Normally Open vs Normally Closed Contactors: Differences & How to Choose

Quick Answer: Normally Open vs Normally Closed Contactors

For EV charging, battery systems, and energy storage applications, NO contactors are commonly used for main DC circuit switching.

What Is a Normally Open (NO) Contactor?

A Normally Open (NO) contactor remains open when the coil is not energized and closes only when power is applied.

What Is a Normally Closed (NC) Contactor?

A Normally Closed (NC) contactor remains closed when de-energized and opens when the coil is energized.

▼ Next, learn how these contactors differ in AC/DC systems and how to choose the right type for your application.

In electrical control and new energy applications, contactors are essential components widely used in EV charging systems, energy storage equipment, and industrial automation. During the selection process, engineers often encounter Normally Open (NO) and Normally Closed (NC) contactor structures. These two types differ significantly in functionality and application scenarios. A correct understanding and choice can greatly improve system safety and reliability.

1. Normally Open Contactors (NO)

Definition:

A Normally Open (NO) contactor keeps its contacts open when the coil is de-energized. The contacts close, and the circuit becomes conductive only when the coil is energized.

Features:

Default safe state: the circuit remains off when not energized

Commonly used for controlling high-power loads

Matches the power supply on/off status directly

Typical Applications:

EV charging stations: Keep the circuit open before charging begins to prevent accidental discharge or electric shock.

Energy storage systems: Stay open during standby and close only when charging or discharging is required.

Motor control: Used for start/stop circuits, ensuring equipment operates only when needed.

2. Normally Closed Contactors (NC) : Definition and Applications

Definition:

A Normally Closed (NC) contactor keeps its contacts closed when the coil is de-energized. Once the coil is energized, the contacts open and the circuit is cut off.

Features:

Default conductive state; the circuit is cut off when the coil is energized

Often used for protection and emergency cutoff circuits

Suitable for “fail-safe” applications where power loss should stop the system

Typical Applications:

Safety circuits:Automatically cut off critical circuits in the event of power failure or system fault to prevent further damage.

Overload protection: Often paired with overload relays to disconnect circuits under abnormal current conditions.

Emergency stop systems:Ensure equipment shuts down immediately during power loss.

3. Application Differences in AC and DC Contactors

The choice between NO and NC depends mainly on the required default state of the circuit and how the system should respond when the control coil is not energized.

Although the concepts of “Normally Open” and “Normally Closed” are universal, their application focus differs between AC contactors and DC contactors:

AC Contactors:

NO contacts are mainly used for motor, lighting, and heating equipment control.

NC contacts are often applied in interlocking control and safety circuits, ensuring loads are disconnected during abnormal or power-off conditions.

Widely used in factory automation and industrial control systems where NO and NC contacts are combined for logic control.

DC Contactors:

NO contacts are commonly used as main circuit control in EV charging stations, energy storage inverters, and photovoltaic systems.

NC contacts are often used for fault protection, disconnecting the circuit automatically when the system loses power or detects anomalies.

Since DC arcs are more difficult to extinguish than AC, DC contactors require advanced contact design and arc suppression technology.

4. Selection Logic: NO vs NC

In real-world engineering, the choice depends on application needs:

Safety-first approach:

If the control logic requires a circuit to remain closed when the coil is de-energized, an NC contactor may be appropriate. For fail-safe designs, the contactor configuration should be evaluated together with the overall protection and control architecture.

Energy-saving and control efficiency:

If the system should remain idle without power consumption and operate only when required → use a Normally Open contactor.

Trends in new energy applications:

In EV charging and energy storage systems, NO contactors are more widely used to keep circuits safely open before activation.

In safety protection and emergency shutdown, NC contactors remain indispensable.

5. How to Choose the Right DC Contactor for Your Application

Selecting between Normally Open and Normally Closed is only the first step when choosing a DC contactor. For EV charging, battery systems, and energy storage applications, the contactor should also match the system voltage, current, coil voltage, and application requirements.

Before selecting a high-voltage DC contactor, consider the following:

Need help selecting the right DC contactor? Send us your voltage, current, coil voltage, and application requirements, and ESTAR can help recommend a suitable solution.

Get a DC Contactor Recommendation →

Recommended High-Voltage DC Contactors

If you are looking for a Normally Open DC contactor for EV charging, battery systems, or energy storage, these models are a good starting point based on current and application requirements.

100A High-Voltage DC Contactor — EVD100G

The EVD100G is a SPST-NO high-voltage DC contactor designed for EV, EV charging, and energy storage applications. It supports 100A current, 12V/24V/48V coil options, and voltage ratings up to 1500VDC.

[View EVD100G Specifications →]

100A Hermetically Sealed DC Contactor — EVD100E

The EVD100E is a hermetically sealed SPST-NO 100A DC contactor with no auxiliary contact. It supports 12V/24V/48V coil options and voltage versions up to 1500VDC.

[View EVD100E Specifications →]

150A High-Voltage DC Contactor —EVK150

The EVK150 is a 150A SPST-NO high-voltage DC contactor designed for higher-current applications including commercial energy storage, charging modules, electric machinery, and other new-energy systems. It supports 12V/24V/48V coils and voltage versions up to 1500VDC.

[View EVK150 Specifications→]

Need More Help Choosing a DC Contactor?

Choosing the right contactor involves more than selecting NO or NC. Learn how voltage, current, coil voltage, switching characteristics, and application requirements affect DC contactor selection.

[Read: How to Select the Right DC Contactor for Different Systems →]

Need Help Selecting the Right DC Contactor?

Every application has different voltage, current, coil, and installation requirements.

Send ESTAR your:

• Rated voltage

• Continuous current

• Coil voltage

• Application

• Required quantity

Our team can recommend a suitable high-voltage DC contactor for your application.

Get a DC Contactor Recommendation →

Contact ESTAR →

6. Conclusion

Normally Open and Normally Closed contactors serve different control and protection requirements. For EV charging, battery systems, and energy storage, NO contactors are commonly used for main DC circuit switching, while NC configurations may be appropriate for specific control and protection functions.

When selecting a high-voltage DC contactor, consider not only NO or NC configuration, but also voltage rating, current rating, coil voltage, auxiliary contacts, and application requirements.

If you are unsure which contactor fits your system, contact ESTAR with your basic electrical requirements for a product recommendation.