URD Cable

[seamusliam51]

Curious about the use of URD as a feeder for a 100 amp subpanel in a residential garage. Ampacity for 2awg al is listed at 155a for Southwire brand URD. Wanted to use quadplex URD as a direct bury....? Not listed in NFPA 70.. thoughts?

 

[electrofelon]

Curious about the use of URD as a feeder for a 100 amp subpanel in a residential garage. Ampacity for 2awg al is listed at 155a for Southwire brand URD. Wanted to use quadplex URD as a direct bury....? Not listed in NFPA 70.. thoughts?

Probably no problem, just make sure it is marked with a NEC wire type, usually USE or RHH. I have no idea how they are getting 155 amps for number 2. Per the NEC it would be 90 amps for number 2 aluminum

 

[seamusliam51]

Compressed Aluminum apparently has a much higher amperage capacity??

 

[seamusliam51]

Actually listed as USE-2

 

[hillbilly1]

Probably no problem, just make sure it is marked with a NEC wire type, usually USE or RHH. I have no idea how they are getting 155 amps for number 2. Per the NEC it would be 90 amps for number 2 aluminum

Probably due to the lower ambient temperature underground, along with heat disapation, but then when you come out of the ground, all of that would change.

 

[infinity]

Here's what Southwire says about their USE-2:

Ampacity: 90°C conductor temperature, 20°C ambient, RHO 90, 100% load factor for three conductor triplex with neutral carrying
only unbalanced load.
Technical data for cable with solid black neutral is identical to yellow extruded stripe data except for the “YES” suffix to code word.
Also available in paralleled construction.
For NEC Applications, use NEC Table 310.16 Ampacities.

 

[electrofelon]

Probably due to the lower ambient temperature underground, along with heat disapation, but then when you come out of the ground, all of that would change.

But that is way out of the ballpark, I suspect either as a typo or perhaps he was looking at 2/0

 

[infinity]

But that is way out of the ballpark, I suspect either as a typo or perhaps he was looking at 2/0

This document actually says 165 amps for #2.

https://www.mysouthwire.com/medias/sys_master/product-specifications/product-specifications/h59/hbd/8854082813982/Triplex-RHH-RHW-2-USE-2-AlumaFlex-Underground-Service-Entrance.pdf

 

[seamusliam51]

This document actually says 165 amps for #2.

https://www.mysouthwire.com/medias/sys_master/product-specifications/product-specifications/h59/hbd/8854082813982/Triplex-RHH-RHW-2-USE-2-AlumaFlex-Underground-Service-Entrance.pdf

Kinda makes 310.15 (B) (16) obsolete!

 

[electrofelon]

This document actually says 165 amps for #2.

https://www.mysouthwire.com/medias/sys_master/product-specifications/product-specifications/h59/hbd/8854082813982/Triplex-RHH-RHW-2-USE-2-AlumaFlex-Underground-Service-Entrance.pdf

Wow, I'm going to start using that table.

 

[infinity]

Wow, I'm going to start using that table.

Yeah, if you look at the notes in post #6 you're stuck with the NEC ampacities.

 

[hillbilly1]

Probably the table the utilities use, around here, they run 4/0 for a 400 amp service.

 

[seamusliam51]

Thank you ... The note referring you back to NEC for ampacities clears it up.... but the utilities are indeed using these higher ampacities for service... Curious about the reasoning for that... Does their equipment have much higher temperature ratings?

 

[hillbilly1]

Thank you ... The note referring you back to NEC for ampacities clears it up.... but the utilities are indeed using these higher ampacities for service... Curious about the reasoning for that... Does their equipment have much higher temperature ratings?

I think they use actual projected loads instead of possible maximum loads. Most services are very seldom see over 50% of their rating. Same way with transformers.