110.14(C)(1) vs 370.80 - Cablebus Ampacity at SWBD terminations

[ron]

370.80 says we can use the free air ampacities of 310.15(B)(17) to size a feeder using cablebus (conductors on factory cable tray held apart with spacers). Since we would terminate in a SWBD, we would use the 75 deg column for ampacities.

110.14(C)(1) says unless the equipment is listed and marked otherwise conductor ampacities should be based on the regular 310.15(B)(16) conductors in raceway. The SWBD is not "listed and marked otherwise".

Any way around this other than putting an intermediate pull / splice section on both ends? The cablebus run is only about 50' and not worth the headache of a bunch of splices to go from 8 sets to 12 sets per phase.

 

[jap]

370.80 says we can use the free air ampacities of 310.15(B)(17) to size a feeder using cablebus (conductors on factory cable tray held apart with spacers). Since we would terminate in a SWBD, we would use the 75 deg column for ampacities.

110.14(C)(1) says unless the equipment is listed and marked otherwise conductor ampacities should be based on the regular 310.15(B)(16) conductors in raceway. The SWBD is not "listed and marked otherwise".

Any way around this other than putting an intermediate pull / splice section on both ends? The cablebus run is only about 50' and not worth the headache of a bunch of splices to go from 8 sets to 12 sets per phase.

One thing to keep in mind,sometimes on a large switchboard the incoming feeder is cable connected to a buss not always the 75d lugs on a main breaker of such.

If the incoming terminations are crimped and bolted instead of on a lug there's a good possibility they are rated at 90d c and there is some wiggle room.

JAP>

 

[david luchini]

110.14(C)(1) says unless the equipment is listed and marked otherwise conductor ampacities should be based on the regular 310.15(B)(16) conductors in raceway. The SWBD is not "listed and marked otherwise".

That's not what 110.14(C)(1) says. 110.14(C)(1) says the conductor ampacities used in determining the equipment termination provisions shall be based on T310.15(B)(16).

For example, a 2000A feeder. The termination provision per 110.14(C)(1) could be for 5 sets of 600mcm to allow for 5 conductors per phase to terminate when using cable in conduit (420Ax5=2100A at 75deg.) Using the cable bus, I only need 3 conductors per phase (690Ax3=2070A at 75deg.) I haven't exceeded the temperature rating of the termination provision or of the conductor.

 

[ron]

One thing to keep in mind,sometimes on a large switchboard the incoming feeder is cable connected to a buss not always the 75d lugs on a main breaker of such.

If the incoming terminations are crimped and bolted instead of on a lug there's a good possibility they are rated at 90d c and there is some wiggle room.

JAP>

This will likely be to rear connected runbacks on a SWBD. The SWBD runbacks are generally tested at 75 deg

 

[ron]

That's not what 110.14(C)(1) says. 110.14(C)(1) says the conductor ampacities used in determining the equipment termination provisions shall be based on T310.15(B)(16).

For example, a 2000A feeder. The termination provision per 110.14(C)(1) could be for 5 sets of 600mcm to allow for 5 conductors per phase to terminate when using cable in conduit (420Ax5=2100A at 75deg.) Using the cable bus, I only need 3 conductors per phase (690Ax3=2070A at 75deg.) I haven't exceeded the temperature rating of the termination provision or of the conductor.

I'm sure there is some emphasis on the words in red that I'm missing, but I don't understand. It still seems that the conductor ampacities come from T310.15(B)(16).

I don't think you are saying that the manufacturer of the SWBD is coming to the NEC 110.14(c)(1) and seeing that it tells them to check T310.15(B)(16) before deciding how many lugs to provide for our use in the feild. That would be a UL, NEMA or White Book standards type thing.

 

[jap]

I don't think you are saying that the manufacturer of the SWBD is coming to the NEC 110.14(c)(1) and seeing that it tells them to check T310.15(B)(16) before deciding how many lugs to provide for our use in the feild.

That is the exact question I was fixing to ask.
It may in fact be for that purpose.

JAP>

 

[david luchini]

I don't think you are saying that the manufacturer of the SWBD is coming to the NEC 110.14(c)(1) and seeing that it tells them to check T310.15(B)(16) before deciding how many lugs to provide for our use in the feild. That would be a UL, NEMA or White Book standards type thing.

The switchboard manufacturer is going to provide lugs rated for, say 2000A rated at 75deg, for example. You are going to connect cable bus with an ampacity of 2000A at 75 deg. Your load is going to be 2000A or less non-continuous or 1600A or less continuous, or something in between. You have complied with 110.14(C), 215.2(A), and 370.80.

 

[david luchini]

I'm sure there is some emphasis on the words in red that I'm missing, but I don't understand. It still seems that the conductor ampacities come from T310.15(B)(16).

Maybe it will make more sense this way...

You have a single conductor #6awg-250mcm lug. 110.14(C)(1) tells you the lug is rated 255A at 75deg (from T310.15(B)(16)).

I am running a 250mcm cable bus (ampacity = 405 at 75deg from T310.15(B)(17)) for a 400A feeder and decide to terminate it on the #6awg-250mcm lug. I have violated 110.14(C).

Instead, I run a 2/0 cable bus (ampacity = 265 at 75 deg) for a 250A feeder and decide to terminate it on the #6awg-250mcm lug. In this case I am compliance with 110.14(C).

 

[jap]

Maybe it will make more sense this way...

You have a single conductor #6awg-250mcm lug. 110.14(C)(1) tells you the lug is rated 255A at 75deg (from T310.15(B)(16)).

I am running a 250mcm cable bus (ampacity = 405 at 75deg from T310.15(B)(17)) for a 400A feeder and decide to terminate it on the #6awg-250mcm lug. I have violated 110.14(C).

Instead, I run a 2/0 cable bus (ampacity = 265 at 75 deg) for a 250A feeder and decide to terminate it on the #6awg-250mcm lug. In this case I am compliance with 110.14(C).

That's a lot to think about.

So if the lug in your 1st example was rated to 600mcm then the 250 mcm cable would be okay?

JAP>

 

[jonesjimbo]

Quote Originally Posted by david luchini View Post
Maybe it will make more sense this way...

You have a single conductor #6awg-250mcm lug. 110.14(C)(1) tells you the lug is rated 255A at 75deg (from T310.15(B)(16)).

I am running a 250mcm cable bus (ampacity = 405 at 75deg from T310.15(B)(17)) for a 400A feeder and decide to terminate it on the #6awg-250mcm lug. I have violated 110.14(C).

Instead, I run a 2/0 cable bus (ampacity = 265 at 75 deg) for a 250A feeder and decide to terminate it on the #6awg-250mcm lug. In this case I am compliance with 110.14(C).



So if you are using compression lugs instead of mechanical lugs, would that mean you would be limited by T310.15(B)(16)?

 

[ron]

I appreciate these responses, but there has to be some other way to understand the intent of 110.14(C)(1) because it seems silly in the way we are currently using it. I guess I need to write a change for the next NEC edition.

I can understand if there was a criteria modification like for underground feeders such as B.310.15(B )(3), like you are running long distances and for a short distance , such as entering a SWBD the conditions change, you can ignore it.