Test Blocks as “Safety Valves” in Nuclear Secondary Circuits In nuclear power projects, test blocks are not small accessories. They are engineered “safety valves” that make secondary circuits measurable, isolatable, and recoverable during commissioning and periodic testing. A single wiring error or unsafe CT open-circuit condition is unacceptable in this environment. In a recent 400 V low-voltage switchgear project for a nuclear plant, the cabinet integrator and design in