Why perform cable calculations?

What does a cable calculation ensure?

• Correct voltage drop. You calculate the conductor cross-section so that the voltage drop at the end of the cable stays within acceptable limits. This ensures that motors, power supplies and measuring circuits work as intended and prevents poor starting, flickering or error messages.
• Thermal current-carrying capacity in practice. You take into account the installation method (cable tray, conduit, underground), ambient temperature, grouping and duty cycle. This prevents overheating and reduces the risk of fire.
• Fast and reliable disconnection in the event of a fault. The cable impedance determines the fault current in the event of a short circuit or earth fault. You verify that protective devices (circuit breakers, fuses, RCDs) disconnect within the required time and that the loop impedance is adequate.
• Short-circuit withstand. You check that the selected cross-section and insulation can withstand the I²t of a short circuit until the protective device opens.
• Selectivity and coordination. By knowing currents and impedances, you can achieve selectivity between upstream and downstream protective devices, so that faults remain local.
• Functional performance. You verify inrush/starting currents against voltage drop, so that drives start reliably.
• Power quality & EMC. You look at harmonics and (where relevant) neutral currents, so that N conductors are not overloaded and measuring/control circuits remain free of interference.
• Fire load & route selection. You assess the fill ratio of trays and risers and take reaction-to-fire/smoke classes (CPR) into account.
• Expandability & lifecycle cost. A sufficient cross-section prevents premature capacity limits and reduces losses.