What should never be done across a voltage source according to safety practices?

Short circuiting a voltage source is a highly risky action that can lead to dangerous situations. This practice involves creating a direct connection between the positive and negative terminals of the voltage source, which effectively allows an unrestricted flow of current. Such an action can result in excessive heat, potential fires, and damage to the voltage source itself, along with the risk of electric shock to individuals nearby.

Safety practices emphasize avoiding short circuits because they can lead to catastrophic failures not only of the voltage source but also of any connected equipment. It is important to ensure that all connections to a voltage source are made with the intention of controlling and measuring the electrical parameters safely, rather than allowing an uncontrolled current flow as seen in a short circuit condition.

In contrast, measuring resistance, connecting test equipment, and proper grounding, when done correctly, are part of safe electrical measurement practices. Measuring resistance involves disconnecting power to avoid injury or damage, connecting test equipment is typically done with specific precautions and procedures, and grounding is a necessary safety procedure aimed at preventing electrical shock. Thus, avoiding short circuiting is crucial for maintaining safety around voltage sources.