TrueLine – One-Line Diagrams

509 Electric

About this app

Build clean, professional electrical one-line (single-line) diagrams right on your phone or tablet — on the jobsite, in the truck, or at the plan table. TrueLine turns a service, panels, and a list of loads into a properly drawn one-line, with conductor and overcurrent sizing referenced to the NEC as you build.

WHAT IT DOES
- Interactive one-line canvas — drag-and-drop utility source, meter/main, service, panels, feeders, sub-panels, and branch loads. The diagram stays readable as the project grows.
- NEC-referenced sizing on the diagram — conductor ampacity (Table 310.16), dwelling service/feeder conductors (310.12), overcurrent and small-conductor rules (240.4), equipment grounding conductors (250.122), grounding electrode conductors (250.66), feeder sizing (215.2), and conduit fill (Chapter 9).
- Live NEC check panel — flags panel-fill overages and parallel-conductor minimums (310.10(G)), and lists the review items a plan checker expects: load calc, demand factors, terminal temperature, derating, voltage drop, grounding and bonding.
- Ready-made templates — Service Upgrade, Solar + Battery, EV Charger, Generator + ATS, Sub-Panel, Commercial Service, Motor Control Center, Emergency/Standby, and Transformer-Fed — or a blank canvas.
- Real equipment symbols — meter-mains, disconnects, breakers, busbars, transformers, generators, automatic transfer switches (ATS), MCCs, inverters, and motor loads, each with the callouts electricians actually label.

PRO UNLOCK
- Commercial and three-phase (208Y/120V, 480Y/277V) diagrams, generators, ATS, sub-panels, motor and transformer circuits.
- Permit-ready vector PDF export on Letter, Tabloid (11x17), or ARCH D (24x36) with a custom title block and a FOR REVIEW status note.

WHO IT'S FOR
Electricians, apprentices, estimators, and inspectors who need a real one-line fast — for a permit set, a service upgrade, a generator/ATS hookup, or a quick sketch to talk through with the AHJ.

ACCURACY
Sizing is based on the referenced NEC articles (2023 edition by default). TrueLine is a design aid for qualified professionals, not a substitute for engineering judgment — load calculations, demand factors, terminal ratings, ambient and derating conditions, voltage drop, grounding and bonding details, available fault current, and AHJ requirements are yours to verify before a drawing is used for permit or construction. Motor branch circuits (430), transformer protection (450/240), and optional standby systems (702) are flagged for your review. Always verify against the NEC edition adopted in your jurisdiction.

PRICE
TrueLine is free to download and use for residential single-phase (120/240V) one-line work — build diagrams, use the residential templates, and see NEC-referenced sizing on screen. A one-time Pro Unlock ($9.99 — no subscription, no renewals) adds commercial and three-phase diagrams, generators, ATS, sub-panels, motor and transformer circuits, and vector PDF export with a custom title block. Buy once, own it forever.

PRIVACY
Every calculation and diagram runs on your device. TrueLine collects no personal data, requires no account, and works fully offline. Projects stay in local storage on your phone and are never transmitted.

Built by 509 Electric, a licensed Washington electrical contractor (EL01) in Yakima — field tools made by people who wire buildings for a living. Part of the True suite of NEC field calculators for electricians.

What’s new

Maintenance update: now targets Android 16 (API level 36) to meet Google Play's target API level requirements. No functional changes.