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.
NEC table for aerial bare wire ampacity medium voltage
- Thread starter Aaro
- Start date
- Location
- Connecticut
- Occupation
- Engineer
I would think 310.21 is what you are looking for.
Speedskater
Senior Member
- Location
- Cleveland, Ohio
- Occupation
- retired broadcast, audio and industrial R&D engineering
Bare copper 6AWG will carry a huge amount of 50/60Hz current before fusing. Something over 600 Amps !
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At 4160 Volts, that's 2 & 1/2 million Watts.
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At 4160 Volts, that's 2 & 1/2 million Watts.
Wow! Do you know of where I can find out that information? Thank you.
Article 310.21 says that it is for up to 2000V. I am working with 4160/2400V.
- Location
- Connecticut
- Occupation
- Engineer
There is no voltage listed in the conditions of use in 310.21.
wwhitney
Senior Member
- Location
- Berkeley, CA
- Occupation
- Retired
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
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.
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.