Table 310.15(B)(21) vs 310.15(B)(20)

[mta820]

Looking to see if anyone can give me an explanation of the difference in these tables? I sized QUADOH 1/0-1/0-1/0-1/0 3 covered one bare as steel a steel strand as messenger wire to run from a 200amp meter main single phase panel to a mobile home overhead using table Table 310.15(B)(21). the mobile home will be a sub panel thus the QUAD cable needed. I have used 4\0 urd in the risers with #4 al equipment ground on load side and ran the QUADOH to mobile home 95' away. I have done this in the city and inspector signed off in past. Now the county inspector is telling me that 310.15(B)(20) must be used due to the messenger in the cable? Do i refer the prior job that passed to inspector or will this possibly open up a situation where i may have to go back and upgrade the wire there? 310.15(B)(20) says 4/0-4/0-4/04/0 is good for 224amps this is what county inspector says is correct. Dont want to get in bad with the city inspector i have to deal with all the time. Anyone have any input on what i should do here?

Thank you

 

[david luchini]

I would think the biggest difference is that (20) is for Insulated Conductors and (21) is for Bare or Covered Conductors.

 

[Smart $]

You will still be limited by the terminal temperature limitation of 110.14(C), which goes by Table 310.15(B)(16)... 4/0 AL will only get you to 180A... okay for 200A feeder if load is that or less.