Motor starters, soft starters and variable speed drives (VSDs) keep pumps, fans, compressors and conveyors running day after day. Because they usually work quietly in the background, they’re easy to overlook until one fails. But most failures don’t come out of nowhere. Loose connections, blocked cooling, worn contacts and ageing components give warning signs long before they cause a breakdown.
A simple preventative maintenance routine catches those problems early. This checklist covers the key checks for motor control equipment, how often to carry them out, and how to keep critical motors running while maintenance takes place.
Download the printable version of this checklist to use on site and keep with your maintenance records. [Download link]
Safety first
All electrical maintenance must be carried out by competent people, in line with the Electricity at Work Regulations 1989 and your site’s safe systems of work. Before any hands-on work:
☐ Isolate the supply, lock off and tag out
☐ Prove dead using an approved voltage indicator
☐ Allow drive capacitors to discharge for the time stated by the manufacturer, then confirm the DC bus is dead
☐ Check for other sources of supply, such as control circuits fed from elsewhere or back-feeds
☐ Confirm the driven equipment can’t move unexpectedly
Some checks, such as thermal imaging and listening for abnormal noise, are carried out with equipment live and under load. These should only be done by suitably trained people using the right PPE.
1. Visual and environmental checks
Many problems are visible if you know what to look for.
☐ Enclosure is clean, undamaged and doors close and seal properly
☐ Door seals, gland plates and cable entries intact, maintaining the enclosure’s IP rating
☐ No signs of water ingress, condensation or corrosion
☐ Anti-condensation heaters (where fitted) working
☐ No dust, debris or stored materials blocking ventilation
☐ No discoloured terminals, scorched cables or burning smells
☐ Labels, circuit identification and warning signs present and legible
2. Thermal checks
Heat is one of the clearest indicators of developing faults.
☐ Carry out a thermographic survey under normal load to find hot spots at connections, contactors, fuses and overloads
☐ Compare phase temperatures; an imbalance can point to loose connections or supply issues
☐ Check panel and plant room temperatures are within the equipment’s rated limits
☐ Record findings so trends can be compared over time
3. Cooling system
Drives and soft starters depend on effective cooling.
☐ Clean or replace air filters
☐ Clean heatsinks and internal surfaces (using methods approved by the manufacturer)
☐ Check cooling fans run freely and quietly
☐ Replace fans at the interval recommended by the manufacturer
☐ Confirm panel extract fans and air conditioning units are working
4. Connections and wiring
Loose connections cause heat, arcing and nuisance tripping.
☐ Check power terminals are tight, using the manufacturer’s torque settings
☐ Inspect control wiring for damage, loose ferrules or chafing
☐ Check earth connections and bonding are secure
☐ Check cable screens on drive motor cables are correctly terminated
☐ Inspect busbars and links for discolouration or damage
5. Contactors, overloads and switchgear
Mechanical components wear with every operation.
☐ Inspect contactor contacts for pitting, burning or welding where accessible
☐ Check contactors operate cleanly without chatter or buzzing
☐ Confirm overload settings match the motor’s full load current
☐ Test overload and protection devices where practical
☐ Check isolators, fuses and circuit breakers for condition and correct ratings
6. Soft starter and drive checks
Electronic starters and drives need some extra attention.
☐ Review fault and alarm logs for recurring issues
☐ Check parameter settings haven’t been changed without record
☐ Back up drive and soft starter parameters and store a copy securely
☐ Check the bypass contactor on soft starters operates correctly
☐ Check DC bus capacitor condition and age; plan replacement in line with manufacturer guidance
☐ Check firmware version and any manufacturer notices
☐ Listen for unusual motor noise at different speeds on drive-controlled motors
7. Motor and load checks
The starter and the motor work as a system, so check both.
☐ Carry out insulation resistance testing on the motor and cable. Disconnect drives and soft starters first, as test voltages can damage their electronics
☐ Measure running current and compare with the rating plate and previous readings
☐ Check for excessive vibration, noise or bearing heat
☐ Check belts, couplings and the driven load for wear
8. Controls and safety functions
☐ Test emergency stops and interlocks
☐ Check start/stop controls, selector switches and indicator lamps
☐ Check float switches, pressure switches and sensors respond correctly
☐ Confirm remote control and BMS signals are working
9. Records and planning
☐ Record all readings, findings and actions taken
☐ Note any parts nearing end of life and plan replacements
☐ Keep a list of critical motors and their starter details for quick reference in a breakdown
☐ Review your contingency plan for critical equipment
How often should you carry out these checks?
The right frequency depends on how critical the equipment is, its operating environment and the manufacturer’s recommendations. As a typical starting point:
- Visual and environmental checks – Monthly
- Filter cleaning, fan checks, fault log review – Quarterly
- Thermographic survey – Annually, or more often for critical plant
- Connection torque checks, contactor inspection, protection testing -Annually
- Motor insulation resistance testing – Annually
- Fan and capacitor replacement – As recommended by the manufacturer
Dusty, hot, damp or heavily used installations will usually need more frequent attention.
Keep running while maintenance happens
The biggest barrier to maintenance is often downtime. Critical pumps, fans and production lines can’t always be switched off for long. Temporary motor control hire solves that problem. A hire starter, soft starter or VSD can run your motor while your own equipment is serviced, repaired or upgraded. And if maintenance uncovers a fault that needs parts or a replacement, a hire unit keeps you running until the permanent fix is in place.
It’s also worth building hire into your contingency plan. Knowing exactly what you’d need if a critical starter failed means a quick call rather than a scramble in an emergency.
Talk to our team about hire options to support your maintenance programme.
Written by Neil Parsons, Technical Director – With over 35 years in electrical engineering across various sectors, these articles are written by a specialist with hands-on experience in electrical design and commissioning, PLC and variable speed drive programming and installation.
Frequently Asked Questions
What is preventative maintenance for motor control equipment?
It’s a planned programme of inspections, tests and servicing designed to find and fix problems in starters, soft starters and drives before they cause a breakdown.
How often should motor control equipment be maintained?
Many sites carry out visual checks monthly, cooling and fault log checks quarterly, and full inspections and testing annually. Critical equipment and harsh environments usually need more frequent checks.
Why is thermal imaging useful?
A thermographic survey shows hot spots caused by loose connections, overloaded components or failing parts while equipment is running, often before any other symptoms appear.
Can I insulation test a motor connected to a drive?
No. Disconnect the drive or soft starter before insulation resistance testing, as the test voltage can damage electronic components.
Why should I back up drive parameters?
If a drive fails or is replaced, a parameter backup lets it be set up quickly and correctly, reducing downtime.
Who should carry out motor control maintenance?
Only competent, suitably trained people should work on electrical equipment, following safe isolation procedures and the Electricity at Work Regulations 1989.
How can I avoid downtime during maintenance?
Hiring a temporary starter, soft starter or drive lets critical motors keep running while your own equipment is serviced or repaired.
