You're asking a very common and important question about voltage drop calculations. Here's the breakdown

You should generally base your voltage drop calculations on the calculated load (175 amps in your case), even if you believe the actual load will be lower.

Here's why: Code Compliance and Safety

Article 215.2(A)(3) and 215.2(A)(4) specifically address voltage drop. The NEC intends for the system to be capable of handling the calculated load without excessive voltage drop. While voltage drop is not strictly enforced by inspectors, it is a design consideration and can be legally binding depending on the specification (i.e. Engineer of Record may require strict adherence).

Future Proofing

Your apartment may have a different tenant in the future, or the current tenant's usage habits could change. You don't want to undersize conductors and create a voltage drop problem later if the load increases. What if a tenant installs a large aquarium with heaters, or starts using more electric space heaters?

Worst-Case Scenario

Voltage drop is most critical during periods of high demand. Calculating based on the calculated load ensures you're designing for the worst-case scenario the system is designed for.

Component Longevity

Excessive voltage drop can stress electrical equipment (motors, appliances, etc.), shortening their lifespan and potentially causing failures.

Accuracy of Calculation

The 220 calculation can be seen as an estimation to the peak amperage that your apartment can experience.

When Might You Consider Deviating (Very Carefully)



Demand Factors with Solid Evidence

If you have documented and reliable data proving that the actual maximum demand of similar apartments in the same building complex is consistently and significantly lower, you might consider using a lower demand factor, but you would have to be able to justify and defend this to an inspector.

Engineering Supervision

You should only consider this with the direction of a qualified engineer.

Therefore

Start your voltage drop calculations with the 175-amp calculated load. You can use voltage drop calculators or formulas to determine the appropriate conductor size for the length of the run.

Key Code References



NEC 215.2(A)(3) and (4) Feeders. Voltage drop in feeder conductors shall not exceed 3% and the total voltage drop on both feeder and branch circuit conductors to the farthest point of utilization shall not exceed 5%.* NEC 210.19(A) FPN 4 Branch Circuits. Voltage drop in branch circuit conductors should not exceed 3% and the total voltage drop on both branch circuit and feeder conductors to the farthest point of utilization should not exceed 5%.

In summary: Design for the calculated load. Undersizing based on assumptions about actual usage is a false economy and can lead to problems later. Flag for review