# Is it acceptable to put 4x S4s on a dimmer?



## derekleffew

20A (2400W) dimmer. Four fixtures with HPL575/115 lamps. Discuss.


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## Sean

derekleffew said:


> 20A (2400W) dimmer. Four fixtures with HPL575/115 lamps. Discuss.



Yes.

--Sean


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## waynehoskins

My opinion = yes.


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## seanandkate

Barring obnoxiously long cable runs, yes.


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## len

Theoretically, yes.

Real world, probably not.


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## clbarker

Works for me everytime! So, yes!


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## soundlight

Done it multiple times, and it hasn't tripped a breaker yet.


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## propmonkey

isnt that way they made the lamps 575w?


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## David Ashton

Yes and no, while 4 certainly can run off a dimmer if you blow a lamp it will almost certainly take out the breaker and you lose 4 lights out of your rig,-black hole.If you can split them it's safer.


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## Pip

Well, it's possible, but I wouldn't say it's advisable.

Consider the almighty power equation:
Watts equals Volts times Amps:
W = V * A

You have 4 instruments, 575W each, for a total of 2,300W (2.3kW):
4 * 575W = 2300 W
That's cutting it fairly close if you're on a 2.4kW dimmer. Let's look at that in terms of current (Amperage)

Going back to our power equation...
2300W = 120V * A
A = 2300 / 120 = 19.17A


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## David Ashton

Bear in mind that 2.4k is a conservative rating, there is a built in tolerance so that it is quite safe to run at that output.Your output devices are normally 40A and the breaker will not trip unless there is a prolonged or severe overload.


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## Pip

Yes, but that is a built in safety feature. By saying that and going about business in that manner, you're circumventing one of the ways these things are designed to keep you (and your audiences, your facilities, etc) safe.

It's not just about the inconvenience of popping the breaker - it's about actual safety when dealing with dangerous electrical equipment.


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## David Ashton

What I said is that it is safe to run 2.4k on a 2.4k dimmer because there is a safety factor built in, unlike others who were saying that you should further de-rate it to be on the safe side, I am sure no-one would ever consider pushing them a bit further even though you could possibly get away with it.


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## Chris15

And the average mains supply voltage is?


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## David Ashton

I think we have to assume that we are talking 115 or 120v with the appropriate lamp, in Australia or UK the above discussion would revolve around 10A 240v dimmers, also 2.4kw.


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## Chris15

I was taking that voltage range as a given, but at 120V, 115V 575W lamps draw more that 575W... Rather my sums put it at about 626W, 5.2A. 4 times that and you are into the range where a fuse will trip in time but a breaker may not...

Put a voltage spike on that and I think you'll find breakers going tripsies.

Can you do it? Yes. Should you do it? perhaps not...


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## David Ashton

If you don't use the correct voltage lamp you're very likely to blow it as the life reduces dramatically, but in answering questions like this it is fair to assume that a 575 lamp is using 575w.If you look at fuse ratings you will see that they run at a slight overload for a long time, certainly up to an hour.Over-running a lamp is not a linear increase as the resistance is very non linear with temperature so a simple calculation is inaccurate.


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## STEVETERRY

derekleffew said:


> 20A (2400W) dimmer. Four fixtures with HPL575/115 lamps. Discuss.



ETC Sensor dimmers are Listed for 100% loading, 100% duty-cycle operation. Four x 575W is no problem.

Some dimmers with thermal breakers can only be loaded to 80%, or 1920W on a 2400W dimmer.

You need to determine the rating of your dimmer to answer this question.

ST


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## David Ashton

Steve, could we have some examples of 2.4k dimmers which only take 1.9k as I've never come across any in Australia?.


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## Chris15

allthingstheatre said:


> If you don't use the correct voltage lamp you're very likely to blow it as the life reduces dramatically, but in answering questions like this it is fair to assume that a 575 lamp is using 575w.If you look at fuse ratings you will see that they run at a slight overload for a long time, certainly up to an hour.Over-running a lamp is not a linear increase as the resistance is very non linear with temperature so a simple calculation is inaccurate.



Err I thought it was a not uncommon practice for our American brothers to use a 115V lamp on a 120V supply to get some extra brightness. Someone wanting brownie points can go back into the archives and find Ship's percentages for lamp life change, colour temperature change, output change etc with over or under voltaging a lamp.

I looked at a breaker curve a while back and from memory, you could run indefinitely at 127%... Fuses are normally a little more sensitive.

Yes the resistance is very non linear, a 500w flood lamp is only a few ohms cold at DC... I suspect current draw will still go up, though it won't be linear and hence my number will be out...


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## David Ashton

Steve, could we have some examples of 2.4k dimmers which only take 1.9k as I've never come across any in Australia?.


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## derekleffew

Chris15 said:


> ...Someone wanting brownie points can go back into the archives and find Ship's percentages for lamp life change, colour temperature change, output change etc with over or under voltaging a lamp.


I prefer Mike Wood's formulae, detailed here: http://www.controlbooth.com/forums/collaborative-articles/7664-mathematical-formulas-lighting.html. 

Here's a follow up question:
Given four fixtures with HPL575/115 lamps; which of the following currents would flow through the dimmer?
a) 19.2A
b) 20.0A
c) 20.8A
d) 24.8A

For our International contingent, I'm speaking only of US practices and theories, where supply voltage is based on 120V.


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## STEVETERRY

allthingstheatre said:


> Steve, could we have some examples of 2.4k dimmers which only take 1.9k as I've never come across any in Australia?.



Any Lutron dimmer, and there are probably others that use thermal/magnetic breakers. This would be especially true in 230V markets where ABB or Merlin-Gerin standard thermal magnetic breakers are normal in a lot of dimmers. 

BTW, that's 1920W continuous, which means three hours or more. We assume loads in the theatre to be continuous in the US, simply because they can be.

Also, long tradition has dictated that professional theatrical dimmers be rated at 100% loading, using fully magnetic breakers.

ST


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## derekleffew

Pip said:


> ...Consider the almighty power equation:
> Watts equals Volts times Amps:
> W = V * A
> 
> You have 4 instruments, 575W each, for a total of 2,300W (2.3kW):
> 4 * 575W = 2300 W
> That's cutting it fairly close if you're on a 2.4kW dimmer. Let's look at that in terms of current (Amperage)
> 
> Going back to our power equation...
> 2300W = 120V * A
> A = 2300 / 120 = 19.17A


Anyone want to show Pip where he went wrong?

Again the follow-up question:
Given four fixtures with HPL575/115 lamps; which of the following currents would flow through the 120V dimmer?
a) 19.2A
b) 20.0A
c) 20.8A
d) 24.8A


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## Pip

derekleffew said:


> Anyone want to show Pip where he went wrong?
> 
> Again the follow-up question:
> Given four fixtures with HPL575/115 lamps; which of the following currents would flow through the 120V dimmer?
> a) 19.2A
> b) 20.0A
> c) 20.8A
> d) 24.8A



Crap... ^^ I checked my math... O noes! What did I do? *shakes head*


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## Grog12

Pip said:


> Crap... ^^ I checked my math... O noes! What did I do? *shakes head*



As I said in an earlier post Pip...reread the original question. There's a very important piece to this puzzle you're walking right over. 

Here's a hint, your answer to Derek's question would be A).

And for the record it would be wrong.

Also for the record. 4 HPL 575w 115v lamps on a 20a 2400w dimmer is a bad idea.

(((psssst Pip! all the information you need is in the previous sentence)))


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## gafftaper

How many volts are the lamps running at Pip?


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## philhaney

STEVETERRY said:


> Some dimmers with thermal breakers can only be loaded to 80%, or 1920W on a 2400W dimmer.



I was always taught never to load a breaker at more than 80% of its rated capacity so I would say "no," but from the various posts here, I could be wrong. 

When I worked at Colortran our resident electrical guru (this guy was one of the guys on the panel that wrote the theatre section of the NEC) explained that we used magnetic breakers because they have a built-in time delay (governed by how long the magnetic field in a coil takes to pull a slug through some sort of goo. When the slug reaches its limit of travel it pushes a button (or lever) and trips the breaker. A spring then pulls the slug back to its starting point). I don't know if we used breakers that were thermal as well, but vaguely recalling a discussion I had with said guru, I doubt it


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## Pip

Grog12 said:


> As I said in an earlier post Pip...reread the original question. There's a very important piece to this puzzle you're walking right over.
> 
> Here's a hint, your answer to Derek's question would be A).
> 
> And for the record it would be wrong.
> 
> Also for the record. 4 HPL 575w 115v lamps on a 20a 2400w dimmer is a bad idea.
> 
> (((psssst Pip! all the information you need is in the previous sentence)))



Oh yeahh I totally missed the 115 part... ****it to hell. Hehe in that case, less voltage = higher current necessary = bad.
The wattage of the lamps stays the same: 2.3kW
Math:
Again: W = V * A
2,300 = 115 * A
A = 20

I wouldn't fully load a dimmer, if I were you.


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## Les

Pip said:


> I wouldn't fully load a dimmer, if I were you.



Unless it's an ETC Sensor


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## Pip

Yeah?


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## Les

STEVETERRY said:


> ETC Sensor dimmers are Listed for 100% loading, 100% duty-cycle operation. Four x 575W is no problem. ST



Said by STEVETERRY himself


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## Pip

Les said:


> Said by STEVETERRY himself



haha kickass!


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## STEVETERRY

Les said:


> Unless it's an ETC Sensor



Guys, what you are missing here is that a dimmer rated for 120V nominal does not deliver 120V at the outlet. You have the drop across the SCR, the choke, and the cable run to the outlet. That is precisely why a 575W HPL lamp is rated at 115V--so that you can get the expected lumen output and color temperature despite those voltage drops.

So, 4x575W 115V lamps on a 120V 20A dimmer rated for continuous full loading is just fine--as long as you don't exceed 115V at the outlet. And that would be hard to do without a line voltage higher than 120V.

ST


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## timeblazer

Yes, especially in houses that have duplicated circuits - i.e. runs that repeat a circuit sequence in the FOH or permanent electrics to save install or upgrade cost.


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## McCready00

I might be wrong here, but depending of the type of dimmer you are using, there is a heat dessipation consideration:

1. Portable Triac Based Dimmer : 2%
2. Thyristor Based Dimmer : 2.5%
3. IGBT or Sine Wave Based Dimmer : 3%

1. 2400W x .02 : 48W --- 2352W
2. 2400W x .025 : 60W --- 2340W
3. 2400W x .03 : 72W --- 2328W

575W x 4 : 2300

And as said before in this thread, the ETC Sensor Module will take 100% of the load: 

*CIRCUIT BREAKERS* : Fully magnetic to eliminate nuisance tripping
20x inrush current rating
125%, 10-120 seconds, must- trip rating
_Rated for 100% switching duty applications at
full load_

I would not use it for an important event even though I still think it is safe. There is many factors inside the dimmer that can play with the numbers. So, I would use it for a small event but I would better play safe if I needed for something important. 

Please kids, play safe !


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## renegadeblack

I've done it. However, if you're ever using S4s on a household circuit with a leviton D4DMX sort of device, guess what, it doesn't work.  And after the first 5 times, it still doesn't work!


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## SPA

I concur with Pip. Thats just too risky to shut down a part of the show if the breaker blows.


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## Benchtech

Excuse me for butting in, but if I may, I'll drop some info that may answer the question.
A HPL575/115 lamp is "factory rated" to draw 575 WATTS at a line voltage of 115 VAC. Given that information, we can figure operating amperage of 5 AMPS and the resistance of the filament to be 23 OHMS when hot.
Now if your line voltage is 120 VAC, the current goes to 5.21 AMPS and the wattage increases to 625 watts.
If you are one of the lucky ones with a stiff power grid and run 125 Volts, then the current will run up to 5.43 amps, and the wattage will be a whopping 678 WATTS! 

Now if you are running the lamps at less than 100% or you have your dimmers trimmed, or you don't pull them up to full immediately and you are running a preheat setting, you may get by running 4 fixtures. 
Otherwise the full load at higher line voltages or the inrush current on cold filaments will most likely cause you trouble.
Had it happen on a stage where we had 4 575/115 watt lamps and kept tripping the breaker. If you ran the fader up slow it would hold, but if you ramped up fast, it would trip everytime. I have a factory note fron Leprechan about this very problem running 3 fixtures on a pack with a 15 amp cord on it. They were concerned about three lamps pulling over 16 Amps. 
I'm pretty sure that Osram has 120 volt rated lamps for the S-4 fixtures and that may be an out if you have problems.
Break a leg!


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## Chris15

Benchtech, that would be true if a lamp were ohmic. It's not. As you up the power being dissipated, the internal temperature increases - which is the colour temp change we see and as the temperature changes, the filament resistance changes, a higher resistance at a higher temperature. This then drops the current flow back, you have a negative feedback cycle. It will find an equilibrium at some point, but it most certainly will not be at the linear ohmic value you calculated...


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## SteveB

Benchtech said:


> Excuse me for butting in, but if I may, I'll drop some info that may answer the question.
> A HPL575/115 lamp is "factory rated" to draw 575 WATTS at a line voltage of 115 VAC. Given that information, we can figure operating amperage of 5 AMPS and the resistance of the filament to be 23 OHMS when hot.
> Now if your line voltage is 120 VAC, the current goes to 5.21 AMPS and the wattage increases to 625 watts.
> If you are one of the lucky ones with a stiff power grid and run 125 Volts, then the current will run up to 5.43 amps, and the wattage will be a whopping 678 WATTS!



I am one of the "lucky" ones, as incoming voltage varies between 123 and 127. That's one reason I like Sensor dimmers, as I can set the circuit voltage, which I keep at 115v. Most Sensor systems come factory set in the CEM/CEM+ for 115v lamps. 

Now that 123-127 plays havoc with UPS's, but that's another thread.

Steve B.


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## venuetech

Not advisable
The dimmer is not going to be the problem. the problem will be with the cable/wiring.

The circuit breaker is there to protect the wire from going up in smoke and starting a fire.

Any imperfection in the wiring, plug/connector will over time start to cause problems. 

just pick the cable up that is feeding these four units, it may not be hot but it will be very warm. carefully check each plug and connector for excessive heat.

you may not find a problem today but 4 or 5 months or more down the line. 

not good, not wise.

fire safety, its your call


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## Casey

Yes. Of course you can run 4 - HPL 575/115 off of a single 2.4k dimmer. They were built to be used that way, and many people do so on a daily basis. I've never had any problems, but if you do run into one worst case scenerio is it will trip the breaker and you will have to run another circuit to the light.


venuetech said:


> Not advisable
> The dimmer is not going to be the problem. the problem will be with the cable/wiring.
> 
> The circuit breaker is there to protect the wire from going up in smoke and starting a fire.
> 
> Any imperfection in the wiring, plug/connector will over time start to cause problems.
> 
> just pick the cable up that is feeding these four units, it may not be hot but it will be very warm. carefully check each plug and connector for excessive heat.
> 
> you may not find a problem today but 4 or 5 months or more down the line.
> 
> not good, not wise.
> 
> fire safety, its your call



I'm not sure what kind of cable you use, but in the markets that I work in primarily, the only cable I see aside from zip cord for practicals is #12 (12/3) SJO. You can easily run 2.4Kw through it. It will get warm, but again, it was designed to be used that way.

Right now I have a rig up where there are many circuits running at 2.4Kw, this is in a setup where the power (from a good generator, so it is consistent voltage) runs through about 300' of Soca, and another 50' or so broken out. No problems.


*So... Yes. Of Course its OK!*


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## midgetgreen11

I've had four sets of Strips (150W lamps, each strip w/ 4) daisy chained into one dimmer, adding up to 2.4k. Haven't had any issues as of yet.


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## cdub260

Casey said:


> I'm not sure what kind of cable you use, but in the markets that I work in primarily, the only cable I see aside from zip cord for practicals is #12 (12/3) SJO. You can easily run 2.4Kw through it. It will get warm, but again, it was designed to be used that way.
> 
> Right now I have a rig up where there are many circuits running at 2.4Kw, this is in a setup where the power (from a good generator, so it is consistent voltage) runs through about 300' of Soca, and another 50' or so broken out. No problems.



Be aware that NEC Article 520 specifies the use of hard usage or extra hard usage cable on stages. SJO is junior hard usage cable and does not meet code requirements for use on a stage.

Also be aware that if your cable runs are bundled together, you are required to derate the cable to 80% of its normal capacity. This means that while a single 12/3 SO cable is rated at 20 amps, if you run several of these cables bundled together on your electrics, they are now considered 16 amp cables. Socapex is considered a bundled cable run. As such code limits you to 16 amps per circuit. There is an exception to this. There is a type of socapex that is a flat cable rather than a round bundle. I've seen it, but I've never worked with it.

And before the usual, "But I've been doing it this way for years and nothing bad has happened." explanations start, consider that just because nothing has happened, doesn't mean your doing the job in the proper manner. While it was not an incident with electricity, I had to learn this lesson the hard way. Eight years later, I still hurt.


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## techieman33

We do it on a regular basis, but they're generally used as wash light and never over 80% at the most so we don't worry about it.


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## Les

techieman33 said:


> We do it on a regular basis, but they're generally used as wash light and never over 80% at the most so we don't worry about it.



I'm not saying what you are doing is wrong, but it is helpful to know that even though the lights are at 80% does not mean they are only using 80% of 2400 watts. Theatrical lights typically draw their full wattage well below 100%.


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## SteveB

"Be aware that NEC Article 520 specifies the use of hard usage or extra hard usage cable on stages. SJO is junior hard usage cable and does not meet code requirements for use on a stage."

My understanding is that SJ is acceptable in lengths up to 20ft, provided it's in the air and not used on deck. Which is why it's acceptable cable for use in 2-fers and breakouts, with some 6 circuit breakouts being of staggered length up to 20ft..

"Socapex is considered a bundled cable run."

"Socapex" is the name of the manufacturer of the typical (and probably most common) multi-pin connector. Multi circuit cable is the cable itself. Good installation practice is to use one wire size up from the over current rating, thus it's not unusual to see #10 wire on multi-circuit cables running to raceways, etc... that are breakered at 20 amps (Sensor D20 dimmer as example). 

Steve B.


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## David Ashton

only using 80% of 2400 watts. Theatrical lights typically draw their full wattage well below 100%.[/QUOTE]
A properly set dimmer will only draw its full current when at full, but it is very non linear so at 80 on the dimmer you are drawing maybe 90% of your current,
and the main reason is the non linearity of the resistance of the lamp with heat.


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## coldnorth57

derekleffew said:


> 20A (2400W) dimmer. Four fixtures with HPL575/115 lamps. Discuss.



NO the breakers in the dimmer pack are reated for 2400watts ....but their true running load is 2000watts ...80% that is the continuse laod but for short time they can ruun at fulll load of 2400 watts


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## Les

> Originally posted by coldnorth57
> NO the breakers in the dimmer pack are reated for 2400watts ....but their true running load is 2000watts ...80% that is the continuse laod but for short time they can ruun at fulll load of 2400 watts




STEVETERRY said:


> ETC Sensor dimmers are Listed for 100% loading, 100% duty-cycle operation. Four x 575W is no problem.
> 
> Some dimmers with thermal breakers can only be loaded to 80%, or 1920W on a 2400W dimmer.
> 
> You need to determine the rating of your dimmer to answer this question.
> 
> ST



What dimmers are you talking about, coldnorth57?


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## rmarston

No, not acceptable to run four 575W S4s on a 2.4KW rated dimmer. Good design practice says the dimmer rating should be derated by some amount. 20% derating will allow 3 S4s to operate even under voltage transient conditions. Why gamble with failures during a production caused by loading a dimmer to close to its rating.


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## philhaney

rmarston said:


> No, not acceptable to run four 575W S4s on a 2.4KW rated dimmer. Good design practice says the dimmer rating should be derated by some amount. 20% derating will allow 3 S4s to operate even under voltage transient conditions. Why gamble with failures during a production caused by loading a dimmer to close to its rating.



I, too, was told by an electrician that you're not supposed to load a dimmer more than 80% of its rated capacity. On the other hand, if SteveTerry says his dimmers are rated for 100% load, I believe him.


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## STEVETERRY

coldnorth57 said:


> NO the breakers in the dimmer pack are reated for 2400watts ....but their true running load is 2000watts ...80% that is the continuse laod but for short time they can ruun at fulll load of 2400 watts



No, the breakers on most theatrical dimmers are fully magnetic units that are listed for 100% load 100% duty cycle. A 20A dimmer like ETC Sensor is rated for 2400W continuous.

Please see the attached article for more on this

ST


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## STEVETERRY

philhaney said:


> I, too, was told by an electrician that you're not supposed to load a dimmer more than 80% of its rated capacity. On the other hand, if SteveTerry says his dimmers are rated for 100% load, I believe him.



The difference is that a Sensor dimmer (and some other manufacturers' theatrical dimmers) are UL Listed for 100% loading, 100% duty cycle. Please see article attcahed to another post in this thread for an explanation.

ST


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## STEVETERRY

cdub260 said:


> Be aware that NEC Article 520 specifies the use of hard usage or extra hard usage cable on stages. SJO is junior hard usage cable and does not meet code requirements for use on a stage.
> 
> Also be aware that if your cable runs are bundled together, you are required to derate the cable to 80% of its normal capacity. This means that while a single 12/3 SO cable is rated at 20 amps, if you run several of these cables bundled together on your electrics, they are now considered 16 amp cables. Socapex is considered a bundled cable run. As such code limits you to 16 amps per circuit. There is an exception to this. There is a type of socapex that is a flat cable rather than a round bundle. I've seen it, but I've never worked with it.
> 
> And before the usual, "But I've been doing it this way for years and nothing bad has happened." explanations start, consider that just because nothing has happened, doesn't mean your doing the job in the proper manner. While it was not an incident with electricity, I had to learn this lesson the hard way. Eight years later, I still hurt.



1. Junior hard service cord is acceptable in Art 520 venues for twofers, adapters, and breakout assemblies--subject to the limitations of 520.68 and 520.69.

2. If you bundle cables together you may be subject to more derating than 80%, per table 400.5. However, if you meet the requirements of table 520.44 for borderlight cables (multicables), you are subject to a different derating and ampacity table. The key requirement of 520.44 is 50% diversity in loading or number of energized circuits.

3. Socapex cables are not bundled cables--they are a specific cable type with a specific ampacity and temperature rating that _may_ be determined by table 520.44 if the diversity requirements are met. 

Does everyone on this thread have a copy of the NEC? If not, you know what to do! 


ST


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## cdub260

STEVETERRY said:


> 1. Junior hard service cord is acceptable in Art 520 venues for twofers, adapters, and breakout assemblies--subject to the limitations of 520.68 and 520.69.
> 
> 2. If you bundle cables together you may be subject to more derating than 80%, per table 400.5. However, if you meet the requirements of table 520.44 for borderlight cables (multicables), you are subject to a different derating and ampacity table. The key requirement of 520.44 is 50% diversity in loading or number of energized circuits.
> 
> 3. Socapex cables are not bundled cables--they are a specific cable type with a specific ampacity and temperature rating that _may_ be determined by table 520.44 if the diversity requirements are met.
> 
> Does everyone on this thread have a copy of the NEC? If not, you know what to do!
> 
> 
> ST



Thank you for the corrections Steve Terry.

I did not have my NEC Codebook with me when I wrote my post, so I had to generalize from memory.

Just one of the dangers of posting while on vacation.


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