Control/Dimming Touring Dimmers

[lighttechie5948]

Hi guys,

I'm working on a production in June that is renting a High School theatre to produce their show. This venue's overstage electrics only have six 2.4k dimmers per electric, which isn't enough with the amount of lights I hang per electric and the booms which I need to run cable to.

In the past I have rented "shoebox dimmers" as the rental shop calls them. They are basically dimmer boxes with 4 1.2k dimmers. I then plugged those into the 2.4ks overstage and hot patched them, so I'd get 4 channels per original dimmer.

However, I've been thinking it'd be much easier to just bring in a 48 channel touring rack than to spend all that time hanging the dimmer packs, addressing every single one, and putting a stage pin adapter in each edison input.

How hard would it be to set up a touring rack in this theater? I know we would need to get power somehow to it. Is this done easily? Could one of my lighting electricians do it or would it require a licensed electrician? Is it simple or would the school get mad at us for doing it?


All help is appreciated.


Joe

 

[Footer]

It really just depends on how much, if any, power there is on stage. You would need a company switch or a disconnect on stage with at least as much power as you are going to draw.

Keep in mind, your going to have to rent a good amount of socopex, the rack itself, and feeder. Your probably going to end up running much more cable then you would with the shoebox dimmers.

If you don't have any power in the venue, it is possible to put a disconnect or company switch in. This could be easy to do, it could be VERY hard and VERY expensive to do.

 

[SteveB]

Hi guys,

In the past I have rented "shoebox dimmers" as the rental shop calls them. They are basically dimmer boxes with 4 1.2k dimmers. I then plugged those into the 2.4ks overstage and hot patched them, so I'd get 4 channels per original dimmer.

Joe

This is, BTW a huge No-No. You've gotten away with it, but dimmers set to Hot-Patch and/or Non-Dim mode can still skew the 60 cycle waveform, which in turn can cause trouble with the electronics in the shoebox dimmers. Such dimmers really want dedicated power direct from a distro, any regular AC outlets and/or relay or constant modules in place of the 2.4kw dimmers.

As to the 48 dimmer touring rack ?. You need to have a qualified and licensed electrician survey the available power to see if there's a tap point (also known as a Company Switch) to provide the power to the touring rack. Also check with the rental company to make sure, but typically a 48 x 2.4kw rack comes with a built in 200 amp feed circuit breaker. If you can "tie-in" the rack within 5 ft of the switch providing power, you don't need a separate distro. just for the dimmer rack. Typically rent along with the rack a set of 5ft., 5 wire Camlok "tails", sized to the rack, which have the appropriate connectors to connect the rack to the switch as well as bare ends to connect to the service panel lugs (if any).

Note also that local codes prevail, but the US National Electrical Code does not require you to connect to a panel that has capacity equal to the connected load of the rack. Connected load is the number of breakers times their rating (20 amps typical) divided by 3 phases - IF it's a 3 phase switch. Thus a 48x2.4kw dimmer rack has a "connected " load of 320 amps per phase (typical commercial 3 phase supply). The Nat'l code essentially say's you supply a feed sufficient for actual "Demand" load, which is the quantity of lighting fixtures, times their wattage, etc... Typical calculation might be a single S4 @575 watts per dimmer, times 48 dimmers/fixtures, total wattage of 27,600, divided by 120 volts = 230 total amps, divided by 3 phases = approx. 77 amps per phase.

 

[JD]

That's opening up Pandora's shoe box dimmer! What will rule the moment is the budget. Using a rack based system with feeders, company switch, tons of Soco is the right way to do things but it's going to blow the lid off the budget. Generally, shoe box dimmers are cheap to rent, but make sure they are run on clean supply circuits and that the dimers themselves are UL pieces.

 

[bishopthomas]

If you can "tie-in" the rack within 5 ft of the switch providing power, you don't need a separate distro. just for the dimmer rack.

Is this a code issue? I've never heard of that one. What does it matter if the distro is part of the rack or not, and what does 5' have anything to do with it? I've NEVER seen anyone use a separate distro because the dimmer rack was more than 5' from the mains supply. I'm not questioning that you know something that I don't, but I really don't understand the thinking here.

 

[Footer]

Is this a code issue? I've never heard of that one. What does it matter if the distro is part of the rack or not, and what does 5' have anything to do with it? I've NEVER seen anyone use a separate distro because the dimmer rack was more than 5' from the mains supply. I'm not questioning that you know something that I don't, but I really don't understand the thinking here.

What he is speaking of is tie in directly to the feeder lugs of a panel bypassing the panel completely. Its something film guys do pretty often. If done to code, you can do this. Its a short term and very temporary solution. If you are ever going to bring a rack into this place more then once, get a proper disconnect installed. If there is a panel you can tie into on stage already, it would be pretty easy to put in a disconnect.

 

[SteveB]

Bishop you're not crazy and Kyle interpreted it correctly, so here's what my brain was thinking but fingers forgot to add. If your tie-in panel has no sufficient feeder protection, as long as you are within 5ft. of the panel, the rack breaker can serve as the protection. You also see this on occasion with an added piggy-back panel permanently installed after-the-fact. The installer will place new panel within 5ft. of old panel, tapping the old panel feed lugs directly, with new panel having the main for the new panel. Easier then trying to retro-fit a main breaker into old panel.

Note that this is far from ideal and hopefully the electrician doing the connection will have a panel with over current protection of a size at or smaller then the connected load of the rack.

 

[len]

T If you can "tie-in" the rack within 5 ft of the switch providing power, you don't need a separate distro. just for the dimmer rack. Typically rent along with the rack a set of 5ft., 5 wire Camlok "tails", sized to the rack, which have the appropriate connectors to connect the rack to the switch as well as bare ends to connect to the service panel lugs (if any).

Most dimmer racks I've seen have a main breaker, and a breaker on each soca side, along with test switches for each circuit. I can't imagine needing a distro as well just to act as a main circuit breaker for the dimmer rack. As for 5', I think that's just the length of most common tail sets. I've run dimmers and distros with 100' and more of feeder because the panel was not where the dimmer needed to be.

To the OP, if you rent a rack dimmer, sit down with them and ask them based on what you're trying to do. Most rental shops who have this kind of equipment will work with you to get you what you need. They won't just give you a bunch of equipment just because you ask for it. They will have nearly as much invested in your success as you do.

 

[bishopthomas]

Thanks for the clarification, guys. Although, like Len, I don't see the point if the distro has a main breaker. Furthermore, I have been to venues where the staff city electricians tie us in directly to the lugs. We're running at least 100' of feeder every gig, plus sometimes on outdoor gigs they're running cabling to get it from the street to the stage. Maybe it's not "code" but it is certainly done and I see no issue with it.

 

[derekleffew]

Bishop you're not crazy and Kyle interpreted it correctly, so here's what my brain was thinking but fingers forgot to add. If your tie-in panel has no sufficient feeder protection, as long as you are within 5ft. of the panel, the rack breaker can serve as the protection. You also see this on occasion with an added piggy-back panel permanently installed after-the-fact. The installer will place new panel within 5ft. of old panel, tapping the old panel feed lugs directly, with new panel having the main for the new panel. Easier then trying to retro-fit a main breaker into old panel. ...

Can someone explain where this "5 foot rule" is coming from. Perhaps from Tap rule?
Tails are limited to no longer than 10 feet, according to the draft of BSR E1.18-1 Standard For The Selection, Installation, And Use Of Single-Conductor Portable Power Feeder Cable Systems For Use At 600 Volts Nominal Or Less For The Distribution Of Electrical Energy In The Entertainment And Live-Event Industries.

... Its something film guys do pretty often. If done to code, you can do this. ...

I find it rare that film guys, when on location, do anything "to code." FWIW.

 

[SteveB]

Can someone explain where this "5 foot rule" is coming from. Perhaps from Tap rule?
Tails are limited to no longer than 10 feet, according to the draft of BSR E1.18-1 Standard For The Selection, Installation, And Use Of Single-Conductor Portable Power Feeder Cable Systems For Use At 600 Volts Nominal Or Less For The Distribution Of Electrical Energy In The Entertainment And Live-Event Industries.


I find it rare that film guys, when on location, do anything "to code." FWIW.

Derek, My understanding of this, and I could well be mistaken, is it's not a section 520 issue, but a general electrical code issue about how a second distribution panel (such as a dimmer rack) must be located in such a way so as to be in proximity to the primary distribution panel so that the feeders are no longer then 5ft in length, when the feeders for the secondary panel are connected to the primary feed taps, with no over current device(s) provided for in the primary panel.

The general application I've encountered is when a new permanent secondary circuit breaker panel is being installed and the feed to it is coming off an existing panel. Often there's no method to provide for a main breaker in the existing panel of sufficient size to protect the new panel, thus the new panel comes with a main breaker and the new panel is 5ft or less from the existing.

My understanding and having asked an electrical engineer about this, was it applied to dimmer racks as well. Typical application would be a connection to a panel with no disconnect ability. You need to use tails of 5ft or less connected to the dimmer rack, OR use a disconnect within 5ft, then feed the dimmer rack downstream at desired feeder length. Which is how I've always done such a connection, on a live tap, having a main disconnect local and dimmers downstream.

Perhaps Steve T might know a more definitive answer.

 

[bishopthomas]

... OR use a disconnect within 5ft, then feed the dimmer rack downstream at desired feeder length.

Which is what the mains breaker in the distro/dimmer rack is for.

 

[SteveB]

Which is what the mains breaker in the distro/dimmer rack is for.

True, but the million dollar question is, when tie'ing in to a panel with no breaker does a mains breaker for the rack need to be within 5 ft. ?.

Note that I could be smokin' crack on this, bit will do some add'l research in my '08 Nat'l Code book.

SB