BK/GMD-125MA Equivalent & Substitute Parts

Part Overview

The BK/GMD-125MA is a 125 mA, 250 V AC/DC glass cartridge fuse with a 5mm x 20mm form factor, manufactured by Eaton - Electronics Division. This component is classified as obsolete but remains functionally equivalent to several active production alternatives. The slow-blow response characteristic and cartridge design requiring a holder make this fuse suitable for general-purpose circuit protection applications. Due to its obsolete status, identifying equivalent substitute parts with active product status ensures continued availability and supply chain reliability for replacement and new designs.

Key Parameters

Parameter	Value
Current Rating	125 mA
Voltage Rating (AC)	250 V
Fuse Type	Cartridge, Glass
Package / Case	5mm x 20mm
Response Time	Slow Blow
Mounting Type	Requires Holder
Breaking Capacity @ Rated Voltage	35A
Size / Dimension	0.205" Dia x 0.787" L (5.20mm x 20.00mm)

Substitute Part Grouping Explanation

Substitution eligibility for the BK/GMD-125MA is determined by strict equivalence across the following critical parameters:

Primary Substitution Criteria:

Current Rating: 125 mA (exact match required)
Voltage Rating (AC): 250 V (exact match required)
Package / Case: 5mm x 20mm (exact match required)
Fuse Type: Cartridge, Glass (exact match required)
Response Time: Slow Blow (exact match required)
Mounting Type: Requires Holder (exact match required)
Breaking Capacity @ Rated Voltage: 35A (exact match required)

Secondary Considerations:

Melting I²t: Variations permitted within functional tolerance
DC Cold Resistance: Variations permitted within functional tolerance
Approval Agencies: Compliance certifications determine application suitability
RoHS Status: Regulatory compliance requirement for specific markets
Product Status: Active status preferred for supply continuity

All substitute parts listed meet the primary substitution criteria. Differences in melting I²t, DC cold resistance, and approval certifications reflect design variations between manufacturers and series designations while maintaining functional equivalence for the specified electrical and mechanical parameters.

Parameter Comparison

Part Number	Manufacturer	Series	Current Rating	Voltage (AC)	Package	Response Time	Breaking Capacity	Melting I²t	DC Cold Resistance (Ohms)	Product Status	RoHS Status
BK/GMD-125MA	Eaton	GMD	125 mA	250 V	5x20mm	Slow Blow	35A	0.043	8.125	Obsolete	Non-compliant
BK/GMD-125-R	Eaton	GMD	125 mA	250 V	5x20mm	Slow Blow	35A	0.043	8.125	Active	ROHS3 Compliant
BK/GDC-125MA	Eaton	GDC	125 mA	250 V	5x20mm	Slow Blow	35A	0.063	1.97	Active	RoHS Compliant
BK/S506-125-R	Eaton	S506	125 mA	250 V	5x20mm	Slow Blow	35A	0.063	1.97	Active	ROHS3 Compliant
BK1/GMD-125-R	Eaton	GMD	125 mA	250 V	5x20mm	Slow Blow	35A	0.043	8.125	Active	ROHS3 Compliant
BK1/S506-125-R	Eaton	S506	125 mA	250 V	5x20mm	Slow Blow	35A	0.063	1.97	Active	ROHS3 Compliant
GDC-125MA	Eaton	GDC	125 mA	250 V	5x20mm	Slow Blow	35A	0.063	1.97	Active	RoHS Compliant
GMD-125-R	Eaton	GMD	125 mA	250 V	5x20mm	Slow Blow	35A	0.043	8.125	Active	ROHS3 Compliant
S506-125-R	Eaton	S506	125 mA	250 V	5x20mm	Slow Blow	35A	0.063	1.97	Active	ROHS3 Compliant
0239.125MXP	Littelfuse	239	125 mA	250 V	5x20mm	Slow Blow	35A	0.085	11.6	Active	ROHS3 Compliant
0218.125HXP	Littelfuse	218	125 mA	250 V	5x20mm	Slow Blow	35A	0.1465	4.2	Active	ROHS3 Compliant

Engineering Selection Recommendations

Eaton GMD Series (Direct Mechanical & Electrical Match): BK/GMD-125-R, BK1/GMD-125-R, and GMD-125-R are direct functional equivalents to the obsolete BK/GMD-125MA. All three maintain identical melting I²t (0.043) and DC cold resistance (8.125 Ohms), ensuring identical thermal and electrical response characteristics. All three are active production parts with ROHS3 compliance. Selection among these three variants depends on packaging requirements and inventory availability.

Eaton GDC Series (Parametric Equivalent): BK/GDC-125MA and GDC-125MA are parametrically equivalent with identical current, voltage, and mechanical specifications. These parts feature lower DC cold resistance (1.97 Ohms) and higher melting I²t (0.063) compared to the GMD series. Both are active production parts with RoHS compliance. The GDC series carries broader approval certifications (cULus, IMQ) compared to GMD (CSA, UL).

Eaton S506 Series (Parametric Equivalent with Extended Certifications): BK/S506-125-R, BK1/S506-125-R, and S506-125-R are parametrically equivalent with identical current, voltage, and mechanical specifications. These parts feature lower DC cold resistance (1.97 Ohms) and higher melting I²t (0.063). All three are active production parts with ROHS3 compliance. The S506 series carries the broadest approval certifications (BSI, CCC, CSA, IMQ, SEMKO, UR, VDE), making these parts suitable for international applications requiring multiple regulatory approvals.

Littelfuse 239 Series (Cross-Manufacturer Equivalent): 0239.125MXP is a cross-manufacturer equivalent from Littelfuse with identical electrical and mechanical parameters. This part features higher melting I²t (0.085) and DC cold resistance (11.6 Ohms). It is an active production part with ROHS3 compliance and operating temperature range of -55°C to 125°C. Approval certifications include CE and UL.

Littelfuse 218 Series (Cross-Manufacturer Similar): 0218.125HXP is a cross-manufacturer similar part from Littelfuse with identical electrical and mechanical parameters. This part features the highest melting I²t (0.1465) and mid-range DC cold resistance (4.2 Ohms). It is an active production part with ROHS3 compliance and operating temperature range of -55°C to 125°C. Approval certifications include CCC, CE, CSA, K-MARK, SEMKO, UL, and VDE, providing the broadest regulatory coverage among all listed alternatives.

Frequently Asked Questions (FAQ)

Q: Can BK/GMD-125-R directly replace the obsolete BK/GMD-125MA?

A: Yes. BK/GMD-125-R is a direct functional equivalent with identical current rating (125 mA), voltage rating (250 V), package (5x20mm), response time (slow blow), and breaking capacity (35A). Both parts share identical melting I²t (0.043) and DC cold resistance (8.125 Ohms). The primary difference is product status: BK/GMD-125MA is obsolete while BK/GMD-125-R is active production with ROHS3 compliance.

Q: What is the difference between GMD and GDC series fuses?

A: Both GMD and GDC series meet the primary substitution criteria for current, voltage, package, and breaking capacity. The key differences are: GMD series has melting I²t of 0.043 and DC cold resistance of 8.125 Ohms; GDC series has melting I²t of 0.063 and DC cold resistance of 1.97 Ohms. GDC series carries cULus and IMQ certifications, while GMD series carries CSA and UL certifications. Selection depends on specific approval requirements and thermal response characteristics needed for the application.

Q: Are Littelfuse 239 and 218 series fuses compatible with Eaton fuse holders?

A: Littelfuse 239 and 218 series fuses share identical mechanical dimensions (5mm x 20mm) and electrical parameters (125 mA, 250 V, slow blow, 35A breaking capacity) with Eaton equivalents. Both are cartridge glass fuses requiring holders. Mechanical compatibility is confirmed by identical package specifications. Electrical compatibility is confirmed by identical current, voltage, and breaking capacity ratings. Verification of holder compatibility with specific holder models is required for final installation confirmation.

Q: What does melting I²t indicate and why does it vary among substitutes?

A: Melting I²t is a thermal characteristic indicating the energy required to melt the fuse element. Variations in melting I²t among substitute parts reflect design differences between manufacturers and series designations. GMD series parts have melting I²t of 0.043, while GDC and S506 series have 0.063, and Littelfuse 239 has 0.085. All listed parts maintain the same current rating (125 mA) and voltage rating (250 V), ensuring functional equivalence for the specified electrical parameters. Melting I²t differences do not affect compatibility with standard 5x20mm fuse holders or basic circuit protection function at the rated current.

Q: Which substitute part has the broadest regulatory approvals?

A: Littelfuse 0218.125HXP (218 series) carries the broadest approval certifications: CCC, CE, CSA, K-MARK, SEMKO, UL, and VDE. Among Eaton parts, S506 series (BK/S506-125-R, BK1/S506-125-R, S506-125-R) carries the broadest certifications: BSI, CCC, CSA, IMQ, SEMKO, UR, and VDE. Selection of parts with extended certifications is recommended for applications requiring compliance with multiple international regulatory standards.

Q: Is RoHS compliance a critical factor for substitution?

A: RoHS compliance is a regulatory requirement for specific markets and applications. The obsolete BK/GMD-125MA is RoHS non-compliant. All active substitute parts listed are either ROHS3 compliant or RoHS compliant, meeting current regulatory requirements. For new designs and applications subject to RoHS regulations, selection of ROHS3 or RoHS compliant alternatives is mandatory. For legacy system maintenance where RoHS compliance is not required, non-compliant parts may remain acceptable.

Q: Can I use S506 series fuses as a direct replacement for GMD series?

A: S506 and GMD series fuses are parametrically equivalent with identical current (125 mA), voltage (250 V), package (5x20mm), response time (slow blow), and breaking capacity (35A). However, they differ in melting I²t (GMD: 0.043 vs. S506: 0.063) and DC cold resistance (GMD: 8.125 Ohms vs. S506: 1.97 Ohms). Both are mechanically and electrically compatible with standard 5x20mm fuse holders. Selection between series depends on specific thermal response requirements and approval certifications needed for the application. Both are suitable for general-purpose circuit protection at the rated 125 mA current level.

Request Quote (Ships tomorrow)

Part Number

Quantity

Company

Contact Name

E-mail

Message