What was the outcome of the vault test when a bonded conductive mat was used and the neutral switch was open?

When a bonded conductive mat is used and the neutral switch is open during a vault test, the test is designed to assess the safety and effectiveness of grounding and bonding practices in electrical installations. The scenario suggests that while the mat should ideally help to dissipate any electrical currents safely, the open neutral switch can create a potentially hazardous condition.

In this situation, the open neutral can result in a lack of a proper return path for fault currents, which may cause dangerous levels of electric current to flow through the workers standing on the mat. This could lead to the series of events outlined in the correct choice, where fatal body currents flowed, indicating a critical failure of safety measures. Essentially, the design of the test illustrates that without a properly functioning neutral connection, the grounding system may not provide the shock protection necessary for safety, resulting in very serious consequences for individuals in that environment.

The bond of the conductive mat is intended to create a low-resistance path to ground, but if conditions like an open neutral are present, it can lead to unsafe levels of current being present and creating a life-threatening situation for those exposed. Therefore, the outcome of the vault test under these specified conditions indicates a serious safety concern.