What is equipment earthing?
Connecting the exposed metal of AGL equipment to earth, so a fault that energises a case sends current to ground instead of through whoever touches it.
Equipment earthing joins every exposed metal part of the lighting system, such as the CCR cabinet, sign housings, fixture bodies and base cans, to earth through a bonding lead and the earthing conductor, with ground rods making the connection to the soil.
The series circuit itself is deliberately isolated from earth, so a metal case should never be live. Earthing is the safeguard for the day insulation fails: the case is held at earth potential so its voltage stays too low to be dangerous to someone touching it, leakage current has a low-resistance path to earth, and the fault can be picked up by the CCR’s earth-fault monitoring. Because the loop is a constant-current circuit, a single fault to a bonded case draws little extra current; the real dangers are a case left floating at circuit voltage and a second earth fault elsewhere.
Metal parts tied to earth on purpose. Protects people and equipment.
Kept insulated from earth. A connection to earth here is an earth fault.
- Identify. List every exposed metal part: cabinets, housings, frames, base cans and covers.
- Bond. Fit a bonding lead from each part to the earthing conductor.
- Connect. Join the conductor to ground rods at the points the design specifies.
- Protect. Use suitable connectors and guard the joints against corrosion and damage.
- Test. Check each bond for continuity and measure earth resistance, then record the results.
Frequently Asked Questions
Q1What is equipment earthing in airfield lighting?
Bonding the exposed metal parts of AGL equipment to the earthing system, so that if a fault energises a metal case the current has a safe path to earth.
Q2Why earth equipment if the series circuit is isolated from earth?
Isolation means a metal case should never be live in normal service. Earthing covers the failure case: if insulation breaks down, the case is held close to earth potential and the fault current has somewhere to go.
Q3How is equipment earthing different from the earthing network?
Equipment earthing is the purpose: every exposed metal part is bonded to earth. The earthing network, with its counterpoise and ground rods along the circuit, is the infrastructure those bonding leads connect to, and it also carries lightning surge energy.
Q4Which equipment is earthed?
The exposed metal parts: CCR and control cabinets, sign housings and frames, metal fixture bodies, base cans and covers, and metal supports on approach-light structures, as the project design specifies.
Q5Is an earthed case the same as an earth fault?
No. An earthed case is intended. An earth fault is an unintended connection between the series-circuit conductor and earth, for example damaged insulation touching wet soil or a metal housing.
Q6How is equipment earthing checked?
By inspecting the bonding leads and connectors, testing the continuity of each bond and measuring earth resistance, then comparing the results with earlier readings and the design values.
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