1. Scope & Purpose
This manual provides a detailed, practice-oriented step-by-step plan for the maintenance of industrial switches (contactors) and relays. The primary purpose of this maintenance is to ensure continuous, safe and efficient operation of electrical control systems. Through periodic inspection of contacts, thorough cleaning of switching chambers (arc chutes) and accurate coil resistance testing, we minimize the risk of unexpected failures, extend the life of components and prevent costly unplanned production downtime.
This preventative maintenance is critical in environments where these components are subject to high switching frequencies, significant electrical loads or exposure to aggressive environmental factors such as dust, moisture or corrosive fumes. Correctly carried out maintenance, in accordance with the procedures described here, is a fundamental pillar for the operational reliability of your machines and installations, in accordance with NEN and EN guidelines.
Negligence in this maintenance can lead to a range of serious problems, including contact erosion, overheating, short circuits, fire hazards and ultimately catastrophic machine failure, posing both financial and safety risks.
2. Safety measures
WARNING: Any intervention on electrical installations requires strict compliance with the LOTO (Lockout/Tagout) procedure. Ensure that the entire power supply to the circuit being worked on is isolated and interlocked. Check the absence of voltage on all poles with a suitable and calibrated voltage measuring device (e.g. a multimeter set to AC/DC voltage, range CAT III 600V or higher) before making any physical contact with the components. Failure to follow this procedure may result in electrocution, serious injury or death.
Personal Protective Equipment (PPE) is mandatory and includes at least:Residual Potential Energy:
- Safety glasses: Compliant with EN 166, to protect against sparks and projectiles.
- Insulating gloves: Compliant with EN 60903, class 00 (up to 500V) or class 0 (up to 1000V), depending on the expected voltages. Check for damage before each use.
- Flame-retardant work clothing: In accordance with EN ISO 11612, as protection against arcs and heat.
- Safety shoes: Compliant with EN ISO 20345 (S1P or S3), with anti-static properties and toe protection.
- Capacitors: Large capacitors in the control or power circuits can retain a dangerous electrical charge even after the power has been turned off. Ensure adequate discharge time and verify the discharged condition with a multimeter.
- Mechanical energy: Some switches contain spring mechanisms that may be live. Be careful when disassembling.
3. Required Tools & Materials
| Tools / Materials | Specification | Quantity | Comments |
|---|---|---|---|
| Multimeter | Digital, True RMS, CAT III 600V (or higher), with resistance measuring range up to at least 2 kΩ | 1 | Calibrated, with intact test leads. |
| Torque wrench | Range 0.5-5 Nm (for control terminals) and 3-10 Nm (for main circuit terminals), 1/4" and 3/8" mounting | 1 per range | Calibrated, with suitable bits (Torx, Phillips, flat). |
| Screwdriver set | Insulated (VDE-certified EN 60900), various sizes (flat 3.0-6.5mm, Phillips PH1, PH2, Pozidriv PZ1, PZ2) | 1 set | Check insulation for damage. |
| Contact cleaner | Non-conductive, quick-drying, residue-free (e.g. isopropyl alcohol based) | 1-2 spray cans | Only use on de-energized parts. |
| Fine sandpaper / sanding block | Grit P400 to P600, or special contact cleaning strips | Single sheets/strips | For light oxidation only; see procedure. |
| Lint-free cloths/cleaning rags | Microfiber or cotton | Various | For thorough cleaning and drying. |
| Non-abrasive wire brush | Nylon or brass, small head | 1 | For removing stubborn carbon deposits in the switching chamber. |
| Feeler gauge set | Range 0.05 - 1.0 mm, in 0.05 mm increments | 1 set | For checking contact openings. |
| Cable ties | Various sizes, UV-resistant when outdoors | Package | For organizing wiring after installation. |
| Electrical insulation tape | Black, PVC, conforming to EN 60454-3-1 | 1 roll | For insulating minor damage to wire insulation (temporary solution). |
| Highlighters | Permanent, fine point, various colours | Various colours | For wire identification. |
| Camera (phone/tablet) | With good resolution | 1 | For documentation of the original situation. |
4. Pre-Maintenance Inspection Checklist
Perform these visual and operational checks before beginning disassembly. Note all deviations. This helps identify the cause of any problems and plan necessary spare parts.
| Item | Check | Acceptance criteria | Rejection criteria / Comments |
|---|---|---|---|
| Housing | Visual inspection for physical damage, cracks, deformation, discoloration. | No visible damage, no signs of overheating (discoloration, blistering). | Cracks, melt marks, severe discoloration (brown/black) indicate overheating or mechanical stress. |
| Terminals & Wiring | Visual inspection for loose or corroded wires, frayed insulation, signs of overheating. | All connections secure, wires intact and clean, insulation undamaged, no blue-black discoloration of terminals. | Loose terminals, corrosion, bare wires, or discoloration of wire insulation or terminals require immediate attention and repair/replacement. |
| Environmental pollution | Presence of dust, dirt, metal particles, oil, moisture or chemical residues on and around the switch/relay. | Switch/relay is clean and dry. | Thick layers of dust, moisture or conductive particles can lead to flashover or poor heat dissipation. |
| Operational Sound | Listen for abnormal sounds during a short function test (if safely possible). | Normal operating sounds: a clear, rapid "click" when the contactor is turned on; no persistent humming (with AC coils). | Humming noises at AC contactors indicate dirty pole surfaces or mechanical wear. A slow "click" may indicate low control voltage or coil problems. |
| Smell | Observe the odor around the component. | No unusual odors. | A burnt, 'electric' or sour smell indicates overheating, insulation faults or unwanted chemical reactions. |
| Manual Operation | If equipped, operate the manual control mechanism for smoothness. | Mechanism moves freely, without stuttering or excessive resistance. The contacts make and break clear. | Stretches or roughness indicate mechanical contamination or wear. |
5. Step-by-Step Procedure
5.1. Preparation & Safety
- SAFETY: Implement the LOTO procedure for the circuit in question. Ensure complete insulation of all phases and the neutral conductor. Lock the disconnector or circuit breaker in the "OFF" position and hang the warning label.
- Check the absence of voltage at the input and output terminals of the switch/relay with a calibrated multimeter. Measure both phase-neutral, phase-earth and phase-phase voltages (if applicable).
- Wear the mandatory PPE at all times: safety glasses, insulating gloves and flame-retardant clothing.
- Document the original wiring by taking clear photos with a camera and/or marking each wire with marker pens or numbered ferrule tags. This prevents wiring errors during reassembly.
5.2. Disassembly & Initial Inspection
- Disconnect the wires from the terminals. Use a suitable screwdriver and note the torque values. For control current terminals (up to 2.5 mm²) these are usually 1.5 Nm to 2.0 Nm. For main circuit terminals (up to 6 mm²) often 2.5 Nm to 3.5 Nm. Keep all screws and small parts in a container.
- Carefully remove the switch or relay from its mounting position. Please refer to the OEM documentation for exact disassembly instructions.
- Open the housing, if possible and necessary, to gain access to the contacts and the switching chamber. Use the correct tools to prevent damage.
- Inspect the general condition of the internal components. Look for loose parts, broken springs, or excessive dust buildup or corrosion.
5.3. Contact Inspection & Cleaning
- Carefully inspect the fixed and moving main contacts and auxiliary contacts for the following aspects:
- Pitting: Small craters or pits on the contact surface caused by the electric arc when switching on and off. Slight pitting is acceptable.
- Erosion: Material loss and uneven wear, which can reduce contact pressure. Severe erosion requires contact replacement.
- Carbon deposits: Black, sooty deposits due to arcing. This is conductive and can cause flashover.
- Discoloration: Excessive dark discoloration indicates overheating.
- Cleaning of contacts:
- For light oxidation or carbon deposits: Gently clean the contact surfaces with a lint-free cloth moistened with contact cleaner. Make sure there is absolutely no residue left behind. Let dry completely.
- For heavier deposits or light pitting: Use very fine sandpaper (P400-P600) or special contact cleaning strips. Sand with light, even pressure, preferably in one direction, parallel to the flow direction. This minimizes the removal of contact material and preserves the original shape. Do not use files, wire brushes or coarse sandpaper; this damages the surface and significantly shortens its lifespan.
- After sanding: Remove all sanding residue thoroughly with contact cleaner and a clean, lint-free cloth.
- Check the spring pressure of the contacts. The contacts must be pressed together with sufficient force to ensure low contact resistance. Weak spring pressure leads to overheating.
- Use a feeler gauge to check the contact gap, if specified by the manufacturer. Deviations may indicate wear of the mechanism or contact material.
5.4. Switchroom cleaning (Arc Chute)
- Remove the switch chamber, if it can be dismantled (consult the manufacturer's manual). The switching chamber consists of metal slats that divide the electric arc created when the contacts open into smaller, easily extinguished segments.
- Inspect the switch chamber for carbon deposits, soot, and physical damage (cracks, melting spots, missing or bent fins). Severe damage requires replacement of the switch chamber or the entire switch.
- Clean the slats thoroughly with a dry, lint-free cloth. For stubborn carbon deposits, you can use a non-abrasive wire brush (nylon or brass) to gently remove them. Do not use liquids unless the manufacturer explicitly allows this and it concerns a specifically suitable, non-conductive cleaner.
- Ensure that all carbon residue and particles are completely removed as these can be conductive and cause arc flashover between the fins or to the housing, resulting in a short circuit.
- Replace the cleaned switch chamber. Ensure correct and firm positioning.
5.5. Coil resistance test
- Measure the resistance of the coil with a calibrated multimeter. Select the resistance measurement mode (Ohm, Ω) with an appropriate range. Connect the test leads to the coil terminals.
- Refer to the manufacturer's technical specifications for the nominal resistance value of the coil. This value can vary considerably depending on the coil type (AC or DC) and the rated voltage (e.g. 24V DC coil: ~20-50 Ω; 230V AC coil: ~150-500 Ω).
- Compare the measured value with the specified nominal value. A deviation of more than ±10% from the nominal value may indicate an incipient flushing error. A higher resistance may indicate partial breaks or overheating; a lower resistance to winding short circuits. An 'OL' (Open Loop) indication on the multimeter means a completely open coil, requiring replacement of the coil or the entire unit.
- If applicable and possible, measure the insulation resistance between the coil and the chassis (earth) with an insulation tester (megger) at a minimum of 500V DC. The value must be >1 MΩ. An insulation resistance lower than 1 MΩ indicates damaged insulation, which can lead to leakage currents, short circuits or earth faults, and is a critical failure.
- Visually inspect the coil for signs of overheating (discoloration of the winding or insulation) or physical damage.
5.6. Reassembly & Control
- Properly replace all internal components, including contacts, springs and mechanical parts, in the housing. Make sure everything moves freely.
- Close the housing carefully and check that all seals are correctly positioned to prevent dust and moisture from entering.
- Securely reattach the switch/relay to its mounting position. Check that the mounting points are undamaged.
- Reconnect all wires according to the markings or photos previously made. Use the torque wrench to tighten the clamps to the correct torque values (e.g. 1.5 - 2.5 Nm for control terminals and 3.0 - 5.0 Nm for 10 mm² main circuit terminals). Clamps that are too loose lead to high transition resistance, resulting in overheating, sparking and a fire hazard. Over-tightening may damage the wire or clamp.
- Perform a final visual inspection for proper wiring, insulation integrity, and absence of loose materials or tools.
6. Post-Maintenance Verification Checklist
After completing the maintenance procedure, it is essential to verify the functionality and safety of the switch/relay before returning the installation to service.
| Test | Expected Result | Actual Result | Pass/Fail |
|---|---|---|---|
| Voltage supply | Nominal supply and control voltage present at the respective terminals. Check L1-L2, L2-L3, L3-L1 and L-N/L ground. | ||
| Function test | The switch/relay switches on and off immediately and reliably when activated (via control panel or test button). | ||
| Contact status | Check with a multimeter whether the make contacts close and the break contacts open when the switch is on, and vice versa when off. | ||
| Thermal inspection | During operation and under load: no abnormal temperature increase on the terminals, contacts or housing. Maximum temperature of the connections must remain below 70°C. Use a thermographic camera if available. | ||
| Sound production | No abnormal humming or clicking noises during operation. Only a clear, short "click" when shifting. | ||
| Visual inspection | All covers and shields are properly closed and secured. No open wires. All components are correctly assembled and marked. | ||
| Leakage current test (if relevant) | Leakage current to earth within acceptable tolerances, in accordance with NEN 1010 or machine manufacturer specification. |
7. Troubleshooting Guide
This table provides guidance on common problems that can occur with switches and relays, along with possible causes and corrective actions.
| Symptom | Probable Cause | Corrective Action |
|---|---|---|
| Switch/relay does not switch on | 1. No control voltage on the coil. 2. Coil defective (open circuit, too high resistance). 3. Mechanical blockage of the armature or contact mechanism. 4. Defective auxiliary contacts in the control circuit (e.g. in series with the coil). | 1. Check the control voltage with a multimeter. 2. Measure the coil resistance; replace coil or entire unit if 'OL' or significantly off. 3. Inspect and clean the mechanism; replace if worn or damaged. 4. Check and replace defective auxiliary contacts. |
| Switch/relay fails immediately or does not switch off | 1. Excessive vibration. 2. Coil defect (internal short circuit, too high temperature, too low voltage). 3. Sticky main contacts due to overload or arcing. 4. Mechanical fault: stuck armature or contact mechanism. 5. Residual magnetism in the core package (with AC coils). | 1. Check installation; eliminate vibration sources. 2. Measure coil resistance; check control voltage; replace coil/unit. 3. Inspect contacts and clean/replace contact set. 4. Check mechanism for free movement; clean or replace. 5. Clean the pole surfaces and check the anchor for dirt. |
| Overheating of terminals/wires | 1. Loose connections on the terminals. 2. Circuit overload (current exceeds rated value). 3. Corroded or heavily oxidized contacts. 4. Wire diameter too small for the load. | 1. Tighten connections with the torque wrench (1.5-5.0 Nm depending on the clamp). 2. Check the load compared to the rated current of the switch and the cabling; reduce load or upgrade components. 3. Clean or replace the main contacts. 4. Check the wire diameter in accordance with NEN 1010; replace if too small. |
| Frequent contact burning/sparking | 1. Excessive or repetitive strain. 2. Insufficient contact pressure. 3. Dirty, damaged or missing switch chamber. 4. Inductive load without adequate shielding (snubber, RC filter or diode). 5. Too frequent switching cycles for the switch type. | 1. Check load; consider a more heavily dimensioned switch. 2. Check spring pressure contacts; replace contact set. 3. Clean, repair or replace the switch chamber. 4. Install a suitable arc extinguishing device across the inductive load. 5. Evaluate the application; consider a switch with higher switching frequency or electronic switching. |
| Humming noise (with AC coils) | 1. Dirt, rust or dust between the pole faces of the anchor and the core. 2. Broken short circuit ring in the core. 3. Control voltage too low. 4. Mechanical wear of the anchor guide. | 1. Thoroughly clean the pile surfaces and anchor. 2. Replace the coil or the entire unit. 3. Check the coil supply voltage. 4. Inspect and replace mechanical parts showing wear. |
8. Recommended Maintenance Schedule
The following diagram is a general guideline. The exact frequency of maintenance activities may vary based on operating conditions, component loads, ambient temperature and the presence of contaminants. Always refer to the manufacturer's specific recommendations.
| Task | Frequency | Estimated Duration | Skill level |
|---|---|---|---|
| Visual inspection of external housing and connections | Monthly | 10-15 minutes per unit | Technician |
| Thorough internal inspection, contact cleaning & switch room cleaning | Annually or every 250,000 switching cycles (whichever comes first) | 30-60 minutes per unit | Qualified Technician |
| Coil resistance test & insulation resistance test | Annually (together with internal inspection) | 10-15 minutes extra per unit | Qualified Technician |
| Replacement of wear parts (contact sets, coils) | Every 5 years or every 1,000,000 switching cycles | 45-90 minutes per unit | Qualified Technician |
| Checking torque values on all terminals | Semi-annually | 15-30 minutes per panel | Technician |
An increased frequency is recommended for critical applications or when exposed to harsh environmental conditions.
9. Reference Spare Parts
The use of original or equivalent quality parts is essential for the reliability and safety of your installation. UNITEC-D offers a wide range of spare parts for switches and relays.
| Part description | Typical Specification | UNITEC Category |
|---|---|---|
| Main contact set | AgNi (Silver-Nickel) alloy, rated current (e.g. 25A, 50A, 100A), number of poles (3P, 4P) | Electrical Components & Accessories |
| Auxiliary contact block | Type (1NO+1NC, 2NO, 2NC, etc.), mounting (front mounting, side mounting), rated current (e.g. 10A) | Electrical Components & Accessories |
| Rinse | Nominal voltage (e.g. 24V DC, 230V AC), frequency (50/60 Hz), power (VA/W) | Electrical Components & Accessories |
| Switch Room (Arc Chute) | Type and size according to original material (e.g. ceramic, plastic) | Electrical Components & Accessories |
| Replacement springs | Type (compression spring, tension spring), material (hardened steel) | Mechanical Components |
| Mounting bracket / adapter | Specific to contactor type and mounting rail (DIN rail, panel mounting) | Fastening materials |
For a complete overview of spare parts, detailed specifications and current availability, visit our e-catalogue:
10. References
- NEN 1010: Safety provisions for low-voltage installations in the Netherlands.
- EN 60947-4-1: Low voltage switchgear - Contactors and motor starters - Electromechanical contactors and motor starters.
- ISO 13849-1: Safety of machinery - Safety-related parts of control systems - Part 1: General design principles.
- Working Conditions Decree (Netherlands) and relevant European Machinery Directive 2006/42/EC regarding safe working practices.
- Manufacturer's documentation (OEM) and datasheets for specific contactors and relay models.
- Certification standards such as CE, ATEX (for explosive atmospheres) and TÜV quality marks, if applicable to the installation.
