What precaution must be taken when single conductors enter metal boxes through openings over 200A?

When single conductors enter metal boxes through openings rated for over 200A, preventing overheating by induction is crucial. Induction heating can occur due to the electromagnetic fields generated around high-current conductors, particularly in metal enclosures. This is because as current flows through a conductor, it creates a magnetic field. If the metallic box is in close proximity or connected with these conductors, it may induce currents in the metal which can lead to increased temperatures if not properly managed.

In the context of installations over 200A, the risk of overheating becomes more pronounced due to the higher current levels, making it essential to take precautions against induction effects. Proper grounding, bonding, and using materials with appropriate electromagnetic shielding can help mitigate these risks, ensuring safe operation and longevity of electrical installations.