NFPA 79 wire ampacity in raceway, specifically slotted panduit

[czd50w]

We build industrial machine enclosures, usually 120VAC with 24VDC on the interior. We have typical NEMA 12 or 4x enclosures (Hoffman brand), back panels and slotted panduit.
I have never used the adjustment factors (Table 12.5.5.(b)) for the wires in this panduit. I usually interpreted this table for conduit or raceway trough after it leaves the enclosure.
Usually our enclosures will also have a fan, not not always. Is this more of an open air environment inside the enclosure?

Do I need to de-rate the ampacity based on the conductors in the panduit, or not? I understand fill levels are important, but a different topic for now. This assumes not to exceed the stated fill levels of the panduit. It would not surprise me to have 10-20 load carry conductors in a single panduit channel.
Does 12.5.5 include these conductors?

Thanks.

 

[jim dungar]

The slotted wire duct is not the same as free air, regardless how much air you pass over it.
The slotted wire duct is not a conduit.
If anything the wire duct is similar to a 'wireway'.

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[petersonra]

We build industrial machine enclosures, usually 120VAC with 24VDC on the interior. We have typical NEMA 12 or 4x enclosures (Hoffman brand), back panels and slotted panduit.
I have never used the adjustment factors (Table 12.5.5.(b)) for the wires in this panduit. I usually interpreted this table for conduit or raceway trough after it leaves the enclosure.
Usually our enclosures will also have a fan, not not always. Is this more of an open air environment inside the enclosure?

Do I need to de-rate the ampacity based on the conductors in the panduit, or not? I understand fill levels are important, but a different topic for now. This assumes not to exceed the stated fill levels of the panduit. It would not surprise me to have 10-20 load carry conductors in a single panduit channel.
Does 12.5.5 include these conductors?

Thanks.

I would look closely at what 12.5.5 says. Most of your conductors are probably not "current carrying".

 

[czd50w]

we build for many customers as we are an integrator. we typically follow nfpa 79 as our standard, with reference to UL508 as a guide. We are not a UL shop, so our panels are not listed.

I'm assuming you mean look closely at the definition of class 1 conductors in article 725. most of them do carry current, just low amounts of current.
Am i to understand that any conductor carry less than 10% of the conductor ampacity does not count toward my "more than three" total?

 

[czd50w]

The slotted wire duct is not the same as free air, regardless how much air you pass over it.
The slotted wire duct is not a conduit.
If anything the wire duct is similar to a 'wireway'.

----

The definitions are causing some of my confusion.
I understand that is is not conduit.
The derating chart 12.5.5(b) says Raceway (and cable). Raceway is defined as many things including conduits, but also includes wireways.

So if panduit brand wire duct is a wireway (i would think so), then it must also be a Raceway (by the definition in nfpa 79), thus it must be derated, maybe
this is why i'm confused.
maybe it has never been an issue before because enough of them are have current loads below 10% of the conductor ampacity.

 

[jim dungar]

The definitions are causing some of my confusion.
I understand that is is not conduit.
The derating chart 12.5.5(b) says Raceway (and cable). Raceway is defined as many things including conduits, but also includes wireways.

So if panduit brand wire duct is a wireway (i would think so), then it must also be a Raceway (by the definition in nfpa 79), thus it must be derated, maybe
this is why i'm confused.
maybe it has never been an issue before because enough of them are have current loads below 10% of the conductor ampacity.

Wireways would be the things that run between panels, not internal to them.

Wire duct is simpley a wire management device, not different than using spiral wrap, lashing rope, or a whole lot of wire ties.

I am not near a NFPA79 book, so I cannot look up the wording that is giving you grief.

 

[petersonra]

The 2011 edition also uses the term "wiring channels". no idea what that is supposed to mean.

Typical wire duct is not a raceway, but I don't know if it is a "wiring channel".