Motor Overload Protection Setup for Roll Forming Machines (Thermal & Electronic Relay Guide)

Motor Overload Protection Setup

Protecting AC & Servo Motors in Roll Forming Machines

Motor overload protection is one of the most misunderstood and incorrectly set elements in roll forming electrical systems.

Improper overload setup causes:

• Nuisance tripping during production

• Motors running without protection

• Overheating and insulation failure

• Hidden phase loss damage

• Bearing failure

• Premature motor burnout

In roll forming environments — especially high-speed roofing and structural lines — motors operate under:

• Continuous duty

• Cyclic load changes

• High inertia acceleration

• Elevated cabinet temperatures

Overload protection must be engineered — not guessed.

This guide explains how to correctly select, wire, and set motor overload protection for roll forming machines.

1) What Is Motor Overload Protection?

Overload protection protects the motor from:

• Sustained overcurrent

• Thermal overload

• Phase imbalance

• Mechanical jam conditions

It does NOT protect against:

• Short circuit (handled by MCCB or fuse)

• Ground fault (handled by protective devices)

Overload devices protect the motor windings from overheating.

2) Types of Overload Protection Used in Roll Forming Machines

1) Thermal Overload Relay (Bimetal Type)

• Installed after contactor

• Adjustable current dial

• Trips when sustained current exceeds setting

Common in older relay-based systems.

2) Electronic Overload Relay

• More accurate

• Adjustable trip curve

• Phase loss detection

• Communication capability

Recommended for modern roll forming lines.

3) VFD Integrated Motor Protection

• Uses internal current monitoring

• Requires correct motor parameters

• Must be configured properly

Often used on main roll forming drives.

3) Where Overload Is Installed (Word-Based Flow)

3-Phase Supply → MCCB → Contactor → Overload Relay → Motor

Control Circuit:

Overload NC Contact → In Series With Contactor Coil

If overload trips:

Contactor drops → Motor stops.

4) Reading Motor Nameplate Data

Before setting overload, identify:

• Rated voltage

• Rated full-load current (FLA)

• Frequency

• Power (kW or HP)

• Service factor

• Insulation class

Overload setting must match motor full-load current.

Never guess based on motor size alone.

5) Setting Thermal Overload Relay

Basic rule:

Set overload dial to motor FLA (from nameplate).

Example:

Motor rated current = 18.5 A
Overload dial = 18–19 A

Do not arbitrarily increase setting to stop nuisance trips.

If nuisance trips occur:

Investigate cause before adjusting.

6) Service Factor Consideration

If motor has service factor (e.g., 1.15):

Overload may be set up to:

FLA × Service Factor

Example:

18.5 A × 1.15 = 21.3 A maximum

Only if allowed by motor manufacturer.

Do not exceed safe limits.

7) Trip Class Selection

Overload relays have trip classes:

• Class 10
• Class 20
• Class 30

• Class 10 → Fast trip
• Class 20 → Medium
• Class 30 → Slow (for high inertia loads)

Roll forming main drives typically use Class 10 or 20.

Structural heavy lines may require Class 20.

Too slow trip class risks motor damage.

8) Overload in VFD Systems

When motor controlled by VFD:

Motor protection often handled internally.

Required settings:

• Motor rated current

• Motor rated speed

• Thermal protection enabled

• Electronic overload function active

Disable thermal protection only for testing — never permanently.

9) Phase Loss Protection

Phase loss can:

• Cause severe overheating

• Reduce torque

• Damage windings

Electronic overload relays detect phase imbalance.

Thermal overloads often do not detect partial phase loss effectively.

Modern systems should include phase monitoring.

10) Hydraulic Pump Motor Protection

Hydraulic pumps in roll forming lines:

• Run continuously

• Experience temperature buildup

• May stall during pressure spike

Overload must be properly set.

Frequent hydraulic overload trips indicate:

• Mechanical jam

• Pressure relief malfunction

• Motor undersizing

Do not bypass overload to “keep running.”

11) Common Causes of Overload Trips in Roll Forming

1. Material jam

2. Bearing failure

3. Misalignment

4. Over-tight chain drive

5. Incorrect voltage supply

6. Loose terminal connection

7. Poor ventilation

8. Undersized motor

Electrical symptoms often reflect mechanical problems.

12) Control Circuit Integration

Word-Based Control:

24VDC → E-STOP OK → START → Overload NC → Contactor Coil

Overload trip breaks control circuit.

PLC may also monitor overload auxiliary contact for diagnostics.

Modern systems display overload fault on HMI.

13) Temperature Effects Inside Cabinet

Roll forming cabinets may reach:

40–50°C internal temperature.

Thermal overload relays calibrated at 20–30°C.

Higher temperature reduces trip margin.

Consider cabinet ventilation when setting overload.

14) Testing Overload Protection

Testing procedure:

1. Verify overload setting

2. Check current draw under full load

3. Confirm phase balance

4. Simulate overload condition carefully (if safe)

5. Confirm control circuit drop-out

6. Confirm PLC fault indication

Do not test by forcing mechanical jam unless controlled.

15) Coordination with Short-Circuit Protection

Overload relay protects motor from sustained overload.

MCCB or fuse protects from short circuit.

Protection coordination must ensure:

Short circuit trips instantly
Overload trips under sustained current

Improper coordination may damage motor before breaker trips.

16) Main Drive vs Auxiliary Motors

Main roll forming motor:

• Continuous load

• High inertia

• Critical to production

Requires precise overload setting.

Auxiliary motors (stacker, decoiler):

• Intermittent load

• Lower inertia

May tolerate slightly different trip classes.

Each motor must be evaluated individually.

17) Export Considerations

When exporting roll forming machines:

• Confirm motor voltage matches country supply

• Confirm overload relay rating matches frequency (50/60Hz)

• Provide overload setting documentation

• Label motor FLA clearly in panel

• Include spare overload unit

Incorrect overload setting after export causes nuisance trips.

18) Buyer Strategy (30%)

Before purchasing a roll forming machine, verify:

1. Overload relay installed for every motor

2. Overload set to motor FLA

3. Trip class appropriate for load

4. Phase loss protection included

5. VFD motor protection enabled

6. Hydraulic motor protection correctly set

7. Documentation includes motor current data

8. Current measured under production load

Red flag:

“Overload dial turned up to stop tripping.”

That hides mechanical or electrical problems.

6 Frequently Asked Questions

1) Should overload be set higher than motor FLA?

No, unless service factor allows and manufacturer approves.

2) Why does overload trip during startup?

Acceleration current too high or trip class too fast.

3) Can I disable overload to stop nuisance trips?

Never. Identify root cause instead.

4) Does VFD replace overload relay?

Often yes, if configured correctly.

5) Why does hydraulic motor overload frequently?

Possible pressure spike or mechanical issue.

6) What is most common overload mistake?

Setting relay above motor rated current.

Final Engineering Summary

Proper motor overload protection setup in roll forming machines requires:

• Accurate reading of motor nameplate data

• Correct trip class selection

• Proper current dial setting

• Phase loss consideration

• Control circuit integration

• VFD thermal protection configuration

• Testing under real production load

Incorrect overload setup causes:

• Motor damage

• Hidden overheating

• Production downtime

• Unsafe operation

In industrial roll forming production, overload protection is a critical safeguard — not a nuisance device to bypass.