Cable Tray - Parallel Feeders - Inspector AHJ Discrepancy

[Fieldgoal00]

Currently working on a project where we have an electrical building with an overhead cable tray (BLine Ladder Type) with no covers. Currently the cable tray has a mixture of cables larger than 4/0 & smaller than 4/0 in the tray which has been properly sized per the 2023 NFPA 70, section 392.22(A)(1)(c).

The issue is that the 3rd Party inspector (Authority Having Jurisdiction), for the building manufacturer is trying to state that the multiconductor feeder cables that we have run in the tray between the 480V switchboard feeder breaker and the MLO of the Motor Control Center need to be derated per 2023 NFPA 70, section 310.15(C)(1).

It is clear to me that he is getting confused between the terms "Raceway" and "Cable Tray" as they are not the same device. He is stating the section in 310.15(C)(1) that says "Each current carrying conductor of a paralleled set of conductors shall be counted as a current-carrying conductor" which would therefore lead him to believe that the 5 parallel sets of 3/C 500MCM w/Gnd cables would need to follow the ampacity rating of Table 310.16 (90C XHHW conductors) which we would also derate for ambient temperature Table 310.15(B)(1)(1). He however is stating that we need to also derate based on Table 310.15(C)(1) based on the number of current carrying conductors (He understands this to be 5 times 3 = 15 current carrying conductors because of the parrallel conductor statement in 310.15(C)(1)) This would require us to derate the 500MCM cable to 50% of its rated value in Table 310.16.

We are trying to explain to him that section 392.80(A)(1)(a) states you should only go to 310.15(C)(1) only for multiconductor cables with more than three current carrying conductors. None of the multiconductor power cables that we have include more than three current carrying conductors, only 3 Phase conductors and a Ground - No Neutral.

Furthermore, the section he is referencing also states that "Where conductors are installed in cable trays, 392.80 shall apply", NFPA 70 310.15(C)(1)(a), negating any of this information he has brought up regarding counting each parallel conductor as an individual current carrying conductor.

Thoughts??

 

[infinity]

The issue is that the 3rd Party inspector (Authority Having Jurisdiction), for the building manufacturer is trying to state that the multiconductor feeder cables that we have run in the tray between the 480V switchboard feeder breaker and the MLO of the Motor Control Center need to be derated per 2023 NFPA 70, section 310.15(C)(1).

A cable tray is not a raceway it is a conductor support system. Your installation would comply with 392.80(A)(1) since you have only 3 CCC's in each cable.

 

[Fieldgoal00]

A cable tray is not a raceway it is a conductor support system. Your installation would comply with 392.80(A)(1) since you have only 3 CCC's in each cable.

I completely agree. Sometimes when things that are so straightforward get questioned it sometimes make you think twice.

The sad thing is that since he's the AHJ unless he agrees, regardless if we a the EOR on the project, he won't provide the compliance sticker for the building.

I've already had one hour long conversation with him when he tried to mix up the requirements of 392.22 (Cable Tray Fill Requirements) and 392.80 (Cable Ampacity in Cable Tray). He was trying to force it down our throats that we needed to have all the cables 4/0 larger in a single layer spaced 1 cable diameter apart. I had to explain to him, unless we're doing the 310.14(B) hand calculation in the NEC to get a higher ampacity rating other than what is listed in 310.16 for our XHHW cable, the additional cable diameter apart spacing is not required.

It took almost 2 weeks of emails back and forth, prior to the 1 hour phone call for him to even agree that he was wrong there.

He just now sent us his response by saying basically if we don't want to space the parallel feeder cables apart we have to derate them by a ridiculous percent based on 310.15(C)(1) that I mentioned in my initial post.

 

[don_resqcapt19]

This points out a problem with the code, specifically 90.3. There is no provision in 90.3 that actually permits the rule in Article 392 to modify the rule in Article 310. Of course that is the intent and the typical application of the rule in 392, yet the code arrangement does not actually permit that. This is not the only place where a rule in on Chapter 1-4 article modifies a rule in another Chapter 1-4 article.
A change needs to be made in the 90.3 language.

 

[infinity]

This points out a problem with the code, specifically 90.3. There is no provision in 90.3 that actually permits the rule in Article 392 to modify the rule in Article 310. Of course that is the intent and the typical application of the rule in 392, yet the code arrangement does not actually permit that. This is not the only place where a rule in on Chapter 1-4 article modifies a rule in another Chapter 1-4 article.
A change needs to be made in the 90.3 language.

But even if you apply the rules in Article 310 if there is a space between the cables why would you need to apply any derating?

 

[LarryFine]

There should be an appeal procedure to challenge his ruling. Contact his supervisor.

 

[steve66]

There should be an appeal procedure to challenge his ruling. Contact his supervisor.

In theory that should lead to the right code interpretation.

But in my experience, the supervisor usually has some motivation to support their subordinate‘s interpretation, and absolutely no motivation to make the right call. In fact, they may just default to the most strict interpretation that anyone could ever come up with either because they feel the code should be followed letter by letter, with no consideration for the actual intent, or because they feel like they can be held liable for any missed interpretation.

i sincerely hope the OP has better luck than I have had in the past. But I feel like there should be a third party that disputes like this go to, especially when big $$ is involved. NFPA seems like the obvious candidate, but unfortunately, getting an official interpretation is not usually an option, and an unofficial interpretation has about as much creditability as a magic 8 ball.

I wish it wasn‘t so.

 

[winnie]

IMHO you don't get out of jail free because the 5 parallel sets are in separate cables. The question is if the cable tray supports the cables in such fashion that they have separate cooling.

Put these same cables in a large RMC, and I agree with the inspector, you have 15 CCCs in a single raceway.

Take these same conductors, and clamp them separately to a strut trapeze, neatly side by side with sufficient airspace between, and now you have 5 separate instances of 3 CCCs each.

The fill area rules for cable tray are specifically there to provide the necessary cooling so that you can treat the cables as separate.

The 'spaced apart by one cable diameter' is in the code, but only to get to the even higher 'free air' ampacity.

Jon

 

[Fieldgoal00]

IMHO you don't get out of jail free because the 5 parallel sets are in separate cables. The question is if the cable tray supports the cables in such fashion that they have separate cooling.

Put these same cables in a large RMC, and I agree with the inspector, you have 15 CCCs in a single raceway.

Take these same conductors, and clamp them separately to a strut trapeze, neatly side by side with sufficient airspace between, and now you have 5 separate instances of 3 CCCs each.

The fill area rules for cable tray are specifically there to provide the necessary cooling so that you can treat the cables as separate.

The 'spaced apart by one cable diameter' is in the code, but only to get to the even higher 'free air' ampacity.

Jon

Jon,

Again, I totally agree. If we could find a conduit large enough for 5 parallel sets of 3/C 500MCM cables we'd definitely have to derate them from the number of CCC's in the raceway lol.

This just goes back to what I've told my coworkers time and time again, although the code does allow for some interpretation, it doesn't allow blatant manipulation of the code where someone is trying to mend phrases of the code between independent sections of the code.

When dealing with cable tray the only sections that the inspector should be concerned with are 392.22 & 392.80. Those two sections will tell him how to handle tray fill calculations and ampacity rating for cables 2000V or less, regardless of the composition of cable sizes that are in the tray.

 

[infinity]

The issue is that the 3rd Party inspector (Authority Having Jurisdiction), for the building manufacturer is trying to state that the multiconductor feeder cables that we have run in the tray between the 480V switchboard feeder breaker and the MLO of the Motor Control Center need to be derated per 2023 NFPA 70, section 310.15(C)(1).

Applicable or not as I said prior if you have spacing between the cables you have complied with 310.15(C)(1) so the point is moot.

310.15(C)(1) More than Three Current-Carrying Conductors.
The ampacity of each conductor shall be reduced as shown in Table 310.15(C)(1) where the number of current-carrying conductors in a raceway or cable exceeds three, or where single conductors or multiconductor cables not installed in raceways are installed without maintaining spacing for a continuous length longer than 600 mm (24 in.). Each current-carrying conductor of a paralleled set of conductors shall be counted as a current-carrying conductor. Where conductors of different systems, as provided in 300.3, are installed in a common raceway or cable, the adjustment factors shown in Table 310.15(C)(1) shall apply only to the number of power and lighting conductors (Articles 210, 215, 220, and 230).
Informational Note No. 1: See Annex B for adjustment factors for more than three current-carrying conductors in a raceway or cable with load diversity.
Informational Note No. 2: See 366.23 for adjustment factors for conductors and ampacity for bare copper and aluminum bars in auxiliary gutters and 376.22(B) for adjustment factors for conductors in metal wireways.
(a)Where conductors are installed in cable trays, the provisions of 392.80 shall apply.

 

[Fieldgoal00]

Applicable or not as I said prior if you have spacing between the cables you have complied with 310.15(C)(1) so the point is moot.

Infinity,

The PARALLEL sets of cables are installed in a single layer in the tray, we are not spacing them any specific distance apart from one another. I don't believe that assumption was anywhere in my OP. Just trying to understand your latest post, regardless of what the initial paragraph in 310.15(C)(1) states, subpart (a) that you have also highlighted in bold is telling the reader to follow the provisions of 392.80 since these conductors are installed in cable tray.

 

[winnie]

I think @infinity is trying to say you have two ways to approach this.

1) Cables can be installed in ay way at all, but if you maintain spacing than 310.15(C)(1) lets you treat them as separate

2) Cables can be installed in cable trays following the provisions of 392.80

Either approach gets you want you want: not having to derate.

-Jon

 

[JoeStillman]

If you pose a yes-or-no question to NFPA, I'm sure they would support your interpretation. It could result in some documents that would assist in your AHJ having a learning experience.