Continuous and intermittent loads describe how long an electrical load runs, and the distinction matters because continuous loads require extra capacity in the circuit that serves them. Under the electrical code, a continuous load is one that runs for a long stretch, and circuits serving continuous loads must be sized larger to handle the sustained heat. Understanding the difference explains why some circuits are sized the way they are.

Here is what continuous versus intermittent load means on a panel.

What a continuous load is

A continuous load is defined by code as one where the maximum current is expected to continue for three hours or more. Because the load runs at full current for a long time, it generates sustained heat in the wiring and connections, which is the key reason it needs special treatment.

Common examples of continuous loads include EV charging, which can run for hours, and certain lighting and equipment that stays on for long periods.

What an intermittent load is

An intermittent, or noncontinuous, load is one that runs for shorter periods rather than continuously at full current for three hours or more. Many household loads are intermittent, turning on and off or running for shorter durations. Because they do not sustain full current for long stretches, they do not generate the same prolonged heat and are not subject to the same extra sizing.

The 125 percent rule

The practical reason the distinction matters is the 125 percent rule. Code requires that a circuit serving a continuous load be sized at 125 percent of that load, meaning the conductors and overcurrent protection must be rated for more than the load’s actual current. This extra 25 percent provides a safety margin for the sustained heat a continuous load produces.

This is why, for example, an EV charger that draws 40 amps continuously needs a 50-amp circuit: 40 amps times 125 percent is 50 amps. The circuit is sized larger than the load because the load is continuous.

How this affects circuit sizing

When an electrician sizes a circuit, they account for whether the load is continuous or intermittent:

• Continuous loads are sized at 125 percent of the load for the conductor and overcurrent protection.
• Intermittent loads are generally sized at 100 percent of the load.
• Mixed circuits combine 125 percent of the continuous portion and 100 percent of the noncontinuous portion.

This ensures the wiring and breaker can safely handle the actual usage without overheating.

Why it matters for your home

Understanding continuous loads matters most when adding equipment that runs for long periods, like an EV charger. Because these require circuits sized larger than the load itself, they can have a bigger impact on your panel and service capacity than their raw current suggests. This is one reason a load calculation, which accounts for continuous loads, is part of planning major additions.

A continuous load runs at full current for three hours or more and generates sustained heat, while an intermittent load runs for shorter periods. Because of the heat, code requires circuits serving continuous loads to be sized at 125 percent of the load, which is why an EV charger and similar equipment need circuits larger than their actual current. A licensed electrician accounts for continuous versus intermittent loads when sizing circuits and planning additions.

Stella Electric sizes circuits correctly for continuous and intermittent loads for homeowners across the Baltimore area and throughout Maryland, with flat-rate pricing and no overtime charges. If you are adding a major load, we will size it right. Financing is available on qualifying projects.