When to use: Use during panel design or troubleshooting to verify that single-phase loads are balanced across all three phases. Unbalanced panels cause neutral overcurrent, transformer overheating, and voltage unbalance — which damages motors and sensitive electronics. NEMA MG 1 recommends keeping voltage unbalance below 1%, which corresponds to roughly keeping phase load imbalance under 10%. This calculator helps you assign circuits to phases for optimal balance.
This free panel schedule designer lets you build a complete electrical panel schedule — assign circuit breakers, label loads, calculate total connected load and demand load per NEC Article 220, and export a print-ready schedule for permit drawings.
An electrical panel schedule is a tabular document attached to a distribution panel (breaker panel, load center, or switchboard) that lists every circuit breaker, its ampere rating, pole configuration (1-pole, 2-pole, 3-pole), the load it serves, and the calculated load in watts or amps.
Panel schedules are required on all permitted electrical construction drawings under the NEC and are reviewed by the AHJ during plan check. They serve as the primary reference for the electrician during rough-in and for the inspector during final walk-through.
NEC Article 220 defines how to calculate the connected load and demand load for a panel:
1. General lighting: 3 VA/sq ft (residential) or per occupancy table (commercial) 2. Small appliance circuits: 1,500 VA per 20A kitchen/laundry circuit 3. Fixed appliances: nameplate VA × demand factor 4. HVAC: largest motor FLA × 125% + all other motor FLA × 100% 5. Apply demand factors from NEC 220.42 (lighting) and 220.53 (appliances)
The total demand load determines the minimum service size. Residential services are typically 100A, 150A, or 200A; commercial services range from 400A to several thousand amps.
Residential and small commercial panels are single-phase 120/240V. The panel has two "legs" (A and B buses), and loads are balanced across both legs. A 2-pole 240V circuit uses both legs simultaneously.
Commercial and industrial panels are typically three-phase 208Y/120V or 480Y/277V. Three-phase panels have three buses (A, B, C) and 3-pole circuits draw from all three. Proper load balancing — keeping total amps per leg within 10% of each other — minimizes neutral current and improves power quality.
This panel schedule tool supports both single-phase and three-phase configurations.
Most AHJs require panel schedules on electrical permit drawings that show: panel designation (e.g., "MDP", "Panel A"), bus rating (amps), main breaker or main lugs only, voltage and phases, mounting location, and a table of all circuits with breaker size, poles, load description, and calculated load.
NEC 408.4 requires all circuits and modifications to be legibly identified as to their clear, evident, and specific purpose or use on a directory mounted at each panelboard.
List all loads with their phase assignment (A, B, or C). Sum the amps on each phase. Reassign circuits to minimize the difference between the highest and lowest loaded phase — ideally within 10%. Single-phase 120V loads go on one leg; 208V 2-pole loads go on two legs; 3-phase loads balance automatically. This tool calculates per-phase totals automatically as you add circuits.
The main breaker must be rated at or above the calculated demand load per NEC 220. For residential: apply the optional method (NEC 220.82) — add all loads and apply demand factors. For commercial: use the standard method (NEC 220.40–220.65). As a rule of thumb, size the service 125% above the calculated demand to allow for future expansion.
Yes — this is called a multi-wire branch circuit (MWBC) or shared-neutral circuit. Under NEC 210.4, a 2-pole 20A breaker with a shared neutral can feed two 120V circuits on opposite legs. The neutral carries only the unbalance current. However, NEC 210.4(B) requires that MWBCs be identified at the panelboard and controlled by a handle-tied or common-trip breaker.
NEC 408.54 (2020 edition) requires that all new panelboards have a minimum of 20% spare circuit capacity (spare breaker spaces or breakers that are not assigned to circuits). This applies to new construction and panel replacements.
A load center (residential panel) is a pre-engineered unit for 120/240V single-phase service, typically rated 100A–200A with 24–40 circuit spaces. A distribution panel (or panelboard) is a commercial or industrial unit rated for higher ampacity (100A–2500A), available in single-phase or three-phase, and field-configured with plug-in or bolt-in breakers per the design.
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