Cable size inside the control panel
Calculate the cross-section of the power wiring in a control panel with the current-carrying capacity table of IEC 60204-1 (EN 60204-1), corrected for the temperature inside the panel and for the circuits sharing a wiring duct.
Calculator
Standards this calculator follows
Current-carrying capacities. IEC 60204-1:2016 (EN 60204-1), table 6: PVC-insulated copper conductors, at 40 °C ambient temperature, with one balanced three-phase circuit.
Corrections. Annex D: table D.1 for another ambient temperature and table D.2 for several grouped loaded circuits. The standard takes these factors from IEC 60364-5-52.
Minimum cross-section. Table 5: inside enclosures, 0.75 mm² for power circuits and 0.2 mm² for control circuits.
For the line that supplies the panel, use the cable sizing guide according to IEC. This calculator is for preliminary sizing: always check the result against the standard.
How it is calculated
The chosen cross-section is the smallest whose corrected current-carrying capacity is not lower than the circuit's design current:
Iz = Iz0 × kT × kG ≥ Ib
Iz0 comes from table 6; kT, from table D.1 according to the temperature inside the panel; and kG, from table D.2 according to the loaded circuits running together. Table D.2 gives values for 2, 4, 6 and 9 circuits: for numbers in between, the next value in the table is used, which is on the safe side.
| Method | Installation inside the panel |
|---|---|
| B1 | Single-core conductors in wiring duct or conduit: the usual wiring between devices |
| B2 | Multicore cable in wiring duct or conduit |
| C | Multicore cable fixed to the mounting plate or wall, with no gap between cables |
| E | Multicore cable on a perforated tray |
Temperature inside the panel. In a closed panel the air is hotter than in the room because of the heat the devices dissipate. Use the expected internal temperature, from the panel's thermal calculation or measured, not the room temperature.
Example. A 10 A circuit wired with single-core conductors in a wiring duct (B1), with 40 °C inside the panel and 2 loaded circuits in the same duct: kT = 1 and kG = 0.8. With 1 mm², Iz = 10.3 × 1 × 0.8 = 8.24 A: not enough. With 1.5 mm², Iz = 13.5 × 1 × 0.8 = 10.8 A ≥ 10 A: it passes.
Tables of the standard
Table 6 · Current-carrying capacity Iz0 (A), copper and PVC, 40 °C
| Cross-section (mm²) | B1 | B2 | C | E |
|---|---|---|---|---|
| 0.75 | 8.6 | 8.5 | 9.8 | 10.4 |
| 1 | 10.3 | 10.1 | 11.7 | 12.4 |
| 1.5 | 13.5 | 13.1 | 15.2 | 16.1 |
| 2.5 | 18.3 | 17.4 | 21 | 22 |
| 4 | 24 | 23 | 28 | 30 |
| 6 | 31 | 30 | 36 | 37 |
| 10 | 44 | 40 | 50 | 52 |
| 16 | 59 | 54 | 66 | 70 |
| 25 | 77 | 70 | 84 | 88 |
| 35 | 96 | 86 | 104 | 110 |
| 50 | 117 | 103 | 125 | 133 |
| 70 | 149 | 130 | 160 | 171 |
| 95 | 180 | 156 | 194 | 207 |
| 120 | 208 | 179 | 225 | 240 |
Table D.1 · Factor kT for ambient temperature
| Temperature (°C) | 30 | 35 | 40 | 45 | 50 | 55 | 60 |
|---|---|---|---|---|---|---|---|
| kT | 1.15 | 1.08 | 1.00 | 0.91 | 0.82 | 0.71 | 0.58 |
Table D.2 · Factor kG for grouped loaded circuits
| Method | 1 | 2 | 4 | 6 | 9 |
|---|---|---|---|---|---|
| B1 and B2 | 1.00 | 0.80 | 0.65 | 0.57 | 0.50 |
| C | 1.00 | 0.85 | 0.75 | 0.72 | 0.70 |
| E | 1.00 | 0.88 | 0.77 | 0.73 | 0.72 |
Common questions
Which method do I use for the wiring inside the panel?
Single-core conductors running in wiring ducts between devices are method B1, the most common case. If multicore cables run in the duct, it is B2; if the multicore cables are fixed to the mounting plate, C.
Which circuits count as grouped?
The circuits that carry current at the same time and run together in the same wiring duct or conduit. The protective conductor does not count, because it carries no current in normal service.
What about control circuits?
Inside the panel the minimum cross-section is 0.2 mm² (table 5). Table 6 of the standard has its own values for control pairs from 0.2 to 0.75 mm², and table D.2 has its own grouping factor for pairs smaller than 0.5 mm².
Can I use it for the line that supplies the panel?
No. The supply line is part of the building installation: in Spain it is sized with the REBT. Use the cable sizing guide according to IEC.
Links
- IEC 60204-1:2016 · Safety of machinery, electrical equipment of machines, part 1 (official IEC page)
- Cable sizing according to IEC · FaseCAD guide
- kW to amps calculator · FaseCAD tool