In rainstorm weather, how to prevent rainwater from flowing back into the inlet and outlet of rural lighting ready board in Africa?

Rainstorm water backflow prevention scheme for inlet and outlet of rural lighting ready board in Africa

The characteristics of the African rural scene: the intensity of rainstorm is strong, the temperature difference between day and night is large, the ultraviolet ray is strong, the sand and dust are abundant, the technical level of the on-site construction personnel is uneven, the ready board is multi wall mounted, the cables are mostly directly buried underground or overhead led down, and the incoming and outgoing lines are the highest places where rainwater flows back, which will cause leakage, short circuit, and prepaid meter failure.

1、 Principles for opening holes in the box and threading cables into the foundation

1. It is strictly prohibited to open the holes at the top of the box or on the box door. All incoming and outgoing holes should be arranged at the bottom of the box or on the lower side wall of the box to prevent water from entering from top to bottom; Prohibit opening holes at high positions on the side.

2. It is advisable to have a hole diameter larger than the outer diameter of the cable by 13mm. If the hole is too large, the seal will fail; The edge of the opening must be deburred to prevent cutting through the outer sheath of the cable.

3. The lighting ready board should prioritize the use of bottom in and bottom out wiring methods; If it is necessary to have a side outlet, the distance between the opening position and the bottom of the box must be ≥ 80mm, and the cable must be bent downwards for dripping.

2、 Sealing method for inlet and outlet (depending on process selection)

1. Cable gland (cable waterproof joint, most recommended on site)

Material: Priority is given to nylon with UV resistance, avoiding rapid aging of ordinary rubber outdoors in Africa; Brass nickel plated gland is selected for high current coarse cables.

Installation points:

1. The cable passes through the gland, and the rubber sealing ring is tightly pressed. The outer sheath of the cable must extend into the interior of the gland, and it is forbidden to only press the core wire.

2. Install EPDM rubber flat washers between the gland thread and the steel plate of the box body, and double washers inside and outside the box body are better to prevent rainwater from seeping through the thread gap.

3. A drip bend (U-shaped downward bend) should be reserved on the outside of the cable, allowing rainwater to drip down the cable without flowing into the opening of the box; The lowest point of the drip bend for overhead cables should be lower than the inlet position of the box.

Attention: Multiple thin cables often share the same large hole in rural Africa. Do not rely solely on glass glue for sealing. Glass glue will crack and fail after 12 years of exposure to sunlight and rain, and must be equipped with multi-core gland heads.

2. Rubber protective coil (grommet, suitable for small batches and simple boxes)

Suitable for multiple cable centralized outgoing lines, with rubber protective coils clamped in the openings of the box; It is only used as a dust prevention aid and cannot be used as rainstorm waterproofing alone. The exterior must be matched with sealant+cable drip loop.

Risk point: cable shaking, thermal expansion and contraction will make gaps between the guard coil and the cable, and rainwater will seep into the box along the surface of the cable in rainstorm.

3. Specification for the use of sealant (auxiliary means, cannot replace Glan)

Select UV resistant, high and low temperature resistant neutral silicone sealant;

Only fill gaps, cannot be used to fix load-bearing cables;

Before construction, the surfaces of steel plates and cables should be wiped clean and free of sand, dust, and oil stains;

Do not apply glue inside the box, only around the outer opening of the box.

1. Directly buried cables, with a small amount of slack curvature reserved at the bottom inlet of the box to avoid settlement, pulling, and damage to the seal.

3、 On site installation and operation avoidance points (high-frequency errors on African construction sites)

one ❌ Error: The cable is directly pierced, and a pile of glass glue is applied without any gland or drip bend; After a rainstorm, rainwater is sucked into the box along the cable skin.

two ❌ Error: The outer sheath of the cable is peeled off from the outside of the box, and the core wire is exposed and enters the box; Rainwater flows directly into the gaps of the core wire.

three ❌ Error: The cable protection pipe mouth is upward, and the ground area water rainstorm is poured into the pipe through the ready board.

four ✅ Key points for operation and maintenance inspection: During rainy season inspection, check whether the gland sealing ring is aging, hardening, or cracking; Is the drip bend deformed or ineffective; Check for sediment blockage in the drainage holes at the bottom of the container.

4、 Summary of simple selection of rainstorm environmental grade

Key principle: There are two main paths for rainwater to flow back: ① direct pouring through the opening gap; ② Capillary effect: rainwater creeps into the box along the surface of the outer sheath of the cable and the gap inside the cable, so it is not enough to block the hole. The drip loop is an indispensable measure to block capillary creepage, especially in the strong rainstorm environment in Africa.