Copy this prompt into ChatGPT, Claude, Copilot or similar, and attach screenshots or PDFs of the one-line diagram and the panel schedules (plus any load summary). The panel schedules are where the AI finds each panel's load.
2
Paste the JSON the AI returns, then import. If it gave you a .json file instead, use Load Project. Importing replaces the circuit on screen.
AI reads drawings imperfectly. Check every bus, conductor, breaker and transformer against the drawing before relying on the results.
Review AI Import
Check what the AI read against the drawing and correct anything it misread or guessed. Values marked possible default are what the AI is told to use when the drawing doesn't show one. Everything else can be edited after import.
Project
Each bus carries only the load it serves directly. The calculator adds downstream loads into every feeder above it. Amps are converted from the drawn kVA / kW at each bus's voltage (kW at the project's power factor). Loads are panel totals, motors included. To model motors, enter the motor portion of a bus's load: it's taken out of the load figure (the total stays the same) and adds motor contribution to fault current. Itemized motors can be added in the tool after import.
Fill them at% of their breaker rating
Bus
Volts
As drawn
Load (A)
Motor portion (A)
Total (A)
Source
Set them all toft
Feeder
Sets
Size
Mat.
OCPD (A)
Length (ft)
Send to Arc Flash
Every bus below goes to the Arc Flash Calculator with its bolted fault current, voltage and Fed From. Each bus's arc duration comes from its breakers: the upstream breaker (the feeder breaker, or a transformer's primary breaker for a bus on its secondary) and, where there is one, the bus's own main. The arc flash tool looks up each one's clearing time at both IEEE 1584 arcing currents, and the label takes the worst case: a main only clears its load side. Click a breaker to set its type and settings, or type a duration to override the upstream one. A bus with no upstream breaker is calculated with a 200 ms placeholder and stays flagged until you enter one. Equipment class sets the gap, enclosure and working distance from the arc flash tool's IEEE 1584 presets.
Arc flash project
Fault current basis
Set them toms
Equipment class for every checked bus
Bus
Fed from
Volts
Bolted fault (kA)
Equipment class
Breaker (sets duration)
Arc duration (ms)
In arc flash
Harmonic Load
Harmonic Spectrum
Harmonic Profiles
AI AIC Check against the Drawings
1
Copy this prompt. It lists every bus and the minimum AIC rating this tool recommends for it, from the circuit on screen right now.
2
Paste it into ChatGPT, Claude, Copilot or similar, and upload the one-line diagram, panel schedules, and any equipment schedules or general notes that state AIC / interrupting ratings.
The AI will report each bus as OK, INADEQUATE, NOT FOUND (no rating located on the drawings), or UNCLEAR, with where it found each rating.
The required ratings are only as good as this circuit's inputs (utility fault current, conductor lengths, transformer data). Update the circuit before copying, and verify the AI's findings on the drawings.
One-Line Studio
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Autosaved locally in this browser — use Export Project above for a portable .json backup
Unsaved project — this draft isn’t in Saved Projects. Save it to keep it as a named project.
Project Info
Presets ▸
Downstream buses (excludes the origin/source bus)
System Inputs
The root bus is set to a transformer or generator — set its own voltage under the root bus below instead.
One Line Diagram
Arc flash
Harmonics
Coordination view
Auto-size feeders
✦Have a one-line drawing? Let AI build this diagram from a screenshot or PDF. Attach the panel schedules too and it fills in the loads.
NavigateDrag the background to pan. Scroll or pinch to zoom.
Edit
BusesClick + to add a bus. Click − to delete that bus.
Select
Results▸
Voltage Drop
Highest bus voltage drop
—%
Within limit
Bus
Volts
% VD
Minimum conductor size for target
Holds every other bus fixed and steps up through the table (same material/conduit as the selected bus's incoming branch) to find the smallest size for that branch that brings its own zone within the selected threshold.
Short Circuit
See Advanced Settings → Short-Circuit for additional detail on the two short-circuit calculation methodologies.
Available short-circuit current by bus
Bus
Available Isc
Min. AIC rating
Check the drawings against these ratings
Get an AI prompt listing every bus's required AIC, to run against your one-line and panel schedules.
Selective Coordination
Upstream breaker
Max fault
Result
Arc Flash (Estimate)
Bus
Equipment class
Bolted kA
Clearing ms
cal/cm²
AF boundary
Harmonics (IEEE 519)
Bus
Harmonic load
THDv
Worst Vh
Harmonic current
THDi
Buses
▸
Bus 1 — Source
Auto-populated from the minimum of Eaton's standard IEEE/ANSI impedance range by kVA for three-phase pad-mount transformers. Check "Custom impedance" to enter a nameplate value directly.
Only a solidly grounded wye secondary gives a single-line-to-ground fault path — the single-line-to-ground (SLG) current shown below assumes a delta primary winding (standard for the distribution transformers this tool models), so the primary-side zero-sequence network is blocked and does not contribute; the transformer's own zero-sequence impedance (not the upstream source) dominates.
Rated PF 0.8; calculations use kVA = kW / 0.8.
Optional, for harmonics only: the datasheet’s negative-sequence reactance. Blank uses X"d. Fault current always uses X"d.
Available fault current feeding this bus from upstream (utility/transformer secondary).
Missing — a transformer root needs a primary available fault current (or check "Infinite Bus") to compute a real secondary fault current. Left blank/zero, this bus's fault current is computed from the transformer's own impedance only, ignoring the utility source entirely — not a substitute for the actual value.
Counted both toward fault-current contribution (via the multiplier below) and toward this bus's own load current for voltage drop — do not also add it to "Load current at this bus" or it will be double-counted.
Current drawn locally at the root bus itself (rare — usually 0). Every downstream bus's own load accumulates back up through the tree on top of this.
Used when the global override is on in Advanced Settings → Loads. Otherwise each load category supplies its own PF.
Diagram & voltage drop
Number connected and spare outgoing OCPDs from left to right above each distribution bus. Numbers follow the current layout and appear in print.
Fixed-width font for one-line data blocks and breaker ratings, including the printed one-line. Fonts unavailable on this device fall back to monospace.
Double-click mode selects on the first click. Enter still opens Properties. Shift selection and blank-space panning stay the same.
Choose where equipment properties open. Remembered in this browser. Press Escape or click empty diagram space to clear selection; dragging empty space still pans.
The "Marginal" voltage-drop status shows when the result is above the selected threshold but at or below threshold × this value; above that, status shows "Exceeds."
Calculation notes
Reset voltage drop calculation at transformers
Yes (default): every voltage zone (the region between transformers) is scored against its own nominal voltage, and the summary above shows the single worst zone's drop anywhere in the tree. No: every zone's own worst-case % is summed together into one figure — for a branched tree this is a conservative approximation (it adds every zone's worst path, not only zones that share one physical path), not a rigorous single-path total. Either way, the zone breakdown table and the diagram's per-bus voltage display are unaffected.
Short-circuit study
Every fault current scales with it. 1.0 is the ANSI and SKM / ETAP default; use 1.05 for a study that assumes the system runs 5 % high. Values outside 0.8–1.2 are ignored.
Calculation notes
Assumed transformer impedance tolerance (%)
Per ANSI C57.12.00, a transformer's actual impedance can vary from its nameplate value by a manufacturing tolerance — 7.5% is commonly used for a conservative worst-case short-circuit study. Reduces the impedance used for short-circuit calculations only (e.g. an entered 5.75% Z at a 7.5% tolerance is calculated as 5.32% Z for short-circuit purposes); the nameplate %Z entered per transformer is still shown as-is on the diagram and in reports.
Short-circuit calculation methodology
NEC Table 9 (default) complex-combines each conductor's own R/XL impedance in series within a zone (real and reactive parts summed separately, not just magnitude) — seeded by the source's own X/R ratio, which becomes editable directly on the diagram (above Isc) once this method is selected and the root bus is a plain Bus; its default is set below. C-Value / Point-to-Point instead uses the classic point-to-point method (f = phase-factor × L × I ÷ (C × n × E); M = 1 ÷ (1 + f)) with conductor "C" constants from Cooper Bussmann's Point-to-Point guide, Table 2 (IEEE Gray/Buff Book-derived), as a scalar-only alternative. Both methods use the same transformer, motor-contribution, and AIC-recommendation logic — only the per-branch conductor Isc reduction differs.
Conductor temperature for short circuit (°C)
Default 25°C — the IEEE 551 / IEEE 141 basis for maximum available fault current: a cooler conductor has lower resistance and yields a few percent higher Isc, the conservative direction for AIC verification. NEC Ch. 9 Table 9 resistance is published at 75°C; set this field to 75°C to use those values as-published with no correction. Applies the standard (234.5 + T) ÷ (234.5 + 75) ratio for copper, (228.1 + T) ÷ (228.1 + 75) for aluminum, to the resistance term of the NEC Table 9 (R/XL) method only. Reactance is unchanged; voltage drop is unaffected (always 75°C); the C-Value / Point-to-Point method is unaffected (its published "C" constants carry a fixed 75°C basis and cannot be cleanly temperature-corrected). Range 10–90°C; blank or out-of-range reverts to 25°C.
Source X/R ratio
Only used by the NEC Table 9 (R/XL) short-circuit method — splits the entered source Isc into real/reactive parts (Rsrc = |Zsource|×cos(atan(X/R)), Xsrc = |Zsource|×sin(atan(X/R))) so it can be complex-combined with downstream conductor impedance instead of just added as a scalar magnitude. Defaults to 5 (a commonly cited round number for an unspecified utility source) if left blank — obtain the actual value from the utility if precision matters. When the root bus is a plain Bus (not a transformer/generator), this also shows and is editable directly on the diagram, above the Isc reading.
Zero-sequence / positive-sequence ratio (Z0/Z1)
Used only for the single-line-to-ground (SLG) fault current shown at solidly-grounded-wye transformer secondaries. 0.85–1.0 is a typical range for standard three-phase distribution transformers (three-legged core vs. shell/5-legged construction) per general industry guidance — use actual nameplate/factory zero-sequence data instead when available and precision matters for AIC selection.
Motor contribution
A motor on a VFD with no bypass sends no fault current to the bus, except an active front end (regenerative) drive, which feeds the fault at this multiple of its running amps. With a bypass the motor counts as a normal motor, per the multiplier above.
Calculation notes
Motor contribution multiplier (×)
Each motor is modeled as an impedance that draws its running amps × this multiplier at full voltage (X/R 6), behind its own feeder if one is entered. With the NEC Table 9 method the fault current at every bus comes from a full-network solve, like SKM and ETAP: every motor in the system contributes, across transformers too, through the real path between it and the fault. The C-value method keeps its point-to-point hand method, where motors in other zones aren't counted.
Motor impedance basis
ANSI C37 first cycle: motors on buses over 1,000 V get the C37.010 first-cycle impedance multipliers (1.0 at 1,000 hp and up, 1.2 from 50 hp, 1.67 below 50 hp; a lumped load or a motor without hp uses its kVA as hp, a lumped load 1.2). Low-voltage motors keep the multiplier above, which is the C37.13 basis. Matches SKM's and ETAP's ANSI first-cycle (momentary) duty, symmetrical.
Bus
Rated PF 0.8; calculations use kVA = kW / 0.8.
Sets the maximum fault current (the first cycles).
Optional, for harmonics only: the datasheet’s negative-sequence reactance. Blank uses X"d. Fault current always uses X"d.
What the generator holds after the first cycles: about 300% with a PMG or auxiliary-winding exciter, often under 100% with a shunt-excited one. Sets the minimum fault case.
Available fault current at this service. It runs at the project source voltage; for a service at another voltage use a utility transformer.
Missing — a transformer needs a primary available fault current (or check "Infinite Bus") to compute a real secondary fault current.
This service's own X/R, used by the NEC Table 9 method (Advanced Settings has the Normal tab's).
Each service is calculated on its own: its fault current, voltage drop and loads never combine with another tab's.
Closed transition sums the independent Normal and Emergency fault currents for the WCR check only. Other studies keep separate source paths.
Normal-side feeder
The feeder fields above (Fed from, conductors, breaker) are the emergency side.
Auto-populated from Eaton aluminum-wound, three-phase transformer data by kVA and insulation class. Check "Custom impedance" to enter a nameplate value directly.
Only a solidly grounded wye secondary gives a single-line-to-ground fault path — assumes a delta primary winding (standard here), so the primary-side zero-sequence network is blocked.
Primary side is whatever voltage is already in effect at the parent bus.
Current on this bus in addition to the downstream loads modeled. Keep at "0" if all downstream loads are modeled with their respective load currents.
Counted both toward fault-current contribution (via the multiplier in Advanced Settings) and toward this bus's own load current for voltage drop — do not also add it to "Load current at this bus" or it will be double-counted.
Blank or 0 shows no rating on the diagram. Only applies where a breaker symbol is actually drawn (not directly off the origin or a transformer secondary).
Sets the arc duration Send to Arc Flash uses for this bus. Until you pick one it is the generic default for the rating.
Optional. Used only by the selective coordination check, against this panel's main and every breaker upstream.