Phase Academy Interactive Power Systems Lab

One-Line Diagram Builder & Explorer

Educational SLD
Edit Properties
Duplicate
Rotate 90°
Delete
Drag equipment from the sidebar (or click to place) · drag port-to-port to connect · right-click equipment to edit · press R to rotate, Delete to remove
Selected Equipment
Click an equipment to view properties.
System Summary
Voltage Levels
Topology
Warnings
Event Log

🔍 Explorer

Distinguishes (a) all physical paths, (b) energized source-to-load paths through closed devices and the selected ATS source, and (c) paths blocked by open devices.

⚡ Energized Source-to-Load Paths
🚫 Blocked Paths (Open Device or ATS)
📋 Equipment List
🔗 Connection Map
❓ Symbol Explanation

⚖️ Load Aggregation / Energized Load Summary

This is NOT a Newton-Raphson power-flow study. Assumptions:

  • Balanced 3-phase, lossless transformers and conductors
  • Loads are aggregated upstream radially. Loops are not solved.
  • Transformer kVA is conserved across primary/secondary. Current is recomputed at each side voltage.
  • Panels use either a user-supplied demand (kW/kVAR/PF) or an “assumed load current” (not the breaker rating).
  • Motors compute steady-state load only when running. Inrush is a separate simulation.
  • Source impedance and voltage drop are not modeled.
🔋 Source Totals
📊 Per-Equipment Aggregated Demand
🔌 Per-Connection Branch Current

Preset Systems & Challenges

Load a preset topology, then explore it in the Builder, Explorer, and Load Aggregation tabs.

Simple Radial System

Utility 13.8kV → 13.8/0.48kV transformer → main bus → feeder breakers to motor and step-down 480/208 transformer feeding a panel.

Beginner9 Components

Ring Bus (Tie Normally Open)

Two utility sources, two bus sections, tie breaker normally open so only one source feeds at a time. Closing the tie creates parallel sources (intentional warning).

Intermediate8 Components

Industrial Plant

13.8kV utility, 2 MVA main XFMR to 480V switchgear, MCC with motors, capacitor bank, and 480/208 step-down for lighting panel.

Advanced13 Components

Emergency Power (ATS)

Normal utility and emergency generator with ATS. Normal source selected by default. 480/208 transformer before critical 208V panel.

Intermediate10 Components

Commercial Building

13.8kV utility, 13.8/0.208 kV step-down transformer, 208V main switchboard, three 208V panels.

Beginner7 Components

About This Tool

The one-line (single-line) diagram is the primary communication tool of power systems engineering, and reading or building one accurately is a foundational skill. This educational builder lets you draw one-line diagrams and inspect them with a simplified balanced 3-phase model. It performs load aggregation (sum of downstream loads as kW/kVAR/kVA and per-side currents), honors open breakers/fuses/disconnects and ATS source selection, and warns when basic engineering rules are violated.

“A one-line diagram is a promise about topology — the Explorer tab checks whether the promise holds.”

What You’ll Learn

  • Place and connect standard one-line diagram symbols for sources, transformers, breakers, buses, and loads
  • Trace energized paths from source to load through radial, ring-bus, and ATS system topologies
  • Explain how an open breaker or an ATS in transfer position changes the energized path in a system
  • Aggregate load demand from individual loads through distribution equipment to the source
  • Identify the key differences between simple radial, main-tie-main, and ring-bus topologies
  • Read and interpret a one-line diagram connection map and equipment list

Symbols

How to Use

  • Drag equipment from the sidebar onto the canvas (or click a palette item to place it).
  • Click and drag a port (blue dot) to another port to make a connection.
  • Right-click equipment to edit, rotate, toggle open/closed, switch ATS source, or start/stop motors.
  • Press R to rotate the selected equipment 90°; Delete removes it.
  • Toggle Load Aggregation to see kW/kVA/A on equipment and connections.
  • Toggle Energized Connectivity to color the wires that are actually energized.
  • Run Self-Tests (header button) to verify the computation engine — your diagram is preserved.

Cable Ampacity (NEC 310.16)

Cable elements carry the raw table ampacity from NEC Table 310.16 (not more than three current-carrying conductors in raceway, cable, or earth, 30°C ambient) for the chosen size, material, and insulation temperature rating, multiplied by the number of parallel sets. Ambient-temperature and conductor-count adjustment factors are not modeled. Remember that NEC 240.4(D) separately limits the overcurrent device for small conductors (14/12/10 AWG copper → 15/20/30 A; 12/10 AWG aluminum → 15/25 A) regardless of insulation rating — that is an overcurrent-protection rule, not an ampacity.

Common Mistakes

  • Connecting a 208 V panel directly to a 480 V bus without a step-down transformer — flagged even when a cable sits in between.
  • Treating an ATS as having “two outputs” — it has two inputs (Normal, Emergency) and one output.
  • Confusing a breaker’s rating with the actual branch load current.
  • Computing connection current using the wrong side voltage of a transformer.
Educational Disclaimer: This is NOT a Newton-Raphson power flow, NOT a short-circuit study, NOT a coordination study, and NOT an arc-flash analysis. Source impedance, transformer impedance, cable impedance, voltage drop, harmonics, unbalance, motor contribution to faults, and dynamic behavior are not modeled. Always consult a licensed electrical engineer for real designs.