Voltage drop

[JoeNorm]

I am wondering about how to accurately assign amperage values for voltage drop calculations.

For example, lets say you have a continuous duty load at 16 amps. After you multiply by 1.25 you arrive at 20 amps. Which number do you use to determine voltage drop in the circuit?

Another example would be a receptacle with no specific load, could be anything plugged in. How would this be approached?

Another example: A PV inverter. These are rated to a certain output but rarely reach 100% possible amp output. Do you have to use max amp output in this situation?

thanks

 

[bwat]

As it looks like you are aware, voltage drop is dependent on the current being delivered to the load. Therefor to calculate a voltage drop, the load has to be specified.

So for your question of 16A vs 20A, both are perfectly valid answers. It’s just a question of which one your are trying to meet. A lot of times I see (and spec) VD to be no more than 3% for actual connected load. So I would tend to use 16A for your example.

 

[ggunn]

Another example: A PV inverter. These are rated to a certain output but rarely reach 100% possible amp output. Do you have to use max amp output in this situation?

Have to? No, you can use any number you like. Best practices, however, say yes. If you use a significantly smaller number you run the risk of the inverter dropping offline when its output approaches its maximum because of voltage rise in the conductors. Also, the losses due to voltage drop come right off the top of the accumulated energy production of the system.