How to Wire a Time Relay for a Motor Starter

The 3 AM Phone Call Every Plant Engineer Dreads

Picture this: Your facility’s main water pumps just tripped—again. It’s 3 AM, production is down, and your maintenance team is scrambling. After an hour of troubleshooting, you discover the culprit: three 50-HP motors trying to start simultaneously, creating a massive inrush current that’s overloading your electrical system. The voltage sag is so severe that your other equipment is dropping offline like dominoes.

This scenario plays out in industrial facilities every day, and the root cause is almost always the same: motors starting without coordinated timing control. When multiple motors fire up at once, the combined inrush current (typically 6-8 times the motor’s full-load current) can exceed your service entrance capacity, trigger nuisance trips on upstream breakers, or cause damaging voltage dips that ripple through your entire facility.

Why Standard Motor Starters Fall Short

Traditional direct-online (DOL) motor starters are designed to do one thing: close their contacts and energize the motor immediately when commanded. There’s no intelligence, no sequencing, and no delay. In single-motor applications, this works fine. But in facilities with multiple motors, conveyor systems, or equipment that requires staged startup sequences, DOL starters alone create three critical problems:

1. Electrical Demand Spikes: Simultaneous starts compound inrush currents, potentially exceeding your utility’s demand charges or tripping main breakers
2. Mechanical Shock: Conveyor belts, pump systems, and process equipment can suffer mechanical damage when all components engage instantly without ramp-up time
3. Process Disruption: Critical sequences (like purge fans before burners, or cooling pumps before compressors) require timed coordination that basic starters can’t provide

The conventional “solution”—manually staggering starts or using complex PLC programming—is either unreliable (human error) or expensive (engineering time and hardware costs).

جهاز VIOX Time Relay

The Aha! Moment: Time Relays as Your Startup Traffic Controller

This is where time relays transform your motor control strategy. Think of a time relay as a traffic light for your electrical system—it controls when power flows to your motor starter coil, not if it flows. By inserting a compact time relay between your control switch and the motor starter’s coil circuit, you gain precise, adjustable control over startup sequences without expensive PLCs or complicated programming.

Here’s the elegant simplicity: When your start button is pressed, the time relay begins its countdown (on-delay) or holds its contacts closed for a set duration (off-delay). Only after this precise interval does it complete the circuit to your motor starter coil, energizing the contactor and starting your motor. The result? Coordinated, sequential motor starts that eliminate inrush conflicts and protect your equipment.

النقطة الرئيسية: Your time relay doesn’t control the motor directly—it controls the motor starter’s coil circuit. This low-current control logic means you can use a compact relay with small contact ratings to command a large motor starter.

The Complete Step-by-Step Wiring Guide

Step 1: Match Your Relay Type to Your Application

Before you touch a single wire, you must identify whether you need an on-delay أو off-delay time relay—get this wrong and your motor will start at completely the wrong time.

مرحلات وقت التأخير على التأخير (also called delay-on-make or DORM relays):

• When to use: When you need a motor to start بعد a specific delay following a start command
• التطبيقات الشائعة: Sequential pump starts, delayed fan startups, conveyor staging
• كيفية عملها: When the relay coil is energized, it begins timing. After the preset delay expires, the output contacts close, energizing the motor starter coil

مرحلات وقت الإيقاف والتأخير (also called delay-on-break or DODB relays):

• When to use: When you need a motor to continue running for a period بعد the stop command
• التطبيقات الشائعة: Purge fans that must run after burners shut down, cooling pumps that continue after process equipment stops
• كيفية عملها: When the relay coil is de-energized, it begins timing. The output contacts remain closed (keeping the motor running) until the delay expires

Pro-Tip: In 80% of industrial sequencing applications, you’ll use on-delay relays. Off-delay relays are specialized for safety interlocks and cooling/purge requirements. If you’re simply trying to stagger multiple motor starts, start with on-delay.

Step 2: Verify Critical Electrical Ratings (The Spec Sheet Doesn’t Lie)

This is where most wiring failures originate—not in the physical connections, but in the specification stage. You must verify three critical ratings:

A. Control Circuit Voltage

Your time relay’s coil voltage must exactly match your motor starter’s control circuit voltage. Common voltages include:

• 24V DC (increasingly common in modern systems with PLC integration)
• 120V AC (North American standard for control circuits)
• 240V AC (used in some industrial and international applications)

Check your motor starter’s wiring diagram—the control circuit voltage is typically labeled on the schematic or on the starter’s coil itself. A mismatch here means instant relay failure or, at best, unreliable operation.

B. Contact Ratings (Load vs. Relay Capacity)

Your time relay’s output contacts must be rated to handle the motor starter’s coil current. Here’s the calculation:

1. Find your motor starter’s coil current rating (typically listed in milliamps or watts on the coil)
2. Add a 25% safety factor
3. Verify your time relay’s contact rating exceeds this value

مثال على ذلك: If your contactor coil draws 50mA at 120V AC, your time relay contacts should be rated for at least 65mA (50mA × 1.25). Most standard time relays have contacts rated for 5A or more at 120/240V AC, which provides plenty of headroom—but always verify.

النقطة الرئيسية: The most common specification error is confusing the relay’s coil voltage with its contact ratings. These are independent specs. Your relay coil might be 24V DC, but its contacts can still switch 240V AC loads—check both.

C. Timing Range

Ensure the relay’s adjustable time range covers your application needs. Common ranges:

• 0.1 to 10 seconds (fast sequencing)
• 1 to 60 seconds (general motor staging)
• 1 to 999 seconds (extended delays for cooling or purge cycles)

Step 3: Wire the Control Circuit (The Critical Connections)

Now we get to the actual wiring. This is where theory meets practice, and where proper technique prevents future failures.

Required Components:

• Time relay (verified specs from Step 2)
• Motor starter with control circuit terminals labeled
• Control power source (transformer or direct line voltage)
• Start/stop push buttons (or control switch)
• Overload relay contacts (typically built into motor starter)
• Wire sized per NEC Article 430 for control circuits (typically 14-18 AWG)

On-Delay Time Relay Wiring Sequence (most common configuration):

1. Establish Control Power:
   • Connect Line 1 (L1) of your control voltage source to one side of your start push button
   • This is your “hot” control leg
2. Wire the Start Button and Time Relay Coil:
   • Connect the normally-open (NO) start button output to one terminal of the time relay coil (often labeled A1)
   • Connect the other time relay coil terminal (often labeled A2) back to Line 2 (L2/Neutral) of your control voltage
   • Important: Wire your stop button (NC contact) and overload relay contacts (NC) in series on the L1 leg before the start button to create a complete safety chain
3. Connect Time Relay Output Contacts to Motor Starter Coil:
   • Identify the time relay’s timed output contacts (typically labeled as NO contacts: 15-18, 25-28, etc.)
   • Connect one side of these timed NO contacts to the same L1 control leg
   • Connect the other side of the timed NO contacts to one terminal of the motor starter coil (labeled A1 or similar)
   • Connect the other motor starter coil terminal (A2) back to L2
   • This is the critical path: When the time relay times out, it closes its NO contacts, completing the circuit to energize the motor starter coil
4. Add Holding Circuit (for maintained operation):
   • Connect an auxiliary NO contact from the motor starter (labeled 13-14 or similar) in parallel with the start button
   • This creates a “seal-in” circuit so the motor continues running after you release the start button

النقطة الرئيسية: The time relay sits between your start button and your motor starter coil—it’s a gatekeeper in the control logic, not the main power circuit. Never wire a time relay in series with the motor’s main power conductors.

Critical Installation Details

• Use ferrule terminals on stranded wire for vibration resistance
• Torque terminal screws to manufacturer specifications (typically 7-9 in-lbs for control terminals)
• Label all wires with wire markers identifying source and destination
• Keep control circuit wiring separated from high-voltage motor power cables to reduce electrical noise

Step 4: Set the Timing and Test the Sequence

With wiring complete, you must properly set and verify the timing function:

Timing Adjustment:

• Locate the time adjustment dial or digital setting (consult relay manual for your specific model)
• For initial startup sequencing, start with longer delays (10-15 seconds between motors)
• You can reduce the delay after observing actual inrush behavior

Testing Protocol (perform with motor disconnected or in test mode):

1. Coil Energization Test: Press the start button. You should hear/see the time relay energize (LED indicator or audible click)
2. Timing Verification: Use a stopwatch to verify the delay matches your setting. The motor starter should energize only after the preset time
3. Stop Function Test: Press stop button. Both time relay and motor starter should de-energize immediately (for on-delay relays)
4. Holding Circuit Test: After timed start, release start button. Motor should continue running via auxiliary contact seal-in

Pro-Tip: In multi-motor sequences, set staggered delays (Motor 1: 0 seconds, Motor 2: 8 seconds, Motor 3: 16 seconds). This creates a “rolling start” that dramatically reduces peak demand.

Real-World Application: Three-Pump Sequencing Solution

Let’s revisit our opening scenario with the tripping water pumps. Here’s how time relays solve this exact problem:

التكوين:

• Three 50-HP pumps, each with its own motor starter
• Single start button initiates full sequence
• Pump 1: Direct start (no delay)
• Pump 2: On-delay relay set to 10 seconds
• Pump 3: On-delay relay set to 20 seconds

النتيجة: Instead of 450A simultaneous inrush (3 motors × 150A each), you get three separate 150A peaks spread 10 seconds apart. Your electrical system handles this easily, voltage remains stable, and downstream equipment continues operating normally.

Cost-benefit: Three time relays ($150 total) versus a PLC-based solution ($2,000+) or accepting ongoing nuisance trips and potential equipment damage ($$$$).

Why Time Relays Are Your Most Cost-Effective Control Solution

الميزة	Value to You
Simple Installation	Mounts on DIN rail, standard control circuit wiring—no programming required
Adjustable Timing	Dial or digital setting allows on-site optimization without hardware changes
Compact Footprint	Fits in existing control panels without major modifications
High Reliability	Solid-state or electromechanical designs with 100,000+ operation cycles
Low Cost	$50-150 per relay versus thousands for PLC-based solutions

خلاصة القول: Time relays give you precise motor startup sequencing at a fraction of the cost and complexity of programmable controllers. For applications requiring simple delays or staging without complex logic, they’re the most reliable and economical solution available.

Common Wiring Mistakes to Avoid

Even experienced electricians make these errors:

1. Wiring the time relay in the motor power circuit: Time relays control the starter coil (low current), never the motor power (high current)
2. Mismatching coil voltages: A 24V relay coil won’t operate reliably on 120V, and vice versa
3. Inadequate wire sizing: Control circuits still require proper AWG sizing per NEC standards
4. Forgetting the holding circuit: Without auxiliary contact seal-in, the motor stops when you release the start button
5. Skipping the timing test: Always verify actual timing matches your setting before commissioning

Ready to Eliminate Startup Problems?

Proper time relay selection and wiring transforms chaotic motor startups into coordinated, reliable sequences. Whether you’re staging multiple pumps, protecting equipment with delayed starts, or implementing safety interlocks, time relays provide the timing intelligence your motor starters need.

Next Steps:

• Review your motor starter control schematics to identify timing opportunities
• Select time relays that match your control voltage and contact requirements
• Follow the wiring steps above for reliable, long-term operation

Need technical support? Major manufacturers like Eaton, ABB, Schneider Electric, and Phoenix Contact offer comprehensive time relay product lines with detailed wiring diagrams and application engineering support. Always consult the specific datasheet for your chosen relay model to verify terminal designations and ratings.

Your motor control system is only as reliable as its weakest link—make sure timing control isn’t yours.