Time Delay Relay Wiring Guide: 8-Pin, 11-Pin & DIN Rail Diagrams

When you’re staring at a time delay relay in a control panel, trying to figure out which terminal connects to what, the frustration is real. Unlike a simple contactor with obvious line and load terminals, time delay relays have multiple circuit paths: power supply, timing input, and output contacts. Get one connection wrong, and you’re looking at equipment that won’t start, timing that doesn’t work, or worse—blown fuses and damaged loads.Time delay relays are fundamental control components in HVAC systems, motor control circuits, and lighting automation. They protect compressors from short-cycling, sequence motor starts to reduce inrush current, and provide automatic lighting shutoff. But their value depends entirely on correct wiring.

This guide walks you through time delay relay wiring step by step, starting with terminal identification and ending with real-world application diagrams. Whether you’re installing an 8-pin plug-in relay in an HVAC system or wiring a DIN rail timer for industrial motor control, you’ll understand exactly which terminals handle power, which respond to timing inputs, and which switch your load. We’ll cover the three standard relay types—8-pin socket, 11-pin socket, and DIN rail mount—plus common applications including HVAC compressor protection, sequential motor starting, and lighting control.

The approach is systematic: understand the terminal functions first, then follow the wiring logic for your specific relay type and application. By the end, you’ll have the confidence to wire time delay relays correctly on the first attempt.

Understanding Time Relay Terminal Functions

Before connecting any wires, you need to recognize three distinct terminal groups on every time delay relay. Industrial timers follow IEC terminal labeling standards, which makes identification consistent across manufacturers once you know the conventions.

Power Supply Terminals (A1/A2)

These terminals energize the relay’s internal timing circuit. Think of them as the relay’s own power source—nothing happens without voltage across A1 and A2. On DIN rail relays, they’re clearly marked on the front panel. On plug-in socket relays, A1/A2 might be labeled on the relay body or correspond to specific pin numbers (check your datasheet for the exact pin mapping, since 8-pin and 11-pin layouts vary by manufacturer).

Critical point: The voltage you apply to A1/A2 must match the relay’s rated control voltage. A 24VDC relay won’t function on 120VAC supply, and vice versa. Common control voltages are 24VDC, 24VAC, 120VAC, and 240VAC. AC/DC universal models exist but cost more.

Control Input Terminal (B1)

Some multifunction relays include a separate control input terminal labeled B1 (sometimes Y1/Y2 on older models). This terminal accepts the external timing trigger signal—a pushbutton, limit switch, or another contact that tells the relay when to start timing. Functions that require a control input include on-delay with external start, interval timers, and certain off-delay modes.

Not all timing functions use B1. Simple on-delay relays that start timing when A1/A2 power is applied don’t need it. Check your timing function diagram: if it shows “external START” or a separate control signal, you’ll wire B1.

Output Contact Terminals (15, 16, 18)

These are the relay’s switching contacts that control your load—motor contactor coil, lighting circuit, solenoid valve, or any device you want to turn on/off after the time delay. IEC numbering uses:

• 15 = Common (COM)
• 16 = Normally Closed (NC)
• 18 = Normally Open (NO)

SPDT (single-pole double-throw) relays have all three terminals: 15-16-18, giving you one changeover contact. DPDT relays double this with a second set: 25-26-28. Your load circuit connects through COM (15) and either NC (16) or NO (18), depending on whether you need the load energized during timing or after timing completes.

For on-delay applications (load energizes after delay), wire through COM (15) to NO (18). For off-delay or run-on applications (load de-energizes after delay), wire through COM (15) to NO (18), with the timing function set to off-delay.

Socket Relays: Pin-to-Terminal Mapping

Plug-in 8-pin and 11-pin socket relays don’t always print IEC labels on the socket. Instead, you see pin numbers (1 through 8 or 1 through 11). The mapping from pin numbers to IEC terminal functions varies by manufacturer and model series. Always consult your specific relay’s datasheet or socket diagram.

For example, a common 8-pin SPDT relay might map:

• Pins 2 & 7 = A1/A2 (power supply)
• Pins 1, 3, 4 = Output contacts (COM, NC, NO)
• Pins 5, 6, 8 = Additional functions or not connected

But another manufacturer’s 8-pin relay could use completely different pin assignments. Never assume. When in doubt, measure with a multimeter (power off!) to identify coil terminals versus contact terminals, or reference the relay’s front-panel function diagram if available.

Step 1: Power Supply Connection (A1/A2 Terminals)

The power supply circuit energizes the timing relay’s internal electronics or coil. This is independent of the load circuit—think of it as the relay’s brain power.

Voltage Matching

First step: verify your relay’s rated control voltage printed on the front panel or datasheet. Common ratings include:

• 24VDC (most common in industrial control panels)
• 24VAC (HVAC systems, especially compressor controls)
• 120VAC (North American line-voltage control)
• 240VAC (international or large equipment control)

Your control power source must match this rating exactly. Applying 120VAC to a 24VDC relay will destroy it instantly. Under-voltage (like 12VDC on a 24VDC relay) means the relay won’t energize reliably or won’t time accurately.

Wiring Polarity Considerations

For DC-powered relays (24VDC, 12VDC), polarity matters. Terminal A1 connects to positive (+), A2 to negative (−) or ground. Reversing polarity on most solid-state timers won’t cause damage but the relay won’t operate. Electromechanical DC coil relays may function regardless of polarity, but follow the marked polarity for consistent performance.

For AC-powered relays (24VAC, 120VAC, 240VAC), polarity doesn’t matter—A1 and A2 are interchangeable. However, it’s good practice to bring the grounded conductor (neutral in 120VAC systems) to A2 for consistent troubleshooting.

Source Circuit Protection

Always protect the control supply circuit with appropriately rated overcurrent protection (fuse or circuit breaker). For most time delay relays drawing under 10VA, a 1A or 2A fuse is sufficient. Refer to your relay’s datasheet for exact VA or watt consumption.

In control panels, you’ll typically wire A1/A2 from a control transformer secondary (24VAC or 24VDC power supply) or from a 120VAC control bus. Keep power supply wiring short and direct to minimize voltage drop and electrical noise pickup.

Step 2: Timing Input Wiring (Control Circuit)

This step applies to multifunction relays with a control input terminal (B1). Not all time delay relays require this—simple on-delay relays start timing automatically when A1/A2 power is applied, and basic off-delay relays start timing when power is removed.

Which Functions Require Control Input (B1)?

• On-Delay with External Start: Relay powers up but doesn’t time until an external contact closes B1 to common
• ເຄື່ອງຈັບເວລາໄລຍະຫ່າງ: A pulse or contact closure at B1 triggers a one-shot output pulse of set duration
• ເຮັດຊ້ຳຕົວຈັບເວລາຮອບວຽນ: Contact at B1 initiates cyclical on-off output timing

Your relay’s function selector or documentation will indicate if B1 is required. Typically, these functions are marked with a “START” or trigger arrow symbol on the timing diagram.

Wiring the Control Input

The control input circuit is a dry-contact input, meaning it expects a switch or relay contact that connects B1 to a reference point (usually A2 or common). Examples of control input sources:

• Pushbutton (momentary or maintained contact)
• Limit switch
• Proximity sensor output (NPN or PNP, depending on relay input type)
• Auxiliary contact from another relay or contactor
• Thermostat contact (for HVAC applications)

Wire the initiating device in series with B1. For example, a pushbutton connects from B1 to A2 (or common ground on DC systems). When pressed, the contact closes and the relay starts timing.

Some advanced multifunction relays offer both enable (level-triggered) and start (edge-triggered) inputs. Enable means timing continues as long as the contact is closed. Start means a momentary contact closure initiates timing, and timing completes regardless of subsequent contact status. Check your specific model’s behavior.

What If My Relay Doesn’t Have B1?

Single-function relays—especially simple on-delay and off-delay types—don’t expose a separate B1 terminal. These relays time based solely on the A1/A2 power supply state:

• On-Delay: Apply A1/A2 power → timing starts → output energizes after delay
• Off-Delay: Remove A1/A2 power → timing starts → output de-energizes after delay

For these relays, you control timing by controlling the A1/A2 power circuit itself, often by wiring an upstream control contact (like a thermostat or start button) in series with A1.

Step 3: Output Contact Wiring (Switching Load)

The output contacts switch your actual load—a contactor coil, motor starter, solenoid valve, pilot light, or alarm. This is where the relay performs its job after timing.

理解触头结构

Most time delay relays offer SPDT contacts (one changeover contact with Common, NC, and NO):

• COM (15): One side of your load circuit always connects here
• NC (16): Normally closed—conducts when the relay is de-energized or before timing completes
• NO (18): Normally open—conducts when the relay is energized or after timing completes

Your load connects between COM (15) and either NC (16) or NO (18), depending on when you want the load energized:

• On-delay applications (load energizes after delay): Wire load through COM (15) to NO (18)
• Off-delay applications (load de-energizes after delay): Wire load through COM (15) to NO (18), with off-delay timing function selected
• Normally-on applications (load energized until timing completes): Wire through COM (15) to NC (16)

Contact Ratings and Load Types

Time delay relay contacts are rated for specific voltage and current combinations, and the ratings differ by load type:

• Resistive loads (heaters, incandescent lamps): highest rating, typically 5A to 10A at 250VAC
• Inductive loads (contactors, relay coils, solenoids): lower rating due to inrush and back-EMF, often 3A to 5A at 250VAC
• Capacitive/lamp loads (transformers, LED drivers): derating required due to inrush, check datasheet

Never exceed the relay’s rated contact current for your load type. If you’re switching a 7A inductive load and your timer is rated for 5A inductive, the contacts will weld, arc, or fail prematurely.

When to Use a Contactor Interface

For loads exceeding the timer’s contact rating, use the timer to control a contactor or motor starter coil instead of switching the load directly:

Timer output (15-18) → Contactor coil (typically 0.2A to 0.5A) → Contactor main contacts → High-current load (motor, heater, etc.)

This approach is standard in motor control and HVAC systems. The timer switches a small coil current, and the contactor handles the heavy load.

Inductive Load Suppression

Inductive loads (coils, motors, transformers) generate voltage spikes when de-energized. These spikes damage contacts and can cause relay malfunction. Suppression methods:

• AC inductive loads: RC snubber (resistor-capacitor network) or MOV (metal-oxide varistor) wired across the load
• DC inductive loads: Flyback diode (1N4007 or similar) wired across the coil, cathode to positive side

Many contactors and solenoids include built-in suppression. If not, add external suppression per the relay manufacturer’s recommendation. Without suppression, contact life drops significantly—from 100,000 operations to under 10,000 in severe cases.

Wiring by Relay Type: 8-Pin Socket Installation

8-pin octal plug-in relays are common in HVAC systems and legacy industrial control panels. The relay plugs into a socket base that mounts to a panel or DIN rail.

Critical Warning: Pin Layouts Vary

Unlike the standardized IEC terminal labels (A1/A2, 15/16/18) found on DIN rail timers, 8-pin socket relay pinouts are not universal. Different manufacturers map the coil and contact terminals to different pins. You must reference your specific relay model’s pinout diagram.

Typical 8-Pin SPDT Layout (Not Universal)

One common configuration found in many timer relay families:

• Pins 2 & 7: Coil supply (A1/A2)
• Pins 1, 3, 4: Output contacts—usually Pin 1 = COM, Pin 3 = NC, Pin 4 = NO
• Pins 5, 6, 8: Unused, or additional contacts on DPDT models

But this is only one example. Always verify your relay’s specific pinout.

Installation Procedure

1. Mount the socket base: Screw-mount or DIN-rail clip onto the panel. Orient the socket so pin 1 is identifiable (usually marked on the base).
2. Wire the socket terminals: Sockets have screw terminals or push-in connectors corresponding to each pin. Connect your control power, input signals, and load per the relay’s wiring diagram.
3. Set timing parameters: If the relay has adjustable timing (potentiometer or DIP switches), set the desired delay before plugging in.
4. Plug in the relay: Align the relay pins with the socket and press firmly until fully seated. The relay should be snug and level.

Advantages and Disadvantages

8-pin socket relays offer easy replacement without disturbing wiring—pull the old relay, plug in the new one. This speeds maintenance. However, they’re bulkier than DIN rail types, the socket adds cost, and pin contact resistance can rise over time in high-vibration or dirty environments.

Wiring by Relay Type: 11-Pin Socket Installation

11-pin socket relays provide more terminals, typically supporting DPDT (two changeover contacts) or additional control functions. They follow the same plug-in socket concept as 8-pin but accommodate more complex timing and switching requirements.

Pin Numbering

11-pin sockets use a circular base with pins arranged around the perimeter, usually numbered 1 through 11 clockwise when viewed from the bottom (socket side). As with 8-pin relays, the specific pin-to-function mapping varies by manufacturer.

Common 11-Pin DPDT Configuration

A typical DPDT time delay relay with 11 pins might allocate:

• Pins 2 & 10: Coil supply (A1/A2)
• Pins 1, 3, 4: First contact set (COM, NC, NO)
• Pins 9, 11, 6: Second contact set (COM, NC, NO)
• Remaining pins: Control inputs, auxiliary functions, or unused

Verify your relay’s exact pinout before wiring—manufacturer datasheets provide clear socket terminal diagrams.

Installation Notes

The installation process mirrors 8-pin socket mounting: secure the base, wire the terminals per the diagram, set timing, and plug in the relay. The added pins increase wiring density, so label wires clearly and observe proper wire management to avoid shorts.

11-pin relays handle applications needing two independent timed outputs or redundant contacts for safety circuits. Industrial motor control and process automation often use 11-pin timers for their versatility.

Wiring by Relay Type: DIN Rail Relay Installation

DIN rail timers represent the modern standard for industrial control panels. They clip directly onto 35mm DIN rail, offering compact installation, clear terminal labeling, and standardized IEC terminal designations.

Terminal Identification on DIN Rail Relays

DIN rail timers print terminal labels directly on the relay body, usually on the bottom edge. You’ll see:

• A1, A2: Power supply terminals
• B1 (if present): Control input terminal
• 15, 16, 18: Output contact terminals (COM, NC, NO)
• 25, 26, 28: Second output set on DPDT models

Terminal Types

DIN rail relays use either:

• Screw terminals: Spring-loaded or screw-clamp, accepting wire sizes from 24 AWG to 12 AWG typically
• Spring-cage (push-in) terminals: Tool-free insertion for solid or ferrule-terminated wire

Check the relay’s specification for exact wire gauge range (usually marked on the terminal block). Multifunction timers commonly specify #14–18 AWG with 0.8 N⋅m torque for screw terminals, or 0.75–2.5 mm² for spring-cage terminals.

ຂັ້ນຕອນການຕິດຕັ້ງ

1. Mount on DIN rail: Engage the top hook onto the rail edge, then snap the bottom into place. The relay should sit flush and secure.
2. Strip wires to proper length: For screw terminals, strip 7–8 mm. For spring-cage terminals, strip 10–12 mm and use ferrules on stranded wire.
3. Wire A1 and A2 first: Connect your control power supply. Observe polarity for DC relays (A1 = +, A2 = −).
4. Wire control input (B1) if required: Connect your timing trigger signal, referencing the function diagram to confirm B1 is needed for your selected timing mode.
5. Wire output contacts: Connect your load circuit through COM (15) to either NO (18) or NC (16) per your application requirements.
6. Select timing function: Many DIN rail timers have a front rotary selector or DIP switches to choose timing mode (on-delay, off-delay, interval, etc.). Set this before energizing.
7. Set time range and delay: Adjust the time range switch and timing potentiometer to your required delay. Most relays offer multiple ranges (0.1–10 sec, 1–100 sec, 1–10 min, etc.).

Wire Management

DIN rail installations allow tight wire routing. Use wire duct or bundling to keep control wiring organized. For high-density panels, allocate sufficient terminal spacing—DIN rail timers are typically 17.5mm to 22.5mm wide, which determines how many relays fit in a given panel width.

Advantage: DIN rail mounting is faster than socket-base installation and produces cleaner, more maintainable panels. Disadvantage: replacing a failed relay requires disconnecting and reconnecting all wires, whereas socket relays just plug out.

Application Wiring Diagrams: Common Use Cases

Now that you understand terminal functions and relay types, let’s look at complete wiring diagrams for real-world applications. These examples show how power, control, and load circuits integrate.

HVAC Compressor Short-Cycle Protection (Off-Delay)

This is the single most common time delay relay application. Air conditioning and refrigeration compressors require a minimum off-time between cycles (typically 3–5 minutes) to allow refrigerant pressure to equalize and prevent hot restart damage.

Circuit Operation:

1. Thermostat calls for cooling → compressor contactor energizes → compressor runs
2. Thermostat satisfies and opens → time delay relay starts timing
3. Timer prevents compressor from restarting until delay expires (enforced off-time)

Wiring (Off-Delay Function):

• ການສະຫນອງພະລັງງານ: 24VAC from control transformer to timer A1/A2
• Thermostat: Wired in series with timer A1 (on single-function off-delay relays) or connected to control input B1 (on multifunction relays)
• Timer output: COM (15) to contactor coil, NO (18) to common return
• ຜົນໄດ້ຮັບ: Contactor energizes only when thermostat calls AND delay has expired since last shutdown

Variant: Some HVAC delay modules are specifically designed as delay-on-break types, which de-energize the compressor immediately when the thermostat opens, then enforce a minimum off-period before allowing the next start. Wire per the manufacturer’s diagram, typically inserting the module in series with the contactor coil circuit.

Motor Sequential Starting (On-Delay)

Industrial systems with multiple motors use time delay relays to stagger motor starts, preventing simultaneous inrush current that would trip upstream breakers or cause voltage sag.

Application Example: Three pump motors, 5-second delay between each start.

ສາຍໄຟ:

• Control power: 120VAC or 24VDC to all three timers’ A1/A2 terminals
• Master start contact: Pushbutton or PLC output wired to Timer 1’s control input (B1) or A1 depending on relay type
• Timer 1: On-delay function, 0-second delay. Output (15–18) energizes Motor 1 starter coil immediately.
• Timer 2: Timer 1’s auxiliary NO contact triggers Timer 2’s control input (B1). Timer 2 set for 5-second on-delay. Output (15–18) energizes Motor 2 starter coil after 5 seconds.
• Timer 3: Timer 2’s auxiliary NO contact triggers Timer 3’s control input. Timer 3 set for 5-second on-delay. Output (15–18) energizes Motor 3 starter coil 10 seconds after start command.

ຜົນໄດ້ຮັບ: Pressing the start button energizes Motor 1 immediately, Motor 2 after 5 seconds, Motor 3 after 10 seconds total. This staggers the inrush current draw.

Stop sequence: A stop button de-energizes the master control circuit, shutting down all motors immediately (or in reverse sequence if you use off-delay relays in the stop circuit).

Lighting Control with Auto-Off (On-Delay or Interval)

Stairwell lighting, parking garage lights, and restroom lighting often use time delay relays for automatic shutoff after a preset time, triggered by a pushbutton or occupancy sensor.

Circuit Operation (Interval Timer Function):

1. Person presses wall-mounted pushbutton
2. Timer receives start pulse at B1 input
3. Timer output energizes lighting contactor immediately
4. After set delay (e.g., 5 minutes), timer output de-energizes contactor
5. Lights turn off automatically

ສາຍໄຟ:

• ການສະຫນອງພະລັງງານ: 120VAC or 24VAC to timer A1/A2
• Pushbutton: Momentary-contact pushbutton wired from B1 to A2 (or common)
• Timer output: COM (15) to NO (18) through lighting contactor coil
• Lighting load: Lighting circuits switched by contactor main contacts

Function setting: Interval (one-shot) or on-delay with automatic reset. Set time delay to desired lighting run-on period (2–10 minutes typical).

Advanced staircase timer relays offer early-warning dimming (lights dim to 50% in the final 30 seconds before shutoff) and extend-on-demand (pressing the button during the delay resets the timer for another full cycle).

Fan Run-On Control (Off-Delay)

HVAC air handlers and equipment cooling fans often need to continue running for a period after the main equipment shuts down. This is called fan run-on or fan delay-off.

ຄໍາຮ້ອງສະຫມັກ: Furnace blower continues running 60–120 seconds after burner shuts off, to extract residual heat.

Wiring (Off-Delay Timer):

• ການສະຫນອງພະລັງງານ: 24VAC or 120VAC to timer A1/A2 in parallel with the main equipment control (furnace sequencer, compressor contactor, etc.)
• Timer output: COM (15) to NO (18) through blower motor contactor or relay
• ການດໍາເນີນງານ: When main equipment energizes, timer energizes and output contacts close immediately, starting the fan. When main equipment de-energizes, timer begins delay, keeping fan running for the set time (60–120 seconds), then timer output drops and fan stops.

This prevents hot-surface damage in furnaces and improves cooling efficiency in air conditioning systems by extracting residual heat/cold from the evaporator coil.

Wire Sizing, Fusing, and Protection Requirements

Proper wire sizing ensures voltage drop stays within acceptable limits and conductors don’t overheat. Time delay relay circuits typically fall under NEC Article 725 (Class 1 or Class 2 control circuits) or Article 430 Part VI for motor control circuits.

Control Circuit Wire Sizing

For timer coil supply (A1/A2) and control input circuits (B1), typical practice:

• Minimum wire size: 18 AWG for most control circuits, though NEC permits 16 AWG minimum for Class 1 circuits over 30V
• ແນະນຳ: 16 AWG or 14 AWG for reliability and mechanical strength in panel wiring
• Check device ratings: Time relay terminal blocks typically accept 14–18 AWG; DIN rail timers specify maximum wire size (often 12 AWG)

Control transformer secondaries (24VAC) and low-voltage DC power supplies should be fused or circuit-breaker protected per NEC 725.43. A 2A to 5A fuse typically protects a control circuit serving multiple timers and contactors.

Load Circuit Wire Sizing

For wiring between timer output contacts (15–18) and the controlled load:

• Direct resistive loads: Wire must handle full load current. Use NEC Table 310.16 (formerly 310.15) to select conductor ampacity.
• Contactor coil loads: Contactor coils draw 0.2A to 1A typically. 16 AWG or 14 AWG wire is standard.
• Motor circuits: If controlling a motor starter coil, wire per Article 430. If switching motor directly (unusual), conductor must handle motor full-load current plus 125% per NEC 430.22.

ການປົກປ້ອງກະແສໄຟຟ້າເກີນ

Time delay relay output contacts have maximum breaking capacity (typically 5A to 10A). Provide circuit protection (fuse or breaker) rated at or below the relay’s contact rating. If the downstream load draws more than the relay can interrupt, a short circuit could weld the relay contacts closed.

For inductive loads like motor contactor coils, consider using fast-acting fuses to protect relay contacts from inrush and fault currents.

ການ​ເຊື່ອມ​ຕໍ່​ພື້ນ​ຖານ​ແລະ​ການ​ຜູກ​ມັດ​

All control panels and metal enclosures must be grounded per NEC Article 250. Time delay relays mounted on DIN rail within metal panels are automatically bonded through the rail mounting (if rail is grounded). For plastic enclosures or isolated mounting, ensure the relay’s ground terminal (if provided) connects to the equipment grounding system.

ການພິຈາລະນາຄວາມປອດໄພແລະການປະຕິບັດຕາມລະຫັດ

Time delay relay installations must comply with electrical codes (NEC in the US, CE/IEC in international markets) and follow basic electrical safety practices.

Working on De-Energized Circuits

Always de-energize circuits before working on time delay relay wiring. Control circuits can be lethal—120VAC and 240VAC control circuits carry the same hazard as power circuits. Even 24VAC circuits can cause injury in wet environments or if arcing occurs.

Follow lockout/tagout (LOTO) procedures in industrial settings. Verify circuits are de-energized with a multimeter or voltage tester before touching terminals.

Enclosure and Environmental Requirements

Time delay relays must be installed in appropriate enclosures rated for the environment:

• ອຸດສາຫະກໍາຄວບຄຸມຫມູ່ຄະນະ: NEMA 12 or IP54 minimum for indoor locations
• ການຕິດຕັ້ງນອກ: NEMA 4/4X or IP65/IP66 weatherproof enclosures
• ສະຖານທີ່ອັນຕະລາຍ: Explosion-proof or intrinsically safe enclosures per NEC Article 500

Check the relay’s operating temperature range. Most timers are rated for 0°C to 50°C ambient, though some industrial models handle −25°C to 70°C. HVAC equipment rooms can exceed 50°C near compressors; use high-temp-rated relays or locate the timer remotely.

ການປະຕິບັດຕາມມາດຕະຖານ

Industrial time delay relays should meet IEC 61812-1 (international product standard for time relays) and carry UL/cUL listing or CE marking:

• IEC 61812-1: Defines timing accuracy, contact ratings, and safety requirements
• UL 508: Listing for industrial control equipment used in North America
• ເຄື່ອງໝາຍ CE: Indicates compliance with EU Low Voltage Directive and EMC Directive

Using listed components helps satisfy authority having jurisdiction (AHJ) requirements and may be mandatory for certain applications (UL-listed panels, CE-marked equipment exports).

Troubleshooting Common Wiring Problems

When a time delay relay doesn’t work as expected, the problem usually traces to one of these wiring issues.

Relay Doesn’t Energize (No Timing, No Output)

• Check A1/A2 voltage: Measure voltage across power terminals with the relay installed. Should match rated voltage (24VDC, 120VAC, etc.). If voltage is present but relay doesn’t energize, wrong voltage type (AC vs DC) or failed relay.
• Check polarity on DC relays: Swap A1 and A2 connections if using DC voltage. Some solid-state relays are polarity-sensitive.
• Blown fuse in control circuit: Check upstream fuses protecting the control transformer or DC power supply.
• ການເຊື່ອມຕໍ່ຢູ່ປາຍຍອດວ່າງ: Tighten all screw terminals per specified torque (typically 0.6–0.8 N⋅m). Loose power terminals prevent operation.

Relay Energizes But Doesn’t Time (Output Activates Immediately or Not at All)

• Wrong timing function selected: Multifunction relays have rotary selectors or DIP switches. Verify the selected function matches your application (on-delay, off-delay, interval, etc.).
• Control input not wired or not activated: Functions requiring external start (B1 input) won’t time without the trigger signal. Check B1 connection and measure voltage between B1 and reference terminal.
• Time delay set to zero or minimum: Rotate timing potentiometer or adjust digital setting to the desired delay value. Some relays ship with minimum delay.
• Time range incorrect: Relays with multiple time ranges (0.1–10 sec, 1–100 sec, etc.) need the range selector set correctly. Wrong range makes timing appear too fast or too slow.

Output Contacts Don’t Switch Load

• Check contact wiring: Verify load is wired through COM (15) to NO (18) or NC (16) per function. Measure continuity across contacts with relay de-energized (NC should show continuity, NO should be open).
• Exceeded contact rating: If load current exceeds relay contact rating, contacts may have welded closed or burned open. Check for visible contact damage.
• Wiring to wrong contact: On DPDT relays, ensure you’re using the correct contact set (15-16-18 vs 25-26-28). Verify terminal numbers against datasheet.
• Load requires suppression: Inductive loads without suppression can damage contacts or cause malfunction. Add RC snubber or flyback diode.

Relay Times Incorrectly (Too Fast, Too Slow, or Erratic)

• Voltage sag or noise: Low or fluctuating A1/A2 voltage affects timing accuracy. Measure voltage under load; should be within ±10% of rated value. Add control circuit filtering if electrical noise is present (contactors and motors nearby).
• Timing adjustment incorrect: Recalibrate timing dial or digital setting. Some analog relays drift over time and need re-adjustment.
• ອຸນຫະພູມສູງສຸດ: Operating outside rated temperature range (typically 0°C to 50°C) affects timing accuracy and relay lifespan. Relocate relay or upgrade to high-temp model.

Intermittent Operation or Nuisance Tripping

• Vibration loosening terminals: In high-vibration environments, screw terminals work loose over time. Use spring-cage terminals or apply thread-locking compound (non-conductive type) to terminal screws.
• EMI/RFI interference: Solid-state timers are sensitive to electrical noise from VFDs, welders, or motors. Route control wiring away from power conductors. Use shielded cable if necessary. Keep timer leads short.
• Contact bounce or chattering: Switching highly inductive loads without suppression causes contact chatter. Add appropriate suppression per manufacturer recommendations.

Conclusion: Wiring Best Practices Checklist

Correct time delay relay wiring comes down to systematic execution and attention to detail. Before calling any installation complete, run through this checklist:

Pre-Installation

• Verify relay voltage rating matches available control power (24VDC, 120VAC, etc.)
• Confirm relay contact rating exceeds load current for your specific load type (resistive, inductive, capacitive)
• Review application wiring diagram and identify all terminal connections
• Gather correct wire gauge per NEC requirements (typically 14–18 AWG for control circuits)

Power Supply (A1/A2)

• Connect A1/A2 to properly rated control power source
• Observe polarity on DC relays (A1 = +, A2 = −)
• Protect control circuit with appropriate fuse or circuit breaker (1A–5A typical)
• Measure voltage at terminals after wiring; should be within ±10% of rated value

Control Input (B1) If Applicable

• Verify if your selected timing function requires control input
• Wire initiating device (pushbutton, contact, sensor) to B1 and reference terminal
• Test control input operation before connecting load

Output Contacts (15, 16, 18)

• Wire load through COM (15) to correct contact (NO or NC) per application
• For high-current loads, use timer to control contactor coil, not load directly
• Add suppression (RC snubber, MOV, or flyback diode) for inductive loads
• Protect output circuit with fuse/breaker rated at or below contact rating

Configuration and Testing

• Set timing function selector (on-delay, off-delay, interval, etc.)
• Set time range and delay value to required settings
• Tighten all terminal screws to specified torque (0.6–0.8 N⋅m typical)
• Label all wiring clearly for future maintenance
• Energize circuit and verify correct timing operation before putting into service
• Document settings and wiring diagram for maintenance records

ຄວາມປອດໄພແລະການປະຕິບັດຕາມ

• De-energize and lockout circuit before working
• Use UL/cUL or IEC 61812-1 compliant relays
• Install in appropriate enclosure (NEMA/IP rating) for environment
• Follow NEC Article 725 for control circuit wiring
• Ground metal enclosures and panels per NEC Article 250

Time delay relays are simple, reliable control devices—when wired correctly. Following the terminal identification logic (A1/A2 for power, B1 for control, 15/16/18 for output) and matching the wiring to your specific timing function ensures the relay performs exactly as intended. Whether protecting an HVAC compressor from short-cycling, sequencing industrial motor starts, or automating lighting control, proper wiring delivers years of trouble-free operation.