Which of the following is not typically a source of EMI in low-voltage circuits?

• A. Variable-speed AC motor drives
• B. Generators
• C. Fiber optic cables
• D. Fluorescent lights

Answer: (C)

EMI in low-voltage systems mainly comes from equipment that switches or generates electrical noise. Variable-speed AC motor drives use fast-switching power electronics, which creates both conducted and radiated EMI that can couple into nearby conductors. Generators produce EMI through their internal electrical processes and mechanical noise, which can radiate or couple into circuits. Fluorescent lights can contribute EMI via ballast operation and switching, especially with modern electronic ballasts. Fiber optic cables, on the other hand, do not carry electricity—they transmit light—so they do not generate or propagate electrical interference. They are immune to EMI and are often used to reduce interference in a system.