GMD-125-R Equivalent & Substitute Parts Reference

Part Overview

The GMD-125-R is a 125 mA, 250 V AC/DC slow blow glass cartridge fuse in 5mm x 20mm package format manufactured by Eaton - Electronics Division. This fuse requires a compatible holder for installation and is designed for circuit protection applications requiring slow blow response characteristics. The part maintains Active product status with 975 pieces in current inventory. Equivalent and substitute parts are identified based on matching electrical ratings, mechanical dimensions, response time classification, and approval agency certifications.

Key Parameters

Parameter	Value
Current Rating	125 mA
Voltage Rating (AC)	250 V
Fuse Type	Cartridge, Glass
Response Time	Slow Blow
Package / Case	5mm x 20mm
Breaking Capacity @ Rated Voltage	35A
Mounting Type	Requires Holder
RoHS Status	ROHS3 Compliant
Approval Agencies	CSA, UL

Substitute Part Grouping Explanation

Substitute parts for GMD-125-R are classified into three categories based on electrical and mechanical parameter alignment:

Direct Manufacturer Equivalents (Eaton - Electronics Division): Parts BK/GMD-125-R, BK/S506-125-R, BK1/S506-125-R, S506-125-R, and GDC-125MA share identical current rating (125 mA), voltage rating (250 V AC), response time (Slow Blow), package dimensions (5mm x 20mm), and breaking capacity (35A). These parts differ in series designation and DC cold resistance values but maintain compatibility within the same manufacturer ecosystem.

Parametric Equivalents (Alternative Manufacturers): Parts 0218.125HXP and 0218.125MXP (Littelfuse Inc.), 0034.3108, 0034.3763, and 0034.5608.11 (SCHURTER Inc.) match all critical electrical parameters: 125 mA current rating, 250 V AC voltage rating, Slow Blow response, 5mm x 20mm package, and 35A breaking capacity. These parts are from different manufacturers but provide functional equivalence for circuit protection applications.

Substitution Criteria: All listed substitutes maintain identical current rating, voltage rating, response time classification, and mechanical package dimensions. Breaking capacity remains constant at 35A across all alternatives. Differences in melting I²t values, DC cold resistance, and approval agency certifications reflect manufacturer-specific design approaches while preserving functional compatibility.

Parameter Comparison

Part Number	Manufacturer	Series	Current Rating (mA)	Voltage (V AC)	Response Time	Package	Breaking Capacity (A)	Melting I²t	DC Cold Resistance (Ω)	Approval Agencies
GMD-125-R	Eaton	GMD	125	250	Slow Blow	5x20mm	35	0.043	8.125	CSA, UL
BK/GMD-125-R	Eaton	GMD	125	250	Slow Blow	5x20mm	35	0.043	8.125	CSA, UL
BK/S506-125-R	Eaton	S506	125	250	Slow Blow	5x20mm	35	0.063	1.97	BSI, CCC, CSA, IMQ, SEMKO, UR, VDE
BK1/S506-125-R	Eaton	S506	125	250	Slow Blow	5x20mm	35	0.063	1.97	BSI, CCC, CSA, IMQ, SEMKO, UR, VDE
S506-125-R	Eaton	S506	125	250	Slow Blow	5x20mm	35	0.063	1.97	BSI, CCC, CSA, IMQ, SEMKO, UR, VDE
GDC-125MA	Eaton	GDC	125	250	Slow Blow	5x20mm	35	0.063	1.97	cURus, IMQ
0218.125HXP	Littelfuse	218	125	250	Slow Blow	5x20mm	35	0.1465	4.2	CCC, CE, CSA, K-MARK, SEMKO, UL, VDE
0218.125MXP	Littelfuse	218	125	250	Slow Blow	5x20mm	35	0.1465	4.2	CCC, CE, CSA, K-MARK, SEMKO, UL, VDE
0034.3108	SCHURTER	FST 5x20	125	250	Slow Blow	5x20mm	35	0.064	Not specified	CCC, cURus, VDE
0034.3763	SCHURTER	FSL 5x20	125	250	Slow Blow	5x20mm	35	0.161	Not specified	cULus
0034.5608.11	SCHURTER	SMD-FST	125	250	Slow Blow	5x20mm	35	0.064	Not specified	cURus, VDE

Engineering Selection Recommendations

Eaton GMD Series (BK/GMD-125-R): Direct equivalent with identical electrical and mechanical specifications. Maintains CSA and UL certifications. Recommended for applications requiring exact parameter matching with the original GMD-125-R specification.

Eaton S506 Series (BK/S506-125-R, BK1/S506-125-R, S506-125-R): Parametric equivalents with expanded approval agency certifications including BSI, CCC, IMQ, SEMKO, UR, and VDE. Melting I²t value of 0.063 differs from GMD-125-R (0.043), reflecting different thermal response characteristics within the slow blow classification. Suitable for applications requiring broader international compliance certifications.

Eaton GDC Series (GDC-125MA): Parametric equivalent with cURus and IMQ certifications. Melting I²t of 0.063 matches S506 series. Applicable for applications requiring cURus certification.

Littelfuse 218 Series (0218.125HXP, 0218.125MXP): Parametric equivalents with comprehensive approval coverage (CCC, CE, CSA, K-MARK, SEMKO, UL, VDE). Operating temperature range -55°C to 125°C. Melting I²t of 0.1465 indicates different thermal response profile. Inventory availability of 19,944 units for 0218.125MXP provides supply continuity. Suitable for applications requiring extended temperature operating range and broad international certifications.

SCHURTER FST 5x20 Series (0034.3108): Parametric equivalent with CCC, cURus, and VDE certifications. Operating temperature -55°C to 125°C. Melting I²t of 0.064. Applicable for applications requiring cURus certification and extended temperature range.

SCHURTER FSL 5x20 Series (0034.3763): Parametric equivalent with cULus certification. Operating temperature -40°C to 85°C. Melting I²t of 0.161 represents the highest thermal response value in the substitute list. Suitable for applications with cULus certification requirement and moderate temperature operating range.

SCHURTER SMD-FST Series (0034.5608.11): Parametric equivalent with cURus and VDE certifications. Operating temperature -55°C to 125°C. Melting I²t of 0.064. Applicable for applications requiring cURus certification and extended temperature range.

Frequently Asked Questions (FAQ)

Q: Can BK/GMD-125-R be used as a direct replacement for GMD-125-R?

A: Yes. BK/GMD-125-R is a direct equivalent with identical current rating (125 mA), voltage rating (250 V AC), response time (Slow Blow), package dimensions (5mm x 20mm), breaking capacity (35A), and approval agencies (CSA, UL). Both parts require a compatible fuse holder for installation.

Q: What is the difference between GMD-125-R and S506-125-R?

A: Both parts share identical electrical ratings (125 mA, 250 V AC, Slow Blow, 35A breaking capacity) and mechanical package (5mm x 20mm). Differences include: S506-125-R has melting I²t of 0.063 versus GMD-125-R at 0.043; S506-125-R has DC cold resistance of 1.97 Ω versus GMD-125-R at 8.125 Ω; S506-125-R carries expanded certifications (BSI, CCC, CSA, IMQ, SEMKO, UR, VDE) versus GMD-125-R (CSA, UL). Both are manufactured by Eaton.

Q: Are Littelfuse 0218.125HXP and 0218.125MXP interchangeable with GMD-125-R?

A: Both Littelfuse parts are parametric equivalents matching the 125 mA, 250 V AC, Slow Blow, 5mm x 20mm, 35A specifications. Key differences: Littelfuse parts have melting I²t of 0.1465 (higher than GMD-125-R at 0.043); operating temperature range of -55°C to 125°C (versus unspecified for GMD-125-R); DC cold resistance of 4.2 Ω; broader certifications (CCC, CE, CSA, K-MARK, SEMKO, UL, VDE). Interchangeability depends on application-specific thermal response requirements and certification mandates.

Q: What does melting I²t value indicate?

A: Melting I²t is a thermal characteristic that defines the fuse's response to overcurrent conditions. Lower I²t values indicate faster thermal response; higher values indicate slower thermal response. All listed substitutes maintain Slow Blow classification, but varying I²t values reflect manufacturer-specific design approaches. Selection should align with circuit protection requirements.

Q: Can SCHURTER parts replace GMD-125-R?

A: SCHURTER parts 0034.3108, 0034.3763, and 0034.5608.11 are parametric equivalents with matching 125 mA, 250 V AC, Slow Blow, 5mm x 20mm, and 35A specifications. Differences include: varying melting I²t values (0.064 for 0034.3108 and 0034.5608.11; 0.161 for 0034.3763); different approval agencies (cURus, VDE, cULus); operating temperature ranges (-55°C to 125°C for 0034.3108 and 0034.5608.11; -40°C to 85°C for 0034.3763). Substitution feasibility depends on certification requirements and thermal response specifications of the target application.

Q: Do all substitute parts require the same fuse holder as GMD-125-R?

A: All listed substitute parts are 5mm x 20mm cartridge fuses requiring a compatible holder. Mechanical compatibility is ensured by identical package dimensions. Verify holder compatibility with the specific fuse series being substituted, as some holders may have series-specific design features.

Q: Which substitute offers the broadest international certification coverage?

A: Littelfuse 0218.125MXP carries certifications from CCC, CE, CSA, K-MARK, SEMKO, UL, and VDE, providing comprehensive international compliance coverage. This part also maintains the highest inventory availability (19,944 units) among all substitutes.

Q: What is the significance of RoHS3 compliance status?

A: RoHS3 Compliant status indicates the part meets Restriction of Hazardous Substances Directive requirements, restricting use of specific hazardous materials. GMD-125-R and most listed substitutes carry ROHS3 Compliant status, ensuring environmental and regulatory compliance for applications subject to RoHS requirements.

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