What’s a stray current?

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Stray current is a flow of electricity through equipment, buildings or the ground due to imbalances in electrical power systems or due to damage to wiring. The electrical systems are connected to earth at regular intervals, both on the phases or on the neutral and earth wires. Power is supplied through the hot phases, with different voltages available depending on the location. Unused electrical current returns to the supplier through the neutral or live wire, and electrical codes in many areas require a separate ground wire that is connected to a rod placed in the earth.

When an electrical system is improperly installed or maintained, electrical current can flow into the ground or through the building or the equipment itself. Stray current can be annoying if a small amount is present, but it can electrocute and kill if it reaches dangerous levels. Along with the potential for electric shock, even small stray currents can cause damage by corroding metals in the ground.

Direct current (DC) systems are used for railroad, subway and some power distribution systems. Stray currents can exist where rail systems contact the ground, particularly in wet areas. The presence of stray currents can cause accelerated corrosion of the metal, because the electrical flow causes the metal to break down into its ions and enter the ground. If not corrected, pipes and metal structures can be destroyed in a short time.

Corrosion from stray currents is a widespread problem in marine systems, particularly in marinas or ports where large numbers of vessels are docked. A boat with bad electrical connections can discharge DC power from its batteries directly into the water. Other boats connected to the marina’s electrical system share common wiring, and stray current can enter other boats through undersea fittings or propeller shafts. With electrical flow now established with the vessel’s system failing, accelerated corrosion can occur and destroy metal fittings fairly quickly.

In the 20th century, it was common for homes to ground their electrical systems with potable water copper pipes entering the homes. Faults in wiring have created electrical flows through copper piping systems and caused widespread corrosion of public water systems. Understanding these issues has led to better grounding systems that use metal ground rods driven deep into the ground to provide a path for current to flow.

Underground pipelines used for oil, gas or water supplies can be damaged by stray currents. Many piping systems use insulators, non-conductive connectors or gaskets, which separate the piping into smaller sections to prevent current from being carried over long distances. Coating the outside of the pipe with plastic or polymer coatings can reduce corrosion by separating the pipe from nearby soil. Sacrificial anodes, which are rods of zinc or other metals that corrode more easily than pipe, can be attached at regular intervals to protect pipes from electrical corrosion. These anodes are also used on boats to protect underwater craft components.

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