Earthing Systems Design and Installation Services

June 25, 2018

The goal of an earthing system is to create an impedance-free ground path. The earthing conductor, coated in green, green/yellow, or some other code-mandated colour combination, acts as a system reference point. Moreover, the earthing system functions as a safety mechanism. If there's a short-circuit or a lightning strike, the current flows straight to ground. Taking all of that into account, what design principles shape these essential circuit structures?

Zero Potential Connectivity

Even when an exposed metal surface doesn't cover electrical circuitry, it could easily become dangerous. Suppose a potential difference were to develop between two metal structures, perhaps in a bathroom. Bonded earthing conductors join all of these parts together so that no potential difference can exist. Then there are earthing conductors in high-voltage appliances and equipment with many exposed metal parts. Still, the final circuits are all in place, which leaves us wondering what's going on back at the distribution board and transformer station.

Earthing System Design

Several alternatives exist, with the selected configurations altering as we hop between country borders and different time periods. Imagine a structure with an outdoor electrode. Plates and electrodes are buried nearby, but there's no direct earthing conductor running back to the transformer. In this case, the earthing system is using a TT (Terra-Terra) configuration. A local electrode outside the property forms a path to the transformer earth, and that path uses the ground as a zero-impedance link. There are, as always, alternative electrical configurations. They're the TN, IT, TN-S, and other technically complex layouts that find use in single-phase and three-phase sites. The point is this, though: the earthing electrode must deliver a no-resistance impedance readout after it's installed.

Installing an Earthing System

The excavation occurs at pipe sites, substation areas, and right outside grid-powered structures. Even off-grid properties require grounding electrodes. Anyway, with the trench open, a series of copper plates, copper rods, and insulated conductors are installed. They're soldered and fastened to each other and attached to the structure's distribution board. Alternatively, back at the transformer, the earthing array is connected to the phased wiring here, where it takes on the role of a return (neutral) wire.

As mentioned earlier in this post, earthing configurations are not simple constructs. There are local and wired grounds to consider, grounding layouts, and single or three-phase cabling arrangements. Still, at the end of the day, the job of the trenching contractor and journeyman electrician is to build a zero-impedance link, one that'll automatically absorb the bulk of any generated fault current.

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