Glossary
SLD
Plain-Language Definition
Single Line Diagram — a simplified electrical drawing showing the main power distribution from utility supply through transformers, switchgear, panels, and major loads using single lines to represent three-phase circuits.
Technical Context
An SLD shows: utility connection, transformers (with ratings), main switchgear, distribution panels, generator connection, ATS (Automatic Transfer Switch), major loads, and protection devices (breakers, fuses, relays). It is the most important electrical drawing for understanding a building's power system. Updated SLDs are essential after any electrical modification.
Why It Matters
Without a current SLD, electrical faults cannot be traced efficiently, capacity cannot be assessed, and modifications are risky. An outdated SLD is dangerous — it may show circuits that no longer exist or miss new ones. Every building should have a current, accurate SLD accessible in the main electrical room.
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