KVA to Amps

Because you forgot the factor of sqrt(3) which comes with 3 phase power. Of course, nothing in the image says the supply is 208Y/120V 4-wire rather than 208V 2-wire, but since the result is 123A, it must be.

Cheers, Wayne
You're probably correct. Even though it's not mentioned in the truncated version of the panel schedule no one is going to install a 1 phase, 208 volt panel.
 
Yes that is one example of where you may see a 1Ø, 208 volt panel.
Yep, but you are most likely to see a 120/240V 1PH3W panel fed by a 120/208V 1PH3Wfeeder.

Particularly if the panel is an off the shelf instead of being a factory special.
 
What is the 1.73 for?
There are a number of ways to think about it, but the one I like is:

In a 3 phase wye system, the L-L voltage is sqrt(3) * the L-N voltage. If you want to covert a given identical current I on all 3 line conductors to a kVA, we can start with the case where the currents come from 3 identical L-N loads connected in a wye pattern. [Note that the neutral currents will cancel to give 0 neutral current.] We know how to calculate the kVA for a 2-wire load, it's just I * V. So since you have 3 identical loads, you end up with 3 * I * VL-N. Given that VL-L = sqrt(3) * VL-N, that's equivalent to sqrt(3) * I * VL-L. Then it turns out that the same formula works even for the 3-phase 3-wire case, where there is no neutral.

Cheers, Wayne
 
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