Template · Generators

Portable generator inlet with interlock single line diagram

Backfed 30A breaker mechanically interlocked with the main. Use this for a portable generator plugged into an inlet box, feeding the main panel through a backfed breaker with a mechanical interlock on the main. It is a simple way to run selected circuits by hand during an outage.

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.

Open this template in the editor Download the SVG

Portable generator inlet with interlock single line diagram: backfed 30A breaker mechanically interlocked with the main. — Portable generator inlet with interlock. 9 devices on an 11 × 17 in sheet with a title block and notes column.

What the reviewer checks on this drawing

The reviewer looks for a listed interlock that stops the main and generator breakers being closed together, a hold-down kit on the backfed breaker, and how the generator neutral is arranged.

What the drawing shows

Every device on the sheet, in the order power reaches it.

Symbol	Label	Rating or detail	Conductors feeding it
Utility source	Utility service	120/240V 1φ 3W
Meter	Utility meter	200A socket	Service conductors, per utility
Circuit breaker	200A 2P	Main breaker
Panel	Main panel	200A bus · 120/240V
Circuit breaker	Existing	Branch breakers
Load	Existing loads
Circuit breaker	30A 2P	Generator backfeed, interlocked with main
Power inlet	Power inlet box	30A · L14-30 · NEMA 3R	4 #10 Cu
Generator	Portable generator	7.2 kW · 120/240V	Cord set

Notes on the sheet

Listed mechanical interlock prevents the main and generator breakers from being closed at the same time.
Generator backfeed breaker secured with a hold-down kit.
Generator with floating neutral; neutral is not switched by the interlock.

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.