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Continuous Load and the 125 Percent Rule

Continuous load is a sizing rule, not a meter reading. Conductors and overcurrent devices are selected at 125 percent of continuous current, while voltage drop still follows the current that actually flows.
Code basis
210.19 / 210.20 / 215.2
Multiplier
125% continuous
Applies to
Conductor & OCPD sizing
Does not replace
Voltage-drop current

The Procedure

5 steps, in the order the code applies them.

  1. Step 1

    Decide if the load is continuous

    A load expected to run for three hours or more at maximum current is continuous. EVSE and many water heaters are the usual examples.

  2. Step 2

    Split continuous and non-continuous portions

    Only the continuous portion gets 125 percent. Add non-continuous load at 100 percent.

  3. Step 3

    Size conductors to the design current

    The conductor must carry the 125 percent continuous plus 100 percent non-continuous total after derating and termination caps.

  4. Step 4

    Size the overcurrent device to the same design current

    Pick a standard breaker at or above that design current, then confirm the conductor can be protected by it.

  5. Step 5

    Keep operating current for voltage drop

    When checking drop, enter the current that flows — not the 125 percent sizing number — unless the sustained load truly equals that value.

Sizing current is not measured current

Continuous load is taken at 125 percent for conductor and overcurrent sizing.

Voltage drop still follows the current that actually flows, so the two checks should not reuse the same adjusted number blindly.

Mixed loads

Apply 125 percent only to the continuous portion, then add non-continuous load at 100 percent.

The calculator exposes this as a flag for simple cases; complex panels need itemized load work.

Decision Guide

The choices that change the answer, and how to make them.

  • EVSE is the teaching example

    48 A continuous charge current needs a 60 A circuit. That single identity prevents most continuous-load mistakes.

  • Do not 125 percent a whole panel by habit

    Apply the multiplier to continuous portions. Inflating every line item produces an oversized fantasy service.

  • Nameplate instructions can redefine the input

    Some equipment states minimum circuit ampacity already including continuous treatment. Do not double-apply 125 percent on top of MCA.

FAQs

What loads are considered continuous?
Loads expected to run for three hours or more at maximum current. EV chargers and many storage water heaters are common continuous loads; a bathroom fan that cycles is usually not.
Does the 125 percent rule change voltage drop?
No. Voltage drop follows operating current. Continuous-load sizing and voltage-drop current are related but not the same number.
How do I size a mixed continuous and non-continuous load?
Take 125 percent of the continuous portion plus 100 percent of the non-continuous portion, then size conductors and overcurrent protection to that total.

Calculated against the NEC 2023 edition using 210.19(A)(1), 210.20(A), 215.2(A)(1). Confirm the edition adopted by your AHJ, which may differ and may carry local amendments.

Not covered by this tool

  • Motor, air-conditioning and welder circuits, which are sized under their own articles.
  • Conductors in free air and photovoltaic circuits.
  • Parallel conductor sets, taps and busbars.
  • Local amendments, which can be stricter than the published code.

Data last verified