# Free air conductors inside switchgear



## MDShunk (Jan 7, 2007)

The switchgear is not a chapter 3 raceway type, so they must be free air. 

The NEC doesn't define free air, but the NECA books teach if it's not in a cable assembly or raceway, it's free air.


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## frenchelectrican (Mar 15, 2007)

The MDP will genrally not cover in NEC codes however as you say free air IIRC there is a chart but I really doubt it will listed in NEC but the cable or conductor manufacter will have the listing on their products. 

So you may get higher rating on free air rating. 

Ya staying on copper or flip over to alum conductors ? 

I have a chart but I dont know if it will do anything good with current conductors. ( that will depending on type of insulation materals )


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## Southeast Power (Jan 18, 2009)

I love aluminum conductors but, this project is in a remote location so, I want to keep the inventory down to as few items as possible.

If I go all 500s my logistics will be minimal.


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## MikeFL (Apr 16, 2016)

I don't think inside switch gear is free air. Free air is aerial construction. Open to free air.

Doesn't the switch gear tell you what temp rating conductor to use?


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## eddy current (Feb 28, 2009)

MDShunk said:


> The switchgear is not a chapter 3 raceway type, so they must be free air.
> 
> The NEC doesn't define free air, but the NECA books teach if it's not in a cable assembly or raceway, it's free air.


Would the switchgear not be considered a wireway?

Imagine a lot of wires inside it. Would there not also be a maximum fill in there?


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## Southeast Power (Jan 18, 2009)

eddy current said:


> Would the switchgear not be considered a wireway?
> 
> Imagine a lot of wires inside it. Would there not also be a maximum fill in there?


It's more of a wire where than a wire way. :smile:

Most panelboards can easily have more than 30 conductors in a cross section.
I can think of a recent install that had 96 500kcmils. This one will have 64-500s In the ATS side and 36-500s in the MDP side


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## eddy current (Feb 28, 2009)

Southeast Power said:


> It's more of a wire where than a wire way. :smile:
> 
> Most panelboards can easily have more than 30 conductors in a cross section.
> I can think of a recent install that had 96 500kcmils. This one will have 64-500s In the ATS side and 36-500s in the MDP side


And that is one of the reasons why I think wires in switchgear are not “in free air”. 
There is potential for heat buildup. To be considered free air don’t the wires have to have a certain amount of spacing between them? Here our code says if the spacing is not maintained, like single conductors running on a rack for instance, the wires would have to be derated.


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## Southeast Power (Jan 18, 2009)

eddy current said:


> And that is one of the reasons why I think wires in switchgear are not “in free air”.
> There is potential for heat buildup. To be considered free air don’t the wires have to have a certain amount of spacing between them? Here our code says if the spacing is not maintained, like single conductors running on a rack for instance, the wires would have to be derated.


Ok.
What about triplex and quadplexed cables in free air.


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## eddy current (Feb 28, 2009)

Southeast Power said:


> Ok.
> What about triplex and quadplexed cables in free air.


Not sure about the NEC but In Canada we don’t consider them “free air”. There are other tables we use for neutral supported tri and quad plex cables. CEC tables 36A and 36B.


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## Southeast Power (Jan 18, 2009)

eddy current said:


> Not sure about the NEC but In Canada we don’t consider them “free air”. There are other tables we use for neutral supported tri and quad plex cables. CEC tables 36A and 36B.


It would be interesting to see how close those table were.


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## eddy current (Feb 28, 2009)

Southeast Power said:


> It would be interesting to see how close those table were.


How is it done using the NEC? Do you just use your free air table or is there a different table for ampacity? Is it the same for 2,3 or 4 conductor neutral supported cable or is derating required.


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## MDShunk (Jan 7, 2007)

MikeFL said:


> I don't think inside switch gear is free air. Free air is aerial construction. Open to free air.
> 
> Doesn't the switch gear tell you what temp rating conductor to use?


You're free to think that but the bottom line is the NEC does not define it. Since it's a permissive code, we're free to use engineering guidance. The NECA manuals, while not code, provide the only standardized definition of free air.


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## eddy current (Feb 28, 2009)

MDShunk said:


> You're free to think that but the bottom line is the NEC does not define it. Since it's a permissive code, we're free to use engineering guidance. The NECA manuals, while not code, provide the only standardized definition of free air.


In the CEC we have a rule that says even if your using the “free air” tables, if you do not maintain the spacing required you must derate as per Table 5B. Also if there are more than four conductors and the spacing required is not maintained we must use our “raceway” tables to determine ampacity.

Is there such a rule in the NEC?


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## Jlarson (Jun 28, 2009)

I'd do the 4x 500's and be good with it.


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