suojajohtojen

Suojajohtojen is the Finnish term for protective conductors, the conductors that connect exposed conductive parts of electrical equipment to the earth. Their primary purpose is to provide a low-impedance path for fault current, enabling protective devices such as fuses or circuit breakers to disconnect power quickly and thereby reduce the risk of electric shock, equipment damage, and fire. They are a central part of the protective earth (PE) system and are used together with bonding of metallic parts to maintain a safe potential in case of a fault.

In normal operation, suojajohtojen form a continuous path from equipment enclosures, metalwork, and outlets to the building’s earth electrode. In the event of insulation faults or contact with live parts, fault current flows through the suojajohtojen to earth, causing overcurrent protection to operate. They also support equipotential bonding between conductive parts to minimize touch voltage. It is essential that these conductors are continuous, adequately sized, and properly terminated at main and distribution boards, outlets, and appliances.

Standards and installation practices for suojajohtojen follow national and international regulations, such as IEC 60364 and corresponding Finnish adaptations (for example, SFS standards). The protective conductor is commonly identified by green-yellow color coding, and it may be realized as a separate conductor or integrated in cable sheaths or metallic systems depending on the earthing arrangement (TN-S, TT, or TN-C-S). Distinctions are made between protective conductors and functional earth conductors (FE); suojajohtojen are designed primarily for safety, not for signal or EMI purposes, and must be maintained to preserve fault-clearing performance.