Electrical Plan Symbols, Homeruns and Circuit Tags

Why this matters

An electrical plan compresses a lot of wiring into a few marks. One arrow with a tag says which panel and which breakers feed a group of devices. A few short strokes across the line say how many conductors run in it. A lowercase letter on a switch says which lights it controls. A letter on a fixture points to a schedule that says what to order. Every other trade working near electrical work benefits from reading these, and the electrician pricing a fit-out depends on it, because the plan does not draw wires, it draws an abbreviation of them. That abbreviation varies by firm, so this card teaches the shapes and leaves the final word to the set's legend.

Reading the plan is desk work. Finding the same circuits in a building means opening panels and testing conductors, and that is work for a qualified electrician under 29 CFR 1910.333 (29 CFR 1926 Subpart K on a construction site) and NFPA 70E, not something this card teaches.

The plan fragment

Two small pieces of a lighting plan and a power plan, drawn in one common set of conventions:

POWER PLAN FRAGMENT, E-102

 =O= 9      =O= 11     =O= 13 GFCI
  |          |          |
  +----------+----------+-/-/-/-|-+->  LP-1 / 9,11,13
                           |    |  |
                 3 short = hots |  hash with dot = ground
                       1 long = neutral

LIGHTING PLAN FRAGMENT, E-101

 [A] a      [A] a      [A] b      [A] b
  |          |          |          |
  +----------+----------+----------+-->  LP-1 / 7
                Sab  = 2-gang switch, legs a and b

The homerun and its tag

The homerun is the run from the last device on a circuit back to the panel. Rather than draw that run across the building, the plan shows a short line ending in an arrow, and beside it a tag: the panel name and the circuit numbers. "LP-1 / 9,11,13" means three circuits, numbers 9, 11 and 13, from the panel named LP-1. The panel's location is on the power plan or the one-line diagram, and its breakers, loads and phases are on the panel schedule. See Panel Schedules on the Drawings, Column by Column, and for following a circuit from the panel to its last device, How to Trace a Circuit from Panel Schedule to Plan.

Devices between the homerun and the end of a circuit are joined by lines that show which devices share a circuit, not the actual cable route. The installer picks the route within the code and the specification.

Hash marks: conductor count, by the legend

The short strokes across a homerun or a circuit line show how many conductors are in that run. A common convention, not a universal one:

• Short hash for each ungrounded conductor, the hots.
• Long hash for the grounded conductor, the neutral.
• A hash with a dot, a flag or a different shape for the equipment grounding conductor.

Some firms draw only the hots and neutral and cover the ground in a general note. Some draw no hash marks at all and state a default ("two 12 AWG and one 12 AWG ground in 3/4 in conduit unless noted"). Some write the count in words beside the run. Read the electrical legend before counting a single mark, because the same three strokes mean three hots on one set and two hots and a neutral on another.

Switches, switch legs and fixture tags

Switches are commonly an S with a subscript or suffix: S for single-pole, S3 three-way, S4 four-way, SD dimmer, OS or SOS an occupancy sensor switch, SK a key switch. The switch leg, the controlled conductor from switch to lights, is shown by a lowercase letter: a switch marked "a" controls every fixture marked "a" on that circuit. A two-gang switch marked "Sab" carries two switches, one for the "a" fixtures and one for the "b" fixtures, which on a plan is how a dual-level or front-and-back lighting scheme shows up.

Fixture type tags, commonly a letter or letter-number (A, B1, X for an exit sign, EM for emergency), point to the luminaire schedule: description, mounting, voltage, wattage or lumen output, lamp or source data, and control notes. The plan says where and how many; the schedule says what. Two fixtures that look the same on the plan with different tags are different products.

Receptacles and their variants

The duplex receptacle, commonly a circle with two short parallel lines, is the base symbol, and variants hang off it with a letter, a fill or a mark:

• GFCI or GFI: ground-fault protected at the device.
• WP: weatherproof, with an in-use cover where the code as adopted requires it.
• IG, or a triangle: isolated ground, with its own grounding conductor.
• A filled or half-filled symbol, or a number of outlets: dedicated, quad or special-purpose devices, depending on the legend.
• A number with a plus sign beside a device, such as +44, commonly a mounting height in inches above the floor, overriding the general note's default.
• Floor boxes and poke-throughs: their own symbols, often keyed to a detail.

See The Symbol Classes Worth Knowing Across Trades for how these sit among the symbol families other trades use.

A worked read: one homerun, two panels

An electrician is pricing the power plan fragment above. The homerun reads LP-1 / 9,11,13 with three short hashes, one long hash and one ground mark. Each receptacle carries its own circuit number, 9, 11 and 13, and the one on 13 is a GFCI.

Decode the run. Three circuits, three hots, one neutral and one ground: a multiwire branch circuit, three hots sharing one neutral. That works only if the three hots are on three different phases, so the neutral carries the imbalance between them rather than their sum.

Check the panel. The panel schedule on E-601 says LP-1 is 208Y/120 volt, three-phase, four-wire. On a standard panelboard the breaker positions run down two columns, odd numbers on the left and even on the right, and each row shares one phase bus, with the rows cycling A, B, C. So circuits 1 and 2 are on A, 3 and 4 on B, 5 and 6 on C, 7 and 8 on A again, 9 and 10 on B, 11 and 12 on C, 13 and 14 on A. Circuits 9, 11 and 13 land on B, C and A: three different phases. With ordinary loads the currents largely cancel in the shared neutral (heavy electronic loads can return current on the neutral, which is why some engineers avoid sharing neutrals for them). The homerun is valid as drawn.

The rule that comes with it. NEC 210.4(B), as adopted by your jurisdiction, requires a means to disconnect all ungrounded conductors of a multiwire branch circuit simultaneously at the point where the circuit originates. Positions 9, 11 and 13 are stacked in one column, so a three-pole breaker or listed handle ties across those three positions can meet it. That belongs on the takeoff.

The same tag on a different panel. Suppose the panel schedule had said LP-1 is 120/240 volt, single-phase. There the rows alternate A, B, A, B: 1 and 2 on A, 3 and 4 on B, 5 and 6 on A, 7 and 8 on B, 9 and 10 on A, 11 and 12 on B, 13 and 14 on A. Circuits 9 and 13 would both land on A. Two hots on the same leg sharing one neutral means the neutral carries the sum of their currents, which can overload it without tripping either breaker. That homerun cannot be built as drawn, and it goes back as an RFI before the conductors are pulled.

The lighting run. LP-1 / 7 feeds four type A fixtures, two on switch leg a and two on leg b, from one two-gang switch. The luminaire schedule gives type A's description and mounting, so the order is four type A fixtures, one two-gang switch assembly, and the circuit's wiring by the general note's default.

Marks for fixtures and circuits that behave differently

A few small marks change how a fixture or circuit is wired, and each one is easy to read past on a crowded lighting plan:

• EM, or a filled or shaded fixture symbol: an emergency fixture, on an emergency circuit or carrying a battery pack, which keeps light on when normal power fails. It is wired differently from its neighbors even when it shares their type tag.
• NL, or "unswitched": a night light fixture wired ahead of the switch so it stays on. On the plan it sits among switched fixtures with no switch-leg letter.
• A circuit number at a device with no homerun drawn: the device joins that circuit, and the homerun is shown elsewhere on the same circuit.
• "To existing" or an arrow to a screened device: the new work extends an existing circuit, whose capacity and condition are not on this sheet. See How a Renovation Set Shows Existing, New and Demolition.

Where the conventions vary most, and what to do about it

Hash mark meaning, receptacle variant symbols and whether circuit numbers appear at each device all vary from firm to firm and sometimes from sheet to sheet within one set, where a consultant drew the lighting and someone else the power. The legend on the electrical 0-series sheet governs the whole discipline; a sheet-specific note governs that sheet. When the two disagree, or a mark appears that is in neither, that is a written question, not a guess. See The Legend and Notes Most Techs Skip.

Checking your read

For each homerun in your scope: the panel and circuits are read from the tag; the conductor count from the hash marks matches the legend's convention; any shared neutral has its circuits checked against the panel's voltage and phase arrangement on the panel schedule; every switch leg letter has a matching set of fixtures; every fixture tag has a luminaire schedule row. Acceptance is a takeoff that traces every item to a tag and a schedule, and any homerun that fails the phase check written up as an RFI before rough-in.

References

• NFPA 70, National Electrical Code, 210.4 (multiwire branch circuits), as adopted by your jurisdiction
• NFPA 70E (current edition), 29 CFR 1910.333 and 29 CFR 1926 Subpart K, for the qualified-person work of tracing circuits in an energized building
• See related: The Symbol Classes Worth Knowing Across Trades; How to Read a Schedule on a Drawing Set
• See related: Panel Schedules on the Drawings, Column by Column; How to Trace a Circuit from Panel Schedule to Plan