Can three-phase current transformers be directly matched with molded case circuit breakers? A practical guide for switchgear manufacturers.

In low-voltage power distribution systems, switchgear manufacturers typically require compact and reliable current measurement and protection solutions. A common problem in switchboard design is:

Can a three-phase current transformer be directly matched with a molded case circuit breaker ?

The answer is yes—but only if the current transformer (CT) is specifically designed for integration with molded case circuit breakers. In this article, we will explain how it works, the factors to consider when selecting one, and why current transformers matched with MCCBs are becoming increasingly popular in modern switchgear design.

Understand the function of a three-phase current transformer.

Three-Phase CTs are used to convert high primary currents into standardized low secondary currents (typically 5A or 1A) so that instruments, protective relays, or monitoring systems can safely measure the current.

In switchgear, current transformers are typically used for:

• Energy metering
• Current monitoring
• Overcurrent protection
• Power Management System

For example, the DASN series of three-phase current transformers are designed for primary currents from 60A to 1600A, covering the typical current range used in MCCB-based distribution systems.

Why do switchgear manufacturers require current transformers that are matched to molded case circuit breakers?

Traditional CT installation typically requires:

• Independent mounting bracket
• Additional wiring space
• Greater panel depth

This presents numerous challenges for switchgear manufacturers:

• Increase panel size
• Higher installation costs
• More complex assembly work

To address these issues, some current transformer models are designed to match the physical structure of molded case circuit breakers, allowing them to be installed directly inside or around the circuit breaker connection area.

This design provides a compact and efficient integrated solution.

Can a three-phase current transformer be directly matched with a molded case circuit breaker?

Yes – if the current transformer is specifically designed for molded case circuit breaker applications.

Some CT models, such as the DASN series Three-Phase CTs, have features that make them suitable for integration with MCCB.

Key design features include:

1.Onboard installation

The CT can be directly installed on the panel or in the MCCB mounting area, simplifying the assembly process.

2.Compact structure

By matching the design of the current transformer (CT) to the size of the molded case circuit breaker (MCCB), the required installation space inside the switch cabinet can be greatly reduced.

3.Integrated three-phase measurement

The three-phase current transformer design allows for monitoring of all phases using a single compact component.

4.Optional terminal protection

Transparent terminal covers help improve safety and circuit reliability.

Technical requirements for MCCB matching current transformers

When selecting current transformers (CTs) for use with molded case circuit breakers (MCCBs), switchgear engineers should check the following parameters:

Current ratio

The CT ratio must be matched with the system current.

Typical options include:

• 100/5A
• 200/5A
• 400/5A
• 800/5A
• 1600/5A

Accuracy level

Common accuracy classes in switchgear applications include:

Class 1.0 – Suitable for general measurements，0.5 grade – higher measurement accuracy

Rated frequency

The operating voltage for most low-voltage systems is:

50 Hz/60 Hz

Thermocurrent capacity

CT scanners should have high heat resistance to cope with malfunctions.

Compliance Standards

Reliable CT scans typically meet the following criteria:

• IEC 60044-1
• EN 60044-1
• VDE 0414
• GB1208

These standards ensure measurement accuracy and electrical safety.

Advantages of three-phase current transformers compatible with molded case circuit breakers

For switchgear manufacturers and switchboard manufacturers, there are many advantages to using current transformers (CTs) specifically designed for MCCB matching.

1.Saves panel space

The compact installation method helps to reduce the depth and floor space of the switch cabinet.

2.Faster installation speed

The integrated installation structure reduces installation steps and labor time.

3.Reduce production costs

Reducing hardware, minimizing brackets, and simplifying wiring can lower manufacturing costs.

4.Improved panel layout

Neater cabling and more organized installation can improve reliability and maintainability.

Typical applications in switchgear

Three-phase MCCB matching current transformers are widely used in:

• low voltage switchboard
• Motion Control Center (MCC)
• Power monitoring cabinet
• Industrial automation panel
• Energy Management System

They are particularly useful for the design of compact switchgear where space optimization is crucial.

Conclusion

For switchgear manufacturers, selecting three-phase current transformers that are directly matched to molded case circuit breakers is an effective way to simplify panel design and reduce installation complexity.

Products such as the DASN series Three-Phase CTs demonstrate how integrated CT solutions can achieve the following goals:

Save installation space

Reduce costs

Improve the efficiency of switchgear

As low-voltage power systems continue to evolve towards more compact and modular designs, current transformers compatible with molded case circuit breakers will become an increasingly important component of modern switchgear engineering.

Compay：HEYI Electrical Co., Ltd.
Brand: HEYI/ASCT
Contact: Bethy
E-mail: heyi@heyiele.com             
Tel: 86-13968747975

--- END ---