Electrical Load Schedule: Plan Every Circuit on One Page

An electrical load schedule is a single table that lists every circuit in an installation: what it supplies, its load, its protective device, its cable, and which phase it sits on. It sounds like paperwork, and in a sense it is, but it is the paperwork that prevents the most expensive mistakes in electrical design. Without a schedule, circuits are added by memory, phases drift out of balance, and nobody knows whether the board or the supply is close to its limit until something trips. With a schedule, those questions have answers on one page. The Electrical Load Schedule Builder helps you assemble that table, but the schedule itself is guidance and a planning tool only. Local electrical codes and a licensed electrician or qualified designer govern real designs, and only qualified people should carry out electrical installation work.

This guide explains what belongs in a load schedule, how to build one step by step, how to balance phases and total demand, and how to keep the schedule useful after the installation is complete. It is general information for understanding and planning, not a design for any particular installation.

What a load schedule contains

A useful load schedule has one row per circuit and columns that answer the questions a designer, an installer, and a future maintainer will ask. Typical columns are: circuit number, description and location, load type, connected load in watts or volt-amperes, design current in amperes, phase for three-phase boards, protective device type and rating, cable size and type, and notes. Some schedules also include demand factor or diversified load per circuit group, voltage drop notes, and the board or distribution board the circuit belongs to. The exact columns matter less than completeness: every circuit in the installation should appear exactly once, and every column that affects sizing should be filled in or marked as not applicable with a reason.

The description column deserves more care than it usually gets. "Socket" is not a useful description; "ground floor living room sockets, east wall" is. A future electrician tracing a fault, or a building owner planning an extension, needs to find the circuit from the description without guessing. Use room names that match the building's actual layout, and keep the numbering consistent with the labels on the board. If the board labels and the schedule disagree, the schedule is wrong in practice even if it is right on paper, because people work from labels in an emergency. Reconciling labels and schedule is therefore part of building the schedule, not an optional tidy-up afterwards.

Building the schedule step by step

Start by walking the building or the design drawings and listing every load: lighting circuits, socket circuits, fixed appliances, heating and cooling, water heating, pumps, motors, lifts, and special equipment. Do not forget loads that are easy to miss: outdoor lighting and sockets, garage equipment, ventilation fans, security systems, and equipment that is installed but rarely used, such as a workshop machine or a backup heater. For each load, record its rating from its nameplate or from the design data. Where a rating is given in watts, note whether it is real power; where it is given in volt-amperes, note that, because the two differ when power factor is less than one. For socket circuits, the load is not a single appliance but an assumed load per the applicable code, because the code sets how socket circuits are estimated. A qualified designer will apply the code's socket allowances; a planner's schedule should at least flag socket circuits clearly so those allowances are not forgotten.

Next, assign each circuit to a board and, for three-phase boards, to a phase. Then calculate the design current for each circuit from its load, voltage, phase, and power factor where relevant. For a single-phase resistive load, current is power divided by voltage. For a three-phase load, current is power divided by the square root of three multiplied by line voltage multiplied by power factor. Keep the working visible, either in the schedule notes or in a supporting calculation, so the numbers can be checked. Then choose, or note for the designer to choose, the protective device and cable for each circuit, and record them in the schedule. The schedule is not complete until the device and cable columns are filled, because a load list without protection and cabling is only half a design.

Finally, total the schedule. Total the connected load, total the demand after applying demand factors by category, and total the current per phase. Those three totals answer three different questions: how much is installed, how much is expected to peak, and whether the phases are balanced. A schedule whose totals do not add up, or whose phase currents differ wildly, has an error or a design problem that should be resolved before installation, when fixing it costs nothing more than editing a table.

Worked example with sample values

Take a sample small three-phase board with six circuits, using sample loads for illustration only. Circuit 1, lighting ground floor, one thousand watts, single phase, phase L1. Circuit 2, lighting first floor, one thousand watts, phase L2. Circuit 3, sockets ground floor, three thousand watts assumed load, phase L3. Circuit 4, sockets first floor, three thousand watts assumed load, phase L1. Circuit 5, cooker, six thousand watts, phase L2, with diversity applied later at board level in a real design. Circuit 6, water heater, three thousand watts, phase L3. Total connected load is one thousand plus one thousand plus three thousand plus three thousand plus six thousand plus three thousand, which equals seventeen thousand watts, or seventeen kilowatts.

Now total per phase, before demand factors. Phase L1 carries circuit 1 at one thousand watts plus circuit 4 at three thousand watts, which equals four thousand watts. Phase L2 carries circuit 2 at one thousand watts plus circuit 5 at six thousand watts, which equals seven thousand watts. Phase L3 carries circuit 3 at three thousand watts plus circuit 6 at three thousand watts, which equals six thousand watts. The phases are unbalanced: L2 carries seven thousand watts while L1 carries only four thousand, a difference of three thousand watts. At two hundred and thirty volts phase voltage, that difference is about thirteen amperes. Moving one three-thousand-watt circuit from L2 or L3 to L1 would improve balance, although the cooker circuit's phase may be constrained by other design factors. In this sample, moving circuit 3 from L3 to L1 would give L1 seven thousand watts, L2 seven thousand watts, and L3 three thousand watts, which is still unbalanced in the other direction, showing that perfect balance is not always achievable with a small number of large circuits. The goal is reasonable balance, not mathematical perfection, and the schedule makes the imbalance visible so it can be discussed rather than discovered after installation.

Now apply a simple board-level illustration. Suppose the designer applies an overall demand factor of zero point eight to the seventeen kilowatts, giving an estimated maximum demand of seventeen multiplied by zero point eight, which equals thirteen point six kilowatts. The three-phase current at four hundred volts line voltage, assuming a power factor of one for simplicity, is thirteen thousand six hundred divided by the square root of three multiplied by four hundred, which is thirteen thousand six hundred divided by about six hundred and ninety-two point eight, which equals about nineteen point six amperes per phase on average if balanced. That figure is a planning illustration, not a board rating, because a real design applies demand by category, checks the largest load rules, and verifies voltage drop and fault performance. The value of the example is in showing the chain: list, total, balance, apply demand, convert to current, and check.

Common mistakes to avoid

The first mistake is an incomplete list, usually missing outdoor, garage, or rarely used loads that later overload a board that looked fine on paper. The second mistake is double-counting a load that appears on two boards or in two categories, which inflates the total and can lead to an oversized supply. The third mistake is ignoring power factor for motor and electronic loads, where volt-amperes exceed watts and current is higher than a watts-only calculation suggests. The fourth mistake is poor phase allocation, often because circuits were added in the order they were thought of rather than distributed deliberately. The fifth mistake is a schedule that is never updated: circuits are added during the building's life, the schedule stays in a drawer, and after a few years nobody trusts it. The sixth mistake is vague descriptions and mismatched board labels, which make the schedule useless in an emergency even when its numbers are correct.

Another mistake is treating the schedule total as the supply size without applying demand, margins, or code rules. Connected load is the starting point, not the answer. Conversely, applying an aggressive demand factor to every category without justification understates the supply and risks nuisance tripping. Both errors come from skipping the step where the designer justifies each assumption and records its source. A schedule with sources and notes is a design document; a schedule with bare numbers is a guess.

Keeping the schedule alive

Treat the load schedule as a living document. When a circuit is added, removed, or changed, update the schedule, update the board labels, and re-total the phases and the demand before the work is signed off. Keep the schedule with the board or in the building's electrical records, in a place the next electrician will actually find it. Version it with a date, and keep old versions so changes can be traced. For a larger building, keep a schedule per board plus a summary schedule for the whole installation, so both the detail and the overview are available without searching through unrelated boards.

Review the schedule at sensible triggers: before an extension or renovation, when a large new appliance is added, after a change of use for a room or a floor, and at each formal periodic inspection. Each review is a chance to catch imbalance, overloaded boards, and circuits that no longer match their labels, before they become faults. A schedule that is reviewed at those triggers stays accurate with little effort; a schedule that is only reviewed when something goes wrong is usually out of date at exactly the moment it is needed most.

For related calculations, the Three Phase Power Calculator helps convert loads to currents, and the Electrical Demand Factor Calculator covers the demand step in more detail. You can also read the related guide on battery backup runtime at /blog/battery-backup-runtime-calculator-guide/ for how load schedules feed into backup sizing. Remember the standing limit: load schedules in this guide are guidance only, local codes and a licensed electrician or qualified designer govern real designs, and only qualified people should install or modify electrical systems.