Wiring and CT Short-Circuit Logic in the ODES TSB-14 Testblock

During protection testing, engineers often need to isolate the protection relay from its connected CT, PT, and control circuits while maintaining circuit integrity and operator safety. The ODES TSB-14 Testblock, when paired with its test handle, performs three critical tasks in one motion:

• Controlled isolation between the relay and external circuits.

• Automatic CT short-circuiting to protect the CT secondary.

• Structured timing that guarantees “short first, open later.”

This combination eliminates the risk of CT overvoltage, simplifies test preparation, and makes the overall process safer and more repeatable.

Left or Right? The Simple Wiring Rule

To prevent accidental CT open-circuits, the TSB-14 follows a clear terminal convention:

• Even-numbered terminals (left side): connect to the primary instrument transformers (CT/PT).

• Odd-numbered terminals (right side): connect to the protection relay.

Think of it as: “Left for primary, right for relay.” Marking this rule on wiring diagrams helps technicians maintain consistency and avoid cross-connections during installation or maintenance.

Built-In Safety Sequencing

The TSB-14’s internal design hardwires the correct operating sequence so the user can’t get it wrong.

1. Before testing – the CT circuit is in a “ready-to-short” state.

2. When the test handle is inserted – the CT shorting contacts close first, ensuring the CT secondary is safely shorted.

3. Only after shorting – the testblock opens the relay side contacts, cleanly isolating the protection device from the primary circuit.

This mechanical interlock embodies the principle of “short first, open later.” It prevents accidental CT open-circuits and removes the need for manual switching or separate shorting plugs.

Why This Matters

An open-circuited CT can develop dangerously high secondary voltages and damage connected equipment. The TSB-14 eliminates that risk automatically. Its internal shorting mechanism operates every time the test handle is used, independent of user skill or experience—making it an engineering safeguard rather than a procedural requirement.

The ODES TSB-14 Testblock transforms a risky manual process into a controlled, fail-safe operation. By following the simple wiring rule—left to primary, right to relay—and relying on the built-in “short first, open later” sequencing, engineers can perform protection testing safely, efficiently, and in full compliance with international practice.

Safety in testing should never rely on memory or habit. Standardize your process with equipment that makes correct sequencing automatic.

• Request the wiring and timing diagrams for the TSB-14 series.

• Speak with our engineers about integrating automatic shorting into your existing test workflow.

• Upgrade your panels with hardware that enforces safety—by design, not by instruction.

Contact: 📩 tonyzhang@odes.com.cn

Or visit: 🌐 https://www.odes-electric.com/

#TSB14 #Testblock #ProtectionTesting #CTShortCircuit #AutomaticShorting #SecondaryCircuits #RelayProtection #TestingSafety #ReliabilityEngineering #SubstationAutomation #IECCompliance #CECertification #ElectricalEngineering #IndustrialAutomation #UtilitySolutions #GridResilience #EnergySystems

ODES Electronics