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.
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.
Installed after contactor
Adjustable current dial
Trips when sustained current exceeds setting
Common in older relay-based systems.
More accurate
Adjustable trip curve
Phase loss detection
Communication capability
Recommended for modern roll forming lines.
Uses internal current monitoring
Requires correct motor parameters
Must be configured properly
Often used on main roll forming drives.
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.
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.
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.
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.
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.
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.
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.
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.”
Material jam
Bearing failure
Misalignment
Over-tight chain drive
Incorrect voltage supply
Loose terminal connection
Poor ventilation
Undersized motor
Electrical symptoms often reflect mechanical problems.
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.
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.
Testing procedure:
Verify overload setting
Check current draw under full load
Confirm phase balance
Simulate overload condition carefully (if safe)
Confirm control circuit drop-out
Confirm PLC fault indication
Do not test by forcing mechanical jam unless controlled.
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.
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.
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.
Before purchasing a roll forming machine, verify:
Overload relay installed for every motor
Overload set to motor FLA
Trip class appropriate for load
Phase loss protection included
VFD motor protection enabled
Hydraulic motor protection correctly set
Documentation includes motor current data
Current measured under production load
Red flag:
“Overload dial turned up to stop tripping.”
That hides mechanical or electrical problems.
No, unless service factor allows and manufacturer approves.
Acceleration current too high or trip class too fast.
Never. Identify root cause instead.
Often yes, if configured correctly.
Possible pressure spike or mechanical issue.
Setting relay above motor rated current.
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.
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