{"schemaVersion":1,"slug":"synchronising-lamps","name":"Synchronising lamps","kind":"symbol","abbreviation":"SL","aliases":["synchroscope lamps","dark lamp method","rotating lamp synchronising"],"category":"measurement-protection","drawingTypes":["Schematic"],"referenceFamilies":["IEC","Manufacturer"],"summary":"Set of lamps connected between incoming and running phases that brighten and dim with the phase difference during synchronising.","description":["Synchronising lamps are connected between corresponding phases of the running system and the incoming machine. As the phase difference changes the lamps brighten and dim, and in the dark-lamp method the breaker is closed when they are dark, showing the voltages are in phase.","Lamps cannot show small residual voltage differences reliably, since a lamp can look dark with a significant voltage across it. They are therefore a backup or visual aid, and the drawing should show a synchroscope or check-synchronising relay for the actual permission to close."],"readingNotes":["Identify which phases each lamp is connected across.","Look for a check-synchronising relay in the closing circuit."],"drawingChecklist":["Show lamp connections per phase","State lamp voltage rating","Reference check-synchronising function"],"distinction":"Synchronising lamps give a visual indication; a synchroscope shows phase angle and slip direction directly.","facts":[{"label":"Connection","value":"Across incoming and running phases"},{"label":"Common method","value":"Dark-lamp closing"},{"label":"Preview","value":"Independent educational concept; consult the applicable standard and project legend for the exact graphic"}],"references":[{"sourceId":"iec-diagrams","relevance":"IEC context for graphical symbols used in diagrams; no IEC graphic is reproduced."},{"sourceId":"generator-controls","relevance":"Public generator paralleling controls context."}],"related":["synchronoscope","double-voltmeter","25-synchronism-check"],"artwork":"s28-synchronising-lamps","publishedOn":"2026-10-28","updatedOn":"2026-10-28","provenance":"independent-public-research","plainEnglish":{"title":"What does Synchronising lamps mean?","introduction":"Synchronising lamps are connected between corresponding phases of the running system and the incoming machine. As the phase difference changes the lamps brighten and dim, and in the dark-lamp method the breaker is closed when they are dark, showing the voltages are in phase.","example":"Lamps cannot show small residual voltage differences reliably, since a lamp can look dark with a significant voltage across it. They are therefore a backup or visual aid, and the drawing should show a synchroscope or check-synchronising relay for the actual permission to close.","drawings":"Identify which phases each lamp is connected across. Look for a check-synchronising relay in the closing circuit. Synchronising lamps give a visual indication; a synchroscope shows phase angle and slip direction directly.","terms":[{"name":"Coil","meaning":"A wound conductor that can produce a magnetic field when energised."},{"name":"Phase","meaning":"One of the related AC waveforms in a power system."},{"name":"Rating","meaning":"A value stating the conditions for which equipment is specified."}],"diagram":"flow","steps":["Identify the device and form","Read the connections and state","Check the equipment reference"],"caption":"A guide to reading this reference. The original symbol illustration and its drawing notes appear below; these boxes are not a wiring diagram.","sources":[{"label":"IEC graphical symbols for diagrams","url":"https://tc3.iec.ch/tc-activity/graphical-symbols-for-diagrams/"},{"label":"Generator switchgear and paralleling controls","url":"https://www.cummins.com/en-na/generators/products/switchgear"}],"detail":"Set of lamps connected between incoming and running phases that brighten and dim with the phase difference during synchronising. Synchronising lamps give a visual indication; a synchroscope shows phase angle and slip direction directly.","profileId":"reviewed-symbol-20261028"},"url":"https://eloragrid.ai/symbols/synchronising-lamps","illustration":{"url":"https://eloragrid.ai/tools/electrical-library/illustrations/synchronising-lamps.svg","scope":"Original educational concept; not an official standard graphic or product footprint","license":"https://creativecommons.org/licenses/by/4.0/"},"sources":[{"id":"iec-diagrams","title":"IEC graphical symbols for diagrams","publisher":"IEC","url":"https://tc3.iec.ch/tc-activity/graphical-symbols-for-diagrams/","type":"standard","scope":"IEC 60617 and related symbol-design publications. Full database access requires a subscription.","checkedOn":"2026-10-13","reuse":"link-only","relevance":"IEC context for graphical symbols used in diagrams; no IEC graphic is reproduced."},{"id":"generator-controls","title":"Generator switchgear and paralleling controls","publisher":"Cummins","url":"https://www.cummins.com/en-na/generators/products/switchgear","type":"manufacturer","scope":"Public description of generator switchgear, controls and system interfaces.","checkedOn":"2026-10-13","reuse":"link-only","relevance":"Public generator paralleling controls context."}]}