Calculation Results


What exactly is a voltage drop? As an electrical current travels through a wire, voltage (also referred to as the electrical potential) pushes it through. The trouble is, the wire creates contrary pressure that “pushes back,” so to speak. For the current to travel through successfully, it has to surpass that contrary pressure.

When electrical current moves through a wire it is pushed by electrical potential (voltage) and it needs to surpass a certain level of contrary pressure caused by the wire. A voltage drop, then, is the amount of voltage loss that the contrary pressure in the wire generates, and excessive voltage drops can result in some distinct problems. For example, a motor could run hotter than it usually does, ultimately burning out well before it ever should have. Some other examples of problems stemming from excessive voltage drops are heaters performing poorly and inconsistent power generation.

We recommend that in a circuit with full load, a voltage drop should be under 5%. That’s possible to do by using the right type of wire for the job. Take advantage of our DC Voltage Drop Calculator for any calculations that you need, and make sure to bookmark this page for handy reference, or share on social media.

  • NEC Data: With this tab, the user can calculate an estimated voltage drop by using resistance and reactance date that comes straight from the National Electric Code, or NEC.
  • Estimated Resistance: Using resistance data based on the size of the wire is how this tab determines an approximate voltage drop.


  1. Length of the run should only account for distance between the source and the load. Length will be multiplied by 2 for single phase and square root of 3 for three phase automatically.
  2. Calculations are based on voltage drop formulas found in IEEE Std 141 (Red Book).
  3. NEC Informational Note suggests a maximum voltage drop of 3% for branch and feeder circuits with combined voltage drop of feeder and branch circuits limited to 5%. It is important to note that the individual branch or feeders will need to be less than 3% to meet the 5% limit.