Voltage drop for a 4-floors condominium 5%VD

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Cartoon1

Cartoon1

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Location
Florida
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Electrical Engineer
Hello! Wanted to see everyone opinion on this.... voltage drop usually makes very paranoid for bigger type buildings. I'm getting a total of less than 5%VD all the way from the utility transformer secondary location for the building to the farthest branch circuit.

Utility transformer to main building metering service (200FT) = 2.08%VD
Building metering service to each condo electrical panel (130FT (Farthest point)) = 2.14%VD
Condo electrical panel to farthest branch circuit 'condenser roof top-unit' = .75%VD
Total = 4.97%VD (this is assuming the building load is at 100% load demand)

I usually like to stay with 3%VD, i worry about the motor operated type equipment like the condenser since it says 230/208V and my service is 208V/120. I understand that motors can usually go as low as -10%VD. Do you think 5% or less VD is sufficient or should i be even more careful and try to make it less than that? Again keep in mind that this is peak 100% load demand.

Thank you,
 
Cartoon1 said:
Do you think 5% or less VD is sufficient or should i be even more careful and try to make it less than that? Again keep in mind that this is peak 100% load demand.
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So the 5% VD is with the system operating at 100% load? I would think that in the real world the load will never be near 100% therefore your VD will never be near 5%.
 
The NEC suggestions for voltage drop generally start at the service, and ignore the drop in the utility wiring or transformer. I don't know energy code requirements, but I suspect they are similar. Under those standards you are at a hair less than 3% drop, and totally fine.

In terms of serving your customer well, it would probably pay to check the exact requirements of the condenser roof top unit. How much current does it draw during startup, and how much voltage drop can it tolerate during start-up? What sort of effect will condenser start-up have on other loads in the same residence?

NEC calculations are notoriously conservative, and in the real world your steady state load for a single residence will _never_ get close to '100%'. The aggregate load for all the residences will be a larger % of the total service, but is unlikely to approach 100%. However a large HVAC load might have transient peaks which exceed the nominal 100% rating of the service.
 
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