Final answer:
In a delta-connected four-wire system, the correct term for the conductor or busbar with a higher voltage to ground from the given options is 'phase'. The neutral and ground are typically at zero volts and are not associated with the higher voltage levels that phases carry.
Step-by-step explanation:
The conductor or busbar with a higher voltage to ground in a delta-connected four-wire system is known as the high-leg or power leg. However, this was not one of the options provided in the question. Among the provided choices, 'a) Neutral b) Ground c) Phase d) Line', the most appropriate term for a conductor with higher voltage in comparison to ground in a three-phase system is typically referred to as a phase. The neutral is typically at zero volts, making it safe to touch; it returns the current to complete the circuit. The ground is the safety path to earth itself, which is also at zero volts, to protect against electrical faults. Therefore, the term 'phase' fits best as the option for a conductor with higher voltage to ground in such a system.