Equivalent & Substitute Parts for BK/ETF-125MA

Part Overview

The BK/ETF-125MA is a 125 mA, 277 V AC board mount fuse manufactured by Eaton - Electronics Division. This component is classified as obsolete, indicating discontinued production and limited availability in the market. The fuse features a radial, can-style vertical mounting configuration with slow-blow response characteristics, designed for through-hole PCB assembly applications.

Due to its obsolete status, sourcing replacement units from the original manufacturer is constrained. Identifying functionally equivalent substitute parts is essential for maintaining system reliability and ensuring continuity in repair, maintenance, and new design implementations where this fuse specification is required.

Substiute Parts

BK/ETF-125MA

Eaton - Electronics DivisionIn Stock: 888BK/ETF-125MA Datasheet

Current PartRFQ

37201250411

Littelfuse Inc.In Stock: 387837201250411 Datasheet

SimilarRFQ

Key Parameters

Substitute Part Grouping Explanation

Substitution of the BK/ETF-125MA is evaluated based on the following critical parameters that must align with the original specification:

Mandatory Matching Parameters:

• Current Rating: 125 mA (exact match required)
• Fuse Type: Board Mount, Through Hole configuration
• Package / Case: Radial, Can, Vertical mounting style
• Response Time: Slow Blow characteristic

Voltage Rating Consideration: The original part is rated for 277 V AC. Substitute parts must maintain voltage ratings that do not fall below the application requirement. A substitute with lower voltage rating (250 V AC) may be acceptable in applications where the actual operating voltage does not exceed the substitute's rating, provided the circuit design permits this constraint.

Physical Compatibility: Mounting footprint and dimensional specifications must accommodate PCB through-hole patterns designed for the original component. Minor dimensional variations within manufacturing tolerances are permissible if the component physically seats and functions within the assembly.

Electrical Performance: Breaking capacity, melting I²t, and DC cold resistance values define the fuse's protective and operational characteristics. These parameters should remain within acceptable ranges for the intended circuit protection function.

Parameter Comparison

Engineering Selection Recommendations

Primary Substitute: 37201250411 (Littelfuse TR5® 372 Series)

The Littelfuse 37201250411 is identified as the functional equivalent for the obsolete BK/ETF-125MA based on the following engineering criteria:

Electrical Compatibility: Both components share identical current ratings (125 mA) and slow-blow response characteristics. The substitute maintains the same fuse type classification and through-hole board mount configuration. The 250 V AC rating of the substitute is lower than the original 277 V specification; however, this substitution is valid for applications where the actual circuit voltage does not exceed 250 V AC.

Physical Compatibility: Dimensional specifications are comparable. The substitute measures 0.335" Dia x 0.315" H (8.50mm x 8.00mm) versus the original 0.329" Dia x 0.303" H (8.35mm x 7.70mm). These minor dimensional differences fall within acceptable manufacturing tolerances and do not preclude PCB mounting compatibility for standard through-hole footprints.

Product Status and Availability: The Littelfuse part is classified as active with 3,776 units in stock, ensuring reliable sourcing compared to the obsolete Eaton component with limited inventory (812 units).

Regulatory Compliance: The substitute carries broader approval certifications (CCC, cURus, SEMKO, VDE) compared to the original (SEMKO, UL), providing enhanced compliance coverage. The substitute is RoHS3 compliant and REACH unaffected, meeting modern regulatory requirements.

Performance Considerations: The substitute exhibits a higher melting I²t value (0.1094 versus 0.04), indicating a slightly different thermal response profile. The breaking capacity is reduced (35 A versus 100 A), which may impact circuit protection in high-fault-current environments. The operating temperature range is narrower (-40°C ~ 85°C versus -55°C ~ 125°C), limiting applicability in extreme temperature conditions.

Frequently Asked Questions (FAQ)

Q: Can the Littelfuse 37201250411 directly replace the Eaton BK/ETF-125MA in all applications?

A: Direct replacement is valid for applications where the circuit voltage does not exceed 250 V AC and the operating temperature remains within -40°C to 85°C. The lower voltage rating and narrower temperature range must be evaluated against specific application requirements. The reduced breaking capacity (35 A versus 100 A) may affect protection in high-fault-current circuits.

Q: What is the significance of the voltage rating difference (277 V versus 250 V)?

A: The original part is rated for 277 V AC, while the substitute is rated for 250 V AC. The substitute can be used in applications operating at or below 250 V AC. If the application circuit operates above 250 V AC, the substitute is not appropriate. Verify the actual operating voltage in your circuit design before substitution.

Q: Are the physical dimensions compatible with existing PCB footprints?

A: The dimensional differences are minimal (0.006" diameter and 0.012" height variations). Standard through-hole PCB footprints designed for radial, can-style fuses typically accommodate these tolerances. However, verify your specific PCB layout to confirm adequate clearance and proper seating.

Q: How do the melting I²t and breaking capacity differences affect circuit protection?

A: The melting I²t value (0.1094 for the substitute versus 0.04 for the original) indicates the substitute has a higher thermal energy threshold before melting. The breaking capacity (35 A for the substitute versus 100 A for the original) defines the maximum fault current the fuse can safely interrupt. In circuits with high fault currents exceeding 35 A, the substitute may not provide adequate protection. Analyze your circuit's maximum fault current to determine suitability.

Q: What regulatory certifications should I consider for my application?

A: The substitute carries CCC, cURus, SEMKO, and VDE certifications, providing broader compliance than the original (SEMKO, UL only). The substitute is RoHS3 compliant and REACH unaffected. Verify that these certifications align with your product's regulatory requirements and target markets.

Q: Is the operating temperature range difference a concern?

A: The original part operates from -55°C to 125°C, while the substitute operates from -40°C to 85°C. If your application requires operation outside the -40°C to 85°C range, the substitute is not suitable. Confirm your application's temperature requirements before substitution.

Q: What is the DC cold resistance difference, and does it matter?

A: The original part has 1.5 Ohms DC cold resistance; the substitute has 1.35 Ohms. This minor difference (0.15 Ohms) has negligible impact on most circuit designs. However, in precision current-limiting or low-voltage applications where resistance is critical, verify that the substitute's resistance remains acceptable for your circuit function.