Which of the following are properties of balanced 3-phase power systems? Select all that apply. 

A.  All 3-phase voltages have equal magnitude and are 90° apart.
B.  Three-phase systems transmit alternating currents.
C.  Neutral wire, if present, carries no current.
D.  Three-phase systems can produce rotating magnetic field.
E.  In a wye connection, the line voltage equals the phase voltage.

Let's analyze the truth behind each of our possible answers:

A. All 3 phase voltages have equal magnitude and are 90 degrees apart - FALSE - The first part of the answer, that 3-phase voltages have equal magnitude, is in fact true. However, 3 phase voltages are 120 degrees apart from each other, not 90 degrees. Since 360$°$/3 = 120$°$, this spacing allows the phases to be balance so that power transfer at any point of time is constant.

B. Three-phase systems transmit alternating currents - TRUE - Three phase power systems carry alternating currents that are equal in frequency and offset by 120 degrees from each other.

C. Neutral wire, if present, carries no current - TRUE - The fundamental purpose of the neutral wire is to serve as a return path. The neutral current is the vector sum of the three line currents. Therefore, when we have a balanced system, this sum will equal 0 and the neutral wire current will be equal to 0.

D. Three-phase systems can produce rotating magnetic field. - TRUE - A rotating magnetic field is produced when a 3-phase winding is energized by a 3-phase supply.

E. In a wye connection, the line voltage equals the phase voltage. - FALSE - It is a delta configuration, not a wye configuration, that produces equal line and phase voltages.

Therefore, our final answer is B, C, and D.