Low-voltage cable sizing

Low-voltage cable sizing module

General

Different installations require different cable design and materials. Eaton's CYME Low Voltage Cable Sizing module calculates the cable size at a given location on the network according to any one of the following standards:

• IEC 60364 5-52 standard: Low-voltage electrical installations – Part 5-52: Selection and erection of electrical equipment – Wiring systems.
• NEC methodology: NFPA-70-2011 National Electricity Code.

Specifically, the module handles three-phase or single-phase systems that are radial and balanced. The conductor materials supported by the calculations are copper or aluminum, while the insulation or cable types are as per the standards.

Calculations

The calculations takes into account conductor material, insulation material and manufacturer:

• Ampacity level – taking into account the installation method of the cable, the software determines the cable size for the installed ampacity. It is executed based on factors that include the soil thermal resistivity and temperature along with the grouping of the circuits
• Voltage drop limit during normal operating conditions – executed based on standard voltage drop formula. The software determines the cable size for the specified voltage drop constraints. It takes into account the resistance, the reactance and the length of the cable and provides data on the maximum voltage drop allowed
• Short-circuit withstand capability (IEC only) – calculates the short-circuit temperature rise based on the maximum fault current and fault duration, either user-defined or based on the short-circuit analysis just performed
• When more than one calculation is performed for one installation, the software will determine an optimal size and will suggest a specific cable from the cable library of the software
• The full load current and power factors can be based on a load flow analysis just performed  or can be defined by the user

Cable library