Earthing for Outdoor Signaling Equipment

The earthing used for conducting current during normal equipment operation.

Earthing designed to dissipate surges and protect equipment from lightning or spikes.

An earth ground provided around a building to protect signalling equipment.

A conductor that bonds equipment chassis to the Main Equi-potential Earth Busbar (MEEB).

The main busbar for earthing, often in the power room.

Earthing protects equipment from electrical surges, including lightning.

Earthing metal screens reduces electromagnetic interference (EMI).

Earthing provides a safety measure to prevent electric shock for humans.

Armoring on unscreened tail cables usually doesn't need earthing unless the cable length exceeds normal limits.

Protection screens on signal cables need to be earthed if they're within 2 meters of electrified tracks.

If multiple metallic objects can be touched simultaneously, they should be connected to the same earth.

Modern electronic equipment in relay rooms need a common earth with a resistance less than 1 ohm.

Earthing wires should be green or green/yellow for easy identification of loose connections.

Earth wires should be straight and not coiled, with a minimum cross-section of 4 square mm of copper.

Protective earthing generally allows up to 10 ohms, but electronic equipment needs less than 1 ohm.

Each signaling equipment block needs its own earthing, with separate earthing for return circuits if needed.

The earthing wire should be shielded from damage and corrosion, especially where it connects to the earth electrode.

The earthing lead is typically made of flat mild steel, measuring 40 mm x 6 mm, or as specified by approved practices.

The earthing lead is securely connected to the earth electrode using soldering, crimping, or preferably, exothermic welding.

The best location for earthing is in wet marshy ground, followed by clay or loam mixed with sand, then clay and loam with varying proportions of sand, gravel, and stone, and lastly damp and wet sand and peat.

The earthing site should be chosen in a location with natural drainage, but a waterlogged area is not essential unless the soil is sand or gravel.

Earthing electrodes should be situated in fine-textured soil, which is tightly packed by watering and ramming. The soil should be sifted and cleared of lumps and stones.

When soil conductivity is poor, chemical treatment can be used. Common salt and charcoal layers can reduce resistivity.

Natural salts produced by decaying plants can improve soil conductivity, as plants have lower resistivity compared to similar soil without plants.

The total resistance encountered by electrical current flowing through the earthing system, mainly determined by the soil's conductivity.

It's the sum of conductor resistance, contact resistance between electrode & soil, and soil resistance.

It's the biggest factor in earth resistance, affecting how easily electrical current can flow through the ground.

Galvanized iron or mild steel are common, but copper or copper clad are better in areas with high corrosion.

Avoid areas with unconsolidated or erodible soil, like recently filled land or areas prone to erosion.

A minimum clearance of 20 meters is required to prevent accidental contact.

Helps retain soil moisture which improves the ground's conductivity.

By measuring the resistance between electrodes placed at known distances, resistivity is calculated using the formula P = 2πSR.

The process of determining the electrical resistance between the earth electrode and the surrounding soil.

A technique used to measure the earth resistance of small earthing systems like single electrodes or ring earths.

Regularly moistening conventional earthing systems to improve conductivity and reduce resistance.

Inspecting and ensuring all earth connections are secure, intact, and properly soldered.

Regular examination of block earths and their connections to detect any problems.

Periodic measurement of resistance in block earths to ensure they're functioning correctly.

Substances added to maintenance-free earths to improve their conductivity and reduce resistance.

A robust and permanent connection method for earthing rods in maintenance-free earth systems.