What type of electrical safety device can be used to protect sensitive instruments during maintenance?

The appropriate choice for protecting sensitive instruments during maintenance is the use of a resistor, particularly a specific value like a 10k ohm resistor. Resistors can limit the amount of current that flows through a circuit, thereby protecting delicate components from the risk of overcurrent, which can cause damage.

When working on sensitive instruments, especially in a maintenance situation, connecting a resistor in series can help by providing a controlled amount of current to the circuit, thus preventing possible surges that could lead to equipment failure. By choosing a resistor value such as 10k ohms, you can provide appropriate resistance based on the specific requirements and characteristics of the sensitive devices.

In contrast, options like fuses are primarily designed for overcurrent protection by breaking the circuit when too much current flows, which may not be ideal during maintenance when you might still need the circuit to function at reduced levels. Relays, while useful for switching applications, do not provide the same level of current limiting and protection for sensitive circuits. Therefore, the use of a resistor, specifically a 10k ohm, is the most effective method for safeguarding sensitive instruments during maintenance work.