What Is a Panel Schedule?
A panel schedule is an engineering document that organizes every circuit in a panelboard — identifying loads, breaker sizes, wire sizes, phasing, and total connected/demand loads per phase. It is both a design tool during construction and a permanent reference document for the building's electrical system.
Panel schedules are required on all permit drawings for commercial and most residential construction. They serve as the engineer's primary coordination document and the electrician's installation guide.
Panel Schedule Layout
Standard panel schedule format: two columns (left = odd breaker numbers 1, 3, 5..., right = even breaker numbers 2, 4, 6...). Each row includes: circuit number, breaker size (A), poles, circuit description, voltage, wire size, conduit size, and connected VA per phase.
Three-phase panels cycle phases: A-B-C-A-B-C pattern. Circuit 1 = Phase A, Circuit 2 = Phase B (opposite column same row), Circuit 3 = Phase C, Circuit 4 = Phase A, etc. Two-pole breakers span two phases; three-pole breakers span all three.
Bottom totals: sum connected VA per phase (A, B, C), total VA, total amperage, percentage loaded vs panel rating, and number of spaces remaining for future circuits.
Load Balancing
Goal: distribute loads evenly across all phases so that no single phase is significantly more loaded than the others. Target: within 10-15% of average across phases.
Unbalanced loads cause: higher neutral current (increasing neutral conductor heating), voltage imbalance at loads (causing motor heating and reduced life), and wasted panel capacity.
Balancing technique: List all single-pole (120V) loads. Sort by VA from largest to smallest. Assign the largest to the most lightly loaded phase. Repeat. Then assign two-pole and three-pole loads. Recalculate phase totals after each assignment.
Example: If Phase A = 12,000 VA, Phase B = 14,500 VA, Phase C = 11,200 VA — the imbalance is (14,500 - 11,200) / 12,567 avg = 26%. Need to move ~1,500 VA from Phase B to Phase C.
Spare Capacity and Future Planning
Industry standard: reserve at least 20-25% spare breaker spaces for future circuits. A 42-space panel should have minimum 8-10 spare spaces.
NEC does not specify a spare capacity percentage, but engineering standards (including many AHJ requirements) mandate it for commercial buildings. Many specifications require separate spare capacity for lighting, receptacle, and mechanical panels.
Avoid 'fill to the brim' panel designs — they generate costly change orders during construction and leave no room for tenant improvements or equipment changes.
NEC Labeling Requirements
NEC 408.4: Every circuit breaker in a panelboard must have a legible, durable circuit directory that identifies the purpose or function of every circuit. 'Spare' or 'space' labels must be included for empty positions. Circuit descriptions must be meaningful — 'Misc' or 'General' is not acceptable.
NEC 408.4(B): Source of power — each panelboard must be marked with the source of power (the panel or transformer feeding it). Example: 'Fed from MDP-1, Breaker 42.'
Good labeling practice: 'Kitchen Receptacles — North Wall', 'Office 201 Lighting', 'HVAC RTU-2 Disconnect'. Bad labeling: 'Outlets', 'Lights', 'Stuff'.