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The importance of One Line Diagrams

3C Electrical can review or create an accurate one-line diagram for your plant’s electrical power system. A one-line diagram is a drawing in which a single line represents three phases of a 3 phase power system. It shows the correct power distribution path from the incoming source to each downstream load, and should include the ratings and sizes of each piece of equipment, their circuit conductors and their protective devices. An accurate one-line diagram must be updated with changes to equipment or other factors that affect its reliability.

An accurate one-line diagram is necessary for several reasons:
  • Meet NFPA 70E requirements
  • Deenergize, lockout and tagout properly
  • Troubleshoot during an emergency
  • Determine available fault current to evaluate potential arc flash hazards
Components of an accurate one-line diagram:
  • Transformer ratings, voltage ratio, impedance and winding connections
  • Feeder cable phase, neutral, and ground sizes;
  • Length of cable, conductor material, conduit size and type
  • Switchgear, switchboards, panelboards, MCCs, fuses, circuit breakers, automatic transfer switches, and continuous current ratings
  • Protective relays with appropriate device numbers
  • CTs with associated ratios

One Line Diagram
Click to download a sample of a one-line diagram

Please call 855-881-3911 today to discuss your electrical power system needs. We take pride in our work and will give you a complete solution to keep your systems running safely and efficiently.

3C Electrical Company | Westborough, MA

3C Electrical Company provides electrical testing, maintenance, engineering, and 24-hour emergency service to the Northeast, including Boston, Worcester, Springfield, Lowell, Cape Cod, and all surrounding towns.