New Dimmers, able to keep 200 amp disconnect?

[nffy212]

I am the Lighting and Sound Designer/Director for a high school and we are replacing our dimmers next week. The old system consists of 216 Electro-Controls quad pack dimmers, several 20 amp breakers and relays for worklights, and a 200 amp breaker for a disconnect on stage- all in 3 racks.

The new system will be 2 full Sensor racks, a 24 dimmer Unison Rack, and smartlink & Net3 equipment. Both systems have been and will be fed from a 800 amp service right off of a transformer in the same room. The new control rack will be wired with a 20 amp leg from another main breaker that is elsewhere, so it is not factored in the equation.

During the electrician's walkthrough, he was not sure that we would be able to keep the 200 amp disconnect that is located on stage. What is Control Booth's take on this? As far as I'm concerned, the load would be the same. The only thing I could think of is if ETC has more strict specs for the power requirements of the racks.

Liability Disclaimer: I am not a licensed electrician, nor do I have any direct authority on the final outcome of the situation. I am just curious of the possible outcomes.

 

[Edrick]

So you want to use the current 200A disconnect to power the new gear or keep the old 200A disconnect to use for future stuff on top of the new system?

 

[derekleffew]

...The only thing I could think of is if ETC has more strict specs for the power requirements of the racks. ...

ETC's specs are no more strict nor lenient than anyone else's.

I'm guessing those in charge are concerned because some of the dimmers will control houselight circuits, in which case NEC 520.27(C)(2) would apply because:
The dimming system or rack is being fed less than the full faceplate rating, and
The system controls egress or emergency lighting.
See the PDF article linked to at Dimmer feeds--How much power is enough? - ControlBooth .

Personal opinion:
The 200A disconnect must be considered a 200A load (whether or not you will ever attach that much to it). This leaves 600A for 192x2.4kW stage dimmers + 24x2.4kW houselight/worklight dimmers, which is a little thin but depends on your existing and anticipated future lighting inventory. Point the powers-that-be to this thread and especially to the Power Play article, and trust that they will make the correct decision.

... and we are replacing our dimmers next week. ...

In that case the decision has already been made, and can be revealed by careful examination of either ETC's or the contractor's drawings.

 

[VCTMike]

The old system consists of 216 Electro-Controls quad pack dimmers, several 20 amp breakers and relays for worklights, and a 200 amp breaker for a disconnect on stage- all in 3 racks.

Couple of questions...

Is the old system spoken for?

If not...
a. What is the condition of it?
b. Are you going to scrap it, donate it to a worthy Upstate NY theatre or try to sell it?
c. Where are you located?

Thanks,
Michael

 

[STEVETERRY]

I am the Lighting and Sound Designer/Director for a high school and we are replacing our dimmers next week. The old system consists of 216 Electro-Controls quad pack dimmers, several 20 amp breakers and relays for worklights, and a 200 amp breaker for a disconnect on stage- all in 3 racks.

The new system will be 2 full Sensor racks, a 24 dimmer Unison Rack, and smartlink & Net3 equipment. Both systems have been and will be fed from a 800 amp service right off of a transformer in the same room. The new control rack will be wired with a 20 amp leg from another main breaker that is elsewhere, so it is not factored in the equation.

During the electrician's walkthrough, he was not sure that we would be able to keep the 200 amp disconnect that is located on stage. What is Control Booth's take on this? As far as I'm concerned, the load would be the same. The only thing I could think of is if ETC has more strict specs for the power requirements of the racks.

Liability Disclaimer: I am not a licensed electrician, nor do I have any direct authority on the final outcome of the situation. I am just curious of the possible outcomes.

So, if I understand your post correctly, the 200A breaker currently feeding the disconnect is going away with the old system. Unless the ETC drawings show a replacement 200A breaker for that purpose, the contractor will have to provide a stand-alone breaker or set of fuses to feed that disconnect. This will no doubt involve tapping the 800A feed (using the NEC "tap rule"), and feeding the disconnect from the new overcurrent protective device. There is no rule to prevent this, but proper fault current coordination will be needed from an engineer or contractor with this ability.

ST

 

[RJMS]

Your Electrician is correct in his assessment. You no longer have a great need for that "company switch" 200a disconnect FOR LIGHTING USE, and it should go away unless it can be fed from a different tap on the new transformer or thru a breaker that is separate then the main breakers for your new gear. Your new dimming equipment will go a very long way in powering your lighting gear, and the 800 amp is needed in it's entirety for the new gear and future expansion of your inventory.

It is possible that the original intent for that 200 amp switch was to power a portable sound system, as that is a normal size that is often provided for that purpose.

The questions are: do you ever hire a professional sound company to provide concert sound? Is there already another "company switch" for sound? If one is not currently there and one is required, it normally is run from a separate transformer (or an isolation transformer is provided in between the main transformer and the new sound "company switch".

 

[derekleffew]

...You no longer have a great need for that "company switch" 200a disconnect FOR LIGHTING USE, and it should go away unless it can be fed from a different tap on the new transformer or thru a breaker that is separate then the main breakers for your new gear. Your new dimming equipment will go a very long way in powering your lighting gear, and the 800 amp is needed in it's entirety for the new gear and future expansion of your inventory. ...

Thinking on this some more...
Old System:
216 EC dimmers + "several 20 amp breakers and relays for worklights"
Likely installed 1982-1986

New System:
216 (192+24) ETC Sensor dimmers

As the OP correctly stated, "As far as I'm concerned, the load would be the same." If anything, the load might go down, as the 575W lamp has replaced the 1000W as the industry standard.

I still think the key is NEC 520.27(C)(2), which [-]probably[/-] didn't exist during the original installation. [EDIT: It didn't, until 1993. See the first paragraph of Mr. Terry's Power Play article.] Any reason you didn't address this, STEVETERRY? Is it because even without the 200A disconnect, the system is in violation of 520.27(C)(2), because since it involves houselight dimmers, the system would need 640+640+160=1440A service?

...You no longer have a great need for that "company switch" 200a disconnect FOR LIGHTING USE, and it should go away unless it can be fed from a different tap on the new transformer or thru a breaker that is separate then the main breakers for your new gear. ...

While I agree with the first part, I would fight like heck to keep the company switch. Audio, projections, automations, lighting for a video shoot, a TV truck--all could find it useful. I'd rather have it there and never use it than not have it and need it.

 

[TimMiller]

I have been to several schools that you would think was a road house with the quantity and quality of gear but did not have a way to tie in power for movers. So out behind their nice theater I had to park a generator which takes away from the show budget.

 

[derekleffew]

...So out behind their nice theater I had to park a generator which takes away from the show budget.

DOH! Yes, moving lights--a very fine reason to have a company switch. Unless one wants to forever limit oneself to the 120V variety.

 

[SteveB]

As others have stated, that 200 will be useful for something and I'd fight to keep it. There's no apparent legal/code reason to remove it, unless the install electrician is not telling you something related to needing to clear out the feed for the 200 to make room for the 800. And just to be clear, that existing 200 is the current feed for all the existing 216 dimmers/relays and work lights ?. Is the 200 currently tapped of the transformer that will feed the 800 ?. If so, obviously the electrician will have to provide some form of over-current protection at/near the transformer for that 200, unless it exists already. Obviously there's going to be a new panel fed from the transformers with circuit breakers feeding the 2 Sensors, as well as the Unison and the SmartLink. Possibly the need to keep and include the 200 with it's resulting increase in cost is driving the decision.

Possibly the electrician is seeing the new 800 for the new dimmers as well as the existing 200 as too much demand on the transformer, not understanding the difference between connected load (all the dimmers if used at full) and demand load, with a much smaller load based on actual fixture count and their wattages.

In general, if you have power in the building, keep that power in the building. If they remove it, they remove all of it, conduits, cabling and company switch. It's cheaper to tie it into the existing sub panels then to have to come back and add all that hardware later.

As separate issue is the power to house lighting. Since you mention a Unison pack it's assumed that is for house lighting, which is a common application for a Unison system. Is there a separate and stand alone flood light system, battery or generator powered that provides emergency egress lighting ?, or is that factored in to the Unison system ?. Is there a automatic transfer system to generator for the Unison pack ?. Many questions exist as to the system design and layout.

 

[STEVETERRY]

Thinking on this some more...
Old System:
216 EC dimmers + "several 20 amp breakers and relays for worklights"
Likely installed 1982-1986

New System:
216 (192+24) ETC Sensor dimmers

As the OP correctly stated, "As far as I'm concerned, the load would be the same." If anything, the load might go down, as the 575W lamp has replaced the 1000W as the industry standard.

I still think the key is NEC 520.27(C)(2), which [-]probably[/-] didn't exist during the original installation. [EDIT: It didn't, until 1993. See the first paragraph of Mr. Terry's Power Play article.] Any reason you didn't address this, STEVETERRY? Is it because even without the 200A disconnect, the system is in violation of 520.27(C)(2), because since it involves houselight dimmers, the system would need 640+640+160=1440A service?

While I agree with the first part, I would fight like heck to keep the company switch. Audio, projections, automations, lighting for a video shoot, a TV truck--all could find it useful. I'd rather have it there and never use it than not have it and need it.

I assumed that either:

A. The houselights were on the Unison rack and a separate feed, or
B. There was some acceptable egress lighting other than houselights (some nasty non-dimmed fluo worklights or some such would comply--1 fc is the life-safety code requirement.)

But if the only egress lighting is fed from the stage dimmer main breaker which also feeds the Unison rack, then your calculation is right.
ST