I know of no situation with our Pocos where it's actually possible to have 480Y277 service AND 240 center-tapped delta.
Indeed, EUSERC has put the hammer down on 240 center-tapped delta. It's being phased out across the board. Legacy system still exist for older structures, though. Don't get your hopes up if you expect to bid and wire a new installation.
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One of the factors that many j-men forget/ ignore is that the neutral for 480Y277 and a derived 208Y120 are 30 degrees out of phase -- with the derived current lagging.
This is noted in every Ugly's -- but its in the fine print.
THIS is the reason why your grays and whites can't get crossed over. You'd end up with an amazing harmonic on the returns.
And, in the same vein, it's a disaster if a hot for BOY is mated to the return for BkRBlu. You'll get wicked harmonics, too.
Those are the conductors that end up getting fried... first.
You might also have your returns undersized, as a result.
In commercial installations, it's my practice to just keep lighting circuits separate from everything else. I isolate them regardless of the Service voltage.
HVAC and lighting are the only loads fed by 480Y277V in commercial practice -- with exceptions for weird equipment, and the elevator system. And those exceptions are really rare.
Industrial is loaded with 480 delta motor loads -- which have largely replaced everything that has come before. With rare exception, I isolate my control circuits. Experience has caused me to shun 480/ 240/ 208 double-pole control relay voltages. They get too much dynamic feed-back from motor EMF.
So, outside of service work, I don't expect to face these troubles.
