Equivalent & Substitute Parts for BK/S504-1A Glass Cartridge Fuse

Part Overview

The BK/S504-1A is a 1 A, 250 V AC/DC glass cartridge fuse manufactured by Eaton - Electronics Division, designed for 5mm x 20mm fuse holders. This component is classified as obsolete, which necessitates identification of active equivalent and substitute parts to maintain circuit protection functionality in applications requiring this current and voltage rating.

The fuse operates with slow-blow response characteristics and is constructed as a glass cartridge requiring a dedicated holder for installation. Due to its obsolete status, direct replacement with active production alternatives is required for new designs and ongoing maintenance applications.

Key Parameters

Parameter	Value	Significance for Substitution
Current Rating	1 A	Must match exactly for circuit protection integrity
Voltage Rating (AC)	250 V	Must match or exceed for safe operation
Package / Case	5mm x 20mm	Physical compatibility with existing fuse holders
Fuse Type	Cartridge, Glass	Mechanical and electrical compatibility requirement
Response Time	Slow Blow	Determines circuit protection behavior and inrush tolerance
Breaking Capacity @ Rated Voltage	35 A (main part)	Fault current interruption capability
Mounting Type	Requires Holder	Installation method compatibility
Product Status	Obsolete (main part)	Availability and long-term supply consideration

Substitute Part Grouping Explanation

Substitute parts for the BK/S504-1A are classified into two categories based on parametric alignment:

Direct Manufacturer Equivalents (Eaton - Electronics Division): These parts maintain identical electrical specifications (1 A, 250 V AC/DC, slow-blow, 5mm x 20mm) and are manufactured by the same supplier. They differ in series designation, product status (all active), and secondary characteristics such as melting I²t and DC cold resistance. These parts are suitable for direct substitution where Eaton product continuity is required.

Parametric Equivalents (Eaton - Electronics Division): These parts share core electrical parameters (1 A, 250 V AC/DC, slow-blow, 5mm x 20mm) but exhibit variations in melting I²t values and DC cold resistance. The melting I²t parameter affects thermal response characteristics; higher values indicate slower thermal response. These parts are functionally equivalent for standard circuit protection applications.

Similar Parts (Alternative Manufacturer - Littelfuse Inc.): These parts match the primary electrical specifications (1 A, 250 V AC/DC, slow-blow, 5mm x 20mm) but are manufactured by Littelfuse Inc. They exhibit different melting I²t characteristics and include specified operating temperature ranges. These parts are suitable for applications where manufacturer flexibility is acceptable.

Key Parameters Determining Substitution Eligibility:

Current Rating: 1 A (exact match required)
Voltage Rating: 250 V AC minimum (exact match in all listed parts)
Package Dimensions: 5mm x 20mm (exact match required for holder compatibility)
Fuse Type: Cartridge, Glass (exact match required)
Response Time: Slow Blow (exact match required)

Parameter Comparison

Part Number	Manufacturer	Series	Current (A)	Voltage (V AC)	Package	Response Time	Breaking Capacity (A)	Melting I²t	DC Cold Resistance (Ω)	Product Status	RoHS Status
BK/S504-1A	Eaton	S504	1	250	5x20mm	Slow Blow	35	3.6	0.064	Obsolete	Non-compliant
BK/S506-1-R	Eaton	S506	1	250	5x20mm	Slow Blow	35	6.45	0.0757	Active	ROHS3 Compliant
BK/GDC-1A	Eaton	GDC	1	250	5x20mm	Slow Blow	35	6.45	0.0757	Active	ROHS3 Compliant
BK/GMD-1-R	Eaton	GMD	1	250	5x20mm	Slow Blow	35	12	0.3065	Active	ROHS3 Compliant
BK1/GMD-1-R	Eaton	GMD	1	250	5x20mm	Slow Blow	100	12	0.3065	Active	ROHS3 Compliant
BK1/S506-1-R-R	Eaton	S506	1	250	5x20mm	Slow Blow	35	6.45	0.0757	Active	ROHS3 Compliant
GDC-1A	Eaton	GDC	1	250	5x20mm	Slow Blow	35	6.45	0.0757	Active	ROHS3 Compliant
GMD-1-R	Eaton	GMD	1	250	5x20mm	Slow Blow	35	12	0.3065	Active	ROHS3 Compliant
S506-1-R	Eaton	S506	1	250	5x20mm	Slow Blow	35	6.45	0.0757	Active	ROHS3 Compliant
0213001.MXP	Littelfuse	213	1	250	5x20mm	Slow Blow	35	19.2	0.1165	Active	ROHS3 Compliant
0218001.MXP	Littelfuse	218	1	250	5x20mm	Slow Blow	35	6.73	0.0613	Active	ROHS3 Compliant

Engineering Selection Recommendations

Primary Recommendation - Eaton S506 Series: The S506-1-R, BK/S506-1-R, BK1/S506-1-R-R, and GDC-1A variants represent the most direct substitutes for the obsolete BK/S504-1A. These parts maintain identical electrical specifications and are manufactured by Eaton, ensuring design continuity. All variants are active products with ROHS3 compliance. The S506 series carries the broadest approval agency certifications (BSI, CCC, CSA, CURUS, IMQ, PSE/JET, SEMKO, VDE), making it suitable for international applications.

Secondary Recommendation - Eaton GMD Series: The GMD-1-R and BK/GMD-1-R variants provide functional equivalence with higher melting I²t values (12 versus 6.45), resulting in slower thermal response. These parts are active products with ROHS3 compliance and carry CSA, PSE/JET, and UL certifications. The GMD series is appropriate for applications requiring extended thermal tolerance or where the original design incorporated GMD specifications.

Alternative Manufacturer Option - Littelfuse: The 0218001.MXP (Littelfuse Series 218) provides parametric equivalence with melting I²t of 6.73, closely matching the S506 series thermal characteristics. This part carries broad international certifications (CCC, CE, CSA, K-MARK, PSE, SEMKO, UL, VDE) and includes specified operating temperature range (-55°C to 125°C). The 0213001.MXP (Littelfuse Series 213) offers higher melting I²t (19.2) for applications requiring extended thermal response.

Compliance Considerations: The original BK/S504-1A is RoHS non-compliant. All recommended substitutes are ROHS3 compliant, meeting current environmental regulations. Littelfuse parts include REACH Unaffected status, providing additional regulatory clarity for European applications.

Frequently Asked Questions (FAQ)

Q: Can the BK/S504-1A be directly replaced with any of the listed substitutes?

A: Yes, all listed substitutes maintain the critical electrical parameters: 1 A current rating, 250 V AC voltage rating, slow-blow response, and 5mm x 20mm physical dimensions. Direct mechanical and electrical compatibility is confirmed for all listed parts when installed in standard 5mm x 20mm fuse holders.

Q: What is the significance of the melting I²t parameter in selecting a substitute?

A: The melting I²t value determines the thermal response speed of the fuse. The original BK/S504-1A has a melting I²t of 3.6. Substitutes with higher I²t values (such as GMD series at 12 or Littelfuse 213 at 19.2) respond more slowly to thermal stress, while those closer to the original value (S506 at 6.45, Littelfuse 218 at 6.73) maintain similar thermal characteristics. Selection depends on whether the application requires preservation of the original thermal response profile.

Q: Are there differences in approval agency certifications between substitute options?

A: Yes. The S506 series carries the broadest certification set (BSI, CCC, CSA, CURUS, IMQ, PSE/JET, SEMKO, VDE), making it suitable for global applications. The GMD series carries CSA, PSE/JET, and UL certifications, appropriate for North American and Japanese markets. Littelfuse parts carry CCC, CE, CSA, K-MARK, PSE, SEMKO, UL, and VDE certifications, providing comprehensive international coverage. Selection should align with target market regulatory requirements.

Q: What is the difference between BK/S506-1-R and S506-1-R?

A: Both parts are from the Eaton S506 series with identical electrical specifications. The BK/ prefix designation indicates a specific product line variant. Both are active products with ROHS3 compliance and are functionally equivalent for substitution purposes.

Q: Can I use the BK1/GMD-1-R as a substitute if it has a higher breaking capacity (100 A versus 35 A)?

A: Yes. The breaking capacity specification indicates the maximum fault current the fuse can safely interrupt. A higher breaking capacity (100 A) provides enhanced fault protection capability and is compatible with the original application. The BK1/GMD-1-R maintains all other critical parameters (1 A current rating, 250 V voltage, slow-blow response, 5mm x 20mm dimensions) required for substitution.

Q: Should I consider the DC cold resistance when selecting a substitute?

A: DC cold resistance affects voltage drop across the fuse during normal operation. The original BK/S504-1A has 0.064 Ω. Substitutes range from 0.0613 Ω (Littelfuse 218) to 0.3065 Ω (GMD series). For applications sensitive to voltage drop or operating at the limits of circuit design margins, select substitutes with DC cold resistance values closest to the original specification. For most standard applications, variations in this range are not significant.

Q: Are Littelfuse parts suitable for applications originally designed for Eaton fuses?

A: Yes. The Littelfuse 0218001.MXP and 0213001.MXP maintain the required electrical specifications (1 A, 250 V AC/DC, slow-blow, 5mm x 20mm) and carry comprehensive international certifications. Littelfuse parts are suitable for applications where manufacturer flexibility is acceptable. The 0218001.MXP provides thermal characteristics (melting I²t 6.73) most closely aligned with the Eaton S506 series.

Q: What is the inventory status of these substitutes?

A: All listed substitutes are active products with confirmed inventory availability. The Littelfuse 0218001.MXP has the highest inventory level (17,900 pcs), followed by 0213001.MXP (10,400 pcs). Eaton S506 variants range from 756 to 1,618 pcs. Littelfuse options provide superior supply security for high-volume applications.

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