Free Tool · IEC 60909-0:2016 · All fault types · 9 locales

IEC 60909 Short-Circuit Current Calculator

Compute initial symmetrical short-circuit current I"k, peak current ip, breaking current I_b, and steady-state I_k per IEC 60909-0:2016 §4. Supports three-phase, single-line-to-ground, line-to-line, and double-line-to-ground faults. Used for breaker selection, transformer sizing, and protection relay settings.

Preset
System Parameters
Network Feed (IEC §4.2.2)
I"kQ = c·Un / (√3·Zk) from §4.2.2 Eq (6). Obtain S"k from grid operator.
Transformer (IEC §4.2.4)
Include transformer
Z_T = ukr% × Un² / S_N per IEC §4.2.4 Eq (12). R_T from copper losses.
Generator (IEC §4.2.5)
Include generator contribution
Synchronous generator subtransient reactance. IEC §4.2.5 voltage correction Kc applied.
Asynchronous Motor (IEC §4.2.6)
Include motor contribution
Motors ≥ 0.5 MVA contribute to initial Ik" per IEC §4.2.6.
Cable / Feeder (Optional)
Include cable impedance (feeder end fault)
Equipment Duty Check
IEC 60947-2 peak make/break: compare ip to 2.5× breaker rated current.
Short-Circuit Results (IEC 60909-0)
8.585
kA
I"k total
21.751
kA
ip peak
1.7916
—
κ factor
8.585
kA
Ib breaking
8.585
kA
Ik steady
12.545
—
X/R bus
Parameter Value
Voltage factor c1.1
I"k — Initial symmetrical SC current (kA)8.585 kA
ip — Peak short-circuit current (kA)21.751 kA
id.c. — DC component at contact parting (kA)2.702 kA
Ib — Symmetrical breaking current (kA)8.585 kA
Ik — Steady-state SC current (kA)8.585 kA
κ — Peak factor1.7916
X/R at fault bus12.545
Fault type multiplier1
Z_k total (Ω)1.4796 Ω
Network contribution (kA) / Contributions
Network contribution (kA)8.585 kA
Equipment Duty
Breaking duty Ib (kA)— kA
Breaking duty (%)—%
Peak duty ip (kA)— kA
Peak limit 2.5× (kA)— kA
OverallPASS
Impedance Breakdown
ElementR (Ω)X (Ω)
Network0.08760.8756
Transformer0.030.5992
Total Zk0.11761.4749
IEC 60909-0:2016 — Key Equations
I"k = c · Un / (√3 · Zk) [§4.2.1 Eq 3 — initial symmetrical] Zk = Z_network + Z_T + Z_cable [series impedance] κ = 1.02 + 0.98 · e^(−3R/X) [§4.3.1 Eq 74] ip = κ · √2 · I"k [§4.3.1 — peak current] id.c.(t) = √2 · I"k · e^(−2πf·t·R/X) [DC offset decay] Ib = μ · I"k [§4.5 — breaking current; μ=1 network feed] Ik = λ · I"k [§4.6 — steady state; λ=1 network feed] I"k_SLG = 3V / (Z1+Z2+Z0) → mult = 3/(2+Z0/Z1) [§4.2.3]
Transformer: Z_T = ukr%/100 × Un²/S_N · (1 + jXR/√(1+XR²)) per §4.2.4
Related Tools
Relay Coordination — IEC 60255 Busbar Rating — IEC 60871 Arc Flash — IEEE 1584 Grounding Grid — IEEE 80
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FAQ — IEC 60909-0:2016
The voltage factor c (IEC 60909-0 Table 1) accounts for the difference between the nominal voltage and the actual driving voltage of the short-circuit current. c_max = 1.05 for LV (≤ 1 kV, EN 50160 ±6% tolerance) and 1.10 for MV/HV (> 1 kV) for maximum fault current (equipment selection, breaker duty). c_min = 0.95 for LV, 1.00 for MV/HV, for minimum fault current (protection relay settings). Using c_max ensures conservative equipment ratings.
The κ factor (IEC 60909-0 §4.3.1 Eq 74: κ = 1.02 + 0.98·e^(−3R/X)) accounts for the DC offset on the first half-cycle of a fault. The peak current ip = κ·√2·I"k is the true maximum instantaneous current a breaker must withstand (make/break capacity). For HV systems with high X/R (low R/X), κ approaches 1.02+0.98 = 2.0, nearly doubling the symmetrical value — this is critical for breaker mechanical withstand ratings.
I"k is the initial symmetrical short-circuit current at t=0 — maximum AC component, before any decay. Ib is the symmetrical breaking current at contact parting (IEC §4.5) — the current the breaker arc must interrupt, reduced by μ factor for generators/motors. Ik is the steady-state current (IEC §4.6) — after all subtransient effects decay, relevant for thermal rating of conductors. For pure network feeds (no local generators), I"k = Ib = Ik.
In solidly-grounded systems where Z0 ≤ Z1, the single line-to-ground (SLG) fault can exceed the three-phase fault current (IEC §4.2.1 — when Z0/Z1 < 1, SLG multiplier 3/(2+Z0/Z1) > 1). In impedance-grounded or unearthed systems, the three-phase fault is always worst-case. The tool computes the fault multiplier based on your Z0/Z1 input — set Z0/Z1 = 1.0 for solidly grounded systems, higher values for impedance grounded.
uk% (ukr on the nameplate) is the short-circuit voltage as a percentage of rated voltage — typically 4–6% for distribution transformers, 8–12% for large power transformers. Higher uk% means higher impedance and lower fault current. The resistive component uR% is derived from copper losses Pk: uR% = (Pk_kW / S_N_kVA) × 100. This gives Z_T = ukr%/100 × Un²/S_N, split into R_T and X_T per IEC §4.2.4.
I"k is the primary input to protection relay time-current coordination: the maximum fault current determines the IDMT curve operating time; the minimum fault current (c_min) must exceed the relay pickup. For arc flash per IEEE 1584, I"k becomes I_bf (bolted fault current) in the arcing current equation I_arc = f(I_bf, V, gap, etc.). Cross-link this calculator to the Relay Coordination and Arc Flash tools to build a complete protection study.