Wire deration for theatre dimming systems

[quogueelectric]

Wire deration for theatre dimming systems. seems to have two different deration factors depending on the different types of dimming systems. Is anyone familiar with this?? I am trying to determine the max ccc's in a 1 1/2 conduit. Separate neutrals off the dimmers.

 

[benaround]

What size wire is being used?

 

[quogueelectric]

What size wire is being used?

None yet I amm trying to decide what size wire is to be used in 1 1/2 conduit but the dimmers are a huge factor in deciding wire size. I dont want to go to #8 for 20 amp ckts but at 35% deration it may be my only option.

 

[480sparky]

This was all done in 1" with 8s, no MWBCs:

Derating wasn't the issue... voltage drop was. EE didn't want some lights dimmer than others.​

 

[benaround]

Can you run a couple more pipes to cut down the derating percentage?

 

[quogueelectric]

Can you run a couple more pipes to cut down the derating percentage?

We are already running 10 1 1/2" every 10 foot for the branches and with the separate neutrals in every dimmer it is a factor of (look under theatre dimmers) One type of dimmer includes the neutrals the other type of dimmer excludes the neutrals
........ BIG DIFFERENCE!!
I am looking for the easy button but not likely to find it here.

 

[benaround]

Well you could put 20 #10's and still use a 20a cb, so that's 10 dimmers, you say you

have 10 conduits, that's 100 dimmers. Do you have more than 100 dimmers? Don't let

the dimmers get you all messed up, it's just like running 10 120v circuits, they are all

CCC.

 

[quogueelectric]

Well you could put 20 #10's and still use a 20a cb, so that's 10 dimmers, you say you

have 10 conduits, that's 100 dimmers. Do you have more than 100 dimmers? Don't let

the dimmers get you all messed up, it's just like running 10 120v circuits, they are all

CCC.

10 rows 200 dimmers. Looks like #8s for 20 amp ckts. I think I am going to throw up. There is an exception in 2008 book where some dimmers dont count the neutral as a ccc I am not sure if it is in 2005.

 

[zbang]

I don't suppose there's an option of moving some of the dimmer racks closer to the loads, is there? That's part of the point to digital control and dimmer-per-circuit (and I'm assuming this is both). Larger pipes?

 

[quogueelectric]

I don't suppose there's an option of moving some of the dimmer racks closer to the loads, is there? That's part of the point to digital control and dimmer-per-circuit (and I'm assuming this is both). Larger pipes?

That is kind of my question.. Is larger pipes or larger wire more cost effective?? I would need to run an estimation software to know for sure. I want to do the best code compliant job as cheaply as possible.

 

[dbuckley]

It's my opinion that in the scenario as described the neutrals shouldn't count as cccs.

The reason that neutrals count sometimes is when you get oversize neutral currents, due to non-linear load harmonic currents combining on a common neutral. If all the circuits have their own neutral back to the dimmer then those derating rules shouldn't apply as there is no current combining until you reach the neutral terminals in the dimmers.

Put it another way, if you can put n 20A circuits in a pipe when they are all connected back to a standard panelboard, each circuit with its own neutral, then in a dimmer driven scenario the circuits will never carry as much current and probably less as (a) the loads are mostly 1KW and (b) loads are often dimmed to less than 100%, so there is no reason why there should be any less circuits in the pipe just because there's dimmers involved.

 

[quogueelectric]

It's my opinion that in the scenario as described the neutrals shouldn't count as cccs.

The reason that neutrals count sometimes is when you get oversize neutral currents, due to non-linear load harmonic currents combining on a common neutral. If all the circuits have their own neutral back to the dimmer then those derating rules shouldn't apply as there is no current combining until you reach the neutral terminals in the dimmers.

Put it another way, if you can put n 20A circuits in a pipe when they are all connected back to a standard panelboard, each circuit with its own neutral, then in a dimmer driven scenario the circuits will never carry as much current and probably less as (a) the loads are mostly 1KW and (b) loads are often dimmed to less than 100%, so there is no reason why there should be any less circuits in the pipe just because there's dimmers involved.

I was thinking there may be harmonics involved due to the clipping of the sine wave.

 

[curt swartz]

How could the neutrals NOT be considered current carrying? They will always carry the same current as their paired phase conductor. The only time neutrals can be considered non current carrying (for derating purposes) is if they are part of a multi-wire circuit but that would not apply to this installation as planned.

 

[e57]

I'm also going to agree with Curt on the CCC count.

On the dimming isue - I assume you have the job and looking to hold a price you bid sans going negitive, or low $?

I do a lot of dimming panels in residential - which is different due to the lower loads.... ( i.e. 4 300-500w loads off of a 20A circuit... ) I bundle them up - sure why not, each load is only a few amps each....

In your situation you'll need to derate in the first place (2-two-wire ciruits is more than 3...), and the loads will be high across the board. And since it doesn't sound as you have too much in way of choice of respec'ing the lighting or controls to say some sort of 0-10v dimming product??? Or 'shoe box' (Remote) DMX controlled dimmer?

I ran circuits for a few of these a few years back - it took 2-roundhouses each. Which is an effective way to get the power up there as a MWBC - closer to the loads, where they should be. That is if you have a place to put them????

Either way sounds like a gutter job and spliting out of that to me - at least from my comfy chair....

 

[quogueelectric]

How could the neutrals NOT be considered current carrying? They will always carry the same current as their paired phase conductor. The only time neutrals can be considered non current carrying (for derating purposes) is if they are part of a multi-wire circuit but that would not apply to this installation as planned.

It is in the deration part of 2008 art 520 theatre dimming. It is late and I cant find my 08 book.
I was looking at 05 handbook and the decision was already made to go with 1 1/2 and I am only talking 900' at the most total pipe and wire.
I installed 1/3 of the run today with a rack 10 wide dropping every 10 feet to feed the 15 ckt dimmer loads down each row. Will blast through wall monday and enter the dimmer rack area threading the needle with a 10 pipe rack.
This is not a make or break or lowball number it is just me trying to do the right thing for the customer but the clock keeps ticking and sometimes you just have to go with plan A because you have to get things done.
So its 1 1/2 pipe and # 8s 900'worth cranking up the tripple nickel monday morning and let it roll. There is another fire to put out tommorow.

 

[quogueelectric]

I found the relief in annex B

I found the relief in annex B

I found the relief I was looking for in annex B it let me put 28 CCC #10s in an 1 1/2 pipe at 50% which is 20. 10 65 foot rows with 14 outlets along the row. Awesome!! I dont need 8s !! Hip Hip Hooray.

 

[roger]

I found the relief I was looking for in annex B it let me put 28 CCC #10s in an 1 1/2 pipe at 50% which is 20. 10 65 foot rows with 14 outlets along the row. Awesome!! I dont need 8s !! Hip Hip Hooray.

So you are saying you have an engineer signing off on your proposed installation?

Roger

 

[benaround]

I found the relief I was looking for in annex B it let me put 28 CCC #10s in an 1 1/2 pipe at 50% which is 20. 10 65 foot rows with 14 outlets along the row. Awesome!! I dont need 8s !! Hip Hip Hooray.

Looks like you can go 60% for 28 CCC's, but who cares, I'm glad for you.

Also, nice to know about that table in annex B.

 

[quogueelectric]

So you are saying you have an engineer signing off on your proposed installation?

Roger

Yes as a mater of fact the engineer calls for 10 stranded on the prints. The majority of the jobs that I do involve a full set of blueprints.
This was a given from the start I am trying to install a code compliant installation to the best of my ability I just needed to see how this size was arrived at. No one seemed to know for sure now that I found it I know for sure.
I reported back to help anyone who might run across the same situation where to find it rather than stuffing it under my hat and calling it a day.
Unless someone has a reason that it wont fly this is why I asked the question.

 

[roger]

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