What type of equipment is designed to prevent the entrance of moisture under specified conditions?

The correct choice identifies equipment that is specifically designed to prevent moisture from entering under specified conditions. Watertight equipment is constructed to be impermeable to water, maintaining its functionality even when subjected to conditions like rain or splashing. This characteristic is crucial in applications where exposure to water could compromise the safety and efficacy of electrical systems.

Watertight equipment meets stringent criteria that ensure it can withstand significant moisture exposure, thereby protecting sensitive components from water damage. This is particularly important in marine environments or locations prone to heavy rainfall.

Moisture-resistant equipment, while related, is not specifically designed to be impermeable but instead may reduce the likelihood of moisture ingress. As for environmental-resistant equipment, it generally implies protection against other environmental factors such as dust or corrosion, but it does not specifically guarantee moisture barrier properties. Weatherproof equipment, like watertight equipment, provides protection against moisture but may also include other elements, such as resistance to wind or dust, which could make it less focused than the watertight designation.

Thus, the distinction lies in the specific purpose of watertight equipment to prevent moisture intrusion and maintain operational integrity under water exposure, making it the correct choice.