What Is a Siemens Test Block? Application and Operation in Protection Panels

What Is a Test Block?

A test block (test switch) is one of the most important components of protection and control panels in transmission and distribution substations. It allows protective relays to be tested and calibrated without rewiring or fully disconnecting the circuit. Using a test block, maintenance crews can safely place current and voltage transformer (CT/PT) circuits into test mode.

The Siemens Test Block

Well-known Siemens test block models such as the 7XG22 series are installed in many older substations. Due to their age and long procurement lead times, many utilities look for high-quality locally manufactured alternatives with identical functionality.

How It Works

In the normal (service) position, the test block contacts keep the circuit directly connected to the relay. During testing, turning the handle first short-circuits the CT secondary (preventing dangerous open-circuit CT conditions) and then routes the circuit to the test sockets, ensuring operator and equipment safety.

Local Alternative: Rizmooj Test Switches

Rizmooj Electric Toos manufactures the CXV75 and 2RLMG test switches with a rotary mechanism, providing exactly the same function as imported test blocks. They are available in 14- and 22-contact models in 2U and 4U dimensions and are in service across the country. See the test switch product page for technical details.