Dividers in wireways/wire troughs - conductor derating

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Carultch

Senior Member
Location
Massachusetts
I understand that in wireways and wire troughs, you are permitted to install up to 30 "current carrying conductors" without adjusting ampacity for bundling. The instant you add a 31st wire, the 31-wire derate factor applies.

How does this work when you install a wire trough divider?
Does the full count of wires on both sides matter?
Or just the count of wires per side of the divider?
 

petersonra

Senior Member
Location
Northern illinois
Occupation
engineer
I understand that in wireways and wire troughs, you are permitted to install up to 30 "current carrying conductors" without adjusting ampacity for bundling. The instant you add a 31st wire, the 31-wire derate factor applies.

How does this work when you install a wire trough divider?
Does the full count of wires on both sides matter?
Or just the count of wires per side of the divider?

as strange as it may sound, my understanding is that each side of the divider is counted as a separate raceway for most purposes (except maybe installing).
 

shortcircuit2

Senior Member
Location
South of Bawstin
Good question. I would say you treat each side of the divider as a separate enclosure when applying code rules for conductor fill, etc. The same should apply to cable trays with dividers.

Why are you using the divider? 690.31(B)?
 

qcroanoke

Sometimes I don't know if I'm the boxer or the bag
Location
Roanoke, VA.
Occupation
Sorta retired........
I understand that in wireways and wire troughs, you are permitted to install up to 30 "current carrying conductors" without adjusting ampacity for bundling. The instant you add a 31st wire, the 31-wire derate factor applies.

How does this work when you install a wire trough divider?
Does the full count of wires on both sides matter?
Or just the count of wires per side of the divider?

http://forums.mikeholt.com/showthread.php?t=174197&page=2&highlight=divider

I think Infinity's response in post #12 covers it. For me anyway.
 

Smart $

Esteemed Member
Location
Ohio
as strange as it may sound, my understanding is that each side of the divider is counted as a separate raceway for most purposes (except maybe installing).

http://forums.mikeholt.com/showthread.php?t=174197&page=2&highlight=divider

I think Infinity's response in post #12 covers it. For me anyway.
I'm of the opposite position. The ampacity adjustment stipulation is regarding the wire... which does not auto-magically become two wireways when a divider is added.
 

petersonra

Senior Member
Location
Northern illinois
Occupation
engineer
I'm of the opposite position. The ampacity adjustment stipulation is regarding the wire... which does not auto-magically become two wireways when a divider is added.

suppose you ran some of the wires in the wire way inside of another wire way? then you certainly have two wire ways. would you count the wires in the inner wire way with the wires in the outer wire way for derating the outer wire way conductors? you certainly don't have to count the conductors not in the inner wire way for derating those inside the inner wire way.
 

Carultch

Senior Member
Location
Massachusetts
I'm of the opposite position. The ampacity adjustment stipulation is regarding the wire... which does not auto-magically become two wireways when a divider is added.


Understood. However, it does now becomes two bundling groups, where the wires would be in immediate contact. The divider prevents one portion from being bundled with the other.
 

qcroanoke

Sometimes I don't know if I'm the boxer or the bag
Location
Roanoke, VA.
Occupation
Sorta retired........
suppose you ran some of the wires in the wire way inside of another wire way? then you certainly have two wire ways. would you count the wires in the inner wire way with the wires in the outer wire way for derating the outer wire way conductors? you certainly don't have to count the conductors not in the inner wire way for derating those inside the inner wire way.

What? LOL Are you running for office somewhere? :)
 

GoldDigger

Moderator
Staff member
Location
Placerville, CA, USA
Occupation
Retired PV System Designer
Careful application of basic physics and the Neher McGrath equations convinces me that:
1. The conductors in the inner raceway must be counted along with those only in the outer raceway when determining whether to derate conductors in the outer raceway.
2. If that number calls for derating, that same factor also applies to the conductors in the inner raceway.
3. If the number in the inner raceway requires derating, that occurs independently of what is happening in the outer raceway and does not directly apply to the outer raceway conductors. For that, see 1.
 

Smart $

Esteemed Member
Location
Ohio
Understood. However, it does now becomes two bundling groups, where the wires would be in immediate contact. The divider prevents one portion from being bundled with the other.
The fact remains, it is but one wireway.

My personal contention for looking at it otherwise is compare the one wireway divided to two smaller wireways. You then would not have to derate until going over 30 conductors in either wireway... which allows up to 60 conductors without derating.

My counter to the above contention is to run two smaller wireways and get over it. :p:D:angel:
 

steve66

Senior Member
Location
Illinois
Occupation
Engineer
From a heat dissipation standpoint, I don't see how a wireway with a divider is any different that two separate wireway's ran side by side against each other.

And there is a 20% max. fill to not derate, and a 4 sq inch minimum on surface raceways. So if you are going to put in a divider and count it as two separate wireways, the minimum cross sectional area doubles. Then you have 2 bundles of wire taking up 1/5th the cross sectional area, with 4/5ths of the cross sectional area being empty space.

So in my opinion it becomes two wireways, and you can install a divider and 60 conductors without derating.

Although I would have reservations about doing this if the wires were really loaded. But I would also have reservations about putting 30 conductors in a single wireway with no derating if they were really loaded even if it is clearly allowed.
 

Smart $

Esteemed Member
Location
Ohio
From a heat dissipation standpoint, I don't see how a wireway with a divider is any different that two separate wireway's ran side by side against each other.

And there is a 20% max. fill to not derate, and a 4 sq inch minimum on surface raceways. So if you are going to put in a divider and count it as two separate wireways, the minimum cross sectional area doubles. Then you have 2 bundles of wire taking up 1/5th the cross sectional area, with 4/5ths of the cross sectional area being empty space.

So in my opinion it becomes two wireways, and you can install a divider and 60 conductors without derating.

Although I would have reservations about doing this if the wires were really loaded. But I would also have reservations about putting 30 conductors in a single wireway with no derating if they were really loaded even if it is clearly allowed.
Here's a friendly reminder: Where does Code say it is permitted to consider a divided wireway as two wireways for the purpose of derating?
 

Smart $

Esteemed Member
Location
Ohio
where does it say it is not?
Manufacturer documentation, listing, and/or labeling, or even trade identification. It's a divided wireway, not two wireways.

I'll agree that Code does not require metal wireways to be listed, labeled, or even identified... so if you want to do so with an "undistinguished" wireway, have at it.
:thumbsdown:
 
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steve66

Senior Member
Location
Illinois
Occupation
Engineer
Manufacturer documentation, listing, and/or labeling, or even trade identification. It's a divided wireway, not two wireways.

I'll agree that Code does not require metal wireways to be listed, labeled, or even identified... so if you want to do so with an "undistinguished" wireway, have at it.
:thumbsdown:

Actually, the code does require listed for surface raceways, and a manufacturers label for other metal raceways.

I seriously doubt the "manufacturer documentation" states anything about derating, or if a divided raceway is one raceway, or two. If I'm wrong, please provide an example.
 

Smart $

Esteemed Member
Location
Ohio
Actually, the code does require listed for surface raceways, and a manufacturers label for other metal raceways.

I seriously doubt the "manufacturer documentation" states anything about derating, or if a divided raceway is one raceway, or two. If I'm wrong, please provide an example.
Okay, Mr. Pitnicky Jr. :angel:

I was referring only to Article 376 metal wireways... and requiring manufacturer marking is not the same as requiring equipment to be labeled as per the Article 100 definition.

All I'm really saying is the manufacturer packaging, sticker, etc. will call it wireway. Show me where any one product is marketed as wireways, i.e. plural.
 

ggunn

PE (Electrical), NABCEP certified
Location
Austin, TX, USA
Occupation
Electrical Engineer - Photovoltaic Systems
Okay, Mr. Pitnicky Jr. :angel:

I was referring only to Article 376 metal wireways... and requiring manufacturer marking is not the same as requiring equipment to be labeled as per the Article 100 definition.

All I'm really saying is the manufacturer packaging, sticker, etc. will call it wireway. Show me where any one product is marketed as wireways, i.e. plural.
It's not us whom you need to convince, you know. Let us know how the inspection goes. :D
 

Smart $

Esteemed Member
Location
Ohio
It's not us whom you need to convince, you know. Let us know how the inspection goes. :D
Won't be me any time soon. I haven't even done work that gets inspected in that manner in at least the last 5 years as I've been on the POCO side of things and now not-working disabled.
 
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