Equivalent & Substitute Parts for BK/S504-40MA

Part Overview

The BK/S504-40MA is a 40 mA, 250 V AC/DC slow-blow glass cartridge fuse in a 5mm x 20mm package manufactured by Eaton - Electronics Division. This fuse requires a holder for installation and is designed for circuit protection applications requiring slow-blow response characteristics.

The BK/S504-40MA is classified as obsolete. Equivalent and substitute parts are available from both Eaton and Littelfuse to maintain circuit protection functionality in applications currently using this component.

Key Parameters

Parameter	Value
Current Rating	40 mA
Voltage Rating (AC)	250 V
Fuse Type	Cartridge, Glass
Response Time	Slow Blow
Package / Case	5mm x 20mm
Mounting Type	Requires Holder
Breaking Capacity @ Rated Voltage	35 A
Size / Dimension	0.205" Dia x 0.787" L (5.20mm x 20.00mm)

Substitute Part Grouping Explanation

Substitution for the BK/S504-40MA is determined by the following critical parameters:

Mandatory Matching Parameters:

Current Rating: 40 mA
Voltage Rating (AC): 250 V
Fuse Type: Cartridge, Glass
Response Time: Slow Blow
Package / Case: 5mm x 20mm
Mounting Type: Requires Holder
Breaking Capacity @ Rated Voltage: 35 A

All substitute parts listed maintain these electrical and mechanical specifications. Substitutes are grouped into two categories:

Category 1: Direct Eaton Substitutes (Active Status)

BK/S506-40-R
BK1/S506-40-R
S506-40-R
BK/GDC-40MA
GDC-40MA

Category 2: Littelfuse Parametric Equivalents (Active Status)

0218.040HXP
0218.040MXBP
0218.040MXP
0218.040TXP
0218.040VXP

Parameter Comparison

Part Number	Manufacturer	Current Rating	Voltage Rating (AC)	Response Time	Package	Breaking Capacity	Melting I²t	DC Cold Resistance (Ohms)	Product Status	RoHS Status
BK/S504-40MA	Eaton	40 mA	250 V	Slow Blow	5x20mm	35 A	0.0034	14.2	Obsolete	Non-compliant
BK/S506-40-R	Eaton	40 mA	250 V	Slow Blow	5x20mm	35 A	0.0072	13.9	Active	ROHS3 Compliant
BK1/S506-40-R	Eaton	40 mA	250 V	Slow Blow	5x20mm	35 A	0.0072	13.9	Active	ROHS3 Compliant
S506-40-R	Eaton	40 mA	250 V	Slow Blow	5x20mm	35 A	0.0072	13.9	Active	ROHS3 Compliant
BK/GDC-40MA	Eaton	40 mA	250 V	Slow Blow	5x20mm	35 A	0.0072	13.9	Active	RoHS Compliant
GDC-40MA	Eaton	40 mA	250 V	Slow Blow	5x20mm	35 A	0.0072	13.9	Active	Not specified
0218.040HXP	Littelfuse	40 mA	250 V	Slow Blow	5x20mm	35 A	0.00536	35.7	Active	ROHS3 Compliant
0218.040MXBP	Littelfuse	40 mA	250 V	Slow Blow	5x20mm	35 A	0.011	31.862	Active	ROHS3 Compliant
0218.040MXP	Littelfuse	40 mA	250 V	Slow Blow	5x20mm	35 A	0.00536	35.7	Active	ROHS3 Compliant
0218.040TXP	Littelfuse	40 mA	250 V	Slow Blow	5x20mm	35 A	0.011	31.862	Active	ROHS3 Compliant
0218.040VXP	Littelfuse	40 mA	250 V	Slow Blow	5x20mm	35 A	0.011	31.862	Active	ROHS3 Compliant

Engineering Selection Recommendations

For Eaton Product Line Continuity:

The S506 series (BK/S506-40-R, BK1/S506-40-R, S506-40-R) represents the direct active-status replacement within the Eaton product family. These parts maintain electrical equivalence while offering ROHS3 compliance, addressing the non-compliance status of the obsolete BK/S504-40MA. All three variants carry identical electrical specifications and are approved by BSI, CCC, IMQ, SEMKO, UL, and VDE.

The GDC series (BK/GDC-40MA, GDC-40MA) provides an alternative Eaton option with RoHS compliance and cULus/cURus and IMQ approvals, suitable for applications requiring these specific certifications.

For Multi-Source Flexibility:

Littelfuse 218 series fuses (0218.040HXP, 0218.040MXBP, 0218.040MXP, 0218.040TXP, 0218.040VXP) are parametric equivalents meeting all mandatory electrical and mechanical specifications. These parts feature extended operating temperature range (-55°C to 125°C) and ROHS3 compliance. Littelfuse parts carry approvals from CCC, CE, CSA, K-MARK, SEMKO, UL, and VDE.

Compliance Considerations:

All substitute parts are RoHS compliant, addressing the non-compliance status of the original BK/S504-40MA. Selection between Eaton and Littelfuse options should be based on existing supply chain relationships, certification requirements specific to the application, and inventory availability.

Frequently Asked Questions (FAQ)

Q: Can I directly replace BK/S504-40MA with any of the listed substitutes?

A: Yes. All listed substitute parts maintain the mandatory electrical parameters (40 mA current rating, 250 V AC voltage rating, slow-blow response, 35 A breaking capacity) and mechanical specifications (5mm x 20mm package, cartridge glass type, holder-mount configuration). Physical dimensions are identical.

Q: What is the difference between Eaton S506 variants (BK/S506-40-R, BK1/S506-40-R, S506-40-R)?

A: These three part numbers represent the same electrical and mechanical specifications within the Eaton S506 series. Differences are in packaging designation and internal Eaton product coding. All three are active-status products with ROHS3 compliance and identical approval agencies.

Q: Why do Littelfuse parts have different DC cold resistance values compared to Eaton parts?

A: DC cold resistance variation is a characteristic difference between manufacturers' designs while maintaining the same functional performance at rated current and voltage. The 40 mA current rating and 250 V voltage rating remain identical across all substitutes.

Q: Are there operating temperature differences I should consider?

A: Littelfuse 218 series parts specify an operating temperature range of -55°C to 125°C. Eaton parts do not specify operating temperature limits in the provided data. For applications with extreme temperature requirements, Littelfuse parts provide documented temperature performance.

Q: What certifications should I verify for my specific application?

A: Eaton S506 series carries BSI, CCC, IMQ, SEMKO, UL, and VDE approvals. Eaton GDC series carries cULus, cURus, and IMQ approvals. Littelfuse 218 series carries CCC, CE, CSA, K-MARK, SEMKO, UL, and VDE approvals. Verify which certifications are required by your application standards before final selection.

Q: Is the melting I²t value critical for substitution?

A: Melting I²t values vary among the substitutes (ranging from 0.00536 to 0.011) while all parts maintain the same 40 mA current rating and slow-blow response classification. The variation reflects different thermal designs within the slow-blow category. All parts meet the 35 A breaking capacity specification.

Q: Can I mix Eaton and Littelfuse fuses in the same circuit board or equipment?

A: Yes, provided the application does not require single-source component qualification. All substitutes meet identical electrical and mechanical specifications. Verify that your equipment design and certification do not mandate single-manufacturer sourcing.

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