What the Electrical Load Schedule Builder does
This builds a distribution board schedule from a list of circuits. Each line carries a name, the phase it sits on, its connected kW, its power factor and its demand factor; the tool returns the current each circuit draws, the diversified load and current on each of the three phases, the imbalance between them and a printable schedule you can export as CSV or JSON.
It also suggests a rebalance: single-phase circuits reassigned heaviest-first onto whichever phase is lightest. That is a suggestion for you to accept or ignore, not an instruction - real boards have to keep related circuits together and respect the physical layout of the ways.
How to use it
- Set the line voltage and say whether the system has a neutral. In a four-wire system single-phase circuits sit between a line and neutral at 230 V on a 400 V supply; in a three-wire system they sit across two lines at the full 400 V.
- Type or paste the circuit list, one circuit per line: name, phase, kW, power factor, demand factor. Phase is L1, L2, L3, a pair such as L1-L2, or 3PH for a three-phase circuit. The last two columns may be left off and default to 0.9 and 1.
- Read the per-phase bars. A three-phase circuit spreads equally across all three legs; a line-to-line circuit puts half of itself on each of two legs.
- Check the imbalance figure. Under 10% is usually comfortable; over 20% is worth fixing before the board is built rather than afterwards.
- Press "Suggest a balance" to see a greedy reassignment of the single-phase circuits, then edit it to suit the real board layout.
- Export the schedule as CSV for the drawing office, or print it straight from the page.
Reading the results
Connected kW is the sum of the nameplate ratings. Diversified demand is the sum after each circuit's demand factor - the figure that matters for the incomer and the supply.
Per-circuit current uses that circuit's own power factor and the voltage appropriate to its phase configuration, so a 7.4 kW EV charger across two lines draws a very different current from the same 7.4 kW on one line and neutral.
Per-phase current uses the assumed overall power factor rather than any one circuit's, because the circuits on a phase do not peak together and a weighted figure would imply more precision than the data supports.
Imbalance is the largest deviation of a phase from the mean, divided by the mean. It is the definition used for current imbalance in most design guidance, and it is not the same as the NEMA voltage-imbalance definition used for motors.
Worked example: an office board with three equal socket circuits and an EV charger
Three socket circuits of 6 kW each at demand factor 0.5 contribute 3 kW to each of L1, L2 and L3 - perfectly balanced. A three-phase 11 kW air-handling fan at 0.9 demand adds 9.9 kW, which spreads as 3.3 kW on every leg, so it does not disturb the balance either.
The 7.4 kW EV charger on L1-L2 at 0.8 demand contributes 5.92 kW, but split between two legs: 2.96 kW each on L1 and L2 and nothing on L3. That one circuit is what pushes the board out of balance.
Its current is 5,920 / (400 x 0.99) = 14.95 A - the full line voltage applies because it sits across two lines. The same 7.4 kW connected between L3 and neutral would draw 5,920 / (230.9 x 0.99) = 25.90 A, which is a different breaker and quite possibly a different cable.
With the whole office example loaded, the diversified demand comes to about 52 kW over 18 circuits, and the imbalance is a few per cent. Moving the signage and the security supply between phases changes it by less than a kilowatt, which tells you the board is already as balanced as this set of circuits allows.
Formulas and scoring rules
- Single-phase circuit current (with neutral)
I = demand kW x 1000 / (V_line / root-three x pf)- Line-to-line circuit current
I = demand kW x 1000 / (V_line x pf)Half the load is counted on each of the two legs.- Three-phase circuit current
I = demand kW x 1000 / (root-three x V_line x pf)A third of the load is counted on each leg.- Demand
demand kW = connected kW x demand factor- Phase imbalance
max |phase kW - mean| / meanZero for a perfectly balanced board; reported as a percentage.- Phase current total
I_phase = phase kW x 1000 / (V_phase x assumed pf)
Why balance matters
An unbalanced board wastes capacity: the incomer, the main cable and the transformer are all sized for the worst phase, so 40% imbalance means paying for capacity that two of the three phases never use. It also produces neutral current, and neutral conductors are not always sized for it.
There is a second-order effect that bites harder than people expect. An unbalanced load produces a small negative-sequence voltage on the supply, and any three-phase motor fed from the same board sees that as a heating current in its rotor out of all proportion to the imbalance. A 2% voltage imbalance can raise motor losses by a quarter.
Neutral current and the third harmonic
With balanced linear loads the three phase currents cancel in the neutral and it carries almost nothing - which is why some older installations used a reduced neutral. With single-phase electronic loads that is no longer true. Third-harmonic currents from switch-mode supplies are in phase with each other in all three lines, so they add rather than cancel, and the neutral can carry up to root-three times a phase current.
This tool does not estimate neutral current, because doing it honestly needs the harmonic spectrum of each load rather than its kW. Where the board feeds a lot of IT or LED lighting, a full-size or oversized neutral and a measurement are the safe answers.
Limitations: what the result does not prove
- It does not size cables, breakers, busbars or the neutral. Take each circuit's current to the cable and breaker calculators.
- Neutral current is not estimated. Three balanced linear circuits cancel in the neutral; non-linear single-phase loads do not, and may exceed a phase current.
- Demand factors are your judgement. The tool does the arithmetic exactly as you specify it, and does not apply any code's prescriptive method.
- The balance suggestion is greedy and ignores everything a real board cares about: way positions, RCD grouping, circuits that must stay together, and mechanical layout.
- Nothing here is a compliance statement. A qualified engineer must verify the board design against the applicable standard and local regulations.
Privacy: where your data goes
Everything you paste, type or drop is processed in this browser tab. It is not uploaded, logged, stored or sent to analytics. Session recording and tag-manager scripts are switched off on this page.
Standards and sources
- IEC 61439-1 - Low-voltage switchgear and controlgear assemblies - checked 19 Sep 2026
- IEC 60364-5-52 - Selection and erection of wiring systems
- NFPA 70 - National Electrical Code, Article 220
Frequently asked questions
How much phase imbalance is acceptable?
Design guidance commonly aims for current imbalance under 10% on a distribution board, and most designers treat anything over 20% as something to fix. There is rarely a hard numerical limit in the wiring rules themselves; the limits that bite are the incomer rating, the neutral conductor and, for connected motors, the voltage imbalance they experience.
Why does a line-to-line circuit draw less current than the same kW on a single phase?
Because it sits across the full line voltage rather than the phase voltage. On a 400 V system that is 400 V against 230.9 V - a factor of root-three - so the current is 42% lower for the same power. It also loads two phases with half each instead of one phase with all of it.
Should I schedule connected load or demand?
Both, which is why the schedule shows them side by side. Individual circuit protection is sized on the circuit's own design current, which usually means its connected load. The incomer, the main cable and the supply are sized on the diversified total. Confusing the two is how boards end up with a 400 A incomer feeding 120 A of real load.
What power factor should I put on a circuit I do not know?
0.9 is a reasonable default for a mixed circuit and is what the tool assumes if you leave the column off. Use 0.95 to 1.0 for heating and modern lighting, 0.8 to 0.88 for motors, and something closer to 0.7 for welding or older fluorescent gear. If the answer changes a breaker size, measure rather than assume.
Can I paste this straight out of a spreadsheet?
Yes. Copy the five columns in the order name, phase, kW, power factor, demand factor and paste them in; a header row is detected and ignored, blank lines are skipped, and lines starting with # are treated as comments. Anything without a readable kW figure is skipped with a note rather than breaking the whole schedule.
Does the balance suggestion respect RCD grouping?
No. It only looks at kW, and it moves single-phase circuits only. Real boards group circuits behind RCDs or RCBOs, keep related circuits adjacent, and often have a fixed physical order. Treat the suggestion as an upper bound on how well the board could be balanced, then apply the constraints by hand.
Is a spare way with 0 kW worth listing?
Yes. It keeps the schedule matching the physical board, so the drawing, the labels and the as-built record stay aligned, and it makes future capacity visible. The zero contributes nothing to any total.
Does the tool send my circuit list anywhere?
No. The parsing and the arithmetic all happen in your browser, and the page makes no request with anything you type. The exports are generated locally and downloaded from the page itself.
Last reviewed by the A2Z.Tools team against the sources listed above.
