New York State Master Electrician Practice Exam

Where should the ferromagnetic envelope be bonded where skin effect exists?

1. At one end only

2. At both ends

3. It need not be bonded

4. At the center

The correct answer is: At both ends

Bonding the ferromagnetic envelope at both ends is crucial in applications where skin effect is present. The skin effect refers to the phenomenon in which alternating current (AC) tends to flow primarily at the surface of a conductor, rather than uniformly throughout its cross-section. This creates localized electromagnetic fields that can induce eddy currents in nearby conductive materials. By bonding the ferromagnetic envelope at both ends, you create a continuous path for any induced currents to return through. This helps in minimizing the potential differences that might arise due to fluctuating magnetic fields, ensuring that any induced currents or voltages are effectively managed. Such bonding reduces the risk of overheating, loss of energy, and electromagnetic interference in the system. In contrast, bonding at only one end or at the center may not provide a sufficient return path for the induced currents, increasing the risk of localized heating and reduced efficiency. Not bonding the envelope at all could leave the system vulnerable to the unwanted effects of the skin effect, compromising safety and operational effectiveness.