How to Read Single Line Diagrams for Switchgear Procurement
A practical guide for overseas buyers on reading and preparing single line diagrams (SLD) for switchgear and electrical distribution equipment procurement.
What a single line diagram shows
A single line diagram (SLD) shows the electrical power flow from incoming source to final distribution. For switchgear procurement, the SLD should show voltage level, main incoming rating, feeder configuration, protection devices, metering points, and earthing arrangement.
Buyers should provide a clear SLD with load schedule, cable sizes, fault level, and protection requirements to get accurate technical proposals.
Key parameters to confirm before RFQ
Before sending RFQ, confirm: rated voltage, rated current, short-circuit withstand capacity, frequency, number of incoming and outgoing feeders, component brand preference, protection relay type, communication protocol, and enclosure rating (IP/IK).
Also specify environmental conditions: ambient temperature, altitude, humidity, pollution degree, and seismic requirements if applicable.
Common SLD symbols and what they mean
Standard symbols for circuit breakers, disconnectors, transformers, CT/PT, and protection relays help avoid misinterpretation. IEC 60617 or IEEE 315 standards are commonly used.
If the buyer's SLD uses non-standard symbols, include a legend or key to avoid quotation errors.