DLO Ampacity for Close-Coupled Gear

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Sunny_92

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I have a situation where we have a dry-type MV transformer set right next to the switchboard it feeds. There are (6) sets of 444 kcmil RHH/RHW-2/DLO conductors that run from the XFMR secondary terminals, through a window cut out between the XFMR & SWBD, and to the SWBD main breaker.

What is the correct allowable ampacity for these conductors? I'm trying to determine the appropriate long-time trip setting for the main breaker.

I'm thinking that I should be using the ampacity for 400 kcmil from NEC table 310.15(B)(16), which would give me 2010A, but I'm not sure since the conductors don't seem to actually enter a raceway.
 
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oldsparky52

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Sunny_92 said:
I have a situation where we have a dry-type MV transformer set right next to the switchboard it feeds. There are (6) sets of 444 kcmil RHH/RHW-2/DLO conductors that run from the XFMR secondary terminals, through a window cut out between the XFMR & SWBD, and to the SWBD main breaker.

What is the correct allowable ampacity for these conductors? I'm trying to determine the appropriate long-time trip setting for the main breaker.

I'm thinking that I should be using the ampacity for 400 kcmil from NEC table 310.15(B)(16), which would give me 2010A, but I'm not sure since the conductors don't seem to actually enter a raceway.
Click to expand...

I think 110.14(C) confirms your thinking that you should use the ampacity table 310.15(B)(16) 75C column, unless the equipment (main breaker and assembly) is listed otherwise.
 
ron

ron

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Sunny_92 said:
I'm thinking that I should be using the ampacity for 400 kcmil from NEC table 310.15(B)(16), which would give me 2010A, but I'm not sure since the conductors don't seem to actually enter a raceway.
Click to expand...
I agree with you and oldsparky52. The terminations and the listing of the assembly make the decision
 
david luchini

david luchini

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Sunny_92 said:
I have a situation where we have a dry-type MV transformer set right next to the switchboard it feeds. There are (6) sets of 444 kcmil RHH/RHW-2/DLO conductors that run from the XFMR secondary terminals, through a window cut out between the XFMR & SWBD, and to the SWBD main breaker.

What is the correct allowable ampacity for these conductors? I'm trying to determine the appropriate long-time trip setting for the main breaker.

I'm thinking that I should be using the ampacity for 400 kcmil from NEC table 310.15(B)(16), which would give me 2010A, but I'm not sure since the conductors don't seem to actually enter a raceway.
Click to expand...

What size/voltage is the transformer and what is the rating of the main breaker?
 
david luchini

david luchini

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Sunny_92 said:
Cabling was provided by contractor. They arrived at that size by not understanding how to properly size conductors for this situation. Future load on the gear is unknown/undecided at this point.
Click to expand...

I would have thought that the manufacturer would have provided direction on what that cabling should be on close-coupled gear.

I don't think T310.15(B)(16) would be the right table. Maybe (B)(17)?
 
ron

ron

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david luchini said:
I would have thought that the manufacturer would have provided direction on what that cabling should be on close-coupled gear.

I don't think T310.15(B)(16) would be the right table. Maybe (B)(17)?
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Many times the transformer and SWGR or SWBD are purchased as separate pieces of equipment and not integrated as one line-up, and the interconnecting conductors are selected by the Engineering Drawings.

Section 110.14(C)(1) forces the reader to Table 310.15(B)(16). The manufacturer doesn't typically have any special listings for using other tables.

Although dated, the last page of this PDF has a good paragraph to reference "Use of Other Than Table 310.16" https://www.schneider-electric.com/...5/en_US/Wire Terminations 0110DB9901R2-02.pdf
 
ron

ron

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david luchini said:
110.14(C)(1) forces the reader to Table 310.15(B)(16) for determining equipment termination provisions.

That is different from determining conductor ampacity.
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If the terminations are only good up to Table 310.15(B)(16) ampacity values, how will you draw higher currents through those terminations (rated at a relatively low ampacity based on the "regular ampacity table) to conductors connected based on some other table? I think that is why the Schneider PDF indicated not to use another table.

I realize you have likely had this argument many times and may be baiting me, but be gentle.
 
david luchini

david luchini

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ron said:
If the terminations are only good up to Table 310.15(B)(16) ampacity values, how will you draw higher currents through those terminations (rated at a relatively low ampacity based on the "regular ampacity table) to conductors connected based on some other table? I think that is why the Schneider PDF indicated not to use another table.
Click to expand...

You wouldn't draw higher current through those terminations. You would use them up to the rating of the termination or the device.

For example, if you were running a 400A feeder for a 380A load, in cable tray, where single conductors maintained spacing of one cable diameter...Art 392 directs you to table 310.15(B)(17) for the ampacity.

310.15(B)(17) says that a 250mcm would be sufficient for that load. The breaker is rated for 400A, and the breaker termination supports (2) 2/0-500mcm, which would be good for 760A. None of the equipment or devices are being used beyond their rating.
 
Jraef

Jraef

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Speaking of terminations, you do know that you cannot use standard terminals for building wire like THHN, right? The DLO requires terminal that are listed for "Class I" stranding or higher on that cable. This will preclude most mechanical lugs and if you go for crimped, you must make sure you have the right versions and the right crimp die.

As to ampacity, I (and several other denizens of this forum) have always used the rule of sizing it as if it were the closest LOWER standard size, so in your case 400kCMIL RHH/RHW-2 and I have never been challenged on that by an AHJ. I know people who have used the manufacturter's tables to try to squeeze a few more amps out of it and ended up in a lengthy argument with the AHJ over the way those values are derived, causing project delays. Keep that in mind...
 
ron

ron

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david luchini said:
You wouldn't draw higher current through those terminations. You would use them up to the rating of the termination or the device.

For example, if you were running a 400A feeder for a 380A load, in cable tray, where single conductors maintained spacing of one cable diameter...Art 392 directs you to table 310.15(B)(17) for the ampacity.

310.15(B)(17) says that a 250mcm would be sufficient for that load. The breaker is rated for 400A, and the breaker termination supports (2) 2/0-500mcm, which would be good for 760A. None of the equipment or devices are being used beyond their rating.
Click to expand...
The terminations per Table 310.15(B)(16) may be 2010A in this case and if the wiring per 310.15(B)(17) would be 3270A (6 sets of 400's).

The OP said the load is not yet determined. The protection or the eventual load limits will likely be chosen based on the ampacity of the conductors (2010A or 3270A), not the hidden value of the termination ampacity later on.

I would guess the 4000A Frame secondary breaker will have its LTPU set based on the ampacity of the conductors.
 
david luchini

david luchini

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ron said:
The terminations per Table 310.15(B)(16) may be 2010A in this case and if the wiring per 310.15(B)(17) would be 3270A (6 sets of 400's).
Click to expand...

I can't see how it would be either. A 4000A c/b is going to have terminations that are rated for at least 4000A.
 
david luchini

david luchini

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ron said:
The OP said it was 6 sets of 444 DLO's which I would size as 6 sets of 400's

Wire was pre-selected
Click to expand...

He said 6 sets of conductors were run. He didn't say anything about the terminations.

Let me try it this way. If you had a 75deg termination that is rated for 2 sets of #2-#3/0 conductors, how much current would you say that the termination could carry without exceeding its 75deg temperature rating, based on 310.15(B)(16)?
 
ron

ron

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david luchini said:
He said 6 sets of conductors were run. He didn't say anything about the terminations.

Let me try it this way. If you had a 75deg termination that is rated for 2 sets of #2-#3/0 conductors, how much current would you say that the termination could carry without exceeding its 75deg temperature rating, based on 310.15(B)(16)?
Click to expand...

He said there are (6) sets of 444 kcmil RHH/RHW-2/DLO conductors that run from the XFMR secondary terminals, through a window cut out between the XFMR & SWBD, and to the SWBD main breaker. It is not a long jump to the conclusion that there are no special terminations on the transformer side or the SWBD side to avoid the use of Section 110.14(C)(1) which forces the reader to Table 310.15(B)(16).
 
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