Allen-Bradley 817-A

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SKU: 817-A Category: Drive Brand: Allen-Bradley

The Allen-Bradley 817-A is a timing relay belonging to Allen-Bradley's 817 series of pneumatic timing relays. This electromechanical device is designed to provide time-delay control functions in industrial control circuits, offering on-delay or off-delay timing operations depending on configuration. The SKU 817-A is manufactured by Allen-Bradley, a brand of Rockwell Automation, and is intended for use in hardwired relay logic control panels.

The 817-A utilizes a pneumatic timing mechanism to achieve its time-delay function, which provides reliable and adjustable timing without the need for electronic components or external power supplies for the timing element itself. The timing range is adjustable, typically spanning from fractions of a second up to several seconds or minutes depending on the specific variant, and is set via a mechanical adjustment dial on the pneumatic bellows assembly. The relay contacts are rated for standard industrial control voltages and currents, and the unit is designed to mount directly onto a standard NEMA-style control relay base, making it compatible with existing relay infrastructure.

The 817-A timing relay is commonly used in motor control centers, conveyor systems, pump control panels, and general-purpose industrial machinery where a simple, hardwired time-delay function is required. It is well suited for applications in manufacturing, water and wastewater treatment, material handling, and process industries where reliable electromechanical timing is preferred over electronic alternatives due to environmental robustness or simplicity of maintenance. Its compatibility with standard relay bases makes it a practical replacement or upgrade component in legacy control systems.

Technical Specifications

Series/Product Family	817 Series Pneumatic Timing Relay
Timing Type	Pneumatic (on-delay)
Timing Range	0.2 – 60 seconds (adjustable)
Control Type	Electromechanical / Pneumatic
Coil Voltage	110/120V AC, 60 Hz (standard)
Contact Configuration	DPDT (2 normally open, 2 normally closed)
Contact Rating	10 A at 120V AC
Mounting	Plug-in relay base (NEMA style)
Operating Temperature	0 to 55 degrees C
Insulation Class	NEMA A600 / P300
Timing Adjustment	Mechanical dial on pneumatic bellows
Certifications	UL Listed, CSA Certified

Common Fault Conditions

No Contact Closure: The output contacts fail to close after the set time delay has elapsed, indicating a fault in the pneumatic bellows or contact mechanism.
Inspect the pneumatic bellows for cracks or air leaks. Verify the timing adjustment dial is not set to maximum. Replace the timing relay if the bellows assembly is damaged.
Coil Open Circuit: The relay coil has failed open, preventing the relay from energizing and initiating the timing sequence.
Measure coil resistance with a multimeter. A reading of infinite resistance confirms an open coil. Replace the 817-A unit or the coil assembly if serviceable.
Incorrect Time Delay: The relay operates but the actual time delay does not match the dial setting, indicating a worn or contaminated pneumatic bellows.
Clean the pneumatic orifice and bellows assembly. If timing remains inaccurate after cleaning, replace the timing relay with a new or refurbished 817-A unit.
Contact Welding: Output contacts have welded closed due to excessive inrush current or overload, causing the controlled circuit to remain energized regardless of relay state.
De-energize the circuit and test contact continuity in both energized and de-energized states. If contacts are welded, replace the relay. Investigate and correct the cause of overcurrent in the load circuit.
Coil Hum or Chatter: The relay coil produces excessive audible hum or chattering, typically caused by low supply voltage or a worn shading ring on the coil core.
Verify supply voltage at the coil terminals is within the rated range. Inspect the shading ring on the magnetic core for damage or wear. Replace the relay if the shading ring is broken.
Relay Fails to Reset: After the coil is de-energized, the timing relay contacts do not return to their normal state, indicating a mechanical jam or bellows failure.
Manually actuate the relay mechanism to check for mechanical binding. Inspect the return spring and bellows for damage. Replace the unit if mechanical reset cannot be restored.
Premature Contact Operation: The relay contacts close or open before the set time delay has elapsed, suggesting air leakage in the pneumatic bellows or a misadjusted orifice.
Inspect the bellows and orifice for leaks or blockages. Readjust the timing dial and verify operation. Replace the bellows assembly or the complete relay if the fault persists.

Frequently Asked Questions

What type of timing function does the Allen-Bradley 817-A provide?

The 817-A is an on-delay pneumatic timing relay, meaning the output contacts change state after a set time delay following coil energization. The timing is achieved through a pneumatic bellows mechanism rather than electronic circuitry.

What relay base is compatible with the 817-A?

The 817-A is designed to plug into a standard Allen-Bradley NEMA-style relay base compatible with the 700 and 800 series relay sockets. Verify the base pin configuration matches before installation.

What is the adjustable timing range of the 817-A?

The timing range is adjustable via a mechanical dial on the pneumatic bellows, typically spanning from approximately 0.2 seconds to 60 seconds. The exact range may vary slightly depending on the specific sub-variant.

Can the 817-A be used as a replacement for an electronic timing relay?

The 817-A can replace electronic timing relays in applications where the timing range and contact ratings are compatible. However, its pneumatic timing mechanism is less precise than electronic timers and may be affected by temperature and altitude.

Is the 817-A still in production, and are replacement parts available?

The 817 series pneumatic timing relay is a legacy Allen-Bradley product and is no longer in active production. Replacement units are available through industrial surplus and refurbishment suppliers, and compatible relay bases may still be sourced through Rockwell Automation distributors.

Troubleshooting

Relay coil energizes but contacts do not change state after the set delay

Check for audible click from the relay mechanism when energized. Measure continuity across the output contacts before and after the expected delay period to confirm contact failure.

Inspect the pneumatic bellows for air leaks or blockage at the orifice. Clean the orifice with compressed air. If the bellows is cracked or deformed, replace the 817-A timing relay.

Relay does not energize when control voltage is applied

Measure the supply voltage at the coil terminals with a multimeter to confirm voltage is present and within rated range. Then measure coil resistance to check for an open or shorted coil.

If voltage is present but the coil does not pull in, replace the relay. If voltage is absent, trace the control circuit wiring for open contacts, blown fuses, or broken conductors upstream of the relay coil.

Time delay is inconsistent or drifts from the set value

Operate the relay several times and measure the actual delay with a stopwatch. Compare results across multiple cycles to determine if the variation is random or systematic.

Clean the pneumatic orifice and bellows assembly to remove dust or oil contamination. Recalibrate the timing dial. If inconsistency persists, replace the relay, as the bellows may be worn or the orifice permanently obstructed.

Relay contacts remain closed after coil is de-energized

With power removed, test contact continuity with a multimeter. If contacts show continuity in the de-energized state, they are either welded or the mechanical return mechanism has failed.

Do not attempt to force contacts open manually if welded, as this can cause arcing damage. Replace the 817-A relay. Investigate the load circuit for overcurrent conditions that may have caused contact welding and install appropriate protection.

Excessive coil hum or audible chattering during operation

Measure the AC supply voltage at the coil terminals. Low voltage below the rated coil voltage is a common cause of hum. Also inspect the magnetic core face for dirt or corrosion that prevents full seating.

Correct low supply voltage at the source. Clean the magnetic core mating surfaces with a dry cloth. If the shading ring on the core is broken or missing, replace the relay, as the shading ring is not typically a field-replaceable part.

Condition	Repair, Used, Refurbished, New in box (sealed)

Common defects

Common defects on a Allen-Bradley 817-A are:

Power Supply Related Issues

No power / drive not turning on
Blown fuses
Defective rectifier bridge
Damaged DC bus capacitors
IGBT / MOSFET module failure
Overvoltage / undervoltage errors

Control & Electronics Failures

Faulty control board or PCB damage
Firmware or memory corruption
Fieldbus communication errors (Profibus, Modbus, EtherCAT, CANopen)
Input / output circuit damage
Gate driver module failure

Motor Control Problems

Motor not starting or no output
Unstable speed control
No torque output
Trip during acceleration or deceleration
Encoder feedback errors

Thermal & Cooling Defects

Overheating due to failed cooling fans
Defective temperature sensors
Poor heatsink performance

Mechanical & Environmental Damage

Burnt or loose connectors
PCB track damage
Corrosion or moisture ingress
Oil, dust or contamination damage
Cracked solder joints

Error Codes & Drive Trips

Overcurrent faults (OC)
Ground fault / earth leakage error
Short-circuit fault
Motor or drive overload
Overvoltage or undervoltage error
Undervoltage trip when starting or stopping
Phase loss / imbalance
Synchronization issues with multiple drives

Other

Display defect
Control keys or keypad not working
Parameters no longer readable or lost
Brake resistor problems (brake chopper defect)
Internal relays/contactors defective
EMI/RFI interference due to defective filters