RI-21A Glass Body Reed Switch SPST-NO Equivalent & Substitute Parts

Part Overview

The RI-21A is a glass body reed switch manufactured by Comus International, configured as SPST-NO (single pole single throw, normally open) with a rated switching capacity of 500mA at 250V AC. The device operates within an 18–32AT activation range with a 10W power rating and through-hole axial termination suitable for PCB integration.

The RI-21A is classified as obsolete, making substitution with active alternatives from qualified manufacturers necessary for continued design implementation and supply chain viability. Littelfuse Inc. HA15-2 series reed switches provide functional and mechanical compatibility across multiple operate range configurations.

Key Parameters

Parameter	RI-21A Specification
Manufacturer	Comus International
Series	RI-21
Circuit Configuration	SPST-NO
Type	Glass Body Reed
Operate Range	18 ~ 32AT
Current - Switching (AC/DC)	500mA
Voltage - Switching AC	250 V
Voltage - Switching DC	200 V
Power - Rated	10W
Mounting Type	Through Hole
Termination Style	Axial
Operating Temperature	-55°C ~ 125°C
RoHS Status	RoHS Compliant
Moisture Sensitivity Level (MSL)	1 (Unlimited)

Substitute Part Grouping Explanation

Substitution of the RI-21A with Littelfuse HA15-2 series alternatives is based on the following electrical and mechanical compatibility criteria:

Common Selection Parameters:

Circuit configuration: SPST-NO
Type: Glass body reed switch
Mounting type: Through hole with axial termination
Power rating: 10W
Voltage switching DC: 200 V (equivalent to RI-21A)
Voltage switching AC: 265 V (exceeds RI-21A 250 V minimum)
Current carrying capacity and switching ranges across product family

Grouping Logic: HA15-2 variants are differentiated by operate range threshold (first number) and release threshold (second number). Selection is determined by the application's magnetic field activation requirements. The RI-21A operate range of 18~32AT maps to HA15-2 variants with operate ranges spanning or overlapping this specification window. HA15-2-22-28 and HA15-2-22-38 provide the closest alignment to the 18~32AT RI-21A specification through their 22AT lower threshold.

Parameter Comparison

Parameter	RI-21A	HA15-2-12-18	HA15-2-12-23	HA15-2-12-28	HA15-2-12-38	HA15-2-17-23	HA15-2-17-28	HA15-2-17-38	HA15-2-22-28	HA15-2-22-33	HA15-2-22-38
Manufacturer	Comus International	Littelfuse Inc.
Series	RI-21	HA15-2
Circuit Configuration	SPST-NO	SPST-NO
Type	Glass Body Reed	Glass Body Reed
Operate Range (AT)	18 ~ 32	12 ~ 18	12 ~ 23	12 ~ 28	12 ~ 38	17 ~ 23	17 ~ 28	17 ~ 38	22 ~ 28	22 ~ 33	22 ~ 38
Current - Switching AC	500mA	300mA	300mA	300mA	300mA	300mA	300mA	300mA	350mA	350mA	350mA
Current - Switching DC	500mA	400mA	400mA	400mA	400mA	400mA	400mA	400mA	500mA	500mA	500mA
Voltage - Switching AC	250 V	265 V	265 V	265 V	265 V	265 V	265 V	265 V	265 V	265 V	265 V
Voltage - Switching DC	200 V	200 V	200 V	200 V	200 V	200 V	200 V	200 V	200 V	200 V	200 V
Power - Rated	10W	10W	10W	10W	10W	10W	10W	10W	10W	10W	10W
Operate Time	0.25 ms	0.6 ms	0.6 ms	0.6 ms	0.6 ms	0.6 ms	0.6 ms	0.6 ms	0.6 ms	0.6 ms	0.6 ms
Release Time	0.03 ms	0.2 ms	0.2 ms	0.2 ms	0.2 ms	0.2 ms	0.2 ms	0.2 ms	0.2 ms	0.2 ms	0.2 ms
Mounting Type	Through Hole	Through Hole
Termination Style	Axial	Axial
Length - Overall	1.811" (46.00mm)	1.590" (40.39mm)	1.590" (40.39mm)	1.590" (40.39mm)	1.590" (40.39mm)	1.590" (40.39mm)	1.590" (40.39mm)	1.590" (40.39mm)	1.590" (40.39mm)	1.590" (40.39mm)	1.590" (40.39mm)
Operating Temperature	-55°C ~ 125°C	-20°C ~ 125°C	-20°C ~ 125°C	-20°C ~ 125°C	-20°C ~ 125°C	-20°C ~ 125°C	-20°C ~ 125°C	-20°C ~ 125°C	-20°C ~ 125°C	-20°C ~ 125°C	-20°C ~ 125°C
Capacitance	0.25 pF	0.2 pF	0.2 pF	0.2 pF	0.2 pF	0.2 pF	0.2 pF	0.2 pF	0.2 pF	0.2 pF	0.2 pF
Current - Carry (DC)	2.5A	1.4A	1.4A	1.4A	1.4A	1.4A	1.4A	1.4A	1.5A	1.5A	1.5A
RoHS Status	RoHS Compliant	ROHS3 Compliant	ROHS3 Compliant	ROHS3 Compliant	ROHS3 Compliant	ROHS3 Compliant	ROHS3 Compliant	ROHS3 Compliant	ROHS3 Compliant	ROHS3 Compliant	ROHS3 Compliant
Product Status	Obsolete	Active	Active	Active	Active	Active	Active	Active	Active	Active	Active

Engineering Selection Recommendations

Primary Substitute (Best Match): HA15-2-22-28 and HA15-2-22-38 are the recommended substitutes for the RI-21A. Both variants offer:

Operate range lower threshold of 22AT, which overlaps the RI-21A 18~32AT window
Switching current capacity of 350mA (AC) and 500mA (DC), matching RI-21A DC specification
Active product status with ROHS3 compliance, ensuring long-term availability and regulatory alignment
Equivalent through-hole axial termination and 10W power rating

HA15-2-22-38 extends the upper operate threshold to 38AT, providing broader magnetic field tolerance. HA15-2-22-28 offers a tighter upper threshold of 28AT, approaching the RI-21A maximum specification.

Secondary Substitutes: HA15-2-17-28 and HA15-2-17-38 accommodate applications requiring operate range thresholds between 17AT and the upper limits. These variants maintain equivalent electrical ratings and through-hole configuration.

HA15-2-12-28 and HA15-2-12-38 extend operate range sensitivity to 12AT minimum, suitable for applications requiring lower magnetic field detection thresholds than the RI-21A provides.

Design Considerations: All HA15-2 substitutes feature 265V AC switching voltage, exceeding the RI-21A 250V specification. Operating temperature range for HA15-2 switches extends to -20°C minimum, narrower than the RI-21A -55°C specification; applications requiring sub-zero operation below -20°C must remain with RI-21A or seek alternative manufacturers.

Current carry capacity on HA15-2 variants ranges from 1.4A to 1.5A DC, lower than the RI-21A 2.5A specification. Applications requiring sustained DC carry currents above 1.5A must evaluate additional thermal constraints or alternative component families.

Frequently Asked Questions (FAQ)

Q: Can HA15-2 series switches directly replace the RI-21A in existing designs? A: Direct mechanical and electrical substitution is possible for applications within the HA15-2 operate range specifications. PCB layout compatibility is confirmed due to identical through-hole axial termination. Operate range thresholds differ; verify that the activation magnetic field strength aligns with the selected HA15-2 variant (12AT, 17AT, or 22AT lower thresholds).

Q: What is the significance of the operate range designation (e.g., 22~28AT)? A: The operate range indicates the magnetic field strength in Ampere-Turns (AT) required to activate the reed switch. The first number represents the minimum field strength for activation; the second represents the maximum reliable operating field. The RI-21A requires 18~32AT. HA15-2-22-28 activates between 22~28AT, suitable for applications within this narrower window. HA15-2-22-38 extends to 38AT, accommodating stronger magnetic fields.

Q: Why do HA15-2 switching currents differ from the RI-21A? A: Littelfuse HA15-2 switches are rated for 300–350mA AC and 400–500mA DC depending on variant, versus the RI-21A uniform 500mA AC/DC. The HA15-2-22-28 and HA15-2-22-38 match the RI-21A 500mA DC specification. Applications limited to lower current loads can use HA15-2 variants rated 300mA AC / 400mA DC without derating.

Q: Are all HA15-2 variants pin-compatible with the RI-21A? A: Yes. All HA15-2 series switches share identical through-hole axial termination geometry and spacing. Substitution requires no PCB layout modifications. Physical package dimensions differ slightly: RI-21A measures 1.811" overall length; HA15-2 measures 1.590". This shorter profile may reduce component height, but does not affect electrical function or PCB integration.

Q: How do RoHS3 and REACH compliance affect substitution? A: The RI-21A is RoHS Compliant and REACH Unaffected. HA15-2 variants are ROHS3 Compliant and REACH Unaffected. ROHS3 represents an updated compliance standard incorporating recent regulatory changes. Both statuses confirm lead-free construction and absence of restricted substances, making HA15-2 substitutes compliant for applications subject to environmental regulations.

Q: Can applications operating below -20°C use HA15-2 substitutes? A: No. HA15-2 operating temperature range is -20°C to 125°C. Applications requiring operation below -20°C must retain the RI-21A (-55°C to 125°C) or identify alternatives from other manufacturers. Contact component supplier for extended low-temperature reed switch options.

Q: What is the difference between HA15-2-22-28 and HA15-2-22-38 for substitution purposes? A: Both variants are functionally equivalent substitutes for the RI-21A. HA15-2-22-28 operates between 22~28AT, providing operate range closer to the RI-21A upper threshold of 32AT. HA15-2-22-38 operates between 22~38AT, accommodating higher magnetic field strengths beyond RI-21A specification. Select based on application magnetic field strength: use HA15-2-22-28 for fields up to 28AT; use HA15-2-22-38 for fields between 28AT and 38AT.

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