Cable Cross-Section Selection
- Landis+Gyr – EV Editor 4
- Andrej Zadravec (Deactivated)
Table of Contents
3. Cable Cross-Section Selection
The required cable cross-section is determined considering the maximum current, the allowable voltage drop and the expected short-circuit current. Cross-section can be determined by calculation or from a table, in the usual way, in accordance with IEC 60364-5-52.
When determining the cross-section of the cables, it is also necessary to include the method of installation, the material of the conductors and the insulation material. The temperature conditions at the location and the length of the cable also have an impact.
In general, the cable cross-section for the INCH DUO connection is around 10 - 25 mm2, dependant on the installation method. Larger distances or clustering of several charging stations could require cables with larger cross-section. Direct connection of INCH DUO is possible for cables of cross-section of up to 50 mm2. With use of additional clamps, it is possible to connect cables with cross-section of up to 95 mm2.
We recommend that at least the specified cable cross-section is selected for all phase conductors, for the neutral conductor and for the protective conductor. When choosing cables with a larger cross-section, the losses will be smaller, which is especially important for longer cable routes.
Minimum Cables Cross-Section
The calculation of necessary cables cross-sections should be part of electrical project and should consider the specifics of the actual location. The plan of installation should be prepared by licensed electrician or electrical planner in accordance with national legislation. Values given in this chapter are only informational.
The cables cross-sections are determined by three criteria:
Continuous operating current.
Voltage drop.
Short circuit withstand.
continuous Operating current
The cross-section of cables must be large enough that continuous charging with maximal current is safe and does not damage the cables. Different installation options and environmental conditions are possible.
In the following table, the installation method can be checked for the minimum cable cross-section when connecting one INCH DUO charging station. These values apply for copper conductors with XLPE insulation at reference air temperature of 35 ° C. For installation of cables in the ground, temperature of the ground is set as 25 ° C and soil thermal resistivity as 2.5 K*m/W. Charging current of 64 A is being considered.
Table 1: Minimum cable cross-section for continuous operating current of 64 A.
 | A1 - Insulated single core conductors in conduit in a thermally insulated wall A2 - Multicore cable in conduit in a thermally insulated wall This method also applies to single core or multicore cables installed directly in a thermally insulated wall (use methods A1 and A2 respectively), conductors installed in mouldings, architraves and window frames.
| A1, A2: 16 mm2 |
 | B1 - Insulated single core conductors in conduit on a wall B2 - Multicore cable in conduit on a wall This method applies when a conduit is installed inside a wall, against a wall or spaced less than 0.3 x D (overall diameter of the cable) from the wall. Method B also applies for cables installed in trunking / cable duct against a wall or suspended from a wall and cables installed in building cavities.
| B1, B2: 16 mm2
|
 | C - Single core or multi-core cable on a wooden wall This method also applies to cables fixed directly to walls or ceilings, suspended from ceilings, installed on unperforated cable trays (run horizontally or vertically), and installed directly in a masonry wall (with thermal resistivity less than 2 K·m/W).
| C: 10 mm2 |
 | D1 - Multicore or single core cables installed in conduit buried in the ground D2 - Multicore or single core cables buried directly in the ground | D1, D2: 16 mm2 |
 | E - Multicore cable in free-air This method applies to cables installed on cable ladder, perforated cable tray or cleats provided that the cable is spaced more than 0.3 x D (overall diameter of the cable) from the wall. Note that cables installed on unperforated cable trays are classified under Method C.
| E: 10 mm2 |
 | F - Single core cables touching in free-air This method applies to cables installed on cable ladder, perforated cable tray or cleats provided that the cable is spaced more than 0.3 x D (overall diameter of the cable) from the wall. Note that cables installed on unperforated cable trays are classified under Method C.
| F: 25 mm2 |
 | G - Single-core cables laid flat and spaced in free-air This method applies to cables installed on cable ladder, perforated cable tray or cleats provided that the cable is spaced more than 0.3 x D (overall diameter of the cable) from the wall and with at least 1 x D spacings between cables. Note that cables installed on unperforated cable trays are classified under Method C. This method also applies to cables installed in air supported by insulators.
| G: 25 mm2 |
At sites, where the cross-section of already existent cables is smaller than recommended minimum, the limitation of maximal current can be made in the charging station’s web interface to allow the connection of charging station, without the need to replace all the cables.
Voltage drop
The requirement for the maximum voltage drop of the installation can be different across different countries. Usually, it is required that the voltage drop of the installation is below 4 % (or in some cases below 5 %).
The length of the conductors and charging current are major factors determining the adequacy of cables cross-section, however voltage drop occurs on other components or devices as well. Because of it, some reserve should be considered when selecting cables cross-section.
Table 2: Voltage drop in conductors with 10 mm2 cable cross-section and charging current of 64 A.
Charging current | Conductor | Conductor |
64 A | 10 mm2 | 10 mm2 |
| Single phase | Three phase |
L - length [m] | Voltage drop [%] | Voltage drop [%] |
10 | 1,09 | 0,94 |
20 | 2,18 | 1,88 |
30 | 3,26 | 2,83 |
40 | 4,35 | 3,77 |
Table 3: Voltage drop in conductors with 16 mm2 cable cross-section and charging current of 64 A.
Charging current | Conductor | Conductor |
64 A | 16 mm2 | 16 mm2 |
| Single phase | Three phase |
L - length [m] | Voltage drop [%] | Voltage drop [%] |
10 | 0,69 | 0,60 |
20 | 1,38 | 1,19 |
30 | 2,07 | 1,79 |
40 | 2,75 | 2,39 |
50 | 3,44 | 2,98 |
60 | 4,13 | 3,58 |
Lower voltage drop also means that the power losses of charging process will be lower. The life cycle assessment and calculation of benefit of using cables with larger cross-section could help mitigate the higher cost of investment.
Table 4: Voltage drop in conductors with 25 mm2 cable cross-section and charging current of 64 A.
Charging current | Conductor | Conductor |
64 A | 25 mm2 | 25 mm2 |
| Single phase | Three phase |
L - length [m] | Voltage drop [%] | Voltage drop [%] |
10 | 0,45 | 0,39 |
20 | 0,90 | 0,78 |
30 | 1,35 | 1,17 |
40 | 1,80 | 1,56 |
50 | 2,25 | 1,95 |
60 | 2,70 | 2,33 |
70 | 3,14 | 2,72 |
80 | 3,59 | 3,11 |
90 | 4,04 | 3,50 |
Table 5: Voltage drop in conductors with 35 mm2 cable cross-section and charging current of 64 A.
Charging current | Conductor | Conductor |
64 A | 35 mm2 | 35 mm2 |
| Single phase | Three phase |
L - length [m] | Voltage drop [%] | Voltage drop [%] |
40 | 1,31 | 1,13 |
50 | 1,64 | 1,42 |
60 | 1,97 | 1,70 |
70 | 2,29 | 1,99 |
80 | 2,62 | 2,27 |
90 | 2,95 | 2,55 |
100 | 3,28 | 2,84 |
110 | 3,60 | 3,12 |
120 | 3,93 | 3,40 |
Short circuit withstand
Charging station INCH DUO has already installed miniature circuit breakers which protect against overload and short circuit. This protection can also be part of installation with different tripping characteristics.
Short circuit protection lowers the possible short-circuit and its duration that downstream installed devices can be subjected to. Normally, 2 kA short circuit of 10 ms duration could be considered for calculations of cables cross-section to withstand short circuit.
Cable with cross-section of 6 mm2 is enough to withstand 5 kA, 20 ms. This value suggests that short-circuit withstand will not be the strictest criterion.
Other Consumption or Production of Electricity at the Location
In cases, where there are other loads at the location and there is a possibility that the total load (other loads + charging) overcomes the limitation of the grid connection point, the charging should be controlled.
Because the charging station needs information of other loads (or production) to be able to react appropriately, Etrel Load Guard device can be used.
Load Guard
By using Load Guard device, other loads or production can be measured and used in overload prevention algorithms:
Static limit of maximum allowed charging current per phase.
Static limit of maximum allowed charging current per phase in case connection with Load Guard sensor or with Back-End System is lost.
Detection and visualisation of available supply and automatic adjustment of charging power.
Detection and visualisation of surplus energy returned to the grid (Production from renewable energy sources).
When the user connects EV to charger, and prior to beginning of charging, the charger determines the current available for charging as the difference between the rated current of the main fuse (reduced by a safety margin that can be pre-set by the user via charger’s web interface) and the last measurement received from Load guard.
Figure 5: Use of additional consumption data to prevent overload
When there is local production of energy present at the location (e.g., photovoltaics), the available charging current can be higher, and the use of Load Guard make possible to always charge with maximum available current.
Figure 6: Use of additional consumption and production data to prevent overload
Related content
Warning! Before installing, wiring, handling or accessing the charging station in any way, make sure to read, understand and follow the Safety Guidelines.
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