THHN and THWN dual rating

[bpk]

When you use the thwn rating of a wire can you use the thhn ampacity for dual ratings. For instance I am quoteing a project that has a 225 amp 3 phase disconnect and installing pvc underground to a 225 amp panelboard. The underground wires need to be listed for wet location (right) so they will need to be thwn and 4/0 for 225 amp capacity. If they were thhn 3/0 would work. The reason I would like to know this is because I have some 3/0 copper I would like to use up. Thanks in advance

 

[iwire]

When you use the thwn rating of a wire can you use the thhn ampacity for dual ratings. For instance I am quoteing a project that has a 225 amp 3 phase disconnect and installing pvc underground to a 225 amp panelboard. The underground wires need to be listed for wet location (right) so they will need to be thwn and 4/0 for 225 amp capacity. If they were thhn 3/0 would work. The reason I would like to know this is because I have some 3/0 copper I would like to use up. Thanks in advance

Your terminals will not be rated for more then 75C and that will limit any type of 3/0 to the 75 C 200 amp rating.

 

[hardworkingstiff]

Your terminals will not be rated for more then 75C and that will limit any type of 3/0 to the 75 C 200 amp rating.

The idea of splicing a piece of 4/0 to the 3/0 and making terminations with 4/0 has been discussed here before but I don't remember the outcome. Anyone care to refresh my memory as to the consensus on this methodology?

 

[ohm]

The idea of splicing a piece of 4/0 to the 3/0 and making terminations with 4/0 has been discussed here before but I don't remember the outcome. Anyone care to refresh my memory as to the consensus on this methodology?

It was looked at real hard down here and allowed to correct wire which was pulled in error.