Compare the total copper cross sections in terms of current-carrying capacity for a single-phase and a three-phase 120 V system with effective load resistance of 15 Ω.

For both single-phase and three-phase systems, the current can be calculated using Ohm's Law:

I = V / R

Where:

I is the current,

V is the voltage,

R is the effective load resistance.

Given that the effective load resistance (R) is 15 Ω and the system voltage is 120 V, we can calculate the current for each system:

Single-phase system:

I_single = 120 V / 15 Ω

I_single = 8 A

For a single-phase system, the current-carrying capacity is 8 A.

Three-phase system:

In a three-phase system, the line current is the same as the current through each phase. The voltage used in the calculation is the line-to-neutral voltage (120 V), so:

I_three = 120 V / 15 Ω

I_three = 8 A

The current-carrying capacity for the three-phase system is also 8 A.

Therefore, the correct answer is:

Option B: Single-phase 16 A; three-phase 8 A