William Underhill wrote:


Hmm. Disclaimer first - I'm a naval electrical technician, not civilian,
so am not intimately familiar with civilian code requirements. Further,
I'm Canadian, and if you're not, some of your code requirements may vary.

That said, check out this website:
http://www.friesen.com/manuals/allow...n%20Free%20Air


You actually want table 4 (in conduit/cable) which has even lower amp
ratings.


Depending on your insulation type and ambient temp, you'd need at least
3/0 to meet the requirements, and 4/0 gives you only a 30-amp safety
margin. As I said, I'm not familiar with the details of the NEC, but in
the Navy we'd be using the 4/0, since we have to assume that all loads
are energized at all times. There may indeed be some kind of
'grandfathering' provision, but I'd rather not create an electrical fire
risk.


The US-NEC allows 4/0 Al for 200A residential services. In a residence
all loads are not energized at all times. The major loads, in
particular, cycle on and off. I believe the wire sizes were based on
field studies.

4/0 can not be used for 200A non-residential services where major loads
may be energized all the time.

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