Neutral Conductor Sizing - ELEK Software (2024)

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Neutral Sizing according to Standard AS/NZS 3000 Neutral Sizing according to Standard IEC 60364-5-52 Related Articles: May 29, 2019 Understanding Earth Fault Loop Impedance The purpose of this document is to provide a better understanding of Fault Loop Impedance, also referred to as Earth Fault Loop Impedance so that the requirements of AS/NZS 3000 Wiring Rules for safety, design, installation and testing of electrical installation may be met. November 28, 2018 Cable Current Rating Derating Factors Explained Derating factors are applied to the cable current rating ensuring that cable operating temperature limits are not exceeded. Derating factors are derived to match the specific cable installation conditions. April 6, 2019 Voltage drop limits for Low Voltage installations Voltage Drop Limits per the Wiring Rules AS/NZS 3000 as well as rules of thumb to assist with electrical design. Includes AC and DC voltage drop or rise limits. July 3, 2018 Maximum Demand Tables Reference tables for diversity factors and energy demand from Wiring Rules AS/NZ 3000 for domestic and non-domestic installations. June 24, 2020 Cable Pulling Tension Calculations This article explains how to perform cable pulling tension and sidewall pressure calculations and also includes an example. November 9, 2021 Voltage Drop Calculation Method with Examples Equations and method with all steps for accurate voltage drop calculations including power factor, cable operating temperature, resistance, reactance, DC, 1-phase or 3-phase, balanced/unbalanced with calculation examples provided. April 2, 2020 Voltage Rise Calculations Voltage rise can occur in solar PV systems on the AC side between the power inverters and network connection point. Voltage rise calculations are no different to those for voltage drop. February 22, 2023 Short Circuit Power Cable Sizing Explained The fault current which flows in a power cable causes its temperature to rise dramatically. The adiabatic equations for calculating the minimum conductor size to withstand the short circuit are explained. May 16, 2020 Automatic Maximum Demand Calculations The new maximum demand module provides fast and accurate calculations for loads in accordance with rules from the Standards and for custom loads. An ingenious automatic phase balancing algorithm ensures maximum demand and phase imbalance are both minimised. References

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Requirements of the AS and IEC Standards

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The neutral conductor is connected to the neutral point of a system and is intended to carry current under normal conditions. The neutral conductor is required for each main circuit and there are rules in the Standards for its sizing.

This article summarises the requirements of Standards AS/NZS 3000 and IEC 60364-5-52.

Neutral Sizing according to Standard AS/NZS 3000

The neutral conductor of circuits designed to Australian and New Zealand Standard AS/NZS 3000 must have the same current-carrying capacity (same size) as the associated active conductors.

When there are substantial harmonics then the neutral conductor size may need to be larger than the active conductors or in the case of a multi-core cable the neutral currents may dictate the size of the active.

An exception is for multi-phase circuits feeding predominantly multi-phase loads (balanced phases). In this case the neutral conductor size may be smaller than the active conductor size but must be sized to carry at least the out-of-phase current.

Type of CircuitNeutral conductor size requirement
Single phase two-wire
  • One active conductor
  • Multiple active conductors
Multiphase
  • Consumer mains, submains and final subcircuits
Neutral conductor size not less than active conductor size.Sneutral = Sactive
Multiphase
  • 3rd harmonic currents are substantial
Neutral conductor may be required to be larger than associated active conductors. Refer to IEC 60364-5-52.Sneutral ≥ Sactive
Multiphase
  • Feeds predominantly multiphase loads
Neutral conductor must be capable of carrying the maximum out-of-balance current, including any harmonic component.Sneutral ≤ Sactive

Neutral Sizing according to Standard IEC 60364-5-52

For multiphase circuits:

The neutral conductor size can be smaller than the active size if harmonic current is < 15 %.

When harmonics are between 15 % to 33 % the neutral conductor size shall be the same size as the active conductor.

For multicore cables when harmonics are above 33 % the neutral conductor size and the active conductor size must carry 1.45 times the load current.

For single core cables when harmonics are above 33 % the neutral conductor size must be sufficient to carry 1.45 times the load current and can be larger in size than the active conductors.

Type of CircuitNeutral conductor size requirement
Single phase two-wire
  • One active conductor
Multiphase
  • Copper active size ≤ 16mm2
  • Aluminium active size ≤ 25mm2
Neutral conductor size same as the active conductor size.Sneutral = Sactive
Multiphase
  • Harmonics current < 15 %
Neutral conductor must be capable of carrying the maximum out-of-balance current, including any harmonic component.Sneutral ≤ Sactive
Multiphase
  • Harmonics current between 15 % and 33 %
Neutral conductor size same as the active conductor size.Sneutral = Sactive
Multiphase - multicore cable
  • Harmonics current > 33 %
Neutral conductor must be sized to carry at least 1.45 times the active load currentSneutral = Sactive
Both sized to carry 1.45 x IB
Multiphase - single core cable
  • Harmonics current > 33 %
Neutral sized to carry at least 1.45 times the load currentSneutral > Sactive
Both sized to carry 1.45 x IB

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