Template · Service and panels

Subpanel addition single line diagram

100A four-wire feeder to a new subpanel. Use this for adding a subpanel in the same building, fed by a 100A four-wire feeder from the main panel.

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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Subpanel addition single line diagram: 100A four-wire feeder to a new subpanel. — Subpanel addition. 15 devices on an 11 × 17 in sheet with a title block and notes column.

What the reviewer checks on this drawing

The reviewer checks the feeder breaker and conductor sizes, the isolated neutral bar and bonded ground bar in the subpanel, and the working space in front of it.

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	100A 2P	Subpanel feeder
Panel	Subpanel	100A MLO · 120/240V	3 #3 Cu + #8 G, 1-1/4" EMT
Circuit breaker	20A 1P
Load	Receptacles
Circuit breaker	15A 1P
Load	Lighting
Circuit breaker	30A 2P
Load	Dryer
Circuit breaker	Spare

Notes on the sheet

Subpanel neutral bar isolated from the enclosure; separate equipment grounding bar bonded.
Working space 30 in wide and 36 in deep maintained in front of the subpanel.

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.