# How many Smartpack wall mount racks can I LAN together



## Esoteric (Aug 24, 2011)

How many Smartpack Wallmount Racks can I LAN together using DMX control only?

Mike


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## derekleffew (Aug 24, 2011)

I'd guess a minimum of 31 racks, and if you need more, you probably should consider a different product line (or adding an opto-splitter).


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## chausman (Aug 24, 2011)

Esoteric said:


> How many Smartpack Wallmount Racks can I LAN together using DMX control only?
> 
> Mike


 
DMX is limited to 32 devices. If you are using Cat5/6/6e, I don't know. 


derekleffew said:


> I'd guess a minimum of 31 racks, and if you need more, you probably should consider a different product line (or adding an opto-splitter).


 
Minimum? Talk about savings!


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## Esoteric (Aug 24, 2011)

Hahaha... Well, I have to have 1.2kW dimmers, or else I would use the Sensor line.


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## derekleffew (Aug 24, 2011)

Esoteric said:


> Well, I have to have 1.2kW dimmers, or else I would use the Sensor line.


What need does a 1.2kW dimmer fulfill that a 20A doesn't?

-----


chausman said:


> DMX is limited to 32 devices.


Chase, it's a little more complicated than that. From DMX512 - AusChristmasLighting Wiki :

> Node Limit
> The RS485 standard specifies the maximum number of nodes (dimmers, controller, etc) you can have in a single DMX chain. This is specified as 32 "load units". Traditionally, one RS485 receiver (sometimes referred to as a DMX chip) was equivalent to one "load unit". This meant that you could have 31 receivers in the chain, as the transmitter also counts as a unit.
> 
> Newer variants of the venerable MAX485 IC have a load rating of 1/4 or 1/8. This means that you can use 4 or 8 times as many of them on a single line. In practice it is best to assume that each device still represents one load unit, as there is no easy way of knowing without checking the IC type and looking up its data sheet.
> ...


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## chausman (Aug 24, 2011)

derekleffew said:


> Chase, it's a little more complicated than that.


 
ok. I has read somewhere on here that it was limited to 32 (from JD I think) but I didn't know there was any chips that could allow you to have more then that. 


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## Esoteric (Aug 24, 2011)

Power feed requirements.

I have several 40A three phase breakers. But to pull in a 400A three phase would take....... Days... Maybe weeks...


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## jmabray (Aug 24, 2011)

They are just like any other DMX based device in those terms, so 31 racks. If you need that many, let me know and I can help you get them set up.

You don't need to feed a sensor rack with 400 amps. It is only limited to 800amps 3 phase power max. I have seen a full sr48 fed with 100amps 3 phase power because that was all the load that it had on it. (This was an architectural situation where the loads didn't fluctuate - so this may not apply...)


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## Esoteric (Aug 24, 2011)

Yeah, this is a plugging situation. So I don't know how I feel about feeding it less than its max possible draw.


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## jmabray (Aug 24, 2011)

alternatively you could load up a sr-6 with 10 amp dimmer modules.....

But several Sensor racks will be slightly more costly than the smartpacks....


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## Esoteric (Aug 24, 2011)

Yes they would.


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## Esoteric (Aug 24, 2011)

Totally unrelated, but what would the draw be for a three phase Sensor setup with 62 10A dimmers (32 modules) and 4 AFMs?

210A per phase?


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## derekleffew (Aug 24, 2011)

jmabray said:


> alternatively you could load up a sr-6 with 10 amp dimmer modules ...


At the beginning of this thread I looked for 10A Sensor modules, and all I found was the L10 Dual 10A Low Wattage Dimmer Module. Would that be the proper one, or is there an undocumented D10 or D10AF? Previously, an ETC spokesperson has commented that there's virtually no cost savings associated with using less than 20A modules.
-----
Esoteric, since you have partial infrastructure in place, SmartPack likely makes sense. If starting from scratch however, Sensor is probably more cost effective, in a largish system. Out of curiosity, how many 10A dimmers are you thinking?
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Esoteric said:


> ...210A per phase?


206.67A per leg. But remember, you don't HAVE to feed the dimmer rack with its full faceplace rating. See NEC 2011 520.27(C), and also the article at http://www.controlbooth.com/wiki/Collaborative+Articles:Dimmer+feeds--How+much+power+is+enough .


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## Esoteric (Aug 24, 2011)

This one would be 48 10A dimmers. And yes, they already have the 6 40A three phase breakers already in place.

Yes, I would like to know if there is a 10A module. I kind of took jm's word for it since he works for the ETC power up guys down here.

I have another project where 10A modules in a Sensor rack would be great (it has several 225A three phase breakers already in place).

We are in the prime renovation season. New installs begin in January.


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## SteveB (Aug 24, 2011)

Esoteric said:


> This one would be 48 10A dimmers. And yes, they already have the 6 40A three phase breakers already in place.
> 
> Yes, I would like to know if there is a 10A module. I kind of took jm's word for it since he works for the ETC power up guys down here.
> 
> ...



Some random thoughts:

There is no cost advantage to using 10a dimmers in a Sensor. Unlike the old LMI quad cards, you still only get 48 module slots in a full sized install rack. And it matters not how much power you provide. 

The issue then becomes real estate for a full size rack, as well as HVAC issues as compared to distributed.

Seems that if you have the infrastructure for shoebox packs, then that can be cost effective. Note though that a lot of shoebox are Triacs, which tend to be noisier (electronically) then regular SSR's with better chokes, which is one of the reasons the SSR systems are more expensive. Are you sharing power with audio ?.

Then consider that with shoebox you have a more complicated data distro scheme and you'd have to decide on old-school DMX everywhere (if the packs only take DMX, and Smartpack don't take Net2/3) or to do Cat5 and buy nodes to get DMX near the packs. That can add up in terms of infrastructure and hardware. And maybe check that the packs continue to pass DMX with zero power as daisy'ing 30 packs off one DMX line is sketchy ?. 

Then there's the continuous load issues. The distro breakers feeding the 40a outlets are not likely to be continuous rated, thus you downrate them by 20% for over 3hr use. So it's really a 32 amp breaker. Factor that into the equation in terms of add'l dimmers needed for the expected demand load.


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## derekleffew (Aug 24, 2011)

I agree with what you're saying, SteveB, except I wouldn't lump SmartPack Wall Mount Racks in with shoebox dimmers. We're not talking about the SmartModule here.


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## Esoteric (Aug 24, 2011)

Yeah, shoe boxes are completely out of the question. That is why I am looking at SmartPacks.

I am not talking about 40A outlets, I am talking about 40A 3 phase breakers.

There can be an advantage to using 10A dimmers in a Sensor. For example in the other project I have 225A to power 60 odd circuits. So being able to put 10A modules in a Sensor rack would be perfect. I don't want to use 20A dimmers because then there would be a chance of pulling too much power through the system.


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## JD (Aug 24, 2011)

chausman said:


> ok. I has read somewhere on here that it was limited to 32 (from JD I think) but I didn't know there was any chips that could allow you to have more then that.


 
Even without the MAX chips, you could tie 30 opto-splitters on. If each had 4 outputs, and each string had 30 dimmers, movers, etc. you would total 3600 units.

Also, a 96 channel rack with a common CEM only counts as one !

As you can see, even off the shelf equipment allows for almost unlimited data loading using "star" topology. Only single runs with standard chips have the limit.


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## chausman (Aug 24, 2011)

JD said:


> As you can see, even off the shelf equipment allows for almost unlimited data loading using "star" topology. Only single runs with standard chips have the limit.


 
I was just thinking single run when I said that.


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## Footer (Aug 25, 2011)

Esoteric said:


> Yeah, shoe boxes are completely out of the question. That is why I am looking at SmartPacks.
> 
> I am not talking about 40A outlets, I am talking about 40A 3 phase breakers.



Its the breakers that need to be down-rated. Most breakers/electrical systems are designed to hold their max load for a total of 3 hours. After that, they will theoretically trip. If you intend on loading them endlessly, you can only load them up to 80% of their max power. So, as Steve said, a 40 amp breaker becomes 32 amps. It has nothing to do with the method of connection to the service panel. You can get continuous load breakers that will allow you to use 100% of the power 100% of the time, however cooling needs to be taken into account. 


Esoteric said:


> There can be an advantage to using 10A dimmers in a Sensor. For example in the other project I have 225A to power 60 odd circuits. So being able to put 10A modules in a Sensor rack would be perfect. I don't want to use 20A dimmers because then there would be a chance of pulling too much power through the system.


 
The point is you will only be able to load up the system to the 225a amount. Use all 20amp modules you will be able to load 33 circuits fully. If you go beyond that, your disconnect trips. However, in a traditional setting this is really not a problem. ETC did a study a few years back and found that most modern venues put no more then a 1500w load on most dimmers. Therefore, at the "average" load, you can load up 54 dimmers, getting you really closed to that 60 mark. Bust down to 575 watt lamps and you will never hit it. The same thing is done in houses all the time. Most house have a 100 amp service. However, they might have 150 amps of distrobution. They assume that at no time will you be running the dishwasher, hot water heater, a/c, and have every single outlet in the house fully loaded at the same time. Its the same concept.


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## Esoteric (Aug 25, 2011)

Footer said:


> Its the breakers that need to be down-rated. Most breakers/electrical systems are designed to hold their max load for a total of 3 hours. After that, they will theoretically trip. If you intend on loading them endlessly, you can only load them up to 80% of their max power. So, as Steve said, a 40 amp breaker becomes 32 amps. It has nothing to do with the method of connection to the service panel. You can get continuous load breakers that will allow you to use 100% of the power 100% of the time, however cooling needs to be taken into account.
> 
> 
> 
> The point is you will only be able to load up the system to the 225a amount. Use all 20amp modules you will be able to load 33 circuits fully. If you go beyond that, your disconnect trips. However, in a traditional setting this is really not a problem. ETC did a study a few years back and found that most modern venues put no more then a 1500w load on most dimmers. Therefore, at the "average" load, you can load up 54 dimmers, getting you really closed to that 60 mark. Bust down to 575 watt lamps and you will never hit it. The same thing is done in houses all the time. Most house have a 100 amp service. However, they might have 150 amps of distrobution. They assume that at no time will you be running the dishwasher, hot water heater, a/c, and have every single outlet in the house fully loaded at the same time. Its the same concept.


 
You are correct on the top, but on the bottom:

They want all 62 circuits to get their own dimmer. So 62 20A circuits puts me well above the 225A breaker (It puts me in the 450A range). And, as an installer, I do not feel comfortable with doing that on a 225A breaker. Their current setup runs off of 24 20A dimmers and they still have room left over.

But what happens 3 years from now when they add equipment and someone new comes in who doesn't know the rack is limited, and maybe the breaker doesn't trip in time and a fire starts.

Not something I want anyone looking anywhere near me for.

That being said, does anyone have the part number on this 10A dimmer?


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## derekleffew (Aug 25, 2011)

Esoteric said:


> You are correct on the top, but on the bottom:


I'd argue the opposite, but we'll let that go for now. The "ETC Survey" alluded to can also be found via the wiki link cited:

derekleffew said:


> ... See NEC 2011 520.27(C), and also the article at Dimmer feeds--How much power is enough? - ControlBooth .




Esoteric said:


> ... And, as an installer, I do not feel comfortable with doing that on a 225A breaker. Their current setup runs off of 24 20A dimmers and they still have room left over.
> 
> But what happens 3 years from now when they add equipment and someone new comes in who doesn't know the rack is limited, and maybe the breaker doesn't trip in time and a fire starts.
> 
> Not something I want anyone looking anywhere near me for. ...


While I understand your concern (and it may be very valid in a non-professional setting) reduced feeders are used all the time. Did you read Steve Terry's Power Play article linked to above? There's currently a thread with this same debate on LightNetwork. 

Taking the other side, if you install only 10A dimmers, what happens if/when the user decides (s)he wants to use some 2K Fresnel s or cyc light s, or just has to two-fer two 750W lamps on one circuit?


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## Esoteric (Aug 25, 2011)

There won't be any 2K Fresnels or cyc lights (this is a church installation). In addition I don't think I would call this a "professional" setting. 90% of the users are volunteers.

Yup, I read the article. Doesn't mean I agree. We always do feeders at least 25% larger than needed. In this case it makes me very nervous to do simply the full feed.

Anyone have a part number on the 10A Sensor Module?


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## Esoteric (Aug 25, 2011)

I would love to hear from someone at ETC. I don't see a D10 listed on their site. But I do see a 10A module listed.


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## sk8rsdad (Aug 25, 2011)

Esoteric said:


> But what happens 3 years from now when they add equipment and someone new comes in who doesn't know the rack is limited, and maybe the breaker doesn't trip in time and a fire starts.



Two things:

3 years from now they will be bringing in LED fixtures and get no where near the theoretical maximum.
A fire won't start because the main breaker will trip when it is overloaded, even though individual branch circuits won't. At no point in the system is the wire undersized for the load. The weakest link is the breaker, not the rack.

Take for example my venue where we have 2 Sensor 48s (89 D20s, 6 R20s, and 1 D50) fed by a 400a service. It is theoretically possible for somebody to connect way more than 400a load, but it is highly unlikely. That would be one heck of a lot of instruments for my venue. It is also highly unlikely the entire rig would be running at full power at any point during a show.

Take for another example, it is always possible to connect a bigger load to that 15 amp receptacle near your computer. That's why they put the circuit breaker in the circuit.


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## Esoteric (Aug 25, 2011)

Yeah, but sometimes the breaker fails and then your house catches on fire.


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## starksk (Aug 25, 2011)

Esoteric said:


> I would love to hear from someone at ETC. I don't see a D10 listed on their site. But I do see a 10A module listed.


 
We do have a D10 Module as an option, but it is a custom module. There is not a standard part number because it is not often made.

I now return you to your debate on the use of 20A modules underloaded versus 10A modules fully loaded.


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## derekleffew (Aug 25, 2011)

Not so fast there, Kirk. 

In what application would the L10 Dual 10A Low Wattage Dimmer Module be used?

EDIT:
http://www.etcconnect.com/community/wikis/products/fluorescent-dimming.aspx :

> ETC in the past produced some forward phase modules that handled low loads better, known as the L10(110V) and AL5 (277V). The L series used MOSFET and IBGT technology to more accurately dim low wattage loads. Due to dimming control improvements in the Unison DRd rack and Sensor CEM+ control modules, these modules were discontinued as they were no longer needed.


So that's a big NO to the L10!

------

And if the D10 is a "custom module, not often made," does that make it more expensive than a D15 or D20?


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## starksk (Aug 25, 2011)

derekleffew said:


> Not so fast there, Kirk. In what application would the L10 Dual 10A Low Wattage Dimmer Module be used?


I see you found the answer as I was replying...


derekleffew said:


> And if the D10 is a custom module, not often made, does that make it more expensive than a D15 or D20?


I honestly do not know. Because it is a custom module, its list price is P.O.A....

 (I now? return you to your previous debate)


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## SteveB (Aug 25, 2011)

Additional to the issue of whether to use a 10 amp or 20 amp dimmer is going to be the wiring. 

I could be wrong but I believe the NEC requires a 20 amp minimum rated branch circuit wiring be used for theatrical systems ?. As well you are probably going to use 2P&G pin connectors ?. So zero cost savings at that end. 

If the D10 is custom, I'm betting all they do is swap the breaker to a 10 amp breaker, which is what they did for a 15 amp dimmer for the old NYC house lighting circuits. Everything else stays the same, SSR's and chokes and you don't get any add'l dimmers in the rack by downsizing. 

And if you go the SmartPack and still need to install wiring rated to 20a or better, as well as 2P&G, what do you save over a 20a Sensor rack, except possibly a lower cost for the SmartPack wall unit. 

One option might be to swap the 40amp 3 pole breakers for an 80 or so, letting you use a 12x2.4kw Sensor. It's not unusual to see a CB panel have space for a different sized breaker. We did this when we renovated a black box that had 4 - TTI 6x2.4kw packs fed on 40a, 3 pole breakers and we swapped the 4 40a breakers for 2 - 80 amp 3 pole breakers. It was pretty cheap.


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## Esoteric (Aug 26, 2011)

I have to get 48 dimmers. They already have distribution in place. So 12x2.4kW doesn't help anything, that is only 1/4 of the amount of dimmers the project needs. I would have to do 48x2.4kW which would require a 300A breaker.


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## sk8rsdad (Aug 26, 2011)

Esoteric said:


> I have to get 48 dimmers. They already have distribution in place. So 12x2.4kW doesn't help anything, that is only 1/4 of the amount of dimmers the project needs. I would have to do 48x2.4kW which would require a 300A breaker.



I know it has been said before but I feel like pounding my head against a brick wall  

It's OK to have engineering guidelines that say you can attach a maximum of 2.4kW to any individual circuit to a maximum of whatever the main breaker will sustain. It is done all the time. Heck, even shoebox dimmers do it.


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## Esoteric (Aug 26, 2011)

You can keep saying it again and again, but my ME won't do it, and my lawyer advised me that there could be liability issues if the system was not used properly and damage resulted. So, I am not going to do it.


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## shiben (Aug 27, 2011)

I happen to agree with Esoteric on this one. Its called minimizing risk, and with a 90% volunteer situation, you just dont want to run that risk, even if its tiny, that someone does something stupid and ends up burning the place. In a different thread we discussed BillESC? getting sued for selling some lifts that got blown over by wind. I wouldnt want to be the one who could be on the end of a "you installed a product that didnt trip before the main building breaker and that caused a fire due to some oddball situation". Spend 15 minutes on the dodgy technicians FB page and see how many times you find breakers taped to the open position so that it wont throw. I have seen it done in about 6 venues for various reasons, the one I left in a hurry and didnt touch anything more was "because it keeps popping". So I think Esoteric has the right idea here, make the system as safe as possible, then you can simply say "I installed the safest possible system available". Of course, hes gonna do it, and in a year and a half, we are gonna get a new guy on here from Dallas posting "some **** moron put 10A dimmers in our rack at my church, and I need to get a 2k Fresnel on one circuit. I thought about plugging it into 2 outlets, will this maim/kill anyone?"...


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## Gern (Aug 27, 2011)

Esoteric said:


> You can keep saying it again and again, but my ME won't do it, and my lawyer advised me that there could be liability issues if the system was not used properly and damage resulted. So, I am not going to do it.


 
Cool. Then its settled. 
Either you: 
1. Pay for the 10A dimmers. This sounds like what you'll end up doing.
2. Pay for the larger service, and use 20A dimmers. 
Find out what your AHJ says.
My stage 31 Strand racks @ Paramount have 606 dimmers equalling a total of 26,400A. 
The dead front switchboard has a 2500A breaker allowing me to only pull 7500A before it trips. The breaker is there to prevent over amping. When I (and the rest of my fellow 728 S.E.L.T.'s) feed a 1200A temporary distro box on set with anything smaller than 4/0, we are aware of the cables limitations. We do it all the time. 
I can see how you could doubt any thing I say, but I don't understand you doubting Steve Terry and the National Electric Code, if your AHJ says it is acceptable.


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## derekleffew (Aug 27, 2011)

shiben said:


> ...Spend 15 minutes on the dodgy technicians FB page and see how many times you find breakers taped to the open position so that it wont throw. I have seen it done in about 6 venues for various reasons, the one I left in a hurry and didnt touch anything more was "because it keeps popping". ...



NEC 2011 240.80:

> Circuit breakers shall be trip free and ...



From TRIP-FREE/NONTRIP-FREE CIRCUIT BREAKERS :

> A trip-free circuit breaker is a circuit breaker that will trip (open) even if the operating mechanism (ON-OFF switch) is held in the ON position.



While you have your code book out, again I'll point you to NEC 2011 520.27(C) . There's no changing Esoteric's mind on this, and that's fine, but I encourage others to read Mr. Terry's and others' wisdom expressed in the Light Network thread "Install Question".


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## Esoteric (Aug 27, 2011)

shiben said:


> I happen to agree with Esoteric on this one. Its called minimizing risk, and with a 90% volunteer situation, you just dont want to run that risk, even if its tiny, that someone does something stupid and ends up burning the place. In a different thread we discussed BillESC? getting sued for selling some lifts that got blown over by wind. I wouldnt want to be the one who could be on the end of a "you installed a product that didnt trip before the main building breaker and that caused a fire due to some oddball situation". Spend 15 minutes on the dodgy technicians FB page and see how many times you find breakers taped to the open position so that it wont throw. I have seen it done in about 6 venues for various reasons, the one I left in a hurry and didnt touch anything more was "because it keeps popping". So I think Esoteric has the right idea here, make the system as safe as possible, then you can simply say "I installed the safest possible system available". Of course, hes gonna do it, and in a year and a half, we are gonna get a new guy on here from Dallas posting "some **** moron put 10A dimmers in our rack at my church, and I need to get a 2k Fresnel on one circuit. I thought about plugging it into 2 outlets, will this maim/kill anyone?"...


 
Hahahaha... You know, 10 years ago I was that guy!!! I couldn't understand things like budget considerations, so I would spout off "well, they should have pulled new wire in from the main service, blah, blah, blah." *lol* 

But yes, we have gone over the limitations of such a system. And I also went over the possibility of putting in a larger rack on a smaller service, but I told them I wouldn't do it (because of the liability issues) so they would have to find someone else. They agreed on 10A dimmers.

And I can't imagine why they would want to use a 2K Fresnel in a space with 15'-20' throws. Except to melt singers faces off.

And no, I am not ignoring their thoughts. They are great thoughts, but it isn't their company that might have to pay out a giant settlement because the system was improperly installed. There is theory and then there is real life. I know it is only a 5% chance, but that would bankrupt my company. Heck, the attorney's fees to defend myself would put us behind the 8 ball for a while.


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## DavidNorth (Aug 27, 2011)

The feeds would not be unsafe, they are defined in the NEC, there is no risk of fire. Either solution is completely acceptable and I hope all can see that. You can feed 96 dimmers with a 20A breaker and if you put more than a few lights into the system, the only thing that happens is that the 20A feed breaker trips. Nothing is unsafe but it certainly is inconvenient when a show is being lit.

Do some math. Tell me how in the world you would ever take standard theatrical fixtures and create a 2400W load. This is difficult to do. At three 750W units, which is 2250W, you are still only at 18.5A. Over a 96 dimmer system, this is 600A but yet the nameplate rating of the rack is 800A. Unless you are loading up everything and turning it all on at the same time, 400A is plenty.

I think it makes sense to use the feed that is in place at 40A because of cost. Fully loaded 12 channel SmartPacks are going to pull 40A, 3 phase but the breaker will be able to supply 32A. You are still technically overloading the system, but, because the wire is of the NEC prescribed size, there still will be no fire. Oh, and there is no way you are going to fully load it.

Same situation....just a matter of choice and cost. Again, none of the solutions are bad, dangerous, or fire-inducing. There is no magic here.

David


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## Esoteric (Aug 28, 2011)

DavidNorth said:


> The feeds would not be unsafe, they are defined in the NEC, there is no risk of fire. Either solution is completely acceptable and I hope all can see that. You can feed 96 dimmers with a 20A breaker and if you put more than a few lights into the system, the only thing that happens is that the 20A feed breaker trips. Nothing is unsafe but it certainly is inconvenient when a show is being lit.
> 
> Do some math. Tell me how in the world you would ever take standard theatrical fixtures and create a 2400W load. This is difficult to do. At three 750W units, which is 2250W, you are still only at 18.5A. Over a 96 dimmer system, this is 600A but yet the nameplate rating of the rack is 800A. Unless you are loading up everything and turning it all on at the same time, 400A is plenty.
> 
> ...


 
There is a third possibility. The breaker doesn't trip, the wire heats up and causes a building fire. ;-) Breakers have failed in the on position before, I have replaced several.

But you are absolutely correct, I would not put the Smartpack dimmers on the system if the wire gauge could not handle the 40A load. So that even if the breaker fails you are still pulling the load intended for that wire.

All I know is the lawyer said that there was a good chance that system set up like that could be argued that it was setup incorrectly and would bring about liability issues that would cost either a settlement or a long, drawn out court case.

Neither of which is good for business.

So, before you install a system like that, consult your insurance agent and your lawyer.


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## DavidNorth (Aug 28, 2011)

Well, then I trust you will replace all the 40A breakers and wire in the system before it is energized so that you will avoid the possibility of fire. No telling whether they are still really in good shape or not. I'm sure your lawyer and insurance agent will agree.

Dude, I am completely on your side in your specific installation and application.

For all the other readers on this forum, I hope that you will read Steve's article and contact me if you have questions.

David


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## Esoteric (Aug 28, 2011)

Actually, since we aren't replacing the wire there is no liability there (since it is rated at the maximum draw of the fully loaded dimmer pack), and the breaker is rated to the full capacity of the rack, so there is no liability there either (according to the people who know about this stuff). Otherwise, yes we would insist on pulling through new wire and putting in a new breaker.

And I know you are. But I just wanted to get the advice out there.


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## kicknargel (Aug 29, 2011)

What I don't understand (in complete honesty) is: doesn't the code specify whether or not the rack could be connected to the lesser-rated service, and shouldn't the licensed master electrician and inspector on the job be able to make that determination, and if they sign off, shouldn't the lawyer defer to their expertise? Is this really a matter of opinion?


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## Esoteric (Aug 29, 2011)

kicknargel said:


> What I don't understand (in complete honesty) is: doesn't the code specify whether or not the rack could be connected to the lesser-rated service, and shouldn't the licensed master electrician and inspector on the job be able to make that determination, and if they sign off, shouldn't the lawyer defer to their expertise? Is this really a matter of opinion?


 
Keep in mind a lot of the code is in the interpretation. The city inspector has final say in all decisions. He may be reading the code completely wrong, but it doesn't matter if you are talking about getting things done.

We have an inspector in a nearby city that does not include any AV in the inspection. We have done complete installs (dimmers, LEDs, pulling new circuits) and needed no permit and no inspection. The inspector inspected to the breaker for the dimmer rack and no further.

In another city I work in the inspector requires a system rated to 25% more than the maximum labeled draw of the cabinet. It doesn't matter what you say, put in a breaker/wire that only meets the requirements, and he will red tag you.

Same thing with electricians. For example, as I said earlier, my electrician will not install a derated cabinet. He believes it is not safe and will not do it. I am sure I could find an electrician that would, but honestly, I like my guy. I know he doesn't cut corners. Everything is done in the safest way possible, to spec, and beyond code.

Keep in mind also that code is meant to be the MINIMUM guideline. It is the absolute least you should do.

Finally, court is the same way. The law, no matter how much we may think it is, is not black and white (especially in civil cases like we are talking about here). Like Bill said in another thread. You might be able to produce enough evidence to get out of a $125m lawsuit, but it is going to cost enough in attorney costs that it can bankrupt a small/medium sized company.

According to my lawyer, the inspector signing off on it does not end your liability, nor does any paperwork you give to the client, even meeting code does not necessarily end your liability. Everything you do is a risk. The question is how much of a risk do you want to take. I will even readily admit that derating a cabinet if done properly is probably a 1% chance of producing a result that will lead to a lawsuit. But is that a chance you want to take? Some people will say that lessening your probability from 1% to .5% is not worth it. To me, it is. Especially when I am not going beyond what I believe to be necessary.

Maybe it is because my guys aren't entertainment guys. Maybe it is because I learned electrics and engineering from outside the entertainment world. I dunno, but I have gotten legal advice about this and that is how it came out. I have never been in a situation where the savings is worth the risk.


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## Chris15 (Aug 29, 2011)

So I'm confused here.
How is a dimmer rack any different to a standard switchboard in terms of load calculation?
Unless you guys have wildly different electrical codes to us, it's quite safe, normal and legal to have a switchboard sub mains rated at less than the sum of all the breakers installed on it and often by a considerable margin. That's because they recognise the likelihood of everything drawing full load simultaneously is nigh zero and if that did happen the upstream protective device trips...


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## DavidNorth (Aug 29, 2011)

I suggested you replace the breakers because, in your experience, they may at some point fail on and to reduce your liability I would suggest that a new breaker may have a better chance of surviving and keeping you out of legal action. An overload in regular use may not happen, although technically it could [32A rated breaker with a 40A load], but a short-circuit might not open it if you say it can fail on. Where do you draw the liability line?

Listen, I'm being a jerk here to prove a point [isn't that how it usually is??] and mean no ill will. If the safety issue is based on possible overloaded conductors because a breaker may fail, note that the possibility is extremely rare. The NEC does indeed list minimums for a safe installation in order to reduce the possibility of fire. You do not have to do more than that to reduce liability.

A properly designed system relies on several things in order to be safe, none of which you will be liable for. These things include: wire manufactured without weak areas, breakers that operate correctly, wire not knicked or skinned in conduit, proper and sufficient grounding, product without design or manufacturing defects, and more. Will you be called in to court? Yes. Will you be able to show standards of design and installation? Yes. Then you are done.

ETC and other manufacturers, including breaker panel manufacturers, do make the recommendations that all of your resources do not like and we are not being taken to court. While I have no qualms with your specific design choices of full nameplate feed or 125% nameplate feed, I do want everyone to know that this is more than the NEC safe minimums. From there, readers and their customers can decide how to spend their money....on feeds or fixtures. I just can't in good conscience suggest that someone feed a rack with 1000A when it could only ever draw 640A. 

I would like to suggest that the non-entertainment electrician, lawyer, insurance agent and AHJ all be given a copy of Steve's article. It is not snake oil, is legal and safe, NEC-backed, proven, cost prudent, and is used as an education article for a large number of engineers and AHJS.

Design systems anyway you wish but please do not tell people they will end up with an indefensible lawsuit. It's just not true.

David


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## epimetheus (Aug 29, 2011)

Esoteric said:


> Actually, since we aren't replacing the wire there is no liability there (since it is rated at the maximum draw of the fully loaded dimmer pack), and the breaker is rated to the full capacity of the rack, so there is no liability there either (according to the people who know about this stuff). Otherwise, yes we would insist on pulling through new wire and putting in a new breaker.
> 
> And I know you are. But I just wanted to get the advice out there.


 
I almost hate to jump into this thread, but I feel I need to. The above argument applies to the supposedly under-rated main breaker that you're concerned will fail closed, just the same as is does to the 40A branch breakers, yet you're not replacing those and do not consider them a liability.

When I scope a project that requires modifications to an existing facility, I always include a clarification in the scoping document to the effect of "all existing systems are assumed to be in safe working order." Of course, if we find anything that is suspect during the job, we identify it to the client and provide them with a change order cost to resolve. Simply put, the onus is on the owner to maintain their equipment, not the next person who does an install.

You should do your install however you want, but you're essentially saying that following the NEC is unsafe.


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## STEVETERRY (Aug 29, 2011)

Esoteric said:


> Keep in mind a lot of the code is in the interpretation. The city inspector has final say in all decisions. He may be reading the code completely wrong, but it doesn't matter if you are talking about getting things done.
> 
> We have an inspector in a nearby city that does not include any AV in the inspection. We have done complete installs (dimmers, LEDs, pulling new circuits) and needed no permit and no inspection. The inspector inspected to the breaker for the dimmer rack and no further.
> 
> ...


 
I'm coming late to this party, because the power discussion was masquerading as an EIA-485 loading question!

I have a few thoughts:

1. Virtually every circuit breaker panel installed in the US applies derating between the main feed and the total of the pole-spaces in the panel. There is no functional difference between a listed dimmer rack and a breaker panel, for the purposes of this discussion. 

2. Section 520.27(C) was created because inspectors around the country were making up a bogus rule about feeding the dimmer rack at full nameplate rating. It had no basis in safety or even in the NEC prior to the appearance of 520.27(C). Initially, Code Panel 15 told us "You don't need this section, the Code already allows such derating in chapters 1 through 4." We produced an "expert opinion" from the then chief electrical inspector for the state of Washington stating that dimmer racks in article 520 venues had to be fed at the full nameplate rating. Only then did CMP15 realize that there was a big problem of inspectors "making up" code on this issue and that 520.27(C) was sorely needed.

3. If you want to spend your customer's money on fully rated feeds where they are not needed, fine. But please don't use the argument that the breaker might fail and thus set the building on fire. That is simply a specious argument, since the safety of every code-compliant electrical system depends on functional overcurrent protective devices. And, to require 125% of the nameplate rating has no basis in engineering fact or common sense, UNLESS the likely inventory plugged into the system will load it to 100% and be operated at full for more than three hours. This might happen on a very small system in a specialized application, but is so unlikely on a normal dimmer-per-circuit performance lighting system that it is rarely considered.

4. Section 520.27(C) actually contemplates the possibility of overloading the service and tripping the overcurrent protective device. That is why egress lighting must not be fed from a derated service.

5. Even if 10A Sensor modules were available, you would actually be doing the end user a disservice by using them. Why? You are forcing system derating at the dimmer level. the user can no longer deploy the available power where needed, you have forced them into your derating scheme, rather than theirs.

6. Any system derating should allow some reasonable overhead and room for expansion, but that is very unlikely to be 100% of the nameplate rating, except on very,very small systems. It certainly will never be 125% of the nameplate rating, except as in (3) above.

7. If you have an electrician who refuses to install derated feeds per 520.27(C) and an attorney who supports that view due to "liability", all I can say is that such thinking represents a tiny minority, not supported by facts. 

8. Most people who support fully rated feeders to a performance lighting system fail to realize the impact on the cooling system for the building. For instance, if there is 50 kW of fixture inventory in a system, but 230 kW of feeder and dimmer capacity, that can mean 230 kW of air conditioning capacity for the stage and auditorium as well. The cost of such an increase in the cooling system makes the cost of the larger feeders seem like chump change. And these are "empty dollars"--they don't add to the usability of the performance space in any way.



ST


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## Esoteric (Aug 29, 2011)

Well, all this it seems was for naught. The client with the 225A breaker is letting us pull in a new feed. So no need to derate anywhere.

Thanks for the discussion guys.

Mike


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## jonliles (Aug 29, 2011)

Esoteric said:


> Well, all this it seems was for naught...



I would not say it was for naught, solid discussion was held and knowledge was gained.


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## derekleffew (Aug 29, 2011)

Esoteric said:


> Well, all this it seems was for naught. The client with the 225A breaker is letting us pull in a new feed. So no need to derate anywhere. ...




Esoteric said:


> ...They want all 62 circuits to get their own dimmer. ...


So is it your intent to specify a SR-48 rack, load it with 31 dual 20A D20 modules (+17 AFM), and feed it with 413A/leg?


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## STEVETERRY (Aug 29, 2011)

Esoteric said:


> Well, all this it seems was for naught. The client with the 225A breaker is letting us pull in a new feed. So no need to derate anywhere.
> 
> Thanks for the discussion guys.
> 
> Mike


 
I am sorry we were not able to change your view of derating.

ST


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## Esoteric (Aug 29, 2011)

derekleffew said:


> So is it your intent to specify a SR-48 rack, load it with 31 dual 20A D20 modules (+17 AFM), and feed it with 413A/leg?


 
My electrician is pulling a 425A 3 phase breaker for the system (I believe, it has been a long day). Unless I need to pull more to cover the AFMs. But I figured their draw was negligible. I haven't sat down with my ME yet, we just got the okay to pull the new feed today.


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## STEVETERRY (Aug 29, 2011)

Esoteric said:


> My electrician is pulling a 425A 3 phase breaker for the system (I believe, it has been a long day). Unless I need to pull more to cover the AFMs. But I figured their draw was negligible. I haven't sat down with my ME yet, we just got the okay to pull the new feed today.


 
AFM's (air flow modules) don't even consume air, much less power.

ST


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## STEVETERRY (Aug 29, 2011)

jonliles said:


> I would not say it was for naught, solid discussion was held and knowledge was gained.


 
I agree, this kind of discussion is invaluable for everyone participating, even if the unconvinceables remain unconvinced! 

ST


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## Esoteric (Aug 29, 2011)

STEVETERRY said:


> AFM's (air flow modules) don't even consume air, much less power.
> 
> ST


 
Hahaha. Right O!


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## LightStud (Aug 29, 2011)

STEVETERRY said:


> I agree, this kind of discussion is invaluable for everyone participating, even if the unconvinceables remain unconvinced!
> 
> ST


It's like discussing evolution or climate change with a Republican.


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## derekleffew (Aug 29, 2011)

Esoteric said:


> My electrician is pulling a 425A 3 phase breaker for the system (I believe, it has been a long day). Unless I need to pull more to cover the AFMs. But I figured their draw was negligible. I haven't sat down with my ME yet, we just got the okay to pull the new feed today.


So what size wire are you going to use with that 425A 3 phase breaker? Will the neutral be the same, higher, or lower than the hot legs? Size of the grounding conductor?


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## FMEng (Aug 29, 2011)

derekleffew said:


> So what size wire are you going to use with that 425A 3 phase breaker? Will the neutral be the same, higher, or lower than the hot legs? Size of the grounding conductor?


 
Boy, Derek really likes to open a can of worms. Let's be sure to rate the neutral for the waveform peak current, not RMS, because you never know.....

I don't mean this to sound harsh, but I don't suppose anyone gave consideration that up stream of this grossly over-sized 425 Amp breaker is the main service busses, the main service breaker, a transformer, and primary fuses that probably aren't size for anything near this much "real" load being added.

I guess the theory is that it's better if the transformer explodes and the whole building goes dark instead of risking having the dimmer rack trip its feed on the nearly impossible chance that all of the dimmers are somehow loaded to their full rating. 

If the OP is really that concerned with consequences and liability then he should have a licensed electrical engineer review and design the entire service and distribution system and he should stay far away from that portion of it. That's the responsibility that the engineer gets paid the big bucks to take, and even the lawyers and insurance folks would be happy with that decision.


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## Esoteric (Aug 30, 2011)

FMEng said:


> Boy, Derek really likes to open a can of worms. Let's be sure to rate the neutral for the waveform peak current, not RMS, because you never know.....
> 
> I don't mean this to sound harsh, but I don't suppose anyone gave consideration that up stream of this grossly over-sized 425 Amp breaker is the main service busses, the main service breaker, a transformer, and primary fuses that probably aren't size for anything near this much "real" load being added.
> 
> ...


 
Yes, all plans are reviewed by a licensed electrical engineer. And everything upstream is able to handle the "real" load.


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## Esoteric (Aug 30, 2011)

derekleffew said:


> So what size wire are you going to use with that 425A 3 phase breaker? Will the neutral be the same, higher, or lower than the hot legs? Size of the grounding conductor?


 
As soon as I talk to my ME I will let you know.


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## Esoteric (Sep 30, 2011)

Just an update, gave the client the option and they decided not to overpower the system, so we are headed out to Knoxville, TN in November to install an ETC Sensor 96 rack with 62 10A dimmers and a Unison 24 rack full with 20A dimmers.

And yes, all the necessary permits have been applied for. *lol*

Anyone suggest good places to eat in Knoxville?


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