Avenler

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14. Designing to the NEC (USA)

Important before you start. Avenler is an aid, not a permit document. Approval of a US design is decided by the local authority having jurisdiction (AHJ) and the NEC edition in force. Always check the program's NEC values against the text of the official edition. The NEC mode is beta: the program knows the common residential rules, not the whole standard.

This chapter walks through residential design to the US code (NEC, NFPA 70): how to switch a project over, how to draw in feet and inches, how the circuit allocation and the load center work, and what the program checks.

The project region: units and code system

  1. Open the project page (Projects) and find the region settings under More settings at the bottom of the page.
  2. Units can be Metric (mm, m) or Imperial (ft, in).
  3. Electrical code system can be IEC (default) or NEC (USA); NEC carries a beta badge. With NEC you can also choose the Code edition (NEC 2020, 2023 or 2026; the default is 2023).
  4. Voltage level is Automatic by default (IEC: 230/400 V, NEC: 120/240/208 V), but it can also be chosen by hand: 230/400, 220/380, 240/415, 120/240, 277/480 or 100/200 V. The sizing and the voltage drop are calculated with it; the tables of the code system (current-carrying capacity, resistance) stay unchanged. The NEC dwelling load calculation and the load center design still work with the NEC's own voltages.
  5. Only the project owner can change the region. The units and the voltage level can also be set from the ruler button in the drawing editor header. The setting applies to every floor of the project, the checks, the take-off and printing.

In the public calculators (voltage drop, cable selector, power–current) Units and Voltage level can be chosen separately, independently of the code system.

The standard system also offers NBR 5410 (Brasil). For the Brazilian market (pt-BR), a new project starts metric, per NBR 5410, with the "Brasil" symbol set and at 127/220 V. The voltage-drop limit under NBR is 4 %; the drawing check looks at the number of outlets per room (TUG), the ceiling lighting point and the separation of lighting and outlet circuits, and the board check applies the DR, TUE and DPS rules. The Boards page also shows a load estimate table (Quadro de previsão de cargas). In an NBR project the utility data sheet (padrão de entrada) shows Brazilian fields (utility, UC number, supply category, main breaker, service conductor); the program does not suggest the category limits, they come from the utility's standard. The technical description (memorial descritivo) names NBR 5410; the ART number, the responsible designer's name and the CREA/CFT number must be filled in by hand. The Documents menu has Brazilian inspection and measurement report templates, and the plan package has the load estimate sheet. The NBR findings are informative and have not been professionally reviewed.

Quick start: New project from template offers the US Starter House, a one-story house of about 1600 sq ft that starts with imperial units, NEC 2023 circuits, a 200 A load center and the US symbol set. You can modify it freely.

Drawing in feet and inches

In an imperial project the editor fields show and accept lengths in feet and inches. Valid entries include 12'6", 12'-6 1/2", 150" (inches) and 12.5' (decimal feet). While drawing a wall you can also type the length and press Enter.

  • The grid is 6 inches; the arrow keys move the selection by 1 inch, Shift + arrows by 1 foot.
  • Take-off lengths, exports and DXF are produced in the project's unit system too.
  • When printing you can choose Letter, Legal, Tabloid and Arch D paper and an architectural scale (for example 1/4" = 1'-0"); if the drawing does not fit the sheet, the program tells you.

The US symbol set

In the symbol-set selector of the top bar, United States gives the drawing style of "general US practice". It is not a standard symbol set: the program does not claim conformity with any standard.

In an NEC project (or with the US symbol set) the toolbar gains new symbols: GFCI socket-outlet, 20 A socket-outlet, 240 V socket-outlet (NEMA) (the NEMA configuration is set in the device properties), dimmer switch and ceiling fan.

Automatic circuit allocation to the NEC

In an NEC project the floor plan editor's Automatic assignment… button proposes circuits following US practice (you can accept or reject the proposal in the preview):

  • at least two 20 A circuits for the kitchen receptacles and 20 A circuits for the bathroom, laundry and garage receptacles;
  • GFCI protection for receptacles in bathrooms, kitchens, garages, outdoors, basements and laundry rooms, and AFCI protection for the 120 V circuits of living rooms, the kitchen, hallways and similar rooms; where both are needed, a dual-function breaker;
  • 240 V loads (for example dryer, range) on a 2-pole circuit with NM-B cable matched to the rated current.

Receptacles placed with the room template follow the receptacle spacing rule for wall spaces (6 ft, 24 in at countertops). The proposed values are starting values.

Load center and panel schedule

In an NEC project the distribution board type is load center. On the Boards page, a new board gets the type Load center, and you enter the number of spaces (an even number) and the main breaker / bus rating (A).

  • A breaker has 1 or 2 poles and takes one space per pole; a 2-pole breaker gets 240 V (L1 and L2).
  • For every breaker you can set the Protection type: Standard, GFCI, AFCI or Dual function (AFCI + GFCI).
  • If the circuits do not fit, the program proposes a larger number of spaces that you can apply on the spot.
  • The panel schedule shows, per space, the circuit, current, poles, protection and the L1/L2 load (VA). Print drawing set includes it as a sheet, and the single-line diagram is also drawn for the load center.

Dwelling load calculation (NEC Article 220)

On the Boards page of an NEC project the Dwelling load calculation appears: its inputs come from the drawing (the area is the sum of the rooms), and you can override the values (overrides are not saved). The derivation of both the optional (220.82) and the standard method is shown, with the recommended service and conductor.

You can also try it without a drawing, with manual inputs, in the public Power and current calculator: switch the IEC / NEC toggle to NEC and the dwelling load calculator appears below. It is an informative calculation.

To upgrade an existing home (for example for an EV charger or a heat pump), the public service upgrade load calculator shows, by the calculated (220.83) and the measured (220.87) method, whether the existing service is enough and, if not, what service and conductor are needed. It is an informative calculation.

NEC checks and fixes

In an NEC project the Checks panel (see the Checks chapter) also runs the US rules. These include missing GFCI (210.8), missing AFCI (210.12), a missing 20 A circuit (210.11(C)), receptacle spacing (210.52), 125 % of continuous load (210.20(A)), box fill (314.16), a reminder about tamper-resistant receptacles (406.12), and load-center rules: too few spaces, a small main breaker, unbalanced legs. The codes start with the NEC_ prefix.

Some findings offer a fix: Insert receptacles, Replace with GFCI receptacle, Add AFCI to the circuit protection. After Open the fix suggestion, review the suggestion, apply it and save the drawing. The rule settings are on the Check rules and Distribution board rules pages.

Responsibility and limits

Remember: the program is not a permit document. The design must be checked against the local authority (AHJ) and the NEC edition in force, and the program's NEC values against the official text. The NEC mode is beta; the US symbol set is not a standard symbol set. The text of the standards must be obtained from the publisher; the references are on the Standards page.