It's been a while and I want to make sure I've got this.

[rhamblin]

so I’ll be installing 350 KCMIL conductors for a 200 amp panel, that doesn’t seem right, does it?

doesn’t 215.2(A)(1)(exc. no. 1) tell us that the feeders can be rated for 200 amp? So 3/0 awg?

 

[kwired]

Correct. The receipts will not be close to any sources of water.


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Water presence or absence doesn't automatically mean GFCI protection required, areas where there is increased risk of shock is what drives most GFCI requirements, some don't involve water at all. See 210.8 for general GFCI requirements, plus there are specific requirements in other sections, primarily in chapters 5 and 6, GFCI requirements involving swimming pools is one example.

So, are we required to size it based on continuous use? Furthermore, what is the wire between the buss switch and the xfmr? I assume its a feeder, but since it feeds a separately derived system, does that make it a branch circuit?

A branch circuit has an outlet, a transformer does not have an outlet this is a feeder. Secondary conductors are also feeders, since secondary protection is at the load end of the conductor they are feeder tap conductors, except where secondary is allowed to be protected by primary device then they are just feeders.

I plan to use a 200 amp breaker in the panelboard. So then the question becomes, can I use 3/0 AWG (rated 200 amps at 75°C) or do I need to increase by 125% for the possibility of continuous duty (125% x 200 amps = 250 amps, 250KCMIL AWG).
I don't believe I have to because of 215.2(A)(1)(exception No. 1).
Thoughts? I just want to make sure I am doing this correct and remembering it correctly.

You can put a 20 amp breaker in the panelboard and supply it with 12 AWG if you wanted though you spent a lot of $$ on what could have been a much smaller transformer in that case, and presumes you are only supplying maximum of 20 amps of load.

If you want the full 208 amps of rated capacity from the transformer secondary, you need at least a 208 amp conductor and 208 amps protection, use of standard size devices however will make you use a 225 amp device - you need 225 amp conductor to comply 240.21(C)(2)(b).

Is pretty common to see people opt for 200 amp conductor and 200 amp overcurrent protection on a 75 kVA transformer like this but is not a rule you have to do it that way.

Even if you had 300 amp device/conductor that appears to be allowed, transformer rating is still only 208 amps.