What is Continuous Load?
Continuous Load is an electrical load expected to operate at its maximum current for three hours or longer. The National Electrical Code requires conductors and overcurrent devices to account.125 percent of the continuous portion, plus noncontinuous loads. Examples include lighting, electric vehicle charging, heating equipment, and commercial refrigeration.
Quick Facts About Continuous Load
Category
Electrical load classification
Formula
Continuous load multiplied by 125 percent, plus noncontinuous load
Used for
Circuit, conductor, breaker, and panel sizing
Common confusion
A load is not continuous simply because equipment runs often.
Also called
Continuous electrical load, Continuous current load
Often discussed with
Dedicated Circuit Installation, Electrical Code Compliance Inspection
Key Takeaways About Continuous Load
- The National Electrical Code defines continuous operation as three hours or longer at maximum current.
- Designers generally account for 125 percent of continuous current when sizing circuit conductors and protection.
- Lighting, EV charging, heating, and refrigeration often create continuous loads.
- Continuous load calculations help prevent overheating, nuisance trips, and undersized electrical equipment.
Understanding Continuous Load
Continuous Load describes electrical demand. It runs at maximum current for three hours or longer. This time covers expected use during normal operation. It doesn't apply only to devices that never shut off. A lighting system may run through a work shift. Controls may turn it off after business hours.
Related glossary terms: Ampacity, Branch Circuit, Electric Vehicle Supply Equipment.
This classification affects electrical design. Sustained current creates heat in conductors, terminals, breakers, and panel equipment. Common examples include commercial lighting, electric vehicle charging, and electric heating. A motor may run briefly during repeated cycles. It may not qualify unless maximum-current operation reaches three hours.
How Continuous Load Works, Is Measured, or Is Used?
An electrician or electrical designer first identifies equipment. The equipment must operate at maximum current for three hours or more. The designer then finds the equipment's calculated current. They use the nameplate, manufacturer instructions, or an applicable load calculation. The continuous portion is generally multiplied by 125 percent. Then it's added to noncontinuous demand.
For example, a circuit has 16 amperes of continuous lighting. It also has 10 amperes of noncontinuous load. This produces a calculated demand of 30 amperes. The calculation is 16 multiplied by 1.25. This equals 20 amperes, plus 10 amperes. The selected branch circuit, conductor ampacity, and overcurrent protection must meet code rules. They must also meet equipment limits.
Other limits still apply after the calculation. Terminal temperature ratings, conductor insulation, ambient temperature, bundling, voltage drop, and equipment listings can affect selection. A breaker rating alone doesn't prove correct circuit sizing. The conductor and connected equipment must also be compatible.
Why Continuous Load Matters?
Correct treatment of continuous demand reduces excessive heating during normal operation. An undersized circuit may show no problem during a short test. It may run hot after several hours of steady current. Persistent heating can damage insulation, loosen connections, trip a breaker, or shorten equipment life.
The calculation also improves planning for service capacity and panel space. A large EV charger or electric heater may fit on an existing panel. Physical space alone doesn't prove enough panel capacity. Reviewing continuous demand before installation can reveal needed changes. These may include a dedicated circuit, load adjustment, or service upgrade.
When Continuous Load Matters Most?
Continuous load rules matter during new construction, panel changes, tenant improvements, and equipment replacements. They also matter when a property adds EV charging, heat pumps, electric water heating, large lighting systems, or refrigeration. These projects can change branch-circuit demand and total service load.
Useful review questions include the following.
- Will the equipment operate at maximum current for three hours or longer?
- What current appears on the nameplate or in the manufacturer instructions?
- Does the circuit calculation apply the required continuous-load factor?
- Do the breaker, conductor, terminals, panel, and disconnect have compatible ratings?
How to Evaluate Continuous Load?
- Confirm whether expected maximum-current operation lasts three hours or longer.
- Check the equipment nameplate current and manufacturer installation instructions.
- Verify that continuous current receives the applicable 125 percent design factor.
- Compare the calculated demand with conductor ampacity, breaker rating, and panel capacity.
- Look for heat damage, discoloration, loose terminations, or repeated breaker trips.
Related Concepts Compared
Continuous Load vs. Noncontinuous Load
A noncontinuous load operates at maximum current for less than three hours under the applicable design conditions. It is added at its calculated current rather than receiving the continuous-load factor.
Continuous Load vs. Connected Load
Connected load is the total rating of equipment connected to a system. Whether the equipment runs at the same time or not. Continuous load is a classification based on expected operating duration and maximum current.
Continuous Load vs. Demand Load
Demand load represents the calculated amount of power expected at a selected time or operating condition. A demand calculation may include continuous loads, but the two terms do not mean the same thing.
Continuous Load vs. Ampacity
Ampacity is the maximum current a conductor can carry continuously under stated conditions. Continuous-load rules can require a larger conductor or different installation so the conductor has enough usable ampacity.
Expert Note
A three-hour estimate should reflect the equipment's actual duty cycle and control settings. Nameplate current alone may not settle the issue. Terminal ratings, ambient heat, conductor bundling, and manufacturer instructions can change the permitted circuit design.
Common Mistakes or Myths About Continuous Load
- Treating every frequently used appliance as a continuous load without checking maximum-current duration.
- Applying the 125 percent factor to the entire circuit instead of the continuous portion.
- Selecting a breaker first and assuming the conductor automatically matches it.
- Ignoring terminal temperature ratings, ambient temperature, or conductor bundling.
- Assuming available panel spaces prove that the panel has enough calculated capacity.
Continuous Load in Practice: A Real-World Example
A workplace installs a 16-ampere EV charger that operates for six hours each evening. The continuous portion is calculated at 20 amperes after applying 125 percent, so the circuit and protection must satisfy the applicable requirements for that calculated demand.
Sources & Further Reading on Continuous Load
Related Services
Related Terms
Ampacity
Ampacity is the maximum current, measured in amperes, that a conductor can carry continuously under stated…
Branch Circuit
Branch Circuit is the wiring between the final overcurrent device, such as a circuit breaker, and…
Electric Vehicle Supply Equipment
Electric Vehicle Supply Equipment is the equipment that safely delivers electrical power from a building or…
Load Calculation
Load Calculation is the process of estimating the electrical demand that a building, panel, feeder, or…
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