Your go to approach for long runs and voltage drop

[Alan]

Let’s compare real world voltage drop habits, especially what people do when the run gets long and the load is not forgiving. A lot of us have a personal line in the sand where we stop trying to squeeze by and just upsize, because we know the callback risk is higher than the material cost.

What’s your practical process for deciding wire size on long runs, and what warning signs do you watch for during install or troubleshooting that scream voltage drop? If you have a favorite rule of thumb, or a lesson you learned the hard way, drop it here. The goal is to give newer electricians a few solid, repeatable ways to think about it.

 

[AmarantCoral]

I learned the hard way that you can pass a basic check and still have a voltage drop problem under real load. My process is run length plus load plus starting surge, then I’m usually thinking upsizing instead of hoping. During troubleshooting I look for heat at connections and a noticeable sag when a big load kicks on.

 

[PGB1]

When allowed by the money changers, I size my phase conductors for ca 140% for my industrial work.
The reason is periods of voltage drop of the entire service in real life use versus engineering calculations. (Induction load vs. lowering voltage = higher amperage) I like to size the branch circuit conductors and feeders to compensate.

Usually the engineer who specified the project will agree when he or she learns that I have worked that facility and know the infrastructure.

Sizing the grounded circuit conductor (neutral) is a whole different project due to the increased use of non-linear load by electronics.


For the restaurants that I used to specify; any kitchen or prep circuit with a 120 volt 20 amp attachment plug got one gauge over whatever voltage drop calculations desired. Restaurant kitchen users are famous for putting in cube taps and drawing a 20 amp circuit to spot-on 20 for hours in a row. I'd rather the receptacle outlet burn than the conductor in a pipe full of conductors.

But that's just me. Others do things differently.