Cable Calculator App Update – 2019

​Pro Certs Software have updated their cable size calculator for improved usability, a smoother user experience and bug fixes. A cable size calculator is a handy electrical app to have at your side for when the need arises to carry out a quick cable size calculation while out on site, during a site survey or in the office for circuit design.

The cable calculator software incorporates an swa cable calculator which also calculates the cable volt drop, expected Zs value and r1+r2.

Cable Calculator Software

Input your design parameters such as design current, length of circuit, supply voltage and Ze.
Then select from the built-in options for the circuit maximum volt drop % and earthing system type.

Earthing System Types:

  • TN-C-S
  • TN-S
  • TT – No RCD
  • TT – 30mA RCD
  • TT – 100mA RCD
  • TT – 300mA RCD (added in May 2020 update)

RCD Max Zs in TT Earthing Systems Supported

As with most TT earthing systems it can be extremely difficult to achieve a low enough Ze reading to satisfy the maximum permitted Zs value of the circuit protective device, hence RCD’s are required.

This cable calculation software includes support for TT earthing systems, the TT earthing system options supports using the RCD / RCBO maximum permitted Zs values instead of the MCB values, such as 1667 for a 30mA RCD enabling a more precise cable size calculation.

Cable Size Calculation Formula

The cable calculator incorporates all the common protective devices from MCB’s, RCBO’s and fuses which also supports manufacture specific MCCB’s and ACB’s maximum Zs values, allowing the user to manually input the required maximum Zs value for the specific device.

The cable calculation formula used is based on BS 7671 18th edition wiring regulations which also supports correction factors, Zs values and volt drop. For the common protective devices the maximum permitted Zs value is pre-programmed in to the app removing the need to look up the Zs charts for each device.

SWA Cable Calculator

The cable calc app includes many different cable types including 70oC SWA and 90oC SWA cables.

Installation methods for the SWA cable size calculator includes:

  • C – Clipped Direct
  • E – Free Air or Tray
  • D – Buried in Ducting or Directly in the Ground

Cable Size Calculator Excel

This app has a lot of data programmed in to the app. Cable calculations based on Excel such as cable size calculator excel have to have accurate and current data setup by the means of multiple complex formulas, the formulas can easily be accidentally deleted or changed resulting in an incorrect cable size calculation. This app limits the mistakes that would result from using an un-trusted excel formula for cable calculations.

Print the Cable Calculation Results

(Added in May 2020 update)

Print or save a PDF (save PDF function is a device capability dependent) of your cable calculation results and design data.

Volt Drop Calculator

A volt drop calculator is included within this cable calc app along with calculated Zs and calculated r1+r2.

Cable Current Carrying Capacity Calculator

To calculate the final required minimum cable size the software utilises the cable current carrying capacity tables from BS 7671. Correction factors are applied based on your selections such as ambient temperature, grouping or surrounded with thermal insulation. The cable current carrying capacity varies depending on the appropriate correction factors and installation methods.


Get The App!

BS 7671 Cable Size Calculator.
Google Play iOS App Store


Join our newsletter for new apps, updates, blog posts and promotional offers.