BK/ETF-4 Board Mount Fuse - Equivalent & Substitute Parts

Part Overview

The BK/ETF-4 is a 4A, 277VAC board mount fuse manufactured by Eaton - Electronics Division, designed for through-hole radial mounting in vertical orientation. This component is classified as obsolete, making identification of suitable substitute parts essential for ongoing maintenance, repair, and new design applications where equivalent functionality is required.

The BK/ETF-4 operates within a temperature range of -55°C to 125°C and provides slow-blow response characteristics with a breaking capacity of 100A at rated voltage. Due to its obsolete status, sourcing alternatives that maintain electrical and mechanical compatibility is necessary for system continuity.

Substiute Parts

BK/ETF-4

Eaton - Electronics DivisionIn Stock: 845BK/ETF-4 Datasheet

Current PartRFQ

SR-5-4A-BK

Eaton - Electronics DivisionIn Stock: 1077SR-5-4A-BK Datasheet

SimilarRFQ

Key Parameters

Substitute Part Grouping Explanation

Substitution of the BK/ETF-4 is determined by the following critical parameters:

Mandatory Compatibility Criteria:

• Current Rating: 4 A (exact match required)
• Response Time: Slow Blow (functional characteristic must match)
• Mounting Type: Through Hole (physical installation requirement)
• Package / Case: Radial, Can, Vertical (form factor and orientation)
• Fuse Type: Board Mount (Cartridge Style Excluded)

Voltage Consideration: The BK/ETF-4 operates at 277VAC. Substitute parts must be rated for the application voltage or higher. A lower voltage rating does not provide equivalent protection and is not acceptable.

Mechanical Compatibility: Physical dimensions and radial mounting configuration must align with PCB footprint requirements. Dimensional variance within manufacturing tolerances is acceptable.

The substitute part SR-5-4A-BK shares the same current rating (4A), response time (Slow Blow), mounting type (Through Hole), and package configuration (Radial, Can, Vertical). However, the SR-5-4A-BK is rated for 250VAC, which is lower than the BK/ETF-4's 277VAC rating. This voltage difference represents a functional limitation in the substitute part.

Parameter Comparison

Engineering Selection Recommendations

Voltage Rating Limitation: The SR-5-4A-BK substitute is rated for 250VAC, which is 27V lower than the BK/ETF-4's 277VAC rating. In applications where the circuit operates at or near 277VAC, the SR-5-4A-BK does not provide equivalent voltage protection. Selection of this substitute is only appropriate for circuits operating at 250VAC or lower.

Breaking Capacity Difference: The BK/ETF-4 provides 100A breaking capacity at rated voltage, while the SR-5-4A-BK provides 40A. This represents a significant reduction in fault current handling capability. Applications requiring the higher breaking capacity of the original part cannot use the SR-5-4A-BK as a direct substitute.

Temperature Range Consideration: The BK/ETF-4 operates across -55°C to 125°C, while the SR-5-4A-BK operates across -40°C to 85°C. Applications requiring operation below -40°C or above 85°C cannot use the SR-5-4A-BK.

Compliance and Certifications: The SR-5-4A-BK holds broader regulatory approvals (CCC, cULus, KC-MARK, PSE, SEMKO, VDE) compared to the BK/ETF-4 (SEMKO, UL). The SR-5-4A-BK is RoHS3 compliant and REACH unaffected, providing advantages for new designs subject to environmental regulations.

Product Status: The BK/ETF-4 is obsolete. The SR-5-4A-BK is active and currently manufactured, ensuring long-term availability for replacement and new applications.

Dimensional Compatibility: Physical dimensions differ slightly (0.335" Dia x 0.319" H for SR-5-4A-BK versus 0.329" Dia x 0.303" H for BK/ETF-4). PCB footprint verification is required to confirm mechanical fit.

Frequently Asked Questions (FAQ)

Q: Can the SR-5-4A-BK be used as a direct replacement for the BK/ETF-4 in all applications?

A: No. The SR-5-4A-BK is rated for 250VAC maximum, while the BK/ETF-4 is rated for 277VAC. Direct substitution is only valid for circuits operating at 250VAC or lower. Additionally, the SR-5-4A-BK has a lower breaking capacity (40A versus 100A) and narrower operating temperature range (-40°C to 85°C versus -55°C to 125°C).

Q: What are the critical parameters that must match for fuse substitution?

A: Current rating (4A), response time (Slow Blow), mounting type (Through Hole), and package configuration (Radial, Can, Vertical) must match exactly. Voltage rating must be equal to or greater than the original part's rating. Breaking capacity and operating temperature range should be verified against application requirements.

Q: Are there dimensional differences between these parts?

A: Yes. The SR-5-4A-BK measures 0.335" Dia x 0.319" H (8.50mm x 8.10mm), while the BK/ETF-4 measures 0.329" Dia x 0.303" H (8.35mm x 7.70mm). Verify PCB footprint compatibility before substitution.

Q: What is the significance of the melting I²t value difference?

A: The BK/ETF-4 has a melting I²t of 92, while the SR-5-4A-BK has 80. This indicates the thermal energy required to melt the fuse element. The lower value in the SR-5-4A-BK means it will respond to thermal stress more quickly, which may affect circuit protection characteristics in specific applications.

Q: Why does the SR-5-4A-BK have more regulatory approvals?

A: The SR-5-4A-BK is an active product with broader market distribution, requiring compliance with multiple international standards (CCC, cULus, KC-MARK, PSE, SEMKO, VDE). The obsolete BK/ETF-4 was certified to fewer standards (SEMKO, UL) reflecting its historical market scope.

Q: Is the SR-5-4A-BK suitable for applications requiring -55°C operation?

A: No. The SR-5-4A-BK is rated for -40°C minimum operating temperature. Applications requiring operation below -40°C cannot use this substitute.

Q: What does "Slow Blow" response time mean?

A: Slow Blow fuses tolerate temporary current surges and inrush currents without opening. They open only when sustained overcurrent conditions occur. Both the BK/ETF-4 and SR-5-4A-BK share this characteristic, ensuring consistent protection behavior.