The Castair ALT460 is a 460-volt automatic alternator relay for two-compressor systems on three-phase electrical service. It automatically manages the lead/lag operation between two compressors sharing a common air supply — alternating which unit runs as the primary each cycle so both machines accumulate equal operating hours over time. This is the relay-only version: no enclosure included. If you want the relay pre-mounted in a panel enclosure, see the ALT460M.
The 460V rating puts this relay in industrial territory. Three-phase 460V motors are the standard for compressors above roughly 10 HP in manufacturing plants, fleet yards, large collision centers, and heavy commercial facilities. If your compressor motors run on 460V (also labeled 440V or 480V in some installations — verify against your relay specifications), the ALT460 is the correct unit. Installing the 230V version on a 460V circuit is a wiring error that will destroy the relay and may damage the compressor motors.
Why Three-Phase Facilities Need Alternator Relays
High-horsepower three-phase compressors in industrial settings run hard. They are often the backbone of a production air system, running during every shift, every day. In a duplex installation — two compressors sharing a common header or storage system — an alternator relay is not optional. It is how you protect the investment in both machines.
Three specific problems the ALT460 solves:
- Unequal Wear: Without alternation, whichever compressor happens to be wired as the primary runs most of the hours. A 460V industrial compressor can cost $5,000 to $15,000 or more. Running one machine to failure while the second stays nearly new is not a maintenance strategy — it is an expensive mistake. The ALT460 prevents this by automatically rotating lead/lag designation every cycle.
- Duty Cycle Compliance: Every compressor manufacturer specifies maximum duty cycles — the maximum percentage of time the unit should run continuously. Heavy production air demand in a manufacturing plant can push a single compressor well past its rated duty cycle. The ALT460 shares that load across two machines, keeping each within manufacturer-specified limits. This is relevant for warranty compliance on new compressors.
- Actual Redundancy: A second compressor is only useful as backup if it is maintained and ready to run. If the lag unit sits idle for months, its oil degrades and it may not start reliably when the primary goes down. The ALT460 keeps the second unit active and exercised, so the redundancy is real, not theoretical.
How the ALT460 Works
- Lead Compressor Start: When system pressure drops below the cut-in setpoint, the lead compressor starts. The lag unit remains off.
- Lag Compressor Activation: If demand exceeds the lead unit's capacity and pressure continues to drop, the relay brings the lag compressor online to assist. Both units run until pressure recovers.
- Automatic Alternation: After each cycle, the relay swaps lead and lag designations. The unit that just ran as lead becomes lag on the next cycle. No manual input, no rotation schedules, no relying on technicians to remember which machine ran last.
- 460V Three-Phase Operation: Rated for 460V three-phase electrical service. Confirm your compressor motor voltage rating and panel supply voltage before ordering.
Features
- 460V Three-Phase Rated: Designed for industrial 460V electrical systems — the correct unit for three-phase compressor installations above 230V
- Automatic Lead/Lag Swap: No manual intervention — relay alternates lead/lag designation automatically after each pressure cycle
- Dual Compressor Start Coordination: Manages sequenced start and stop for both units, preventing simultaneous starts that spike current draw
- Relay-Only Format: The ALT460 is the relay unit without an enclosure. Install it in your own panel, junction box, or control cabinet. For a pre-mounted panel assembly, order the ALT460M.
- Compatible with Castair Control Accessories: Integrates with Castair hour meters (HRM75, HRM50), time delays (TD100), and low oil controls (6304, 6304B) for a complete duplex compressor control system
- Castair Manufacturing: Designed and built by Cast Air in Minnesota, a manufacturer specializing in duplex and industrial compressor controls
What's in the Box
- Castair ALT460 automatic alternator relay (relay unit only, no enclosure)
- Manufacturer documentation and wiring diagram
Note: The ALT460 is a relay-only unit for integration into your own panel or control cabinet. If you need the relay pre-mounted in an enclosure ready for wall installation, order the ALT460M. Installation by a licensed electrician is required — this is a line-voltage three-phase control component.
Available Configurations — Full Matrix
Castair makes four alternator relay configurations to match your voltage and installation format:
| Model | Voltage | Format | Price | Best For |
|---|---|---|---|---|
| ALT230 | 230V | Relay only — you supply enclosure | $398.86 | 230V systems, installing into existing panel or custom control cabinet |
| ALT230M | 230V | Relay pre-mounted in panel enclosure | Call for pricing | 230V systems, clean permanent wall-mount installation without enclosure fabrication |
| ALT460 (this unit) | 460V | Relay only — you supply enclosure | $398.86 | 460V three-phase systems, installing into existing panel or control cabinet |
| ALT460M | 460V | Relay pre-mounted in panel enclosure | Call for pricing | 460V three-phase systems, clean permanent wall-mount installation |
Voltage is determined by your compressor motor nameplates and your electrical panel supply. Format (relay-only vs. mounted) is a matter of your installation setup. Do not mix voltages. Call 866-217-0063 if you need help confirming the right unit for your system.
When Does a Facility Need This vs. Stepping Up or Down
The ALT460 is the right choice if:
- You are running two compressors on 460V three-phase service with a shared air header or storage system
- Your installation involves a custom control panel or existing cabinet where you are integrating the relay alongside other components
- You want to equalize wear across both compressors without manual tracking or rotation schedules
- You are building a new duplex installation and specifying the correct control components from the start
- Your compressor manufacturer's warranty specifies a maximum duty cycle that demands load-sharing between two units
The ALT460M is better if:
- You want a finished, self-contained panel assembly ready to mount and wire without enclosure fabrication
- Your installation environment requires enclosed electrical components — dusty mechanical rooms, areas with moisture exposure, or anywhere an open relay is not appropriate
- You want a professional, permanent-looking control installation without custom panel work
You need the 230V version (ALT230 or ALT230M) if:
- Your compressor motors run on 230V service — verify on the motor nameplate
- The 460V and 230V versions are not interchangeable — check motor voltage and panel service voltage before ordering
You do not need an alternator relay if:
- You have only one compressor — this relay is specifically for two-compressor systems
- Your two compressors are on completely independent circuits and systems with no shared load — though equal wear is still the correct maintenance approach
Technical Specifications
- Model: ALT460
- Part Number: ALT460
- Manufacturer: Cast Air (Castair), Minnesota
- Voltage: 460 Volt (three-phase)
- Application: Two-compressor automatic alternation (lead/lag control)
- Format: Relay only (no enclosure included)
- Compatible Accessories: HRM75 (hour meter 24-277V), HRM50 (hour meter for gas engines), TD100 (time delay 18-240V, 1-1023 seconds), 6304 (low oil control), 6304B (float switch for low oil)
- Price: $398.86
- Dimensions/Weight: Contact us to confirm shipping dimensions
Why Buy From Air Compressor Factory Direct?
Air Compressor Factory Direct has specialized in compressed air systems and components since 2016. We carry the full Castair control accessory line — alternator relays, hour meters, time delays, low oil controls — and we understand how these components work together in a real duplex compressor installation. The voltage question (230V vs. 460V) and the format question (relay-only vs. mounted) come up on nearly every alternator relay order, and we can help you confirm the right answer for your specific system before anything ships.
- Free Shipping: On qualifying orders — confirm at checkout or by phone
- Free Technical Support: Call 866-217-0063 before or after purchase with installation and specification questions
- Full Manufacturer Warranty: Castair components covered under manufacturer warranty — we handle warranty issues directly
- Honest Guidance: We will tell you if a different model is the better fit for your installation before you order, not after
- Specialist Focus: Compressed air systems and components are our focus — not a sideline. Castair controls are a core part of our inventory and we know the product line well.
Call 866-217-0063 for quick answers and help!
