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An explosion-proof motor that is not maintained to its certified condition is no longer explosion-proof. Flameproof enclosures, cable entries and flame paths degrade quietly — a cracked housing or a loose gland can turn a certified motor into a hazard. This checklist covers the daily, monthly, quarterly and annual inspections that keep Ex d motors safe and reliable, based on IEC 60079-17 and GB 3836.16 practice.
1. Why Explosion-Proof Motors Need Different Maintenance
Standard motors can tolerate small defects for a long time; Ex d motors cannot. The flameproof enclosure is engineered to contain an internal explosion and cool the escaping flame below ignition temperature. Any crack, corroded flame path, missing bolt or damaged cable entry breaks that barrier. Routine maintenance for explosion-proof motors therefore focuses on preserving explosion integrity first, then electrical and mechanical health.
2. Daily Inspection (Visual Walk-Around)
- Surface temperature: touch-check or use an infrared thermometer; compare with the T-rating limit (e.g. T4 = max 135 °C surface);
- Enclosure condition: scan housing, end covers and terminal box for cracks, dents, corrosion or distortion;
- Fasteners: confirm cover bolts and screws are present and tight — never operate with a missing bolt;
- Abnormal noise or vibration: note any change from baseline operation;
- Operating current and voltage: record and watch for deviation beyond ±5% of rated values.
3. Monthly Inspection (Inspection Class)
In line with IEC 60079-17 inspection levels, a monthly (or risk-adjusted) inspection adds detail to the visual check:
- Flame path joints: inspect machined flameproof joints for scratches, rust or paint build-up — flame paths must remain clean and unpainted;
- Cable entries and glands: check glands are correctly tightened, sealing washers intact, unused entries properly blanked off;
- Terminal box seals: verify gaskets are in place, not hardened or cracked;
- Cooling: clean dust from fan cover, fins and ventilation ducts with compressed air or a brush;
- Grounding: verify the external earth connection is tight and corrosion-free.
4. Quarterly Maintenance (Mechanical Health)
| Task | Method | Acceptance |
| Insulation resistance test | 500V/1000V megger between phases and to ground | Typically ≥ 100 MΩ for Class F insulation (compare with previous readings) |
| Bearing condition | Vibration measurement + temperature check + grease inspection | Vibration within ISO 10816 zone, temperature below alarm level |
| Alignment check | Dial gauge or laser alignment | Within coupling manufacturer tolerance |
| Grease replenishment | Per bearing type and motor manual | Correct grade, correct quantity — over-greasing overheats bearings |
5. Annual Overhaul (Explosion-Proof Integrity)
- Flame path dimensional check: measure gap width and joint length against the certificate drawing; repair light scratches only with approved methods — never repaint flame paths;
- Sealing components replacement: ｒｅｐｌａｃｅ aged O-rings and gaskets;
- Winding test: full insulation resistance, winding resistance and, where applicable, surge comparison test;
- Motor cleaning and inspection: remove internal dust, check winding varnish, rotor and shaft condition;
- Nameplate and marking verification: confirm Ex marking, certificate number and efficiency class remain legible and match the certificate.
6. Common Maintenance Mistakes That Void Safety
- Painting the flame paths: paint alters the machined gap geometry — flame paths must stay bare;
- Substituting bolts: replacing cover bolts with non-original or lower-grade fasteners;
- Overtightening or using wrong glands: damaged threads and seals defeat the enclosure;
- Running with missing or loose covers: even temporarily, this breaches the certified design;
- Ignoring vibration trends: rising vibration usually precedes bearing or rotor failure — act on trends, not just alarms.
7. FAQ
Q: How often must explosion-proof motors be inspected?A: IEC 60079-17 bases frequency on a risk assessment; routine walk-around inspection is typically monthly or more frequent in harsh environments, with full overhaul annually.
Q: Can I repair a scratched flameproof joint?A: Minor damage may be reconditioned only with approved procedures and re-verified against the certificate drawing; severe damage requires factory repair or replacement.
Q: Does maintenance affect the Ex certification?A: The certification applies to the design; maintenance must restore the motor to the certified condition. Unapproved modifications void compliance.
Keeping Your Ex Motor Certified and Reliable
Set up a maintenance plan before installation and keep maintenance records for audits. If you need help with motor selection, retrofit or repair guidance, contact our engineers — or review our What Makes an Explosion-Proof Motor Different and IEC Zone vs North American Division guides, and browse the Wolong explosion-proof motor product range.
