The cable calculation procedure for an EV (Electric vehicle) charger

Summary

This video provides a comprehensive guide on how to properly calculate and install an EV charge point, covering key topics such as cable selection, protection devices, overload protection, and the impact of various environmental factors. It walks through the design process, from the installation method and current calculations to voltage drop checks and fault current considerations. The video also highlights the unique challenges of EV charger installations, including considerations for cable sizing, correction factors, and the importance of safety and compliance with regulations. It offers valuable advice on addressing the complexities of modern EV charging setups.

Takeaways

• 😀 The method of installation for an EV charge point involves considering the building's construction, cable choice, and the circuit's length and environment.
• 😀 A key part of the calculation is determining the design current, which is calculated by dividing the charger power (7000 Watts) by the voltage (230V), resulting in 30.43 amps.
• 😀 The protective device selection must consider the rating of the device, ensuring it can handle the design current (32 amps in this case) and DC currents from the EV charger.
• 😀 Overload protection is generally not required for a single EV charger but should be considered if multiple chargers are installed or other high loads are involved.
• 😀 Temperature-related stresses on cables must be accounted for, such as high ambient temperatures or thermal insulation, which could impact the cable’s ability to dissipate heat.
• 😀 After applying correction factors, the cable chosen must have the required current-carrying capacity. In this case, a 6mm² cable is selected to carry 36.78 amps.
• 😀 Voltage drop is a critical factor in ensuring the charger operates efficiently. For this installation, the calculated voltage drop (5.55V) is well below the acceptable 5% limit.
• 😀 Earth loop impedance and automatic disconnection of supply are calculated to confirm safe operation in the event of a fault. The system’s Zs value of 0.66 ohms is within permissible limits.
• 😀 The perspective fault current must be calculated to ensure the protective devices can operate in the required time, with the value (331 amps) being sufficiently higher than the rated trip current (160 amps).
• 😀 The cross-sectional area of the protective conductor (CPC) is checked using the adiabatic equation to confirm it can withstand fault currents. In this case, the 2.5mm² CPC is adequate.
• 😀 The design process for an EV charge point is complex and involves factors such as load management, DC current considerations, and proper circuit protection, requiring careful attention to detail throughout.

Q & A

What is the first step in the cable calculation for an EV charge point?

The first step is selecting the method of installation, which includes determining how the cable will be installed in the building, and considering relevant factors such as temperature and cable type.

How do you calculate the design current for an EV charger?

The design current is calculated by dividing the power of the EV charger (in watts) by the voltage (230V). For a 7000W EV charger, the design current would be 7000W ÷ 230V, which equals 30.43 amps.

Why is a 32-amp protective device chosen for an EV charge point?

A 32-amp protective device is selected because it is the next size up from the design current of 30.43 amps. It ensures the circuit is protected without overloading, and it must also be compatible with the potential for DC currents from the EV charger.

Is overload protection necessary for an EV charger?

Overload protection is generally not required for an EV charger since it has a fixed load. However, it is still important to consider the total load in the building, as multiple chargers or other devices might cause the overall load to exceed the system’s capacity.

What factors affect the current carrying capacity of the cable in an EV charger installation?

The factors include ambient temperature, whether the cable is buried or insulated, and whether it is grouped with other cables. These factors can necessitate correction factors to ensure the cable can safely carry the required current.

How do correction factors for temperature impact the cable size?

When the cable is installed in areas with high ambient temperatures, it may need to carry a higher current than initially calculated. For instance, in a 40°C environment, correction factors would reduce the current carrying capacity of the cable, requiring a larger cross-sectional area to compensate.

What is the purpose of calculating voltage drop in an EV charger installation?

Voltage drop calculations ensure that the voltage at the EV charger remains within acceptable limits. Excessive voltage drop can cause inefficiencies, such as slower battery charging speeds or malfunctioning devices.

How is the acceptable voltage drop for an EV charger determined?

The permissible voltage drop is typically set at 5% for general usage (e.g., EV chargers). For a 230V system, the maximum allowed voltage drop would be 11.5V. The actual voltage drop is calculated based on the cable length, design current, and cable characteristics.

What is the significance of the Earth Loop Impedance (Zs) in the installation?

The Earth Loop Impedance (Zs) must be low enough to ensure that the protective device can operate within the required time during a fault. The total Zs is calculated by adding the external earth impedance (Ze) and the internal impedance (R1 + R2).

What is the adiabatic equation used for in cable design?

The adiabatic equation is used to verify that the protective conductor (CPC) is large enough to withstand fault current without breaking. It ensures that the CPC will not be damaged by the heat generated during a fault condition.