Why must a cable entry face downwards outdoors (drip loop)?
A drip loop is the downward loop given to a cable before the enclosure entry. Rainwater running along the cable collects at the lowest point of the loop and drips off, never reaching the entry hole and the gland. It is standard practice at antenna, camera and outdoor field enclosure entries; together with a downward-facing entry it removes the constant water load on the gland.
Glands and seals are designed to resist splashing and spray, not to have water running over them continuously. Water flowing down the cable under gravity constantly stresses the seal when it reaches the entry and works its way in by capillary action over the years. A drip loop cuts this water path mechanically.
Practice:
- Take the cable below the enclosure entry, form a U loop and bring it back up into the entry. The lowest point of the loop must be clearly below the entry hole.
- Let the entry itself face downwards if possible; with side-facing entries the drip loop matters even more.
- Do not make the loop tighter than the minimum bending radius of the cable; a crushed cable fatigues the conductor.
- Fix the loop with a clamp so that vibration or wind does not distort its shape.
- If you use conduit, the conduit must follow the same loop and must be able to drain the water inside it.
A drip loop alone is not enough. Choose the gland to suit the cable diameter, close unused holes with blanking plugs and use a breather plug with an ePTFE membrane to manage the humidity inside the enclosure; otherwise condensation builds up even if no water gets in.
The full topic: Installation, redundancy and field continuity