GMD-4A Equivalent & Substitute Parts

Part Overview

The GMD-4A is a 4 A, 250 V AC/DC slow-blow glass cartridge fuse in a 5mm x 20mm package manufactured by Eaton - Electronics Division. This component is classified as obsolete, requiring identification of active equivalent and substitute parts for ongoing circuit protection applications. The GMD-4A requires a dedicated fuse holder for installation and is designed for applications demanding slow-blow response characteristics with a 200 A breaking capacity at rated voltage.

Key Parameters

Parameter	Value
Current Rating	4 A
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	200 A
Melting I²t	300
DC Cold Resistance	0.048 Ohms
Product Status	Obsolete

Substitute Part Grouping Explanation

Substitute parts for the GMD-4A are classified into two categories based on electrical and mechanical compatibility:

Direct Manufacturer Equivalents (Eaton GMD Series - Active Status)

These parts maintain identical electrical specifications: 4 A current rating, 250 V AC voltage rating, slow-blow response, 5mm x 20mm package, 200 A breaking capacity, and 0.048 Ohms DC cold resistance. The primary distinction is product status (active versus obsolete) and RoHS compliance level. Parts in this category include BK/GMD-4-R, GMD-4-R, and BK1/GMD-4-R, all from the GMD series.

Parametric Equivalents (Eaton GDC and S506 Series - Active Status)

These parts share the same current rating (4 A), voltage rating (250 V AC), response time (slow-blow), package dimensions (5mm x 20mm), and mounting requirements. However, they differ in breaking capacity (40 A versus 200 A) and melting I²t (71.8 versus 300). These include BK/GDC-4A, GDC-4A, BK/S506-4-R, and S506-4-R. The reduced breaking capacity and melting I²t indicate these parts are suitable for lower-fault-current applications.

Similar Parts (Littelfuse 239 Series - Different Voltage Rating)

The Littelfuse 0239004.HXEP, 0239004.MRET1P, and 0239004.MXEP maintain the 4 A current rating and 5mm x 20mm package but operate at 125 V AC (versus 250 V AC). These are not direct substitutes for 250 V applications but are listed for reference in lower-voltage circuit designs.

Parameter Comparison

Part Number	Manufacturer	Series	Current (A)	Voltage AC (V)	Response Time	Package	Breaking Capacity (A)	Melting I²t	DC Resistance (Ω)	Product Status	RoHS Status
GMD-4A	Eaton	GMD	4	250	Slow Blow	5x20mm	200	300	0.048	Obsolete	Non-compliant
BK/GMD-4-R	Eaton	GMD	4	250	Slow Blow	5x20mm	200	300	0.048	Active	ROHS3 Compliant
GMD-4-R	Eaton	GMD	4	250	Slow Blow	5x20mm	200	300	0.048	Active	ROHS3 Compliant
BK1/GMD-4-R	Eaton	GMD	4	250	Slow Blow	5x20mm	200	300	0.048	Active	ROHS3 Compliant
BK/GDC-4A	Eaton	GDC	4	250	Slow Blow	5x20mm	40	71.8	0.0139	Active	ROHS3 Compliant
GDC-4A	Eaton	GDC	4	250	Slow Blow	5x20mm	40	71.8	0.0139	Active	ROHS3 Compliant
BK/S506-4-R	Eaton	S506	4	250	Slow Blow	5x20mm	40	71.8	0.0139	Active	ROHS3 Compliant
S506-4-R	Eaton	S506	4	250	Slow Blow	5x20mm	40	71.8	0.0139	Active	ROHS3 Compliant
0239004.HXEP	Littelfuse	239	4	125	Slow Blow	5x20mm	10000	270.703	0.0312	Active	ROHS3 Compliant
0239004.MXEP	Littelfuse	239	4	125	Slow Blow	5x20mm	10000	270.703	0.0312	Active	ROHS3 Compliant
0239004.MRET1P	Littelfuse	239	4	125	Slow Blow	5x20mm	10000	270.703	0.0312	Active	ROHS3 Compliant

Engineering Selection Recommendations

For Direct Replacement (Identical Electrical Performance)

Select BK/GMD-4-R, GMD-4-R, or BK1/GMD-4-R when the application requires exact electrical equivalence to the GMD-4A. All three parts maintain the 200 A breaking capacity and 0.048 Ohms DC cold resistance. These parts are active products with ROHS3 compliance, addressing the obsolescence of the original GMD-4A. The GMD-4-R and BK/GMD-4-R variants are preferred for new designs due to broader availability (911 and 3754 units in stock respectively).

For Lower Fault-Current Applications

Select BK/GDC-4A, GDC-4A, BK/S506-4-R, or S506-4-R when the circuit fault current does not exceed 40 A. These parts maintain the 4 A current rating, 250 V AC voltage rating, and slow-blow response but feature reduced breaking capacity (40 A) and melting I²t (71.8). The S506 series offers expanded international certifications (BSI, CCC, CSA, CURUS, IMQ, PSE/JET, SEMKO, VDE), making it suitable for applications requiring multi-regional compliance. The GDC series carries certifications from cURus, IMQ, and MITI/JET.

For 125 V AC Applications Only

The Littelfuse 0239004.HXEP, 0239004.MXEP, and 0239004.MRET1P are not suitable for 250 V AC circuits. These parts are listed for reference only in applications operating at 125 V AC. The 0239004.MRET1P is supplied in tape and reel packaging, while 0239004.HXEP and 0239004.MXEP are supplied in bulk.

Frequently Asked Questions (FAQ)

Q: Can I use BK/GDC-4A or S506-4-R as a direct replacement for GMD-4A?

A: BK/GDC-4A and S506-4-R are parametric equivalents, not direct replacements. They maintain the same current rating (4 A), voltage rating (250 V AC), response time (slow-blow), and package (5mm x 20mm). However, the breaking capacity is reduced from 200 A to 40 A, and the melting I²t is reduced from 300 to 71.8. These parts are suitable only for applications where the maximum fault current does not exceed 40 A.

Q: What is the difference between GMD-4-R and BK/GMD-4-R?

A: Both parts are electrically identical with 4 A current rating, 250 V AC voltage, 200 A breaking capacity, and 0.048 Ohms DC cold resistance. The primary difference is packaging designation and inventory availability. BK/GMD-4-R has 3754 units in stock, while GMD-4-R has 911 units. Both are active products with ROHS3 compliance.

Q: Why is the Littelfuse 0239004.HXEP listed if it operates at 125 V AC?

A: The Littelfuse 0239004.HXEP is listed as a similar part for reference purposes only. It shares the 4 A current rating and 5mm x 20mm package with the GMD-4A but operates at 125 V AC instead of 250 V AC. It is not suitable for 250 V AC applications and should only be considered for circuits designed for 125 V AC operation.

Q: What does "Requires Holder" mean for the mounting type?

A: All listed parts are cartridge fuses that require a dedicated fuse holder for installation. The fuse cannot be directly soldered or mounted to a PCB. A compatible 5mm x 20mm fuse holder must be installed in the circuit to accommodate these components.

Q: Are all substitute parts RoHS compliant?

A: The original GMD-4A is RoHS non-compliant. All active substitute parts listed (BK/GMD-4-R, GMD-4-R, BK1/GMD-4-R, BK/GDC-4A, GDC-4A, BK/S506-4-R, S506-4-R, and all Littelfuse 239 series variants) are ROHS3 compliant, meeting current environmental regulations.

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

A: The melting I²t value indicates the thermal energy required to melt the fuse element. The GMD-4A and its direct equivalents (GMD-4-R, BK/GMD-4-R, BK1/GMD-4-R) have a melting I²t of 300. The parametric equivalents (GDC-4A, S506-4-R series) have a melting I²t of 71.8, indicating faster thermal response. This parameter must match the circuit protection requirements.

Q: Can I substitute a 4 A fuse rated for 125 V AC in a 250 V AC circuit?

A: No. The voltage rating is a critical safety parameter. Using a 125 V AC fuse in a 250 V AC circuit creates a hazardous condition. The fuse may not interrupt the circuit properly at the higher voltage, potentially resulting in component damage or fire. Always match the voltage rating to the circuit specification.

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