be saying that if you have lower voltage entering the building, you will be pulling more amperage for the same fixture. This is NOT my understanding of the way the world works. My understanding is that, ror practical use, you can consider the lamp to be a resistive load. Assuming a 120V lamp, The resistance for a 575 watt lamp can be determined by :
Watts = Volts * Amps -OR- 575 = 120 * Amps - Then Amps = 4.8 Amps. ( You will be putting 4.8 amps through the wire )
Power = AmpsSquared * Resistance. -OR - 575 = 23.04 * Resistance Then Resistance = ~25;

Now if I put a resistive load of 25 ohms in a 100 V circuit = the actual wattage will be :
Amps = Voltage / Resistance -OR- Amps = 100 / 25 Then Amps = 4

So a 120 volt lamp powered at 100 volts will not be as bright, or pull as much power as the same lamp being powered at 120 volts.


Additionally all electronic dimming that I am aware of provide an additional voltage drop in the dimmer ( so you don't really have 120V even if that is what you have at the distribution panel).

I'm also confused by the implication that overloading a circuit by putting too many conventional fixtures on it could damage the fixture - It's not clear to me how that could be so.
 

petercav17

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I think that the first step would be to confirm with the designer that he doesn't need individual control of the lights that you wish to two-fer. I don't know how extensive the plot is, but usually if two lights are able to be two-fer'd, it would be noted. Why do you want to load up those dimmers? Are there not enough tails in the positions where you need them?
 
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You seem to be saying that if you have lower voltage entering the building, you will be pulling more amperage for the same fixture. This is NOT my understanding of the way the world works. [explanations redacted]

I'm also confused by the implication that overloading a circuit by putting too many conventional fixtures on it could damage the fixture - It's not clear to me how that could be so.
That makes sense to me, too - I think perhaps I wasn't clear in my explanation.

My inference was that, should your venue be supplied with less-than-expected voltages, assumptions of what your safe load capacities are go out the window, as the formulas are then also out of whack. If you assume you'll get 120V at 20a and you actually get 110V with an unchanged ampacity, you have less power - so if your circuits were close to the theoretical maximum allowable load, you're now underpowering those circuits; i.e. you won't get a full 2.4K from your dimmers, which may ruin your day. And if you're underpowering a non-dim circuit with a series of automated fixtures with finnicky electronic ballasts, say, your day could get much much worse.

I, too, am confused by the implication that overloading a circuit with conventionals could damage the fixture, and am not certain where you got that. I did suggest paying attention to the amount of power you're putting through your fixtures and cabling, whether it be for conventional or some form of automated fixtures, is important. Think about strings of Christmas lights: Sure, the dimmer is capable of putting out 2.4KW, but should you really install a single string of forty eight 50W strands? That first strand in line could get pretty toasty, pretty quickly. Burny, even. But twelve strings of four, at 200W each, all in the same dimmer, might be just fine (input voltage allowing, of course). Too much of a resistive load on a dimmer will more likely damage the dimmer than the fixtures. There are more and more fixtures coming on the market which accept power throughput, so care should be taken not to exceed their ratings.
 

RickR

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Location
Spokane, WA the great "Inland Northwest"
Standard settings on Sensor racks to have voltage regulation down to 115v. (Thus 115v HPLs are more popular than 120v. Long life aside!) If a facility actually gets lower voltage (regularly) then a lower setting is in order to make sure that everything is consistent.

Electrical basics: The lamp resistance doesn't change. Less voltage means less current and therefore less power. Power is determined by volts and amps, not the other way around.

In the example above, voltage divides evenly so all strings burn the same. (wire resistance not factored in) The more strings you add the lower voltage each gets so it burns cooler. However the total amperage is higher so the dimmer is not so happy. Also you have to get a pretty low voltage to screw up mover electronics, check their label. 110v should be fine, 100 is not.
 

SteveB

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Mar 20, 2004
Location
Brooklyn, NY
And for what it's worth, the Sensor D20 dimmer is designed to handle a 4x575w load on a continuous use basis. The dimmer circuit breakers are continual load rated.

You hopefully have enough circuits to not have to do this as it sucks for control purposes, but it's designed for it.
 

robartsd

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Location
Sacramento, CA
You seem to be saying that if you have lower voltage entering the building, you will be pulling more amperage for the same fixture. This is NOT my understanding of the way the world works. My understanding is that, ror practical use, you can consider the lamp to be a resistive load. Assuming a 120V lamp, The resistance for a 575 watt lamp can be determined by :
Watts = Volts * Amps -OR- 575 = 120 * Amps - Then Amps = 4.8 Amps. ( You will be putting 4.8 amps through the wire )
Power = AmpsSquared * Resistance. -OR - 575 = 23.04 * Resistance Then Resistance = ~25;

Now if I put a resistive load of 25 ohms in a 100 V circuit = the actual wattage will be :
Amps = Voltage / Resistance -OR- Amps = 100 / 25 Then Amps = 4

So a 120 volt lamp powered at 100 volts will not be as bright, or pull as much power as the same lamp being powered at 120 volts.
It is true that conventional incandescent lamps will draw less amperage and use less power at lower voltages; however, reactive loads like switching power supplies used for moving lights might draw more amps to compensate for lower voltages. Each power supply should specify the source amperage required - use this value rather than the watts/volts for calculating how much you are loading your non-dim circuits.
 
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...In the example above, voltage divides evenly so all strings burn the same. (wire resistance not factored in) The more strings you add the lower voltage each gets so it burns cooler. However the total amperage is higher so the dimmer is not so happy. Also you have to get a pretty low voltage to screw up mover electronics, check their label. 110v should be fine, 100 is not.
My point was that, if plugged in in a single series, the entire current load is passing through the initial fixture, and that would typically be unwise. The gauge of wire needed for 2.4K at 120V just isn't found in Christmas lights hereabouts, although your mileage may differ. But plug* them in in parallel, and there's no such issue (until you overload the dimmer).

The tolerance of movers' electronics is a definite factor to consider. Lower-quality transformers, even if auto-ranging - as so many are these days - sometimes can't quite cut it. I've had fixtures balk at 105V (which isn't really all that unreasonable, if they're wired and set for 120V). Check your manuals.


*grow up. :)
 

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