Voltage drop calcualtion

[dahualin]

I always use the connected load ampage to calculated voltage drop for panel feeders. For example, a panel rated 100amps and upstream circuit breaker rated 100amps also. But the connected load is 50amps. I will use 50amps to calculate the voltage drop to make sure no 3% drop to the panel. One EC asked me how about the client connect new load after this project and it will very likely increase the connected load and voltage drop will be bigger than 3%.

How do you guys calculate voltage drop? Thanks.

 

[charlie b]

I use the calculated load as the basis for voltage drop calculations. There is no need to do otherwise. If the owner chooses to add load later, it becomes incumbent on the persons doing that design and installation to deal with all aspects of the remodel. They would have to address any impact of the remodel on the existing configuration, and that would include voltage drop, panel sizing, conductor sizing, and the adequacy of the service to handle the added load.

But if a VD calculation shows a voltage drop that is just barely within the limits I am aiming to achieve, then I will change something. That would usually result in a change to the next larger conductor size. But this would be a design decision, not a code issue.

 

[W6SJK]

I guess using Calculated Load is better than estimated demand. But ff I put in a 200A panel then I size the conductors for 200A operation, including effects of VD. Otherwise, why protect it at 200A? Nearly everyone expects to expand, and some specifically state 25% future capacity be provided.

Besides, I may be the poor guy that comes along and adds load. If nothing else, I ask the client. If the client is an engineer, he always says DO IT.