Product Overview
Square D Class 8501 HDO-40 Industrial Control Relay - 24VDC Coil, 5 Normally Open Contacts, NEMA A600, Panel Mount
Condition
Single unit available. Unused and unboxed - stored without its original packaging but shows no signs of use. Black crackle finish is intact, brass terminals show no oxidation or arc pitting, coil wiring and insulation are undamaged, and contact blocks are clean. Nameplate is legible: Class 8501, Type HDO-40, Form B, Series 6J, NEMA A600, Plant 86, Made in USA. Light surface dust consistent with open storage. Sourced from surplus inventory following a company downsizing.
Carefully packed and shipped same business day from our Idaho warehouse. Online since 1999. Honest equipment and straightforward service.
No hassle resolution if there is an issue. Serving customers since 1999.
Product Overview
Square D Class 8501 Type HDO-40 is a 24VDC industrial control relay with 5 normally open contacts and NEMA A600 contact rating. Designed for panel mounting in industrial control systems, it handles switching duties in motor control circuits, solenoid control, and general-purpose automation logic. The HDO designation specifies a DC coil - the 24VDC coil energizes to close all five N.O. contacts simultaneously. Open frame construction requires mounting in an appropriate enclosure for environments with dust, moisture, or mechanical hazards. Marked Series 6J, Form B, Made in USA.
Key Features
- Coil voltage: 24VDC
- Contact configuration: 5 normally open (5 N.O.)
- Contact rating: NEMA A600 (10A continuous at 600VAC)
- DC contact rating: 1.1A at 120VDC, 0.2A at 240VDC
- Series: Class 8501, Type HDO-40, Series 6J, Form B
- Mounting: Open frame, panel mount
- Certifications: UL Listed, CSA Certified
- Country of manufacture: USA
- Nameplate confirmed via photo: Class 8501 / HDO-40 / NEMA A600 / Plant 86
Applications
- Motor control circuits - start/stop logic and interlocking
- Solenoid valve control in pneumatic and hydraulic systems
- Machine tool control panels requiring DC-coil relay logic
- Process automation and PLC output expansion
- Industrial control panel builds and retrofits where 24VDC logic is already present
Frequently Asked Questions
Will this relay work in an AC control circuit?
No - not directly. The HDO-40 coil requires 24VDC to energize. Using it in an AC system requires an external AC-to-DC power supply matched to the coil voltage. The switched contacts (NEMA A600) handle both AC and DC loads within their ratings.
What is the contact rating for AC loads?
NEMA A600, which specifies 10A continuous at 600VAC, 60A make, and 6A break at 120VAC on inductive loads. For DC switching: 1.1A at 120VDC, 0.2A at 240VDC.
Is this relay suitable for exposed or harsh environments?
No - the open frame construction offers no environmental protection on its own. It should be mounted inside a suitable enclosure when used in environments with dust, moisture, or mechanical hazards.
What is included with this relay?
The relay only - no original box. An instruction label is affixed to the unit and is legible in photos.
How does the HDO-40 differ from the HO-40?
The HO-40 uses an AC coil (typically 120VAC) and has 4 N.O. contacts. The HDO-40 has a 24VDC coil and 5 N.O. contacts. They are not interchangeable in DC control circuits. Verify coil voltage before ordering.
A Square D Class 8501 relay from a working plant, unused and still carrying its original nameplate - the kind of part that disappears from catalogs long before it disappears from machines. Put it where a 24V control circuit needs five reliable closes, and let it do what it was built to do.
