NCEES Power 10

[yaoyaodes]

Can only one explain to me why the question does not need to convert to a single-phase for calculation?
and why does question 11 need to convert to a single-phase?

 

[Zach Stone P.E.]

#10 is a single-phase load connected line to line, it is a single-phase circuit so no need to convert.

#11 is a three-phase load, to simplify circuit analysis you need to convert to a single-phase equivalent circuit.