BK/S506-4A Equivalent & Substitute Parts

Part Overview

The BK/S506-4A is a 4 A, 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, requiring identification of active equivalent alternatives for continued circuit protection applications. The slow-blow response characteristic and cartridge design necessitate holder-based mounting configurations. Substitute parts must maintain electrical and mechanical compatibility while meeting current regulatory compliance standards.

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	40 A
Size / Dimension	0.205" Dia x 0.787" L (5.20mm x 20.00mm)

Substitute Part Grouping Explanation

Substitution eligibility is determined by strict equivalence across the following critical parameters: current rating (4 A), voltage rating (250 V AC), fuse type (cartridge glass), package dimensions (5mm x 20mm), and response time (slow blow). All substitute parts listed maintain these core electrical and mechanical specifications, ensuring direct functional compatibility within existing holder-based mounting systems.

Substitute parts are grouped into two categories based on breaking capacity:

Category 1: 40 A Breaking Capacity – Direct electrical equivalents with identical breaking capacity specifications. These parts are suitable for applications where the original 40 A breaking capacity is required.

Category 2: 200 A Breaking Capacity – Enhanced breaking capacity alternatives. These parts provide higher fault current handling capability while maintaining all other electrical parameters.

Parameter Comparison

Part Number	Manufacturer	Series	Current Rating (A)	Voltage (V AC)	Response Time	Breaking Capacity (A)	Melting I²t	DC Cold Resistance (Ohms)	Product Status	RoHS Status
BK/S506-4A	Eaton	S506	4	250	Slow Blow	40	88	0.012	Obsolete	Non-compliant
BK/S506-4-R	Eaton	S506	4	250	Slow Blow	40	71.8	0.0139	Active	ROHS3 Compliant
BK/GDC-4A	Eaton	GDC	4	250	Slow Blow	40	71.8	0.0139	Active	ROHS3 Compliant
BK/GMD-4-R	Eaton	GMD	4	250	Slow Blow	200	300	0.048	Active	ROHS3 Compliant
BK1/GMD-4-R	Eaton	GMD	4	250	Slow Blow	200	300	0.048	Active	ROHS3 Compliant
GDC-4A	Eaton	GDC	4	250	Slow Blow	40	71.8	0.0139	Active	Not specified
GMD-4-R	Eaton	GMD	4	250	Slow Blow	200	300	0.048	Active	ROHS3 Compliant
S506-4-R	Eaton	S506	4	250	Slow Blow	40	71.8	0.0139	Active	ROHS3 Compliant
0034.3123	SCHURTER	FST 5x20	4	250	Slow Blow	40	68.3	Not specified	Active	ROHS3 Compliant
0034.5049	SCHURTER	FTT 5x20	4	250	Slow Blow	35	410	Not specified	Active	ROHS3 Compliant
0034.5623.11	SCHURTER	SMD-FST	4	250	Slow Blow	40	68.3	Not specified	Active	ROHS3 Compliant

Engineering Selection Recommendations

Primary Recommendation – Eaton S506 Series (Active Status):

The S506-4-R and S506-4-R variants represent the direct active-status successors to the obsolete BK/S506-4A. Both maintain identical electrical specifications (4 A, 250 V, 40 A breaking capacity, slow-blow response) and are ROHS3 compliant. These parts are recommended for applications requiring exact parameter matching with the original design.

Alternative Recommendation – Eaton GDC Series (Active Status):

The BK/GDC-4A and GDC-4A parts provide equivalent electrical performance with active product status and ROHS3 compliance. These alternatives are suitable where GDC series certification requirements align with application standards.

Enhanced Breaking Capacity Option – Eaton GMD Series (Active Status):

The BK/GMD-4-R, BK1/GMD-4-R, and GMD-4-R variants offer 200 A breaking capacity compared to the original 40 A specification. These parts are selected for applications requiring higher fault current protection capability while maintaining all other electrical parameters. ROHS3 compliance and active product status are confirmed.

Cross-Manufacturer Alternative – SCHURTER FST and SMD-FST Series (Active Status):

The SCHURTER 0034.3123 (FST 5x20) and 0034.5623.11 (SMD-FST) parts provide equivalent 4 A, 250 V specifications with 40 A breaking capacity and ROHS3 compliance. These alternatives are suitable for applications where multi-source component availability is required.

Specialized Alternative – SCHURTER FTT Series:

The 0034.5049 (FTT 5x20) provides 4 A, 250 V specifications with 35 A breaking capacity and extended melting I²t (410). This part is selected for applications requiring higher thermal energy absorption characteristics.

All recommended substitutes maintain the 5mm x 20mm form factor, slow-blow response time, and holder-based mounting requirement of the original BK/S506-4A.

Frequently Asked Questions (FAQ)

Q: Can BK/S506-4A be directly replaced with S506-4-R?

A: Yes. The S506-4-R maintains identical electrical specifications (4 A, 250 V, 40 A breaking capacity, slow-blow response) and mechanical form factor (5mm x 20mm). The primary difference is product status (active versus obsolete) and RoHS compliance (ROHS3 compliant). Both require holder-based mounting.

Q: What is the difference between 40 A and 200 A breaking capacity options?

A: Breaking capacity defines the maximum fault current the fuse can safely interrupt. The original BK/S506-4A and most substitutes are rated at 40 A breaking capacity. The GMD series alternatives (BK/GMD-4-R, BK1/GMD-4-R, GMD-4-R) provide 200 A breaking capacity for applications with higher available fault currents. All maintain identical 4 A trip current and 250 V voltage rating.

Q: Are SCHURTER alternatives compatible with existing Eaton fuse holders?

A: SCHURTER parts 0034.3123, 0034.5049, and 0034.5623.11 maintain the 5mm x 20mm form factor and cartridge glass design, ensuring mechanical compatibility with standard 5mm x 20mm fuse holders. Electrical specifications (4 A, 250 V, slow-blow response) are equivalent to the original BK/S506-4A.

Q: What does "slow-blow" response time mean?

A: Slow-blow fuses tolerate temporary current surges without opening, responding only to sustained overcurrent conditions. All listed substitutes maintain this slow-blow characteristic, ensuring compatibility with applications designed for the original BK/S506-4A response profile.

Q: Is RoHS compliance required for my application?

A: The original BK/S506-4A is RoHS non-compliant. All active substitute parts listed (S506-4-R, GDC series, GMD series, and SCHURTER alternatives) are ROHS3 compliant. If RoHS compliance is a regulatory requirement, any of these active alternatives are suitable replacements.

Q: What is the significance of melting I²t values?

A: Melting I²t represents the thermal energy required to melt the fuse element. The original BK/S506-4A has a melting I²t of 88. Substitutes range from 68.3 to 410, depending on series. Lower values indicate faster thermal response; higher values indicate greater thermal energy absorption. Selection depends on application-specific thermal requirements.

Q: Can I use a 200 A breaking capacity fuse in place of a 40 A breaking capacity fuse?

A: Yes, from a mechanical and electrical standpoint. The GMD series (200 A breaking capacity) maintains all other specifications (4 A trip current, 250 V voltage, slow-blow response, 5mm x 20mm form factor). However, application-specific fault current availability and system design should be verified to ensure the higher breaking capacity is appropriate.

Q: What is the operating temperature range for these fuses?

A: The original BK/S506-4A does not specify an operating temperature range. SCHURTER alternatives provide defined ranges: 0034.3123 operates from -55°C to 125°C; 0034.5049 operates from -40°C to 85°C; 0034.5623.11 operates from -55°C to 125°C. Eaton alternatives do not specify operating temperature ranges in the provided data.

Q: Are there any approval agency differences between substitutes?

A: Yes. The original BK/S506-4A carries approvals from BSI, CCC, CSA, cULus, IMQ, MITI, SEMKO, and VDE. Substitute parts carry varying approval combinations. S506-4-R includes all original approvals plus CURUS and PSE/JET. GDC series includes cULus, IMQ, and MITI/JET. GMD series includes PSE/JET and UL. SCHURTER alternatives include CCC, cURus, PSE/JET, and VDE. Application-specific approval requirements should be verified.

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