TrueFault · v1 web demo
Pro

Available fault current,
at every panel.

Build your system, branch it the way the job really runs, and read the fault current at any point. Free — no login.

Branches like the real jobService → panels → sub-panels, any depth
Edit anything, nothing resetsFat-finger a value? Just fix it.
The NEC 110.24 numbers, ready to readWrite your placard straight off the screen
Free forever for the calculation. TrueFault Pro saves your jobs to re-open and edit later.
Available fault current
18.6kA
at Panel B · 480 V, 3Ø
Result
6 components · 4 points — the whole system on one screen.
To branch: tap a bus to select it, then Add — anything you add downstream of the same bus starts a new branch.
Utility source
Utility service
480 V · 3Ø · 50 kA available
at source
50.0kA
Transformer
T-1 · 1000 kVA
5.75 %Z → 480 V
secondary
22.4kA
Main panel · branches here
MDP — Main
600 A · 480 V · 2 feeders
at bus
21.1kA
RESULT HERE
Feeder A → panel
Panel B
250 ft · 500 kcmil Cu
here
18.6kA
Feeder → sub-panel
Sub-panel B1
60 ft · #4 Cu
here
16.9kA
Motor load
Motor M1 · 50 HP
adds fault current upstream
+2.1 kA
Add downstream of Panel B
Feeder C → panel
Panel C
140 ft · #1/0 Al
here
12.1kA
Tap any item to edit — your other entries never reset.
Available fault current
18.6kA
Add componentdownstream of Panel B
Transformer
Conductor
Motor
Generator
Rating
75
kVA
Primary
480typ
V
Secondary
208typ
V
Impedance %Z
5.75typical
%
Don't know the %Z? 5.75% is typical for this size — leave it and refine from the nameplate later.
Material
Wiring method
Aerial / open-air? Covered — open spacing changes the reactance, so we adjust it automatically (triplex, quadruplex, or open run).
Length
250
ft
Size
500 kcmiltyp
Parallel sets
1typ
×
Motor size
50
HP
Voltage
480typ
V
Contribution auto-figured. A running motor feeds the fault — we add ≈4× its full-load amps where it connects. No FLA handy? We estimate from HP.
Rating
500
kVA
Voltage
480typ
V
Sub-trans Xd″
16typ
%
Xd″ is the generator's subtransient reactance — 16% is a safe typical if it's not on the nameplate.
1
2
3
4
5
6
7
8
9
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0
⌫
Available fault current
18.6kA
at Panel B · 480 V, 3Ø
For your NEC 110.24 field marking
Available fault current18,600 A
Date of calculationJun 29, 2026
Nominal voltage480 V
Phase3-phase
LocationPanel B
Copy to your label maker — or write it straight on the placard.
Coming back to this job? TrueFault Pro saves the whole system to re-open and edit — plus emailed one-line + placard PDF.
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The calculation is always free. Pro is for the guy who comes back — save every system and re-edit it any time.

Free, foreverNo login
Fault current at every point
Full branching — any number of panels
NEC 110.24 readout to make your placard
Pro PROsign in to save
Save & re-edit jobs across visits
Emailed placard PDF — cleaner than FC2's
Emailed one-line — with your branching
FIRST YEAR
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then $39/yr
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per month
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Maybe later