Dimmer rack CB/disconnects

Jay Ashworth

Jay Ashworth

Well-Known Member
One of my venues has about a 10x10 room with 2 48-channel (I think) CD-80 racks in it, mostly fully populated.

It's been awhile since I've been in the room, but I think the CBs are inside that room -- and I think code *requires* the disconnecting means to be "in sight of" the devices anyway, right?

So how do you disconnect such a thing if there is, say, a fire, if you *can't go in the room*... and the next upstream is in the power room, two floors and at least 90 seconds of a flat run away?

How would you engineer such a thing, power people? A switch disconnect upstream the CB, in the adjacent room (which is on the other side of a 2H fire door)?
 
The short answer is yes. Generally where the mains come into the building you have your bus bar that fingers off to everything else. High priority/voltage stuff gets a separate disconnect if required by code.
 
Jay Ashworth said:
One of my venues has about a 10x10 room with 2 48-channel (I think) CD-80 racks in it, mostly fully populated.

It's been awhile since I've been in the room, but I think the CBs are inside that room -- and I think code *requires* the disconnecting means to be "in sight of" the devices anyway, right?

So how do you disconnect such a thing if there is, say, a fire, if you *can't go in the room*... and the next upstream is in the power room, two floors and at least 90 seconds of a flat run away?

How would you engineer such a thing, power people? A switch disconnect upstream the CB, in the adjacent room (which is on the other side of a 2H fire door)?
Click to expand...

"It's been awhile since I've been in the room, but I think the CBs are inside that room -- and I think code *requires* the disconnecting means to be "in sight of" the devices anyway, right?"

There is no such NEC requirement for stage switchboards such as those you describe.

However, it is very good design and safety practice.

ST
 
Jay Ashworth said:
Does the NEC term-of-art "stage switchboards" include active Triac dimmer racks then?

I myself would assume that "switchboards" were all passive components, and hence much less likely to start a fire...
Click to expand...

The actual definition from the 2020 NEC:

Stage Switchboard.
A permanently installed switchboard, panelboard, or rack containing dimmers or relays with associated overcurrent protective devices, or overcurrent protective devices alone, used primarily to feed stage equipment.
 
Jay Ashworth said:
Got it.

Is there an easy way to look at NEC history by section? I'm wondering if that was written differently in 1980ish when these racks went in.
Click to expand...

From what I can remember the term stage switchboard never dealt much with the technology that was doing the actual dimming. Its an NEC term that goes back to resistance and auto transformer systems. SCR and Triacs are included.
 
Last edited:
Jay Ashworth said:
Ah; so "stage" switchboard has always been a term of art, meaning "more complicated than 'just' a switchboard".

I think I'm caught up, now; thanks.
Click to expand...

Ive always known it as the dimmer system, not the control system, as the NEC generally doesn't deal with portable equipment, but does deal with methods with how the dimmers are powered and such.
 
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