NEC table for aerial bare wire ampacity medium voltage

[Aaro]

Is there an ampacity table for bare wire ampacity for medium voltage wires run aerial? I am an electrician at an educational institution where we feed the campus with 4160/2400V. Some of the 4160V is overhead power poles. We had to replace a fuse off of one of the poles that had blown up and we were not able to find the fuse size. The ampacity marking was blown off. The others next to it were 80A. The CU aerial conductors are #6AWG. I can only find insolated conductors in the code book. Some tables are for triplex and some for direct burial. Thank you for any help.

 

[david luchini]

I would think 310.21 is what you are looking for.

 

[Aaro]

Article 310.21 says that it is for up to 2000V. I am working with 4160/2400V.

 

[Aaro]

When I look at T311.60(C) (69), I noticed that #6 CU has an ampacity at 110A on the 90D table. But that is insulated. I am wondering about bare wire. I assume I could get more amps through bare than insulated.

 

[Speedskater]

Bare copper 6AWG will carry a huge amount of 50/60Hz current before fusing. Something over 600 Amps !
* * * * * * * * *
At 4160 Volts, that's 2 & 1/2 million Watts.

 

[Aaro]

Bare copper 6AWG will carry a huge amount of 50/60Hz current before fusing. Something over 600 Amps !
* * * * * * * * *
At 4160 Volts, that's 2 & 1/2 million Watts.

Wow! Do you know of where I can find out that information? Thank you.

 

[Aaro]

I would think 310.21 is what you are looking for.

Article 310.21 says that it is for up to 2000V. I am working with 4160/2400V.

 

[david luchini]

Article 310.21 says that it is for up to 2000V. I am working with 4160/2400V.

There is no voltage listed in the conditions of use in 310.21.

 

[wwhitney]

There is no voltage listed in the conditions of use in 310.21.

No, but there is in 2020 NEC 310.1 Scope. While 311.1 Scope says specifies Type MV cable, which 311.2 defines as an insulated cable type. So bare wires are outside of the scope of Article 311. Seems like bare wires above 2000V are an inadvertent blind spot in the coverage of the two articles.

But for an uninsulated wire, is there really any voltage effect on ampacity? Seems like the values in Table 310.21 for uninsulated wires should work above 2000V. As far as I see, that was the case in the 2017 NEC, when there was no Article 311, and 310.1 didn't discuss any voltage limit.

Cheers, Wayne

 

[Aaro]

There is no voltage listed in the conditions of use in 310.21.

Okay. I was looking at the wrong article. Thank you for your help. It looks light the answer is 124A for bare and 130V for covered. I wonder if covered refers to tree wire.

 

[Aaro]

No, but there is in 2020 NEC 310.1 Scope. While 311.1 Scope says specifies Type MV cable, which 311.2 defines as an insulated cable type. So bare wires are outside of the scope of Article 311. Seems like bare wires above 2000V are an inadvertent blind spot in the coverage of the two articles.

But for an uninsulated wire, is there really any voltage effect on ampacity? Seems like the values in Table 310.21 for uninsulated wires should work above 2000V. As far as I see, that was the case in the 2017 NEC, when there was no Article 311, and 310.1 didn't discuss any voltage limit.

Cheers, Wayne

Hmm. This is slightly confusing. I wonder if there is another article that clarifies this. As far as I can see this must be the correct table.