Free Tool · IEEE 575 / IEC 60287-1-2 · MV Cable Systems · Electrical

Concentric Neutral Induced Voltage

Calculates the voltage induced on single-point bonded concentric neutral (CN) MV cables per IEEE 575 and IEC 60287-1-2. Use this whenever single-point grounding is specified. Cross-discipline — applicable to any MV cable system with single-point bonding.

Cross-discipline — applicable to any MV cable system with single-point bonding.
System Parameters
Cable Configuration
Geometry & Conductor
Waiver Conditions
IEEE 575 / IEC 60287-1-2 limit: 25 V
IEEE 575 / IEC 60287-1-2 limit: 25 V
Results
Induced voltage at cable ends (V)
—
Induced voltage at cable midpoints (V)
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IEEE 575 / IEC 60287-1-2 limit: 25 V
Input Parameters
System voltage (kV)—
Cable configuration—
Bonding method—
Frequency (Hz)—
Load current (A)—
Phase spacing (mm)—
Number of CN wires—
Reel length (m)—
Total length (m)—
Standards—
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FAQ

When is this calculation required?
This calculation is always required when single-point grounding is used. It is also applicable to cross-bonded and both-ends bonded systems for cross-discipline verification. It is waived for multi-grounded systems (trench ground at all terminations, splices, junction boxes, transformers) and for MV cables in trefoil or triplex configuration, where induced voltages are geometrically negligible.
Why does trefoil configuration give lower induced voltage than flat?
In trefoil (triangular) formation, the three phase conductors are equidistant from each other and the geometric mean distance to the sheath is smaller. The mutual inductance between each phase conductor and the concentric neutral is reduced by the geometric factor (~0.5× flat) because the return currents in the neutral are more symmetrically distributed, cancelling a portion of the induced magnetic flux. This effect is even more pronounced in triplex (bundled single-core) configurations (~0.4× flat).
What do I do if the induced voltage exceeds 25 V?
If V_end > 25 V per IEEE 575, you must reduce the induced voltage before proceeding. Options include: (1) Cross-bond the cable sheath at regular intervals — this cancels induced voltage by reversing the phase relationship at each bonding point. (2) Add additional ground rods at the ungrounded end or at intervals along the cable route. (3) Install a sheath voltage limiter (SVL) at the ungrounded end. (4) Reduce segment length by specifying shorter cable reels, allowing more frequent bonding points. (5) For flat configuration, increasing cable spacing increases phase-to-neutral distance and reduces mutual inductance — but this has a modest effect. (6) Increasing CN wire count reduces the current per wire and thus the induced voltage per wire, lowering the total.
What is the significance of cable reel length in this calculation?
The cable reel length represents the longest continuous segment between bonding points — typically the longest available length per the cable owner specification. Since V = ω·M·I·L, induced voltage is directly proportional to segment length. Using the longest available reel length gives the most conservative (highest) induced voltage estimate. For owner-specified short reels, the induced voltage can be significantly lower. Always verify the applicable owner specification for minimum/maximum bonding interval requirements.