Determining if a junction box is completely dry requires both instrument testing and sensory inspection. Relying solely on visual observation or time-based estimations is prone to misjudgment; a comprehensive assessment based on key indicators is essential.
1. Core Judgment Criteria (All Must Be Met)
Insulation Resistance > 100MΩ (500VDC): Use a megohmmeter to measure the insulation resistance of the main circuit to ground. Values below this indicate a short circuit risk.
Internal Humidity < 30%RH: Temporarily insert a small, moisture-proof temperature and humidity sensor to confirm the environment has returned to dryness.
No Water Stains, No Mist, No Odor: Visually inspect the inner walls, terminal blocks, and wire connections for residual moisture or musty smells.
Color-Changing Silica Gel Returns to Blue: If using color-changing silica gel desiccant, a change from red to blue indicates restored moisture absorption capacity and a dry environment.
It is recommended to let the box stand for 10 minutes after drying before testing to avoid temperature differences affecting reading accuracy during operation.
2. Auxiliary Judgment Methods
Contact Resistance < 10mΩ: Use a four-wire micro-ohmmeter to test key connection points to ensure normal conductivity;
Infrared Thermometry Auxiliary Analysis: Scan with an infrared thermal imager. If there are no "cold bridge" areas (abnormally low temperature points), it indicates no moisture accumulation;
Intermittent Power-On Test Before Operation: After confirming the insulation is qualified, briefly power on the equipment to observe whether it trips or leaks. If there are no abnormalities, continue operation.
Special Note for Xiaogan Local Areas: Currently, it is the rainy season, and the air humidity often exceeds 80%RH. The temperature difference between day and night is large, and condensation is very likely to occur in the early morning after the equipment is shut down:
Even if the test results meet the standards, protective measures should be restored immediately; Reapply moisture-proof conductive grease and install the PTC heating module + desiccant pack; Check the junction box status daily, paying particular attention to the early morning hours.
Core Principle: Drying is not just "looking dry," but rather meeting the required conditions + instrument verification to ensure safe restart and prevent short circuits or fires caused by misjudgment.
