The temperature of the environment, the temp rating of the wire, the temp rating of the connector being used. The lowest rating of any of these is the one you use.
This throws another wrench into it. Conductor sizing for a residential service is also different. It does not use the same chart as feeders or branch circuits.thanks guys. i will use the 75 degree column. as for what i'm sizing up, it is a 400 amp ext panel with blade disconnect feeding two 200 amp interior panels. i will need to use 3-0 copper.
That refers to the temperature that wire/cable might be exposed to. For example an attic possibly might get very hot in your region. Or in a factory the temperature conditions could be very hot where the wire is being run.thanks so much. i understand a little better now but am still confused about the temp of the environment part.
Just did a similar installation back in April, I used two 4/0 conductor per leg, but mine was 3 phase. There are some pictures here:thanks guys. i will use the 75 degree column. as for what i'm sizing up, it is a 400 amp ext panel with blade disconnect feeding two 200 amp interior panels. i will need to use 3-0 copper.