NEC Code Applicability

[derekleffew]

Unless your Lightronics RE-121D dimmers have the "XT - Terminal / Barrier Connector Strip with Knockout Cover" option, all permanent building wiring branch circuits must have branch circuit breakers, sized appropriately for the wire, which cannot be less than 14g.

"...and the receptacles are definitely NEMA 5-15P." The receptacles are definitely NOT NEMA 5-15P, as the "P" indicates plug (male).

No offense intended toward Mr. Cadena, but I would rather trust the advice of a long-time member of NEC Code Panel 15.

Code-compliance on this system is out the window; and, as we have mentioned before, your local AHJ has final say. The remaining questions are 1) Is it safe?, and 2) Can you put 2x 575W lamps on one dimmer? I won't answer question1, but I'll bet if you perform [user]TimMiller[/user]'s test for question2, the lamps will burn out before the fuse blows, stopping your clock. The lamp failing could also cause the fuse to blow, though that doesn't happen as often as it used to. Note: NEVER leave illuminated theatrical lighting fixtures unattended! There's a reason for the "Not for Residential Use" label on them.

 

[STEVETERRY]

So I contacted Richard Cadena on the issue as well, and I'm not sure his e-mail was sufficiently helpful. He told me that the dimmer would have protection built in, and that is not the limiting factor. So the issue is with the branch circuit wiring, over-current protection, and connectors.

For the sake of argument, I'm nearly positve it's 12 or 14 AWG, and the receptacles are definitely NEMA 5-15R. So it looks like the issue falls onto the 10A fast-acting fuse.

I don't know enough about fuses though to know if they will only trip at 10A and over, or if cooking them, for an extended period of time, close to 10A is enough to trip 'em.

Falling back to Tim's post, it looks like the easiest method might just be a test.

Edit:

Steve, how do you regard 210.20 (A) in contrast to 210.23 (A)1.

It looks like the latter contradicts the former, in some regards.

210.23 (A)(1) does not apply, since 210.21 allows a circuit with one outlet that is not less than the rating of the overcurrent device, and 210.23 applies to circuits with two or more outlets. 520.9 also modifies 210.21 to eliminate the requirements of table 210.21(B)(2). 210.20 (A) Exception also allows what 210.23(A)(1) does not, as long as the entire assembly of the branch circuit and the device feeding it is LISTED for 100% loading. That means connectors, wiring, and dimmer pack. Bottom line, (even though it takes some digging)in the theatre, 2400 watt loading of a 20A circuit from one fixture is allowed, as long as the 100% LISTING is there.

Getting such a LISTING for a dimmer pack is directly related to the overcurrent protection device on each circuit in the dimmer pack. BTW, if your 12-pack is fed by a 2-pole 60A breaker in a normal building panel, then you cannot exceed 48A continuous load on each group of six dimmers, even if the pack has a 100% rating on its own. That's because the feeder breaker is not 100% rated, since it is a UL489 thermal/magnetic device.

Looking at your particular pack, I am not sure it is LISTED for permanent connection to building wiring, and whether or not it is 100% rated. You need to verify this.

Derek is right, if the pack is a cord-connected device, you need additional breakers on each branch circuit per 520.50. However, this still does not get you to 100% loading if that breaker is not listed for 100% and the dimmer pack is not listed for 100%. Also, the fact that the pack has a terminal strip output does not mean that it is LISTED for direct connection to building wiring. It might be UL RECOGNIZED, which allows it to be included in a larger LISTED dimmer rack (this is the case with the terminal-strip version of the ETC Smartpack, for instance). Or it might have no third-party regulatory compliance at all.

ST

 

[STEVETERRY]

Originally Posted by STEVETERRY View Post
210.23 (A)(1) does not apply, since 210.21 allows a circuit with one outlet that is not less than the rating of the overcurrent device, and 210.23 applies to circuits with two or more outlets. 520.9 also modifies 210.21 to eliminate the requirements of table 210.21(B)(2). 210.20 (A) Exception also allows what 210.23(A)(1) does not, as long as the entire assembly of the branch circuit and the device feeding it is LISTED for 100% loading. That means connectors, wiring, and dimmer pack. Bottom line, (even though it takes some digging)in the theatre, 2400 watt loading of a 20A circuit from one fixture is allowed, as long as the 100% LISTING is there.
Some circuits terminate on one duplex outlet (two receptacles), some have two duplex outlets. So this puts the applicability of codes into question.
[/COLOR]

Not if it's a theatre or similar location covered under article 520. 520.9 allows any number of outlets.

Getting such a LISTING for a dimmer pack is directly related to the overcurrent protection device on each circuit in the dimmer pack. BTW, if your 12-pack is fed by a 2-pole 60A breaker in a normal building panel, then you cannot exceed 48A continuous load on each group of six dimmers, even if the pack has a 100% rating on its own. That's because the feeder breaker is not 100% rated, since it is a UL489 thermal/magnetic device.

Crap, good catch.

Looking at your particular pack, I am not sure it is LISTED for permanent connection to building wiring, and whether or not it is 100% rated. You need to verify this.

So because the pack is not listed, it doesn't fall into the exception anyways?

Not unless it's listed for 100% loading

Derek is right, if the pack is a cord-connected device, you need additional breakers on each branch circuit per 520.50. However, this still does not get you to 100% loading if that breaker is not listed for 100% and the dimmer pack is not listed for 100%. Also, the fact that the pack has a terminal strip output does not mean that it is LISTED for direct connection to building wiring. It might be UL RECOGNIZED, which allows it to be included in a larger LISTED dimmer rack (this is the case with the terminal-strip version of the ETC Smartpack, for instance). Or it might have no third-party regulatory compliance at all.

So the dimmer has a 40A triac, even so, because it does not have a third party listing, then it's a no-go?

The triac rating has nothing to do with it if you want to be code compliant. It's all about the pack listing for 100% loading, and in your case, the pack listing for connection to permanent building wiring.

 

[STEVETERRY]

So for the sake of argument, nothing about the pack is listed (which I think is the case). So does that mean one has to go back to the 80% rule?

Yes, you are correct.

ST

 

[JD]

"So the dimmer has a 40A triac, even so, because it does not have a third party listing, then it's a no-go?" (not sure of who posted this.)

Good time to talk about Triac ratings. The current rating has almost noting to do with the channel rating. Generally, this is the peak amount of current you should expect the device to have to handle. NOT to be confused with the non-repetitive surge rating (usually around 400 amps for a 40 amp triac.) Generally, we want to see a good safety factor between the actual current a dimmer will handle, and the maximum current rating of the device. A factor of 4 is comfortable. The triac used in the RE-121D is a STMicroelectronics BTA41-600B which has a rating of 40 amps for a 10 amp dimmer. This fits this factor quite well. What has always surprised me about the TOP3 case style is that it uses a lead size that is along the lines of a flattened #16 wire, which is then soldered into an eyelet hole on the board. This may be why the pack would not receive a full rating... I don't know this for sure, that is beyond my pay grade. What I do know is that when I service large architectural dimmers which are fully rated, they usually use the stud style, which has a terminal the size or a #10 wire, or a pair of stud style SCRs, or the classic SSR with terminals.

When you get into the actual circuit design, as for example, how much copper trace is on the board, there seems to be a gray area. I suspect in lab testing, the device must undergo the worst case scenario and not present a fire or shock hazard. Again, in higher cost dimmers I have never seen the device soldered into a pcb. In every case the device is directly hard wired using wire gauge that has a minimum or greater capacity then the unit breaker or fuse.

EDIT:
The reason I say "almost" above is that I have seen that factor have wild interpretations. From the Optima using a 15 amp triac for a 10 amp dimmer, to the old EDI packs that use a 130 amp SCR bridge for a 20 amp dimmer.

 

[STEVETERRY]

"So the dimmer has a 40A triac, even so, because it does not have a third party listing, then it's a no-go?" (not sure of who posted this.)

Good time to talk about Triac ratings. The current rating has almost noting to do with the channel rating. Generally, this is the peak amount of current you should expect the device to have to handle. NOT to be confused with the non-repetitive surge rating (usually around 400 amps for a 40 amp triac.) Generally, we want to see a good safety factor between the actual current a dimmer will handle, and the maximum current rating of the device. A factor of 4 is comfortable. The triac used in the RE-121D is a STMicroelectronics BTA41-600B which has a rating of 40 amps for a 10 amp dimmer. This fits this factor quite well. What has always surprised me about the TOP3 case style is that it uses a lead size that is along the lines of a flattened #16 wire, which is then soldered into an eyelet hole on the board. This may be why the pack would not receive a full rating... I don't know this for sure, that is beyond my pay grade. What I do know is that when I service large architectural dimmers which are fully rated, they usually use the stud style, which has a terminal the size or a #10 wire, or a pair of stud style SCRs, or the classic SSR with terminals.

When you get into the actual circuit design, as for example, how much copper trace is on the board, there seems to be a gray area. I suspect in lab testing, the device must undergo the worst case scenario and not present a fire or shock hazard. Again, in higher cost dimmers I have never seen the device soldered into a pcb. In every case the device is directly hard wired using wire gauge that has a minimum or greater capacity then the unit breaker or fuse.

EDIT:
The reason I say "almost" above is that I have seen that factor have wild interpretations. From the Optima using a 15 amp triac for a 10 amp dimmer, to the old EDI packs that use a 130 amp SCR bridge for a 20 amp dimmer.

The other thing to remember is that the single-cycle surge rating (I-squared-t) of a thyristor is not the same as the RMS current rating. A device can have an RMS current rating well above the dimmer rating, but still have poor short-circuit performance. I-Squared-T is measured in Amp-squared seconds.

ST

 

[JD]

The other thing to remember is that the single-cycle surge rating (I-squared-t) of a thyristor is not the same as the RMS current rating. A device can have an RMS current rating well above the dimmer rating, but still have poor short-circuit performance. I-Squared-T is measured in Amp-squared seconds.

ST

True, and since the most common thrysistor failures are caused by the short circuit conditions that happen in lamp flashovers, the survival of the device is going to be governed by its ability to handle the drop current of whatever the end loop (wire to the lamp) is at a given voltage. (Circuit breakers are too slow to intercede at this point.) In the design of thrysistors, there are three parameters that govern this; 1) junction size, 2) thermal bond to case, and 3) junction to termination material. Flashover starts when the junction to termination material goes high in resistance causing a hot spot that modifies the properties of the junction causing a cascade failure. If the material remains intact (most common), the device is now shorted. If the material burns off, the device is now open circuit.

In simple terms, all thrysistors contain smoke. Let the smoke out and they don't work anymore

EDIT:
One thing I do miss in modern dimmers is the Rectifier Fuse (KAA or KAW) which tried to duplicate the burn rate of the termination material. Generally, these fuses had a rating based on the device they were protecting, not the current rating of the dimmer, and were used in conjunction to a circuit breaker at the unit rating. Overload the dimmer, and the breaker tripped, short the dimmer, and the rectifier fuse blew. I guess the thought is that thrysistors have come a long way, and they are not needed anymore.

 

[STEVETERRY]

True, and since the most common thrysistor failures are caused by the short circuit conditions that happen in lamp flashovers, the survival of the device is going to be governed by its ability to handle the drop current of whatever the end loop (wire to the lamp) is at a given voltage. (Circuit breakers are too slow to intercede at this point.) In the design of thrysistors, there are three parameters that govern this; 1) junction size, 2) thermal bond to case, and 3) junction to termination material. Flashover starts when the junction to termination material goes high in resistance causing a hot spot that modifies the properties of the junction causing a cascade failure. If the material remains intact (most common), the device is now shorted. If the material burns off, the device is now open circuit.

In simple terms, all thrysistors contain smoke. Let the smoke out and they don't work anymore

EDIT:
One thing I do miss in modern dimmers is the Rectifier Fuse (KAA or KAW) which tried to duplicate the burn rate of the termination material. Generally, these fuses had a rating based on the device they were protecting, not the current rating of the dimmer, and were used in conjunction to a circuit breaker at the unit rating. Overload the dimmer, and the breaker tripped, short the dimmer, and the rectifier fuse blew. I guess the thought is that thrysistors have come a long way, and they are not needed anymore.

Frankly, I was kind of glad to see them go. The KAW-A-35 Bussman fuse in the TTI MDS 2.4kW dimmer protected its wimpy 35A SCR about half the time in the case of a dead short on a stiff service. The fuse cost about half what the SCR did! And just try to find one on tour in the provinces! No way!

I-squared-T ratings of modern thyristors have increased a hundred fold since those early devices.



ST

 

[ship]

Well put in study all over. Here I am at work worrying about making the next generation three phase 400A 96way 20A AC Distro for moving lights, in between me and the manufacturer more going towards a recommendation of it as a 72way 15A (though in actuality I'm over ruled in 20A per channel distro -instead of at max a bar of them, with a bunch of 20 and 30A extra excessory outlets), and we have a problem here with some situation of 80% of max instead of what percentage of full capacity is full on a 400A three phase circuit one can pull short of main breaker popping - and very few will question it short of it doing so. I'm for that 80% for the 400A distro but not as much for that rating on a 1.2K dimmer circuit given it's temporary and control and above no doubt has the subsections for the NEC allowing a 1.2Kw dimmer to handle a 1Kw load.

In my above problem,
Had to plug in a bunch of fixtures and meter them: (or at least supervise,)
Noted and my concern about the new 1.5Kw fixtures given this new rack.... - noted but not persay taken into account in giving more compensation for the amperage of.


(As written up by a co-worker
A Measurement taken with 1.2Kw fixtures and not the new 1.5Kw XB fixtures or Showguns.



Here are the results of the test.

VL Moving Light Test



72 VariLight 3000 Profiles (same lamp as a Mac 2k)



Metered @ 111v 358A per leg



Extrapolating from that we can assume:



120v will be 331.15A per leg with 20% safety factor comes to 397.45A



115v will be 345A per leg with 20% safety factor comes to 414A



Absolute minimum voltage 100v coming into racks would be 397.38A no saftey factor (with safety factor 476.78)

 

[TimMiller]

All my fixtures out on the road are running at 208V. It makes power distribution much easier, rather than running a bunch of 120 and 208, then trying to keep from plugging the wrong thing in. It also makes the fixtures much happier,. Even an electronic power supply is more efficient off of 208V then 120. It has more to work with and makes both sides of the power supply work, rather then one side just running to neutral. Steve terry, with what you are talking about, the fuses protecting the triac's, why on the older ETC Sensor non dim modules is there a 50 amp fuse in line with the 20A breaker? Also when i had my lightronics racks apart last (been about a year), I remember there was at least 12awg wire (believe it was 10 awg) feeding 50 amp ssr's.

Also when it comes to using dimmer packs, can i use the next highest size of OCPD, based on the 80% load factor? (i am referring to my leprecon LD2400's) they will pull a little over 60A a leg when fully loaded. Or should I build a distro with breakers supporting a 100% load factor?

 

[STEVETERRY]

So, just to confirm, rubber jacketed multicable is a no-no installed permanently through walls?

Portable cord cannot ever be used as a substitute for permanent wiring methods. All in-wall methods prohibit portable cord. Allowable wiring methods for theatres are detailed in section 520.5. Basically, they are

--Wire in metal raceways or conduit. Allowable wire types detailed in Article 310
--Wire in non-metallic raceways or conduit enclosed in at least 2 inches of concrete
--Type MI cable, MC cable, or AC cable with an insulated equipment grounding conductor. These are metal-clad cables.

Lesser requirements pertain for "non-rated" sections of the building that are not required to be of fire-rated construction. As a general rule, these spaces are not anywhere near the theatre itself.

ST

 

[LekoBoy]

Portable cord cannot ever be used as a substitute for permanent wiring methods. All in-wall methods prohibit portable cord. Allowable wiring methods for theatres are detailed in section 520.5. Basically, they are

--Wire in metal raceways or conduit. Allowable wire types detailed in Article 310
--Wire in non-metallic raceways or conduit enclosed in at least 2 inches of concrete
--Type MI cable, MC cable, or AC cable with an insulated equipment grounding conductor. These are metal-clad cables.

Dude, HARSH! There is however a gray area in the definitions of "permanent" and "temporary" (production/show) wiring, isn't there? I've never seen a Touring Dimmer Rack attached to conduit, even though it hadn't moved in ten years. What about cutting a "mouse hole" thru the proscenium wall to get the mults to the Balcony Rail and Box Booms?

 

[STEVETERRY]

Dude, HARSH! There is however a gray area in the definitions of "permanent" and "temporary" (production/show) wiring, isn't there? I've never seen a Touring Dimmer Rack attached to conduit, even though it hadn't moved in ten years. What about cutting a "mouse hole" thru the proscenium wall to get the mults to the Balcony Rail and Box Booms?

Portable cables can penetrate walls, floors, or ceilings through approved "pass-through" chases. (a mouse-hole that was not fire-stopped would no doubt be a stretch). That's not the same as installing portable cables permanently inside a wall.

I agree that the duration of temporary is gray. Some Broadway shows have been "temporarily" installed for 20 years. However, the word we like to use is "portable", otherwise there might be confusion between Art 590 Temporary Installations and Article 520.


From the definitions in Article 520:

Portable Equipment. Equipment fed with portable cords or cables intended to be moved from one place to another.

Finally, Code compliance is harsh.

ST