MTA Transit Electrical Helper (Exam No. 4612) Practice Exam

In the context of a 600-volt electric line, the correct answer reflects the practical application of electrical principles, particularly the safe operating limits of bulbs in a series circuit. When connecting light bulbs in series, each bulb will drop a portion of the total voltage supplied by the line.

Typically, standard incandescent bulbs are rated for lower voltages (commonly 120 volts). When you connect them in series, the voltage divides among the bulbs. For example, with 600 volts, if you assume each bulb is rated for 120 volts, connecting more than five bulbs would exceed the voltage rating for each individual bulb, potentially causing them to burn out or create safety hazards. Therefore, connecting either four or five bulbs would push the voltage per bulb beyond safe limits.

In this case, connecting three bulbs would mean each bulb experiences approximately 200 volts (600 volts/3 bulbs), which is still well within the typical operating range for certain types of higher-rated bulbs. Hence, three series-connected bulbs is considered a safe maximum on a 600-volt line, reflecting an understanding of electrical safety and bulb ratings.