Commercial standby generator with ATS single line diagram
Four-pole transfer switch feeding a standby panel at 120/208V. Use this for a commercial building with a three-phase standby generator feeding a standby panel through a four-pole transfer switch.
A free template with typical ratings, conductor callouts and general notes. Open it, change what differs on your job, fill in the title block and export a PDF.
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What the reviewer checks on this drawing
The reviewer checks the switched neutral, which makes the generator a separately derived system bonded at the generator; the generator breaker; and a separate transfer switch for any emergency (life-safety) loads.
What the drawing shows
Every device on the sheet, in the order power reaches it.
| Symbol | Label | Rating or detail |
|---|---|---|
| Utility source | Utility service | 120/208V 3φ 4W |
| Current transformer | CT cabinet | Utility metering |
| Circuit breaker | 600A 3P | Main |
| Panel | Main distribution panel MDP | 600A · 120/208V 3φ 4W |
| Circuit breaker | 400A 3P | Normal loads |
| Panelboard | Panel NP | Normal power |
| Circuit breaker | 225A 3P | ATS normal feed |
| Transfer switch | Automatic transfer switch | 225A · 4-pole |
| Circuit breaker | 225A 3P | Generator breaker |
| Generator | Standby generator | 60 kW / 75 kVA, 120/208V · diesel |
| Panel | Standby panel SP | 225A MLO · 120/208V |
| Circuit breaker | Branch | Standby circuits |
| Load | Standby loads |
Notes on the sheet
- Four-pole transfer switch: generator is a separately derived system, bonded and grounded at the generator.
- Generator 75 kVA at 208V = 208A, protected at 225A.
- Emergency (life-safety) loads, where present, require a separate transfer switch and wiring.
Diagram is schematic and not to scale. Field-verify existing equipment ratings. Ratings and conductor sizes shown are typical. Confirm against the adopted code, the equipment listing and a load calculation before installation. Code references are to the 2023 NEC and the 2024 Canadian Electrical Code: see references and editions.
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