Quick answer: While electrical equipment is running, its own heat keeps the enclosure warmer than the outside air and its surfaces above the dew point. When it shuts down for a season, the enclosure cools with the weather. Nights then pull surfaces below the dew point, and humid air drawn in by daily breathing and leaks condenses on them. To prevent this, keep auxiliary moisture protection powered (anti-condensation heaters or a cabinet dehumidifier) during the shutdown, keep the enclosure closed and sealed, and record conditions and any power interruptions so the return-to-service review knows what happened.
Quick answer
- Shutdown removes the equipment's heat; surfaces then reach the dew point.
- Keep heaters or dehumidifiers powered on an auxiliary supply.
- Record conditions and interruptions; review them before restart.
Define what is stopping
| State | Moisture protection |
|---|---|
| Main equipment off, auxiliaries powered | Heaters or dehumidifier keep working |
| Main and auxiliaries off | No protection; condensation risk high |
| Intermittent auxiliary power | Gaps in protection; record them |
Check the equipment documentation and the isolation plan for which auxiliaries may stay powered.
Why shutdown increases risk
- No internal heat, so the enclosure follows outdoor temperature swings.
- Daily breathing pulls in humid air as the enclosure warms and cools.
- Long periods with doors closed still allow leakage.
- Seasonal shutdowns often coincide with cold, humid seasons.
See air leakage and door moisture.
During the shutdown
- Keep the enclosure closed and sealed; plug unused entries.
- Keep anti-condensation heaters or a dehumidifier running on dew-point or RH control.
- Log temperature, RH and dew point; set an alarm.
- Check periodically for visible moisture and power interruptions.
Shutdown record
| Record | Include |
|---|---|
| Environment | Time, zone, readings, visible moisture |
| Protection | Auxiliary state, power interruptions, alarms |
| Response | Who checked, action taken, missing periods |
A normal reading today can't reconstruct an unrecorded week.
Return to service
| Situation | Review |
|---|---|
| Protection ran continuously, records complete | Normal return-to-service procedure with records attached |
| Gaps in protection or records | Identify the unknown period; responsible team decides further checks |
| Moisture or contamination observed | Equipment-specific inspection, cleaning, electrical tests before energising |
Electrical tests and the decision to energise follow the equipment's procedures; see insulation resistance and humidity.
Our electrical cabinet dehumidifiers run on low auxiliary power during standby.
FAQ
Frequently asked questions
Why does my panel have condensation after shutdown?
Without equipment heat, surfaces cool below the dew point of air inside the enclosure.
Should cabinet heaters stay on during shutdown?
Where the isolation plan allows, yes; they keep surfaces above the dew point.
What should I check before restarting after a long shutdown?
Moisture and corrosion signs, the shutdown record, and the electrical tests your equipment procedure requires.
Sources
- ASHRAE Handbook—Fundamentals, Psychrometrics.
