★ Sizing Engine — Project Circuits
Stage 5 — every standard size is checked against ampacity, voltage drop, short circuit, motor starting, earth-fault loop and the MV screen; the smallest passing size is recommended (Rev C IEC tables)
Circuits and buses are saved with the project file. Site conditions, voltage-drop limits, minimum sizes and clearing-time basis come from the Project & Design Basis page.
A Buses & Studies (Stage 2)
Enter the fault levels and protection times from the approved short-circuit and coordination studies (or the Fault Level screening module). Ze is calculated as cmin·U0 / Ik1 min. Each circuit takes its fault current, clearing time and Ze from its From-bus.
B Circuits
C Circuit Editor
D Calculation Sheet (selected circuit)
E Construction — drums, pulling, tests, as-built
F Reports & Verification
★ Project & Design Basis
Stage 0 — site, system and criteria shared by every module; feeds report headers and sign-off blocks
💾 Project File
Everything on this page is kept in this browser automatically and can be saved to a file to move between machines or share with a colleague.
★ Logos for the Submittal Cover Sheet
Optional. Upload your own supplier/vendor logo and your client's/consultant's logo — they replace the generic "CE" marks on every report's cover sheet. Small image files (PNG/JPG, a few hundred KB) print best; logos are stored with the project (auto-save and the project file) and never leave this browser.
E Codes & Standards
Tick the standards applicable to this project — the list is carried into the Design Basis Report.
F Client-Specific Requirements
Enter anything in the client specification that differs from the criteria above (clause references are useful). Blank rows are left out of the report.
G Assumptions & Holds
Carried into the submission report. Blank rows are left out.
R Reference Documents & Revision History
Revision history
S1 · Fault Level & Clearing Time
Screening fault levels — IEC 60909 simplified method; clearing time and earth-loop impedance for the short-circuit check
Fill cmax, cmin, LV voltage and the clearing-time basis from the project Design Basis
1 Source & Transformer
iLabel for the bus this calculation describes (e.g. the transformer LV terminals). Used in the report only.
iRated apparent power of the transformer feeding the bus.
iNameplate impedance voltage of the transformer, typically 4–8 %. Sets how much the transformer limits the fault.
iNominal system voltage at the fault point (line-to-line).
iThree-phase short-circuit power of the network on the primary side, from the utility or the MV study. A lower value means a weaker source and a lower LV fault level.
iIEC 60909 factor for the maximum fault current: 1.05 for LV with +6 % tolerance, 1.10 for LV with +10 % and for MV.
iVoltage factor applied to the upstream network impedance. 1.10 is the usual MV value.
iMinimum-voltage factor used for the earth-fault loop check (0.95 is usual for LV).
iTotal full-load current of motors running at the same time on this bus. They feed the fault and add to the bus fault level.
iTypical motor fault contribution is 4–6 × the total full-load current. The contribution is added arithmetically at the source bus (conservative).
2 Downstream Cable to a Remote Bus (optional)
Fill in to get the fault level at the far end of a cable, which is what limits a downstream board. Leave the length at 0 to skip.
Use the cable's resistance at the fault-current temperature for a conservative-low fault level, or at 20 °C for the maximum.
3 Earth-Fault Loop Impedance Ze
i
- From Ik1 min (study) — Ze = cmin·U0 / Ik1min using the minimum earth-fault current at the bus from your fault study. Preferred.
- Screening estimate — from the transformer and network impedances only, assuming a Dyn transformer. It ignores cable, arc and earth-electrode resistance, so it is optimistic.
iMinimum single-phase-to-earth fault current at the bus, from the short-circuit study (cmin, maximum conductor temperature).
iZero-sequence impedance of the transformer as a multiple of its positive-sequence impedance. A Dyn transformer with the star point solidly earthed is close to 1.0.
4 Protection Clearing Time
iRelay or trip-unit operating time for the primary protection at this fault level, from the coordination study.
iOperating time of the backup protection if the primary fails.
iTotal break time of the circuit breaker (opening plus arcing), typically 0.03–0.08 s. Zero for a self-acting MCCB/MCB whose curve already includes it.
iConservative practice uses the backup clearing time for feeders without unit protection; primary is normal for circuits with fast, reliable primary protection.
iFor a current-limiting device clearing in under about 0.1 s. Passed to the short-circuit module so the cable is checked against √(I²t)/k.
iWhich fault level to send on: the source bus (the cable's origin) or the remote bus at its far end. The short-circuit check normally uses the fault level at the cable origin.
iNumber of parallel cables carrying the fault. Set the sharing rule in the Design Basis: dividing is normal, "full" is conservative for a fault at the far end of one run.
✓ Results Summary
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Ik3 at Source Bus
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Ik3 at Remote Bus
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Ze (Earth Loop)
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Clearing Time Used
H1 · Sequence Impedance (HV single-core cables)
Direct/inverse and zero-sequence impedance for a single-core HV cable circuit with a separate earth continuity conductor (ECC) — industry practice (no IEC standard covers this calculation; cross-checked against an approved 220 kV vendor calculation)
ℹ️ This method has no governing IEC standard — it follows accepted cable-industry practice (as used in the reference vendor calculation this module was checked against). Confirm results against the cable manufacturer's own sequence-impedance calculation for anything safety- or protection-critical.
1 Conductor & Cable Geometry
iFrom the cable datasheet — used for the self-geometric-mean-distance term in the positive-sequence reactance.
iFrom IEC 60228 Table 2, or the manufacturer's datasheet.
iAxial distance between adjacent single-core cables in flat formation.
iRatio of metallic-sheath-circuit losses to conductor losses for this circuit's bonding arrangement and spacing (IEC 60287-1-1 §2.3.6). Not calculated here — take it from a current-rating study at this same spacing, or the Sheath Bonding module.
2 Earth Continuity Conductor & Earth Return
i1 or 2 earth continuity conductors run with the circuit. With 2 ECCs their mutual spacing is taken as 1.4× the cable axial distance (√2×S), per the reference method.
iFrom IEC 60228 DC resistance, skin-corrected, at the expected ECC operating temperature — or the manufacturer's value.
iSelf-geometric-mean radius of the ECC conductor for inductance calculations. Defaults to half the external radius (consistent with the reference calculation); confirm against the conductor manufacturer's data if available.
Positive/Negative Sequence |Zdi|
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Zero Sequence (ECC only) |Z0|
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H2 · Induced Sheath Voltage (HV single-core, single-point bonding)
Per-phase (leading/centre/lagging) induced sheath voltage in normal operation and during a single-phase-to-earth fault — Electra 28 cl. 2.2.3 flat formation; cross-checked against two approved 220 kV vendor calculations
ℹ️ Covers single-point bonded, flat-formation single-core circuits with a separate ECC, transposed at route centre. Cross-bonded circuits are not covered here — use the existing Sheath Bonding & Losses module's cross-bonding case for that.
1 Cable & Route Data
iFor single-point bonding, the induced voltage appears at the unearthed end over the full route length.
iUsed for the single-phase-to-earth fault case below, which governs SVL sizing — per Electra 28, the maximum induced voltage in a single-point-bonded system with earthed neutral occurs on a phase-to-earth fault.
2 Earth Continuity Conductor Geometry
iThe sheath voltage limiter's rated voltage — compared against the fault-condition induced voltage to check adequacy.
Normal Operation (phase 1)
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Fault — Phase 1 (leading)
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SVL Check
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H3 · Current Rating — Trench / Duct Bank (Image Method)
Multi-circuit ampacity via the Neher-McGrath image method — IEC 60287-2-1 cl. 2.2.3.2 + IEEE PAS-104 geometric correction. Cross-checked against four approved 220 kV vendor calculations (1, and 6 circuits; trench and duct bank)
ℹ️ Covers N identical circuits of 3 single-core cables, evenly spaced in one row, all at the same depth, directly buried or in a duct bank. Multi-row or irregular layouts are not covered.
1 Conductor, Dielectric & Thermal Resistances
iPer-cable dielectric loss: Wd = ω·C·U0²·tanδ. From the cable datasheet or a capacitance calculation.
iFor a single circuit, use the centre-phase value; for multiple circuits, the value for whichever phase sits nearest the bank's physical centre (usually the lagging phase of the middle circuit) — from the Sheath Bonding module or a detailed IEC 60287-1-1 §2.3.6 eddy/circulation-loss calculation.
2 Bank / Trench Layout
iEach circuit is 3 single-core cables in flat formation, evenly spaced in one row.
iAxial spacing between the 3 cables within one circuit.
iCentre-to-centre distance between adjacent circuits. Not shown when N=1.
iUsed for the duct wall resistance T4'' = (ρ_duct/2π)·ln(Do/Di) (IEC 60287-2-1 §2.2.7.2).
iSets the air-space constants U, V, Y (IEC 60287-2-1 Table 4) and the duct wall resistivity (Table 1).
iDepth from ground level to the centre of the row of cables (or duct row). Used both for the image-method distance matrix and as the "depth to bank centre" for the IEEE PAS-104 correction.
iThe material immediately surrounding the cables: controlled thermal backfill (trench) or duct concrete/bentonite (duct bank). This is what drives the mutual-heating term T40 — not the native soil.
Current Rating
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Power Rating (3-phase)
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External Thermal Resistance T4
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⚡ Quick Size
Size a single cable in a minute — no project setup. Uses the same IEC-based sizing engine as the full Sizing Engine.
1 The Load
2 The Cable
3 Where It Runs
iHow many cables/circuits are grouped together here (including this one) — on the same tray, in the same duct bank, or buried together. Affects the grouping (derating) factor.
4 Advanced — defaults come from the site preset
iDrives the earth-fault loop check. A healthy LV board a couple of transformers from source is often 8–15 kA; a long or weak feeder can be much lower. Use your own fault study value if you have one — this default is a generic placeholder, not a substitute for one.
1 · Design Current & Load Calculator
Load schedule input → design current Ib — first step of the IEC 60364 cable engineering sequence
Fill spare margin and system voltage from the project Design Basis
1 Load Data
iIdentifier for this load, used for report labeling only.
iMotor loads need an efficiency figure to convert shaft power to electrical input power; general loads (heaters, lighting, panel feeders) are usually already rated in electrical kW/kVA, so efficiency is not applied.
iContinuous loads run indefinitely at rated current; intermittent and standby loads may allow relaxed thermal criteria in some designs, but this tool sizes for the full rated current in all cases — duty is recorded for the report only.
iMotor: shaft (mechanical) output power from the nameplate. General load: the rated electrical power of the equipment.
iLine-to-line (3-phase) or line-to-neutral (single-phase) nominal voltage supplying this load.
iMotor nameplate efficiency (typically 0.90–0.97 for LV induction motors). Converts mechanical output power to electrical input power: P_elec = P_shaft / η.
iFull-load power factor from the motor nameplate, or the load's rated power factor for general loads.
2 Demand, Diversity & Spare Capacity
iRatio of the load actually expected to run simultaneously to its full rated capacity. Use 1.0 for a single dedicated load that always runs at full rated power (e.g. a duty pump); apply a lower factor (commonly 0.7–0.9) for feeders/boards supplying multiple loads that don't all peak together.
iExtra current-carrying margin added to the design current so the cable/board isn't run at its absolute limit and can accommodate modest future load growth. Typical practice: 10–20%; use 0% if the circuit is fixed for the life of the plant with no growth expected.
✓ Results Summary
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Base Current
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After Demand Factor
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After Spare Margin
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Design Current Ib
2 · Cable Selection Advisor
Insulation, armour, screen & sheath recommendation — IEC 60502-1/2 guidance
1 Application & Installation
iDetermines insulation thickness class and which IEC 60502 part applies.
- LV (up to 1 kV) — IEC 60502-1.
- MV (1–36 kV) — IEC 60502-2, e.g. 3.6/6 kV, 6/10 kV, 12/20 kV, 18/30 kV classes.
iMatters most for armour choice on single-core circuits: a magnetic (steel) armour on a single-core AC cable sits in an alternating magnetic field and heats up from induced eddy currents — aluminium wire armour (AWA) is used instead when armour is needed on single-core runs. Multi-core cables don't have this issue since the three phases' fields largely cancel inside one sheath.
iMain driver for armour and mechanical protection needs.
- Direct buried — needs armour for mechanical/rodent protection.
- Duct/pipe — armour optional, cable is already protected by the duct.
- Cable tray/ladder (indoor) — armour usually optional unless exposed to impact.
- Submerged/marine — needs special sheath and often lead or extra-heavy armour.
iNon-linear or high-harmonic loads change neutral sizing and can call for a screen sized for skin-effect heating.
- General / linear load — standard sizing rules apply.
- VFD / motor drive — consider screened, symmetrical construction cable.
- Furnace / arc load — very high harmonic content, oversized neutral typically needed.
iIf the cable runs through an escape route, plant room with high fire load, or safety-critical circuit, low-smoke/fire-retardant or fire-survival cable becomes a requirement rather than an option.
2 Site Conditions
iOil, solvent or chemical exposure (tank farms, process areas) degrades standard PVC oversheath — a chemical-resistant oversheath compound is then needed.
iFrequent excavation nearby, vehicle traffic over shallow burial, or rodent activity increases the case for steel wire armour even where the base environment wouldn't otherwise require it.
iSaline soil, coastal sites, or aggressive industrial atmospheres accelerate armour corrosion — galvanized or extra-corrosion-protected armour, or non-metallic armour, may be preferred.
3 MV System & Earth-Fault Category
iNominal phase-to-phase voltage of the MV system. Used with the earth-fault category to select the cable's rated voltage grade U0/U (Um) from the IEC 60502-2 range (3.6/6 to 18/30 kV).
iOn a solidly-earthed system, an earth fault is cleared quickly and the healthy phases see only a small voltage rise. On an unearthed or resistance-earthed system, an earth fault can persist for some time with the healthy phases rising toward full line-to-line voltage (IEC 60183 "Category C" service) — the cable's insulation voltage grade must be stepped up to suit, not just matched to the nominal phase-to-earth voltage.
4 Hazardous Area Classification
iPer IEC 60079-14. Gas atmospheres use Zone 0/1/2 (0 = continuous, 2 = unlikely/short duration); dust atmospheres use the equivalent Zone 20/21/22. Any classified zone brings mechanical protection, flame-retardance, gland and jointing requirements on top of whatever the base environment/voltage already call for.
iIS circuits use a blue cable sheath and must be routed segregated from non-IS cabling for their entire length to preserve the safety barrier.
✓ Recommendation
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Insulation
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Armour
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Screen
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Oversheath
3 · Cable Sizing & Derating
IEC 60287 / IEC 60364-5-52 methodology
Take temperatures, soil and depth from
1 Cable & Circuit Data
iThe circuit or feeder identifier from your cable schedule / SLD. Used for report labeling only.
iAffects the catalog base ampacity you look up, not the derating formulas directly.
- Aluminium — larger cross-section for same ampacity, common for large feeders.
- Copper — smaller size for same ampacity.
iSets θmax used in the K_temp calculation.
- XLPE / TR-XLPE (90°C) — most common MV power cable.
- PVC (70°C) — LV/older cables.
- EPR (85°C) — flexible/marine-duty cables.
iConductor cross-sectional area — for report labeling; the base ampacity below already reflects this size.
i
- 1C — one conductor per cable, three cables per circuit; common for large MV feeders.
- 3C — all phases in one jacket; common for smaller feeders.
iIdentical runs sharing the load per phase; corrected ampacity per run is multiplied by this count.
iManufacturer/catalog rated ampacity at the reference condition: 20°C ground, 0.8 m depth, 1.0 K·m/W soil, isolated circuit.
Reference: 20°C ground, 0.8 m depth, 1.0 K·m/W soil, isolated circuit.
Fills the base rating from the Rev C tables (IEC 60364-5-52 Annex B for LV, IEC 60502-2 Annex B for MV) for the conductor, insulation, cores, size and method selected.
iIf provided, compared against corrected ampacity for a PASS/FAIL verdict with margin %.
2 Installation Conditions
iSelects which correction path applies.
- Buried — uses depth and soil thermal resistivity corrections, reference ground temperature typically 20°C.
- Air / Tray / Ladder — no depth or soil correction; only ambient air temperature and grouping apply, reference ambient temperature typically 30°C per IEC 60364-5-52 (higher than the buried reference, since air-installed cables are catalog-rated differently from buried ones).
iReal/worst-case soil temperature at cable depth — not air temperature.
iGround temperature the base catalog ampacity was originally rated at (commonly 20°C — check your data sheet).
iThe soil-resistivity and depth corrections are relative to the reference conditions your base ampacity table was built on.
- LV cable — IEC 60364-5-52: reference soil 2.5 K·m/W, depth 0.7 m.
- MV cable — IEC 60502-2: reference soil 1.5 K·m/W, depth 0.8 m.
iDepth from ground level to the cable (or duct) centre. Deeper burial lengthens the thermal path to the surface and reduces ampacity; shallower burial slightly increases it. The factor is normalised to the reference depth of the selected rating basis.
Reference depth 0.7 m (LV).
iHow well soil conducts heat away — lower value = better dissipation = higher ampacity. The factor is relative to the reference resistivity of the selected rating basis, so values below the reference give a factor above 1.0.
- 0.5–1.0 — wet/moist native soil.
- 1.2–1.5 — typical controlled backfill.
- 2.0–3.5 — dry sand / arid ground.
Reference resistivity 2.5 K·m/W (LV). Direct-buried and duct tables differ.
iThe physical arrangement of the group, per IEC 60364-5-52 grouping tables (B.52.17–B.52.21). The arrangement list changes with the installation mode: tray/ladder tiers, trefoil and bunching for air; touching/spaced direct-buried and duct arrangements for ground. Spacing is part of the arrangement (e.g. "0.25 m apart").
iTotal loaded circuits (or multicore cables) in the group, counting every parallel run separately. Where the count falls between tabulated values, the next higher tabulated count is used (conservative).
iAny extra engineer-entered correction not covered above (thermal insulation contact, harmonics, trench conditions, solar gain where not already in the ambient). 1.00 = none.
3 Overload Coordination (optional)
iThe protective device's nominal rated current (or set current for an adjustable device). IEC 60364-4-43 requires In to sit between the design current Ib and the corrected cable ampacity Iz: Ib ≤ In ≤ Iz.
iThe current at which the device is guaranteed to trip within the conventional time (e.g. 1.45×In for many MCBs/MCCBs, or the fusing current for a fuse) — from the device's data sheet or standard (e.g. IEC 60898/60269). IEC 60364-4-43 requires I2 ≤ 1.45 × Iz.
✓ Results Summary
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Total Derating Factor
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Corrected Ampacity
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Design Load
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Margin
4 · Voltage Drop Calculator
LV feeder & motor-starting volt drop — IEC 60364-5-52 Annex / BS 7671 limits
Set the drop limits and system voltage for
1 Circuit Data
iCircuit identifier, used for report labeling only.
iLine-to-line (3-phase) or line-to-neutral (single-phase) nominal system voltage — sets the % drop denominator and the √3 factor used in the formula.
iSets the DC resistance (IEC 60228) and temperature coefficient used for R (Cu 0.00393/K, Al 0.00403/K). Aluminium has roughly 1.6× the resistance of copper for the same size, and is available from 16 mm².
iUsed to look up the DC resistance at 20 °C (IEC 60228), the skin/proximity factor and the reactance X from the tables built into this tool.
iMulti-core cable or how many parallel single-core/multi-core runs share the load — splits current per run for the R/X calculation.
iReactance depends on how the phases are laid.
- LV multicore — three/four cores in one sheath.
- LV single-core, trefoil — three single-core cables bound together.
- MV — 6–15 kV cables (16 mm² and above; smaller sizes fall back to the multicore value).
iVoltage drop must be evaluated with R at the conductor's operating temperature, not the 20 °C value — a copper conductor at 90 °C has about 27% more resistance than at 20 °C.
- 90 °C — XLPE/EPR at maximum temperature (conservative).
- 70 °C — PVC at maximum temperature (conservative).
- Estimated — θ = θa + (θmax − θa)(Ib/Iz)², using the ambient and derated ampacity Iz you enter; gives a less conservative value for lightly loaded cables.
iOne-way cable length from source to load — the standard voltage-drop formula already accounts for the return conductor, so do not double it.
iSteady-state full-load current used for the running (steady-state) voltage drop check.
iLower (more lagging) power factor increases the reactive (X·sinφ) contribution to voltage drop, especially on larger cable sizes with higher reactance.
2 Motor Starting (optional)
iMotor starting current (typically 5–7× FLC for DOL start) causes a much larger transient volt drop than running load — checked separately against a looser starting-drop limit.
iRatio of starting (locked-rotor) current to full-load current.
- DOL start — typically 5–7×.
- Star-Delta start — typically 2–2.5× (1/3 of DOL).
- Soft starter/VFD — typically 1.5–3× or user-set.
iMotors typically run at a lower, more lagging power factor during starting than at full load (commonly 0.3–0.4).
iGeneric IEC 60364-5-52 Annex G / BS 7671 guidance suggests an overall limit of about 4% from origin to any load point, commonly applied as 3% for lighting circuits and 5% for other (power) circuits in practice. These are widely-used guideline figures, not a single codified value — always confirm against your project specification, which may set a different limit.
iNot tightly codified in IEC/BS 7671 the way the running limit is — common industry practice allows a larger momentary drop during starting since it's brief and motors can start successfully down to roughly 80–85% of nominal voltage. 15% is a widely-used practical allowance; some specifications are more conservative at 10%.
✓ Results Summary
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Running Drop
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Starting Drop
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Volts Lost (Run)
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R / X per km
5 · Short-Circuit & Earth-Fault Check
Adiabatic equation (IEC 60364-5-54) + LV disconnection time (IEC 60364-4-41)
Fill cmin and Uo from the project Design Basis
1 Short-Circuit Withstand (Adiabatic)
iThe symmetrical rms fault current available at this point in the network, from your short-circuit study.
iTotal time for the upstream protection to clear the fault — from the relay/breaker time-current curve at this fault level. Typically 0.1–1 s for MV, up to a few seconds for some LV distribution circuits.
iSets the k-factor (A·s^½/mm²) per IEC 60364-5-54 Table 43A — how much fault energy the conductor can absorb before its short-circuit temperature limit.
iIEC 60949 constants K and β: copper 226 / 234.5, aluminium 148 / 228, lead 41 / 230, steel 78 / 202. k = K·√ln[(θf+β)/(θi+β)].
iConductor temperature at the start of the fault: 90 °C for XLPE/EPR, 70 °C for PVC at full load.
iPermitted short-circuit limit: 250 °C for XLPE, 160 °C for PVC ≤ 300 mm² (140 °C above). IEC 60949 takes the temperature limit of the insulation, not a generic 90–130 °C.
iFor a current-limiting MCCB / MCB / fuse that clears in less than about 0.1 s, the adiabatic check should use the device's let-through energy instead of prospective current × time: S(min) = √(I²t) / k. Take the value from the manufacturer's let-through curves at the prospective fault current. Leave blank to use fault current × clearing time.
iThe cable size actually selected — compared against the minimum size required to survive the fault.
iParallel runs share the fault current, so total withstand csa is the per-run size × number of runs.
iScreens and separate CPCs are usually much smaller than the phase conductor and often the limiting element in a fault — worth checking separately.
i"Lookup" fills the screen size and withstand directly from a typical published MV copper-tape screen table (6.6 kV and 33 kV, single-core and three-core) — a quick check against standard cable constructions. "Manual" lets you enter any screen size and k-factor, including a 3-core CPC.
ik-factor of the metallic screen from IEC 60949: k = K·√ln[(θf+β)/(θi+β)]. For a copper screen from 80 °C to 200 °C (PVC oversheath; 180 °C for PE) this gives about 128 — much lower than the ~187 that applies to bare conductors, so using 187 would under-size the screen. Use the calculator below, or enter the manufacturer's value.
iCross-sectional area of the screen, tape, or separate circuit protective conductor.
2 Earth-Fault Loop / Disconnection Time (LV)
i230 V for a standard 400/230 V LV system. Drives the maximum permitted earth-fault loop impedance.
iPer IEC 60364-4-41 / BS 7671: 0.4 s for final circuits ≤32 A on TN systems, 5 s for distribution circuits and other final circuits. Select per your circuit type.
iSets the multiplier used to find the fault-clearing current Ia from the rated current In, per the instantaneous/magnetic trip multiplier of the device curve.
- MCB Type B — trips at 3–5× In; this tool uses 5×.
- MCB Type C — trips at 5–10× In; this tool uses 10×.
- MCB Type D — trips at 10–20× In; this tool uses 20×.
- Enter Ia directly — use the exact value from the device's let-through/time-current curve at the required disconnection time (recommended for fuses or MCCBs).
iThe protective device's nominal/rated current setting.
iRead directly from the device's time-current or let-through curve at the required disconnection time.
iMinimum-voltage factor applied to Uo when working out the maximum permitted loop impedance: Zs(max) = cmin·Uo/Ia. 0.95 is the usual value for LV (IEC 60364-4-41 / CENELEC TR 50480 practice); use 1.0 to work from nominal voltage.
i
- Enter Zs — a measured value from a loop tester, or a value already calculated elsewhere.
- Calculate — Zs = Ze + (R1+R2)·L / n, from the external loop impedance Ze at the source and the phase and protective-conductor resistances of the cable at operating temperature.
iMeasured on-site with a loop tester, or calculated elsewhere.
iLoop impedance from the source up to the origin of this circuit — from Ze = cmin·Uo/Ik1min at the bus (single-phase-to-earth fault level), or measured.
iRoute length of this cable.
✓ Results Summary
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Min. CSA Required
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Actual CSA Provided
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Max Permitted Zs
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Actual Zs
6 · Sheath Bonding & Losses
Single-core cable sheath circulating current / induced voltage — IEC 60287-1-1, Cigré guidance
1 Cable & Route Data
iThis module calculates sheath/screen induced voltage from mutual coupling between separate single-core cables. A three-core cable's screen is the return path within the same cable and is not induced into by the other phases in the way a separate single-core screen is — bonding/circulating-current calculations for three-core cable follow a different method and are not covered here. (Source: a published MV cable induced-voltage reference table, which explicitly marks three-core sizes "Not applicable".)
iHow the metallic sheath/screen is earthed along the route.
- Solid bonding (both ends) — simplest, but a circulating current flows in the sheath for the life of the circuit, causing continuous sheath loss.
- Single-point bonding — no circulating current, but a standing induced voltage appears at the unearthed end, needing a sheath voltage limiter (SVL).
- Cross-bonding — sheaths transposed in minor sections so induced voltages largely cancel over a major section; used on longer/higher-current single-core circuits.
iPhysical layout of the three single-core cables.
- Trefoil (bound/touching) — cables bundled together; lower spacing, lower induced voltage.
- Flat, spaced — cables laid flat with a gap; larger spacing increases mutual inductance and induced voltage.
iDistance between adjacent cable centres. For trefoil, this is approximately the cable's own overall diameter; for flat formation, the actual laid spacing.
iMean diameter of the metallic sheath or screen layer — from the cable manufacturer's drawing/data sheet.
iDC resistance of the sheath/screen layer per km, temperature-corrected to its expected operating temperature — from the cable data sheet.
iThe load current in the phase conductor that induces the sheath voltage/circulating current.
iFor single-point bonding, the full route length (induced voltage appears at the far end). For cross-bonding, the length of one minor section (route length ÷ 3).
2 Safety Limit
iTypical guidance: 65 V for sheaths accessible to the general public without additional protection (touch voltage limit), higher (commonly up to a few hundred V) where the joint bay/link box is enclosed, locked, and only accessible to authorized/trained personnel with an SVL fitted. Confirm your project's actual limit.
ℹ️ Three-core cable selected — this module's mutual-coupling induced-voltage and circulating-current calculation applies to separate single-core cables only. A three-core cable's screens are not calculated this way; select "Single-core" above if this circuit uses three separate single-core cables per phase.
✓ Results Summary
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Mutual Reactance Xm
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Induced Voltage
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Circulating Current
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Sheath Loss
7 · IEC 60287 Thermal & Cyclic Rating
Full thermal-resistance method (IEC 60287-1-1/2-1) + cyclic loading guidance
1 Conductor & Losses
iInsulation's continuous operating temperature limit (90°C for XLPE, 70°C for PVC).
iActual ground temperature at cable depth (for buried) or ambient air temperature (for air-installed).
iDC resistance corrected for temperature and, for larger conductors, skin/proximity effect — from the cable manufacturer's data sheet at the operating temperature.
iNumber of current-carrying cores generating heat inside the cable — typically 3 for a 3-phase circuit.
iRatio of sheath/screen loss to conductor loss, from circulating and eddy current effects. Typical guidance: ~0.1–0.3 for solid-bonded single-core cables, ~0.01–0.05 for cross-bonded or 3-core cables with negligible sheath current.
iRatio of armour loss to conductor loss. Typically 0 for non-magnetic (aluminium) armour or unarmoured cable, ~0.05–0.15 for steel wire armour on single-core cables (can be higher — magnetic armour on single-core AC circuits is generally avoided for this reason).
2 Thermal Resistances
iThermal resistance of the insulation layer between conductor and sheath — from the cable manufacturer's data sheet (depends on insulation thickness and material).
iThermal resistance of the layer between sheath and armour (bedding/inner sheath) — from the cable data sheet.
iThermal resistance of the outer serving/oversheath — from the cable data sheet.
iDepth to cable centre, used with soil resistivity to compute T4, the external thermal resistance of the soil path to ambient.
iUsed with depth and cable external diameter to compute T4 = (ρ/2π)·ln(u+√(u²−1)), u = 2L/De, with mutual heating for groups of single-core cables (IEC 60287-2-1).
iOverall cable diameter — from the cable manufacturer's data sheet.
iIEC 60287-2-1 §2.2.2–2.2.3. Three single-core cables heat each other: choose the formation so that mutual heating is included (use n = 1 for single-core cables). The flat formations give T4 for the centre (hottest) cable.
iCentre-to-centre distance between adjacent cables for the flat spaced formation.
iWd = ω·C·U0²·tanδ. Small for MV XLPE (tanδ ≈ 0.001–0.004) and can usually be neglected below about 63.5 kV U0 for XLPE (IEC 60287-1-1 Table 3); enter 0 to ignore.
iRatio of average daily load to peak daily load, from the load profile. A load factor of 1.0 means constant (base) load — no cyclic benefit. Lower load factors (more peaky loads) allow a higher cyclic rating factor M, since the cable can run above its continuous rating for the peak period without exceeding θmax, as the softer periods let it cool.
✓ Results Summary
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T4 (Soil)
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Continuous Rating
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Cyclic Factor M
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Cyclic Rating
8 · Parallel Cable Load Sharing
Current imbalance from geometric arrangement — IEC 60364-5-52 guidance
1 Parallel Run Configuration
iMore parallel runs generally increase the spread of physical positions per phase, worsening imbalance if not carefully arranged or transposed.
iTotal load current for the circuit, shared nominally equally among the parallel runs before imbalance is considered.
i
- Trefoil, per-run bound — each parallel run's three phases bound together in trefoil; good symmetry, least imbalance.
- Flat, un-transposed — all runs laid flat side by side without swapping positions; worst-case imbalance, particularly for 3+ runs.
- Flat, transposed — runs periodically swap physical position along the route to average out the imbalance.
2 Downstream Sizing Basis
iThe corrected ampacity for one run from the Sizing & Derating module — used to check whether the most-loaded run stays within its rating once imbalance is applied.
✓ Results Summary
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Est. Max Imbalance
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Average per Run
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Most-Loaded Run
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Recommended Extra Derate
9 · Harmonic Derating
Neutral sizing & derating for non-linear loads — IEC 60364-5-52 Annex C guidance
1 Load & Cable Data
iTriplen (3rd, 9th, 15th…) harmonics add arithmetically in the neutral of a 3-phase 4-wire system instead of cancelling, so high 3rd-harmonic content drives up neutral current. Typical for VFDs, UPS, LED/electronic ballast lighting, and especially furnace/arc loads. Get this from a power quality survey or the load's known harmonic spectrum where possible.
iThe design/full-load current per phase conductor before harmonic considerations.
i4-core/5-core cables with a full-size neutral in the same cable are covered directly by the standard harmonic derating table; single-core-per-phase-plus-separate-neutral arrangements should be checked individually since the neutral is a separate current-carrying conductor with its own installation conditions.
✓ Results Summary
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Harmonic Derating Factor
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Neutral Sizing Basis
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Cable Sized For
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Est. Neutral Current
10 · Pulling Tension & Sidewall Pressure
Cable-pulling physics — capstan equation, industry-standard practice (NECA 1 / Cigré methodology)
1 Route & Cable Data
iMass per metre of the cable(s) actually being pulled together (sum if pulling multiple cables as one bundle) — from the manufacturer's data sheet.
iBetween cable and duct/tray surface.
- 0.2–0.3 — lubricated PVC/HDPE duct.
- 0.35–0.5 — dry/unlubricated duct or direct tray contact.
iLength of straight duct/tray run the cable travels before reaching the first bend.
iLength of straight run after the last bend, up to the pulling point.
iTreated as identical bends in series for this simplified model — a reasonable worst-case estimate for a route with a few similar bends, not an exact multi-bend route calculation.
iTypical duct/tray bends are 90°, 45°, or 30°.
iRadius of the duct/tray bend itself (not the cable's minimum bend radius) — used for the sidewall pressure calculation.
2 Cable Limits (from manufacturer)
iFrom the cable manufacturer's data sheet — depends on conductor material, size, and pulling method (conductor grip vs pulling eye/basket grip).
iFrom the cable manufacturer's data sheet. Typical published guidance is on the order of 2,000–8,000 N/m depending on construction — always confirm against your specific cable.
iSeveral cables in one duct press on each other, which raises friction (weight correction factor wc) and changes the sidewall pressure on the bottom cable. Cable weight above is the total for all cables. Triangular / cradled formulas per IEEE 1185 / AEIC CG5 practice.
✓ Results Summary
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Final Pulling Tension
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Max Sidewall Pressure
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Tension Limit
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SWP Limit
11 · Bending Radius & Jamming Ratio Check
IEC 60502 guidance multipliers + NECA/Cigré jamming-ratio risk band
1 Minimum Bend Radius
iTypical multipliers of overall cable diameter (D) commonly cited from IEC 60502 guidance:
- Single-core, unarmoured: 15×D
- Single-core, armoured: 20×D
- Multi-core, unarmoured: 12×D
- Multi-core, armoured: 15×D
iEnter the manufacturer's exact minimum-bend-radius multiplier if it differs from the guidance options.
iFrom the manufacturer's data sheet.
iThe smallest radius the cable is actually bent to anywhere on the route (duct bend, gland entry, tray corner, etc).
2 Jamming Ratio (Conduit/Duct, 3 Cables)
iJamming is a risk specific to pulling three similarly-sized round cables together into a single conduit/duct — the cables can wedge against each other and the duct wall within a certain ratio band.
iInternal diameter of the conduit/duct the three cables share.
iOuter diameter of one of the three (assumed similar-sized) cables.
✓ Results Summary
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Min. Bend Radius Required
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Actual Bend Radius
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Jamming Ratio
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Jamming Risk
12 · Cable Tray / Ladder Fill Calculator
Single-layer fill check — IEC 61537 tray guidance
1 Tray & Cable Data
iInternal usable width of the tray or ladder, excluding side rails.
Enter up to 3 cable types with quantity each. Leave a row's OD blank to skip it. Single-layer fill (cables side by side, not stacked) is assumed, per common tray-fill practice.
✓ Results Summary
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Total Cable Width
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Tray Width
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Fill %
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Total Cables
13 · Conduit / Duct Fill Calculator
Cross-sectional area fill check — common international duct-fill practice
1 Conduit & Cable Data
iInternal diameter of the conduit or duct being filled.
iCommon international practice (widely used, not a single IEC clause): 1 cable ≤ 53% fill, 2 cables ≤ 31% fill, 3 or more cables ≤ 40% fill — leaving room for pulling and heat dissipation. Some project specifications set their own figures; confirm against yours.
Auto-selected from total cable count entered above.
✓ Results Summary
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Total Cable Area
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Duct Internal Area
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Fill %
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Allowed Fill
14 · Trench Cross-Section Designer
Trench sizing with drawing output — IEC 60364-5-52 practice
1 Cables in Trench
iClearance from the outermost cable to the trench wall, for backfill compaction and future access.
iDepth from finished ground level to the centre of the cables.
2 Bedding & Cover
✓ Trench Dimensions
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Trench Width
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Total Excavation Depth
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Volume per Metre
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Circuits
15 · Drum Length & Cut Schedule Optimiser
Greedy bin-packing to minimise offcut waste across standard drum lengths
1 Required Cuts
Enter each required cable length (one per line, in metres — tag optional after a comma), e.g. "Feeder A, 420".
iThe standard drum length your supplier stocks — cuts are packed onto drums of this length, greedily fitting the largest remaining cuts first (first-fit-decreasing).
iOffcuts shorter than this are treated as waste rather than a usable remainder for a future small cut.
✓ Drum Allocation
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Drums Needed
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Total Cut Length
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Total Waste
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Waste %
16 · Gland & Lug Selector
Reference lookup from cable OD, armour and conductor size
1 Gland Selection
iThe cable's outer diameter over the outermost layer (armour if fitted) — from the manufacturer's data sheet. Determines which standard metric gland size fits the cable entry and clamps the armour/braid correctly.
iArmoured cables need a gland with an armour clamping ring (e.g. CW/BW gland types); unarmoured cables use a simpler compression gland.
2 Lug Selection
iCross-sectional area of the conductor the lug will terminate.
iCopper and aluminium lugs are not interchangeable — aluminium conductors need aluminium (or bimetallic Cu/Al) lugs to avoid galvanic corrosion at the joint.
✓ Recommendation
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Gland Size
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Gland Type
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Lug Bolt Size
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Lug Material
17 · IR / Megger Evaluator
Temperature correction, PI/DAR, phase imbalance — IEEE 43 guidance
1 Insulation Resistance Readings
iMegger test voltage — higher voltages (2.5–10 kV) are typical for MV cables, 500 V–1 kV for LV.
iActual conductor/insulation temperature at the time of test (not ambient air) — insulation resistance is strongly temperature-dependent, roughly halving for every 10°C rise.
iStandard reporting reference — readings are corrected to this temperature so results from different days/seasons are comparable. 20°C is the near-universal convention.
iFrom the manufacturer's data sheet, project specification, or a general rule of thumb such as 1 MΩ per kV of rated voltage plus a base value — always confirm the exact minimum against your project spec rather than relying on a generic default.
2 Polarization Index / DAR
i
- PI (Polarization Index) = reading at 10 min ÷ reading at 1 min — the standard longer-duration index (IEEE 43).
- DAR (Dielectric Absorption Ratio) = reading at 60 s ÷ reading at 30 s — a faster alternative, less tightly standardized than PI.
iTaken on the representative (typically worst) phase, on the same test as the index calculation.
iLater reading on the same phase, same test.
✓ Results Summary
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Temp. Correction Kt
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Lowest Corrected IR
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Phase Imbalance
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PI / DAR
18 · Conductor Resistance Check
Temperature correction to 20°C, checked against IEC 60228
1 Measured Data
iThe measured loop or conductor resistance from your test set (e.g. micro-ohmmeter), for the length being tested.
iThe length of conductor the measured resistance corresponds to — used to normalize the reading to Ω/km for comparison with the IEC 60228 table.
iActual conductor temperature when the measurement was taken — resistance rises with temperature, so this must be corrected back to the 20°C reference the IEC 60228 table is based on.
2 Conductor Specification
iSets both the temperature coefficient (Cu: 0.00393/K, Al: 0.00403/K, both referenced to 20°C) and which IEC 60228 table column applies.
iNominal cross-sectional area — used to look up the IEC 60228 maximum allowed resistance at 20°C.
iIEC 60228 Class 2 (stranded, compacted) is by far the most common for power cables and is what this tool's lookup table uses. Class 1 (solid) and Class 5/6 (flexible) have different maximum resistance values — if your cable is one of those, treat this as an approximate check only and verify against the exact IEC 60228 table for that class.
✓ Results Summary
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Measured, per km
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Corrected to 20°C
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IEC 60228 Max
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Margin
19 · VLF / AC Withstand Test Planner
Test voltage & duration — IEC 60502-2 / IEEE 400.2 guidance
1 Cable & Test Basis
iThe "Uo" figure from the cable's voltage grade (e.g. for a 6/10 kV cable, Uo = 6 kV). This is the reference the test voltage multiplier is applied to.
iThe "U" figure of the cable's voltage grade (10 kV for a 6/10 kV cable). Needed for the AC test at U.
i
- IEC 60502-2 — tests after installation for cables 6–30 kV: VLF 3U0 for 15 min, AC at U for 15 min, AC at U0 for 24 h, or DC 4U0 (not preferred).
- IEEE 400.2 — VLF field testing with acceptance and maintenance levels.
iThe list depends on the standard basis. AC power-frequency tests need heavy test equipment on long cables; DC is not preferred for extruded cables because it can leave space charge in the insulation.
i
- Acceptance — new cable, higher voltage to confirm workmanship.
- Maintenance — aged in-service cable, lower voltage to screen for degradation.
iNot used in the voltage/duration calculation, but useful on the report for test-set capacitance/sizing considerations.
2 Test Outcome
iThe pass/fail criterion for a withstand test is qualitative: no disruptive discharge or breakdown during the specified voltage and duration. This is a direct observation from the test, not something this tool calculates.
✓ Test Parameters
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Test Voltage
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Duration
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Multiplier
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Outcome
CableEng Suite · Design & Sizing group · Correction factors and lookup tables follow standard published IEC/BS guidance. Verify project-specific values before formal submission where noted.