What Is a BH 0.66 Protective Current Transformer? Applications and Key Specifications
A BH 0.66 protective current transformer is a low-voltage current transformer used to provide a reduced, isolated current signal to a protection relay or other protective device. “0.66” generally refers to a 0.66 kV voltage rating associated with the transformer’s insulation or application class; it does not specify the primary current ratio. The exact meaning and applicable limits should be confirmed against the product nameplate and datasheet. Buyers should also verify the ratio, protection class, rated burden, secondary output, and installation dimensions before ordering.
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In a protection circuit, the transformer reproduces primary current at a lower secondary level so that a relay can detect conditions such as overloads or short circuits. Unlike a current transformer selected mainly for measurement, a protective CT must be assessed for its behavior when fault current is much higher than normal operating current. The right specification depends on the system, relay, wiring, and required protection performance—not the model name alone.
Key Takeaways
- A BH 0.66 CT is intended for current sensing in low-voltage applications, with the “0.66” designation commonly associated with a 0.66 kV voltage class.
- Protection selection requires more than a ratio: check protection accuracy class, accuracy limit factor or other applicable performance data, burden, and fault-current conditions.
- Secondary ratings such as 1 A or 5 A and frequencies such as 50 Hz or 60 Hz are common industry options, but availability and suitability must be confirmed for the specific product.
- Share the system and installation details with ANNEZEE to help identify a suitable configuration and confirm its documentation.
What Is a BH 0.66 Protective Current Transformer?
Definition and operating principle
A current transformer, or CT, transfers a current signal from a power conductor to a secondary circuit through electromagnetic induction. The primary conductor may pass through an aperture or connect to a primary terminal, depending on the CT design. The secondary winding supplies a scaled current to equipment such as a protective relay. The ratio describes the relationship between primary and secondary current, so it must be specified separately from the 0.66 kV designation.
The “BH” portion is a model or series identifier, and its construction details can vary by manufacturer and product configuration. Buyers should not infer the window shape, mounting method, core material, or exact performance from those letters alone. Use the manufacturer’s drawing and datasheet to verify the construction and ratings of the specific unit being considered.
How it supports protection
During normal operation, the CT provides the relay with a current signal corresponding to the primary current. When current rises due to a fault, the relay evaluates that signal against its settings and can initiate a trip command. For dependable protection, the CT must be compatible with the expected fault level and the connected secondary circuit. The relay and CT therefore need to be selected as parts of the same protection design.
Core Functions and Applications
Protection, isolation, and signal reduction
A protective CT performs three related functions: it scales down current for relay inputs, provides electrical separation between the primary circuit and the secondary measurement circuit, and supports fault detection. The CT does not interrupt the fault current itself. A breaker or other switching device acts on the trip command generated by the protection system.
Where buyers may use a BH 0.66 CT
Potential applications include low-voltage switchboards, distribution panels, motor control assemblies, and feeder protection circuits. A CT may also be used in equipment where a relay needs a current input from a busbar or cable. Whether a particular BH 0.66 configuration fits depends on the system voltage, conductor arrangement, fault level, enclosure space, and relay requirements.
For a new project, match the CT to the single-line diagram and protection study rather than choosing by application label alone. For a replacement, record the existing nameplate details and mounting dimensions, then confirm that the replacement also meets the relay and fault-duty requirements. A physically similar transformer is not automatically electrically equivalent.
Types and Configuration Options
Low-voltage CTs may be offered in different primary arrangements, such as window-type designs for a conductor passing through the core or designs with primary terminals. Depending on the product range, manufacturers may also offer different case materials, mounting options, aperture sizes, and secondary terminal arrangements. These are possible configuration categories, not guaranteed features of every BH 0.66 model.
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Core materials and construction can affect magnetic performance, but the material name alone does not establish suitability for protection. Ask for the specified protection class and supporting performance information for the actual configuration. Where multiple cores are available, confirm which core is intended for protection and whether separate cores serve measurement or other functions.
Key Specifications to Evaluate
| Specification | What to confirm | Why it matters |
|---|---|---|
| Rated voltage | Whether the 0.66 kV designation matches the system and insulation requirements | Establishes the voltage application for which the CT is specified; check the full nameplate details. |
| Current ratio | Primary-to-secondary ratio, for example, a project-specific ratio rather than an assumed value | Must suit operating current, relay input, and protection settings. |
| Protection performance | Applicable protection class, accuracy limit factor, or other declared fault-performance data | Helps assess whether the CT can provide an appropriate signal under the required fault conditions. |
| Rated burden | Burden in VA, including relay and secondary wiring effects | Excess secondary burden can affect CT performance and accuracy. |
| Secondary rating and frequency | For example, whether a 1 A or 5 A secondary and 50 Hz or 60 Hz system are required | These are common industry values, not a statement that every BH 0.66 product supports them. |
| Mechanical dimensions | Aperture, overall size, terminals, mounting, and conductor clearance | Confirms that the unit can be installed safely in the intended assembly. |
Protection classes such as 5P or 10P may appear in CT specifications, while other protection applications may use different classes or parameters. These labels should be interpreted with the relevant standard, declared limits, and application requirements; they are not interchangeable shorthand for “protective.” Request the complete datasheet and verify that the relay manufacturer’s requirements are met.
How to Select the Right Unit
Start with the electrical design
Provide the nominal system voltage, maximum operating current, expected fault current, protection relay model or input requirements, and the required CT ratio. Also identify the secondary burden, including the relay and the cable route where known. If a protection engineer has specified a class or performance limit, include it rather than substituting a general-purpose metering specification.
Check fit, connections, and documentation
Compare the CT drawing with the busbar or cable dimensions, panel clearance, and mounting arrangement. Confirm terminal markings, secondary connection details, and whether the requested design has the required number of cores. Ask for the datasheet, dimensional drawing, and nameplate information for the offered configuration so that engineering and procurement review the same product details.
One critical installation rule is that a CT secondary must not be left open while primary current is flowing. An open secondary can produce a hazardous voltage and may damage equipment. Installation and maintenance should be performed by qualified personnel using the project’s applicable safety procedures.
Supplier Support from ANNEZEE
As a supplier of electrical equipment, ANNEZEE can review the application information provided by the buyer and help clarify the required BH 0.66 configuration. Useful details include the current ratio, protection requirements, frequency, secondary rating, burden, installation drawing, and required quantity. This information helps prevent avoidable mismatches between the CT, relay, and switchgear layout.
Before confirming an order, request product-specific documentation and confirm which specifications are guaranteed for the quoted model. If the application involves a replacement, send a clear nameplate image and dimensional requirements for comparison. Any project-specific compliance, inspection, packaging, or delivery requirements should be discussed and confirmed in writing rather than assumed.
Conclusion: What to Do Before You Buy
A BH 0.66 protective current transformer is a low-voltage CT intended to provide current information to protective equipment, but the model designation alone does not establish its complete ratings or suitability. The “0.66” commonly indicates a 0.66 kV voltage class, while the current ratio, protection performance, burden, secondary rating, and physical design require separate verification. The most reliable selection begins with the protection design and ends with a check of the exact product datasheet and drawing.
To move forward, prepare the system voltage, current ratio, fault-current information, relay requirements, wiring burden, and installation dimensions. Send these details to ANNEZEE to discuss a suitable specification and request product documentation for review. Final selection should be approved against the project’s electrical design and applicable safety requirements.
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