Resistor Failure Mode: Does a Burned-Out Resistor Usually Open? Evaluate the statement: “A resistor normally opens when it burns out.”

Introduction / Context:
Knowing typical failure modes helps in troubleshooting. Resistors exposed to overcurrent or overheating can fail in various ways, but practical experience and construction physics favor one outcome most of the time: opening of the element or lead-to-film separation.

Given Data / Assumptions:

• Carbon film, metal film, and wirewound resistors considered.
• Overload or thermal stress as the cause of failure.
• No catastrophic arc-over or conductive debris bridging after failure.

Concept / Approach:

When the resistive element is overheated, it often cracks, vaporizes a section, or separates from a termination, breaking the conduction path. This produces an open circuit. While short failures can occur (e.g., carbonized substrate, molten metal bridging), they are much less common for resistors than opens.

Step-by-Step Solution:

Verification / Alternative check:

Teardown analyses and field returns frequently show fractured films or broken wire in wirewound units, consistent with open-circuit failure. Design guidelines stress derating to avoid such opens.

Why Other Options Are Wrong:

“False” and “usually shorts” contradict observed statistics. “Always perfect insulator/conductor” is absolute and unrealistic; real materials leave finite leakage or irregular contact after damage.

Common Pitfalls:

Confusing resistor failures with electrolytic capacitor shorts or semiconductor shorts. Each component class has different predominant failure modes.

Final Answer:

True