Protection engineers often encounter mixed CT notations on single-line diagrams (SLDs), especially when working on international projects that involve both IEEE and CSA standards. In a recent LinkedIn post, Madjer Santos, PE, P.Eng., PMP, MBA, shared a practical guide to interpreting these designations, drawing on years of real-world experience and study.
According to Santos, early-career engineers frequently struggle when faced with designations such as MR 3000/2000:5A C200, 1200/800/200–5A 2.5L800, or 800–5A 0.15B1.8. While these codes may appear complex, each element follows a clear logic based on whether the transformer follows the IEEE C57.13 or CSA/IEC 61869-2 standard.
For example, the IEEE format typically uses a colon (:) between current ratings, while the CSA format uses a dash (–). The “C” and “L” symbols represent accuracy classifications for relaying applications, while “B” indicates metering accuracy. Some CTs even include dual ratings, allowing them to serve both protection and metering functions when listed on the same nameplate.
Santos’s analysis breaks down these patterns, clarifying how symbols such as MR, L, and B connect to key technical parameters like accuracy class, burden impedance, and rated voltage.
By mastering CT designation reading, protection engineers can more effectively interpret SLDs and ensure precise coordination between protection and measurement systems—a crucial skill in today’s increasingly digitalised power networks.
Source: Madjer Santos, LinkedIn
