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    Interactive calculator

    LV Short-Circuit Current

    Dynamic Main LV → DB1–DB5 radial fault network, auto cable R/X lookup, 3φ/2φ limits and breaker ratings (engineering screening).

    EstimatePreliminary result, not a design verification.
    Before you calculate

    Dynamic LV radial short-circuit network

    Add up to five downstream distribution boards, edit cable sizes and lengths, and inspect calculated 3φ/2φ fault currents at every board. KiloVolt looks up reference cable resistance/reactance automatically. This is a screening model, not a complete IEC 60909 fault study.

    Learn more — engineering guide →
    1 · Supply data

    Dynamic LV radial short-circuit network

    Build Main LV → DB1–DB5 interactively. Each feeder automatically uses internal conductor resistance data and a documented reactance assumption. Results update for every downstream board.

    Use test/nameplate data if available. Optional rated copper/load loss below overrides R/X.
    Leave blank when unknown: minimum-fault current will be marked unverified.
    A single R/X for both cases is a modelling assumption.
    The ±10 % pair is only the initial example. Choose the tolerance of your own supply.

    Applied voltage factors: cmax 1.10, cmin 0.90.

    Voltage factors: documented reference pair for ±10 % LV tolerance (cmax 1.10, cmin 0.90), as DIgSILENT states them for IEC 60909-0:2026 Table 1. Not an independent verification of the standard.

    Open standards issue: public implementations differ. Any other choice is a SENSITIVITY CASE.

    Main LV breaker (optional)

    2 · Network editor

    Radial distribution layout

    Select a board to inspect its calculated fault values. Select a feeder to edit its cable specifications.

    MV grid → Transformer → Main LV

    Main/DB1 feeder

    Built-in IEC 60228 Class 2 max DC R20: 0.124 Ω/km. Actual AC resistance may differ.
    A documented LOWER resistance assumption, not the IEC 60228 maximum. Required to explore potentially higher fault current; still not a verified breaker selection.
    Indicative geometry X: 0.08 Ω/km. Confirm actual installation geometry.

    Optional breaker ratings — DB1

    Phase-to-PE check — DB1 feeder

    Automatic: 95 mm² in the same material as the phase conductors.
    3 · Fault currents

    All distribution boards Estimate

    Fault locationModeled Ik″ 3φ maxIk″ 3φ minNOT VERIFIED: no minimum source levelIk″ 2φ maxIk″ 2φ minip peakBreaker (indicative)
    ≈ 37.6 kA≈ 31.1 kA≈ 32.6 kA≈ 26.9 kA≈ 88.0 kANot assessed
    ≈ 28.3 kA≈ 22.8 kA≈ 24.5 kA≈ 19.7 kA≈ 52.1 kANot assessed

    Estimate, rounded to 0.1 kA. Not included: motor and generator contribution and phase-to-neutral faults (phase-to-PE is estimated in section 4 below). Breaker comparisons are indicative only.

    The minimum here means three-phase or phase-to-phase minimum only, NOT the minimum earth-fault current: see section 4 below for the phase-to-PE estimate (TN-S).

    DB1 · Selected fault location

    Modeled max. initial symmetrical 3φ≈ 28.3 kA
    Min. initial symmetrical 2φ≈ 19.7 kANOT VERIFIED: no minimum source level
    Peak 3φ ip≈ 52.1 kA
    Ib (modelled sources only, = Ik″; no motor contribution)≈ 28.3 kA
    Peak factor κ1.301
    ΣR maximum0.00345 Ω
    ΣX0.00829 Ω

    Selected incoming cable: R20 reference = 0.1240 Ω/km · minimum R20 assumed for modeled Ik,max = 0.1240 Ω/km · X = 0.0800 Ω/km · R at maximum-fault temperature = 0.002480 Ω · IEC 60228 MAX DC R20 (not a verified max-fault bound); indicative geometry X.

    Transformer and upstream impedance

    ∣ZT∣=ULL2STuk100=0.006000 Ω|Z_T|=\frac{U_{LL}^2}{S_T}\frac{u_k}{100}=0.006000\ \Omega
    RT=0.000890 Ω,XT=∣ZT∣2−RT2=0.005934 Ω,xT=XTSTULL2=0.059336R_T=0.000890\ \Omega,\quad X_T=\sqrt{|Z_T|^2-R_T^2}=0.005934\ \Omega,\quad x_T=\frac{X_T S_T}{U_{LL}^2}=0.059336
    KT=0.95 cmax1+0.6 xT=0.95⋅1.101+0.6⋅0.059336=1.009075,ZTK=KTZTK_T=\frac{0.95\,c_{max}}{1+0.6\,x_T}=\frac{0.95\cdot 1.10}{1+0.6\cdot 0.059336}=1.009075,\qquad Z_{TK}=K_T Z_T
    KT,min⁡=KT=1.009075 (formed with cmax, also in the minimum case)K_{T,\min}=K_T=1.009075\ \text{(formed with }c_{max}\text{, also in the minimum case)}
    Minimum case at the Main LV bus under each documented K_T treatment
    TreatmentK_T,minIk″ 3φ min (kA)
    K_T formed with cmax (documented 2026-oriented profile) (used)1.0091≈ 31.1 kA
    K_T,min = max(1, K_T) (legacy v0.1.66 sensitivity)1.0091≈ 31.1 kA
    K_T,min = 1, no correction (what pandapower 3.5.6 does; sensitivity)1.0000≈ 31.3 kA

    Cumulative impedances and fault currents

    ZΣ,k=ZQ+KTZT+∑j=1k(Rc,j+jXc,j)Z_{\Sigma,k}=Z_Q+K_T Z_T+\sum_{j=1}^k(R_{c,j}+\mathrm{j}X_{c,j})
    Ik,3ϕ′′=cULL3∣ZΣ,k∣Ik,2ϕ′′=cULL2∣ZΣ,k∣I''_{k,3\phi}=\frac{cU_{LL}}{\sqrt{3}|Z_{\Sigma,k}|}\qquad I''_{k,2\phi}=\frac{cU_{LL}}{2|Z_{\Sigma,k}|}
    RΣ,max⁡=0.003448 Ω,XΣ,max⁡=0.008288 ΩR_{\Sigma,\max}=0.003448\ \Omega,\quad X_{\Sigma,\max}=0.008288\ \Omega
    Check before relying on this result
    • Minimum source fault level NOT PROVIDED: the minimum case reuses the entered source fault level (250 MVA) as if it were the minimum, but with the MV voltage factor 1.00 instead of the 1.10 of the maximum case, so the source impedance of the minimum case is about 9 % LOWER than that of the maximum case. Ik,min is therefore NOT a verified (conservative) minimum and can be overstated. Enter the utility's minimum fault level.
    • IEC 60228 R20 is the MAXIMUM permitted 20°C DC conductor resistance, NOT a minimum: using it can UNDERSTATE Ik3,max and overstate breaker adequacy. Optional user-entered minimum R20 is a sensitivity assumption, not independently verified. Reactance and AC effects are approximate. No breaker PASS can be issued from this model.
    • Transformer correction in the minimum case: K_T = 1.0091 (formed with cmax 1.1) is applied to the minimum case too, the treatment DIgSILENT documents for IEC 60909-0:2026 section 6.3.3. OPEN STANDARDS ISSUE: public implementations differ. pandapower 3.5.6 applies no K_T in the minimum case; for this network Ik3,min at the Main LV bus would be 31.31 kA instead of 31.05 kA, and the legacy clamp max(1, K_T) would give 31.05 kA. The normative text has not been reviewed.
    Scope and assumptions (4)
    • Upstream R/X: the single value 0.1 is used for both the maximum and the minimum case, a modelling assumption (pandapower distinguishes rx_max and rx_min). Enter a separate minimum R/X if the utility provides one.
    • IEC 60909-oriented radial LV SCREEN: transformer correction K_T applied, but an independently validated IEC 60909 study is required for actual breaker selection. Complete conformity with IEC 60909-0:2026 has NOT been independently verified; rated supply voltage and source reference assumptions affect results.
    • Ik2,min is phase-to-phase only; minimum L–N and L–PE fault currents and disconnection-time compliance are NOT ASSESSED.
    • I_b is reported only as the initial symmetrical Ik″ of the modelled far-from-generator sources (no motor, generator or inverter contribution) and is NOT a verified breaking current; peak uses the IEC 60909 κ expression for a single-source radial path. Breaker Icu/Ics/Icm comparisons are indicative, not full coordination checks.
    4 · Phase-to-PE fault

    Earth-fault loop and instantaneous trip Estimate

    TN-S systems. Choose the PE conductor and the protective device of each feeder under “feeder settings” in the network editor above.

    PE routing assumption: in the same cable (default)

    A separate PE has a larger loop reactance, so the fault current is lower. KiloVolt assumes 10 cm between the phase conductors and the PE; you do not enter it. Steel supports, trays and armour are not modelled.

    Check before relying on this result
    • Basis inherited from the minimum case: c_min = 0.9 (documented ±10 % pair), K_T in the minimum case = 1.0091 (treatment "cmax"), upstream minimum source level NOT provided, so every minimum is NOT VERIFIED. Zero-sequence and earthing assumptions: the transformer and the upstream network are treated as having Z0 = Z1 in a single loop (a Dyn transformer with the PE in the return path is the model the loop was cross-checked against, and the single loop counts the upstream impedance in all three sequence terms, which is on the safe side, by about 4 % or less from a 500 MVA minimum source level and up to about 7 % lower at 100 MVA in the cross-check); TN-S only, no earth-electrode, soil or TT/IT impedance, and no earthing-system verification. A change of c_min, of the K_T treatment or of the minimum source level changes these currents directly.
    • Preliminary phase-to-PE estimate, TN-S only: source/transformer zero-sequence impedance and PE return reactance are assumed; xPE = xphase is NOT guaranteed conservative. Device internal and arc resistance are neglected. Reported current is not a verified minimum. Not valid for TT, IT or TN-C systems.
    • The instantaneous-trip comparison is screening arithmetic only (B 5, C 10, D 20, K 14 × In). All device verdicts are NOT ASSESSED until return-path impedance and the appropriate source/transformer model are verified; thermal-release time, selectivity and protection coordination are outside scope.
    Fault locationPE conductorLoop impedanceIk L–PE minProtective deviceInstantaneous trip
    Main LV—6.7 mΩ≈ 31.1 kA—Not assessed
    DB195 mm² Cu13.0 mΩ≈ 16.0 kA—Not assessed

    Preliminary screening — NOT ASSESSED. The curve comparison uses the upper instantaneous threshold (ABB MCB technical document 9AKK108468A3912) but the phase-to-PE loop model relies on assumed zero-sequence and return-path impedance. Even when the indicative threshold is met, automatic disconnection and clearing time are not verified. Confirm actual Zs, device characteristics and applicable installation requirements before relying on the result.