80% vs 100% Circuit Breaker Ratings: Your Key to Safety, Compliance, and Correct Selection

When you need to choose between an 80% rated breaker and a 100% rated breaker, it's important to understand how you are going to use it, since determining your application requirements will greatly affect your decision. The right breaker will help you stay safe, comply with codes, and operate your electric systems at maximum efficiency, regardless of whether you are using the breakers for residential, commercial, or industrial applications.

Why The Ratings For Circuit Breakers Are Important

Since many electric systems operate continuously, which is also classified as constantly operating for three hours or more, it is critical to understand the ratings of breakers when choosing one. The NEC (National Electric Code) requires special consideration of continuous loads to prevent equipment from overheating and/or causing electrical failures due to overloaded circuits. Selecting the correct breaker also helps you comply with the appropriate codes, reduces downtime, and helps to eliminate the use of expensive equipment due to failures from improper circuit protection.

What is an 80% Rated Circuit Breaker?

The majority of circuit protection devices used today are 80% rated breakers (an industry term for devices that can support sustained loading at 80% of their rating). An example is that if the rating on your breaker is 100 amperes, an 80% rated breaker could support 80 amperes continuously.

Commonly, standard breakers will provide cost-effective operations meeting general operational requirements and general application. But they must not exceed their 80 percent continuous usage capacity. For typical housing usage—like lighting and receptacles (not connected continuously)—an 80 percent-rated Circuit Breaker should provide sufficient operation without reaching maximum value per the National Electrical Code (NEC) required limits.

What is a 100% Rated Circuit Breaker?

A 100% rated Circuit Breakeris designed to allow for continuous circuit loads to be connected/taken from that circuit at or near maximum load (up to 100% of that particular circuit). This type of breaker may connect multiple types of circuits, such as an air conditioning unit, large industrial motors, or a data center. The design of a 100-amp 100% rated Circuit Breaker will support continuous connection of 100 amps to multiple devices over time. Enclosures to dissipate heat are required for these types of breakers due to excessive heat build-up when operating continuously.

Typical Use:A data center with continuous operations (servers) requires 100% rated Circuit Breakers for continuous operation to avoid overheating/Circuit Breaker failure (safety).

Key Differences: 80 Percent vs. 100 Percent Rated Circuit Breakers

• 80 percent rated Circuit Breakers can operate continuously at 80% of their ampacity, while 100 percent rated Circuit Breakers can operate at the full amperage rating for continuous loads.
• For 100% rated Circuit Breakers, enclosures must dissipate sufficient heat generated during continuous operation; this is different from the standard enclosures used for 80% rated Circuit Breakers.
• 100% rated Circuit Breakers are typically more expensive than 80% rated Circuit Breakers and are usually required for industrial or higher-demand applications.

Why Do Most Circuit Breakers Not Say "100% Rated"?

So why are most Circuit Breakers not marked with "100% Rated"? Here are a few reasons:

Default Standards:Most molded-case Circuit Breakers (MCCB) and miniature Circuit Breakers (MCB) are manufactured to the 80% standard. For example, a 32-amp rated breaker should not exceed 25.6 amps for a continuous load (per the ANSI standard). Therefore, manufacturers often do not specify that Circuit Breakers are 80% rated because it is a standard.

Special Applications Are Evaluated with Specific Testing: To be rated for 100-percent continuous load, circuit breakers will have different testing/design requirements and will normally be in specific product lines for that application, therefore no reason to label as "100% Rated". Their capabilities are usually verified through the manufacturer's technical datasheets or documentation and not by a marker on the nameplate.

How Do You Handle A Circuit Breaker Rating of 100% for Continuous Loads?

Instead of looking for a circuit breaker marked “100% Rated,” focus on verifying your requirements as per the electrical code, such as testing and approval for 100% continuous load operation. Verify that the manufacturer's specifications include a certification confirming that the circuit breaker will operate under the specified conditions at 100% continuous load.

Choosing the Right Circuit Breaker for Continuous Loads: A Practical Guide

1. Identify Your Load Requirement

First, determine if your application consists of continuous loads as defined in the NEC. Continuous loads are defined as loads that operate for longer than three (3) hours.

2. Consult Appropriate Documentation

Identify the continuous load capacity referenced in the "Ratings" and "Application Conditions" sections of the manufacturer’s technical data sheet. An example would be “This circuit breaker is rated for 100% continuous current at an ambient temperature of 40 degrees Celsius.”

3. Identify Compatible Product Series

Identify circuit breakers designed specifically to be rated for 100% continuous current operation. One method of identifying these types of circuit breakers would be those with readily available enhanced heat dissipation features (larger heat sinks or specialized trip units).

4. Seek Professional Assistance

When in doubt, contact your supplier or the manufacturer. Provide details about your application, including load conditions and ambient conditions, and request confirmation that the recommended circuit breaker will meet your requirements.

Get Started: Select The Right Circuit Breaker For Your Application

Finding a circuit breaker with a continuous load rating of 100% involves not only looking for the label but also thoroughly researching the product specification information to ensure robust, reliable performance for your application.

This is where we will help you meet your project needs.

Our molded-case circuit breakers have been engineered to meet and exceed the continuous load application requirements. Our complete specifications, along with expert technical support, will make your process of selecting reliable products easier and more confident.

Let's get to work:

✔ Submit Your Application Parameters: Provide us with your project details, and we will provide you with product recommendations and certification for compliance.

✔ Contact Our Experts: Our expertise is available to assist with any project you may have, from standard to complex.

Trust our experience to assist you with your electrical system needs and gain the confidence that your system will perform in any environment.