Wire deration for theatre dimming systems

[quogueelectric]

First we have to understand that Annex B is not part of the code and to use it it must be under an engineers supervision, if it's not under an engineers supervision an inspector can reject the installation.

An inspector could still reject the installation even under an engineers supervision if they didn't like it since it is not part of the requirements of NEC

Roger

Why do they bother to put it in the book if it is not enforceable?? What exactly does annex B mean?? What is the point??

 

[roger]

Why do they bother to put it in the book if it is not enforceable?? What exactly does annex B mean?? What is the point??

It is there only for information as is all the annexes, think of them as large FPN's.

Annex B Application Information for Ampacity Calculation

This annex is not a part of the requirements of this NFPA document but is included for informational purposes only.

B.310.15(B)(1) Formula Application Information.
This annex provides application information for ampacities calculated under engineering supervision.

Roger

 

[quogueelectric]

It is there only for information as is all the annexes, think of them as large FPN's.



Roger

It was the dimming equipment company who steered me to annex b as a cure all for ampacity adjustment.
The reality of the install is that these rows run from the back of stage to the back of audience fed from each pipe times 10 rows in a checkerboard 10x10 grid. The likelyhood of all of the 14 lights being used at the same time is almost zero.
The problem is the phase shift dimming system produces 1st and 3rd harmonics.(I think). There are 3 theatres and the first contractor wired the system in 12 solid. We are doing the next 2 theatres and my boss really doesnt care if I use 10s or 8s he truly wants a compliant job above everything( go figure the first boss in the history of bosses that wants to do the right thing).
I am talking 28 cccs #10 in an 1-1/2 conduit 20 amp breakers. According to the original engineer who drew it up 10s are specified.
I am sure the dimming co who sold us the equipment would have one of thier engineers sign off. We also have on site engineers at our disposal if necessary to rubber stamp something.
This is a big operation state university with a teaching hospital 4-20 story buildings and miles of campus substations and 24kv feeders blowing up on a regular basis where they cross the steam lines installed 30 yrs ago. Lots of action every day I like it. Keeps the old cow on his toes.