In high-humidity environments, condensation forms on the enclosure and drips down. Apart from the heat loss caused by insulation, the risks to electrical components are mostly of a slow, cumulative nature; many early warning signs are subtle, and the circuit will not trip immediately, meaning that the risk of failure gradually increases over the long term.

Condensate slowly seeps into the electrical enclosure through gaps in the sheet metal casing, bolt holes and openings in the cable ducts. Rather than a single, large influx of water, this occurs as a continuous, minute trickle. The moisture adheres to the surfaces of circuit boards and terminal blocks, forming a water film on the copper foil of the circuit boards and the surfaces of the terminals, Salts and dust in the air dissolve into this film, forming a conductive electrolyte film that causes micro-leakage between terminals. Initially, this manifests as a gradual decline in insulation resistance; whilst the equipment does not shut down immediately, signal drift occurs, such as slight fluctuations in the analogue signals from vacuum sensors and level transmitters, or erratic variations in valve position feedback values. Operations and maintenance personnel often attribute this to sensor ageing or signal interference, making it difficult to link the issue to condensation and water ingress through the enclosure. As the electrolyte continues to corrode, dendritic crystals form on the copper foil—a process known as creeping corrosion on the circuit board—gradually causing open circuits or short circuits between adjacent pins, and in severe cases, directly burning out the circuit board.

Water drips down the outer sheath of the cables and accumulates at the sealed joints where the cables enter and exit the electrical enclosure, gradually compromising the cable seals. Prolonged exposure of the cable sheath to condensation accelerates ageing and cracking, whilst moisture migrates inwards along the gaps between the cable cores—a phenomenon known as capillary water absorption. This moisture, trapped inside the cable and invisible to the naked eye, causes the insulation resistance between the cable conductors and earth to steadily decline. In power cables, this may result in false tripping of residual current devices (RCDs), whilst in signal cables it continuously introduces noise interference, which becomes more pronounced during start-up and stop phases.

Condensation dripping from the enclosure onto the surfaces of power components such as contactors, relays and circuit breakers causes corrosion of metal contacts and spring components. When condensation mixes with dust in the air, it forms an oxide layer on the surface of the contacts. As the contacts close, the contact resistance continues to increase; during operation, the contacts overheat abnormally, and this heat accelerates the ageing of surrounding plastic components. Contact erosion is a gradual process; in the early stages, it may only manifest as unstable contactor engagement, occasional chattering and fluctuations in load output. However, once the contacts have melted and fused together over a large area, dangerous operating conditions may arise where valves or pumps cannot be shut down. Once the metal springs and fastening bolts of the terminal blocks have corroded, the bolts lose their clamping torque, leading to loose connections; this exacerbates terminal overheating and, in extreme cases, causes the terminals to burn black.

Condensation also promotes the growth of mould and the accumulation of salt deposits inside the electrical enclosure. Moisture dripping from the outer casing increases the relative humidity inside the enclosure, causing a conductive mould layer to form on the surfaces of component PCBs and plastic sockets. Mould is inherently conductive and gradually erodes the substrate, leading to poor contact at socket pins. Such issues pose a higher risk during the shutdown and thermal insulation phase: once the unit is shut down, the temperature inside the enclosure drops whilst moisture remains trapped. This moisture accumulates continuously in the high-humidity environment at night; when the unit is restarted and the temperature rises, the moisture evaporates, briefly creating a high-humidity, steam-filled environment inside the enclosure. This repeated cycle accelerates the deterioration of components.

There are also latent risks associated with the earthing circuit: condensation and water accumulation on the enclosure will drain to the base and earthing busbar, where impurities and ions in the water reduce the stability of the earth resistance; furthermore, corrosion at the earthing connection points leads to a deterioration in earth continuity. Should the equipment experience an electrical leak, the protective circuit may fail to operate reliably, posing a safety hazard due to the enclosure becoming live; simultaneously, poor earthing amplifies common-mode interference in sensors, significantly increasing noise in vacuum, temperature and liquid level readings, leading to misjudgements by the automatic control logic and resulting in false triggers of vacuum protection and liquid level interlocks.

There are also potential hazards associated with precision components such as small sensors, encoders and solenoid valve coils. Condensation dripping onto the coil casing allows moisture to seep between the enamelled wires, causing a reduction in inter-turn insulation and resulting in latent inter-turn short circuits. Solenoid valves may exhibit insufficient force, delayed gas supply switching and intermittent performance; such faults are difficult to detect until the coil is completely burnt out. If water enters the wiring chamber of vacuum or pressure transmitters, it will corrode the internal amplification circuitry, causing the zero point to drift continuously and necessitating frequent calibration. Even after replacing the transmitter, similar problems may recur after a period of time; the root cause lies in persistent condensation and dripping water.

It is important to distinguish between two key issues: condensation forming inside the electrical enclosure itself and water dripping into the enclosure from the exterior. Water dripping onto the enclosure constitutes a continuous external water supply; even if simple dehumidification measures are implemented within the enclosure, as long as water continues to drip onto the housing, moisture will flow in ceaselessly through the gaps. Relying solely on internal heating and dehumidification makes it difficult to eliminate this隐患. Water droplets may also run down the frame to the motor terminal box, seeping into the terminal chambers of the circulation pump and discharge pump motors. This causes a gradual deterioration of motor insulation, corrosion of motor bearings and end caps, triggering motor insulation alarms; in severe cases, it can lead to the complete burning out of the windings.