Stage area with 800a light dimming rack ?

[Michael J.Kitta]

Is a disconnect switch needed for a stage dimming system rack that only has MLO from supplier? Should a disconnect sw be located beside this dimming rack?

 

[tryinghard]

Are you working from construction drawings? It might be similar to a panelboard if so see 408.36, Article 404 doesn't seem to address this.

 

[dbuckley]

Should a disconnect sw be located beside this dimming rack?

Yes, because people will want to switch the dimmers off from time to time, one one of those times they may want to do it in a hurry.

 

[brantmacga]

dimming racks are subject to article 520, and part IV of 408.

i don't see where you're required to install a disconnect @ the rack; the breaker in the MDP is all you need, and a lock-out if servicing.

 

[Rockyd]

dimming racks are subject to article 520, and part IV of 408.

i don't see where you're required to install a disconnect @ the rack; the breaker in the MDP is all you need, and a lock-out if servicing.

I can see where it would be handy to have a disconnect (speed of show biz) but would have to check otherwise.

 

[brantmacga]

I can see where it would be handy to have a disconnect (speed of show biz) but would have to check otherwise.

If the customer is willing to pay for an 800A 3ph disconnect, go for it. But if I were bidding this, I wouldn't include a disconnect in the price unless the plans called for it.

 

[Besoeker]

If the customer is willing to pay for an 800A 3ph disconnect, go for it. But if I were bidding this, I wouldn't include a disconnect in the price unless the plans called for it.

I looked at this thread a couple of times and wondered what was meant by "800a light dimming rack".
Is it really 800 A 3-phase? That's an awful lot of controlled lighting.

 

[brantmacga]

I looked at this thread a couple of times and wondered what was meant by "800a light dimming rack".
Is it really 800 A 3-phase? That's an awful lot of controlled lighting.

i would certainly think its 3-phase.

can't recall ever seeing a single phase rack that size.

 

[Jacob S]

Not to strange at all. Typically there will be multiple racks bussed to a single 800amp feed. Normally, there is not a local disconnect, unless the transformer is right next to it and the OCP happens to be right there.

 

[sameguy]

I did one about 10 yrs. ago for one of the local high schools here in upstate NY., you should see the head end equipment they put in.
After all it is only tax payer money around here, why not have better than the local tv stations; need to keep up with S.U.

 

[SmithBuilt]

I just finished wiring a 400 amp dimmer rack. I agree a disco is not required as stated above. However, the way the rack is made I liked having the disco close by for service work.

 

[dbuckley]

I looked at this thread a couple of times and wondered what was meant by "800a light dimming rack".
Is it really 800 A 3-phase? That's an awful lot of controlled lighting.

If the dimmers are typical 2.4KW/channel dimmers (20A), then that could be as few as 120 channels if no diversity had been taken into acount. It'll probably be a lot more, as (a) most channels aren't loaded to 20A (these days more lamps are 575W than 2KW), and (b) "dimmer per socket" installations are now almost the norm, meaning that for any given production a lot less than "all" sockets (and thus dimmers) would be needed.

Whatever the NEC says, I still say that it is god practice to put a disco next to the dimmers. As a user of such systems, I'd wonder why the venue would spend $$$$$ on dimmers, and then cheap out by not providing the switch that will be needed when someone touches a the hot pin of a stagepin connector when he's up the top of a ladder and his other hand is on the bar...

 

[brantmacga]

. . . . when someone touches a the hot pin of a stagepin connector when he's up the top of a ladder and his other hand is on the bar...

how are they going to touch a hot pin?

its no different in terms of safety than a 5-15R.

 

[Besoeker]

If the dimmers are typical 2.4KW/channel dimmers (20A), then that could be as few as 120 channels if no diversity had been taken into acount. It'll probably be a lot more, as (a) most channels aren't loaded to 20A (these days more lamps are 575W than 2KW), and (b) "dimmer per socket" installations are now almost the norm, meaning that for any given production a lot less than "all" sockets (and thus dimmers) would be needed.

We, as a company, make dimmers and we have some very large systems installed mostly in commercial applications like theaters and large hotels. It isn't my division of the company - we do almost exclusively industrial power electronic systems. But now and again I get called in to review the design of some of the lighting projects - usually after the event when harmonics have come to bite them in the backside.

A project I'm currently involved with is in the final stages of installation (by others) and, as it happens, is a theatre for the performing arts. I've just taken a look at the project documentation. There are over 600 channels of controlled lighting but they are spread between 24 racks the largest of them with 48 channels. Each rack has a 4-pole breaker at its input for protection and isolation. The largest is 100A but bear in mind that we work with a 400V/230V system.

That's some background on why I questioned an 800A light dimming rack.

 

[Jacob S]

As a user of such systems, I'd wonder why the venue would spend $$$$$ on dimmers, and then cheap out by not providing the switch that will be needed when someone touches a the hot pin of a stagepin connector when he's up the top of a ladder and his other hand is on the bar...

Except in very old venues, I can honestly say I have never seen a stage lighting rack installed near the stage deck or a location that is open and readily accessible to make the installation any safer, in your example.

 

[dbuckley]

how are they going to touch a hot pin?

'cos theres plenty of old style stagepins knocking around that happily let you put the plug in wrong making the metalwork of a fixture hot. If the fixture is clamped onto a bar then theres a flash when you plug the thing in and the breaker pops. if you have the lantern in your hand however...

Except in very old venues, I can honestly say I have never seen a stage lighting rack installed near the stage deck or a location that is open and readily accessible to make the installation any safer, in your example.

Really? I guess US practice must differ from some other jurisdictions then. Permanently installed dimmers usually are in their own room, but often quite close to the stage area. Its usually accessible (ie unlocked) because even with dimmer per channel, the DMX patching often needs looking at, especially when a touring buch arrive with their own controls.

 

[brantmacga]

'cos theres plenty of old style stagepins knocking around that happily let you put the plug in wrong making the metalwork of a fixture hot. .

oh yeh, that is true. i thought you meant touching the actual pin on the male end.

 

[zbang]

'cos theres plenty of old style stagepins knocking around that happily let you put the plug in wrong making the metalwork of a fixture hot. If the fixture is clamped onto a bar then theres a flash when you plug the thing in and the breaker pops. if you have the lantern in your hand however...

I don't think I've seen a 2-pin pin/bates connector in at least 25 years (with the single exception of an old patch panel). You're also assuming that the case is wired to the supposedly-grounded lead, which is even less common. In 35 years, I've probable seen a couple of those, which were quickly fixed. Was it common in your area?

Really? I guess US practice must differ from some other jurisdictions then. Permanently installed dimmers usually are in their own room, but often quite close to the stage area.

Really a case of It Depends. Sometimes it easier or cheaper to put all the dimmers in one place and sometimes they're sprinkled around the building.