Cable Sizing Software

Cable Sizing

Cable Sizing Software

ETAP Cable Sizing software provides various options which can be used for design requirements. These design requirements can be user-defined or automatically determined from load flow, short circuit, and protective device calculation results. 
Cable Constraints editor

ETAP cable sizing study module calculates optimal and alternative cable sizes for phase conductors based on the following criteria:

  • Load current
  • Voltage drop
  • Motor minimum starting voltage
  • Short circuit current
  • Protective device requirements
  • Harmonic Spectrum

Cable Sizing Software Key Features

  • Cable parameters and calculation results
  • Grid based interface for sorting, searching and filtering
  • Multiple filters for selection
  • Batch updating from library
  • Batch selection from library
  • Accessing to Model Forms
  • Individual or Consolidated Report
Cable sizing and ampacity for voltage drop, short circuit, motor start voltage, and protective devices.

Ampacity / Current Carrying Capacity Calculator

  • IEEE Standard 399 - 1997 Recommended Practice for Industrial and Commercial Power Systems Analysis
  • ICEA P-54-440 - 2001 Ampacities of Cables in Open-Top Cable Tray
  • NEC - NFPA 70 - 2002 National Electrical Code
  • British, IEC , and NFC Standards

Voltage Drop

The user can size cables by specifying constraint based on maximum allowable cable voltage drop in percent.

Motor Starting Voltage

This cable sizing calculation program allows you to calculate cable size based on electric motor minimum allowable starting voltage.

Short Circuit Current

ETAP’s cable sizing analysis software can compute the size of the cables based on cable short-circuit capacity to withstand the short-circuit current. The short circuit current can be specified manually or obtained from the short circuit calculation.

Cable sizing editor with results, constraints, and standard

Protective Device Overload

Cable sizing software computes the size of the cable by also considering overload protection. ETAP cable sizing program calculates the minimum size required by meeting the overload protection conditions between derated ampacity, operating current and nominal current. The option to size based on overload current is only enabled when BS 7671 17th Edition or IEC 60364 standards are selected for cable sizing.

Zero Sequence / Triple Harmonic and Other Harmonic (Cf)

If the neutral conductor carries current without any reduction in the load of line conductors, the harmonic current distortion in the neutral conductor needs to be considered in the determination of the current carrying capacity of the circuit. ETAP Cable Sizing module considers zero sequence / triple harmonic constraints as well as other harmonic constraints based on correction / reduction factors for other order of harmonics. The option to size based harmonic spectrum is only enabled when BS 7671 17th Edition or IEC 60364 standards are selected for cable sizing.

Multiplication Factors

The cable sizing calculator applies a multiplication factor to the cable ampacity based on the cable application selected. These multiplications factors can be applied to the calculated ampacity as well.

  • Low Voltage Motors
  • Medium Voltage Motors
  • Motor Operated Valves
  • Small Distribution Transformers
  • Large Distribution Transformers
  • Lighting/Distribution Panels
  • Motor Control Centers
  • LV Switchgear
  • Electric Heaters
  • Battery Chargers
  • Others
  • Up to User Defined Applications
  • Capacitors


The Standard field displays the standard selected in the Ampacity page. When the Load Amp requirement is selected in the Requirements section, the ampacity calculation in cable sizing will be based on the standard displayed.


Using the selected cable type from the library, ETAP recommends an optimal cable size along with the number of conductors per phase that meets the specified requirements. Additionally, ETAP cable sizing module provides one cable size smaller than the optimal size for your selection. For the voltage results, Vd is in percent based on bus nominal kV and Vst is in percent based on motor rated kV.

Along with the cable sizing calculation results, this section also displays the required cable sized, cable ampacity, percent of voltage drop, and percent of starting voltage if cable sizing options for the corresponding requirements are checked. The required cable size is the largest size from Short-Circuit, Overload, and Shock requirements. The requirement ampacity is the larger value from Load Amp and Overload requirements. Note that if the Use MF for Ampacity option is selected, the Load Amp used for cable sizing will be multiplied by the MF value displayed in the Cable Application section.


The user can select one or both requirements for determining the recommended size of cable in the cable sizing software. Note that some of the options are dependent on the installation type and if the cable is an equipment cable for a motor.

Load Amp

If Load Amp is selected as one of the requirements, cable sizing will be conducted to meet the load current requirement based on the cable installation and ambient conditions specified in the Cable Ampacity page. The load ampere value is displayed here based on the option selected in the Loading Current for cable Sizing section in the Loading page.

Voltage Drop (Vd)

If Vd is selected, ETAP will size the cable based on the percent voltage drop value you enter here. Voltage drop is in percent of nominal kV of the bus connected to the cable. If the nominal voltages of the From Bus and To Bus are different, nominal kV of the From Bus is selected. The following table shows the methods used for voltage drop calculation for different types of load currents flowing through the cable.



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