Final answer:
In older series-wired Christmas lights, if one bulb burns out, the entire string goes out, while in newer designs, the other bulbs remain lit due to a shorting mechanism. The operating voltage per bulb is determined by dividing the total voltage by the number of functioning bulbs.
Step-by-step explanation:
Understanding Christmas Light Wiring
When Christmas lights are plugged in and not working, it could be due to several issues, such as a burnt-out bulb, a tripped circuit breaker, or faulty wiring. In older strings of holiday lights wired in series, when a bulb burns out, it breaks the electrical connection, similar to an open switch, causing the entire string to go out. If the string operates on 120 V with 40 identical bulbs, each bulb would normally operate at 3 volts (120 V / 40 bulbs).
In contrast, newer strings are designed with bulbs that short circuit, like a closed switch, when they burn out. This allows the other bulbs to remain lit. Following the same string example, if one bulb in a 120 V string with 40 bulbs burns out, you would now have 39 bulbs. The operating voltage for each would then increase slightly to approximately 3.08 volts (120 V / 39 bulbs).
As for safety concerns, plastic insulation on live or hot wires is intended to prevent both shock and thermal hazards. However, ordinary circuit breakers and fuses are ineffective in preventing shocks because they cannot detect small amounts of current leaking through a person's body. A Ground Fault Interrupter (GFI), on the other hand, may trip if the live (hot) and neutral wires are significantly different in lengths because the different lengths could cause an imbalance in the current flow the GFI monitors for safety.