Current carrying capacity of solar cables simply explained

The current carrying capacity indicates how much current a cable can safely transmit before it overheats and becomes damaged. An incorrectly dimensioned cable can therefore not only lead to a loss of performance but also pose a fire hazard.

What does current carrying capacity mean?

The current carrying capacity (also: permissible current density) indicates how much current (in amperes) a cable can safely transport over a long period of time without overheating.

The decisive factor is:  

• Heating: Any current flow generates heat – excessive temperatures damage the insulation.
• Rated current vs. operating current: The rated current (e.g., 20 A) should not be confused with peak loads.

Example: A 4 mm² solar cable (e.g. KBE Solar DB+) has a current carrying capacity of 57 A when laid freely.

Factors influencing the current carrying capacity

There are many factors that influence current carrying capacity. These are essentially:

Cross-section of the cable

The cable's cross-section is specified in mm² and has an indirect, proportional effect on the resistance. This means: the larger the cross-section, the lower the resistance.

Example: A solar cable with a cross-section of 6 mm² has a higher current-carrying capacity than one with a 4 mm² cross-section because the resistance is lower.

As a rule of thumb: Doubling the cross-section ≈ 40% more current-carrying capacity

Installation type

Installation depends on how well the heat generated is dissipated by the solar cables. If the heat is poorly dissipated, overheating can occur more quickly.

Therefore, the poorer the heat dissipation, the lower the current carrying capacity.

There are different ways solar cables can be installed:

• Single cable laid freely in the air
  ↓
• Individual cable laid on surfaces
  ↓
• Two cables laid touching surfaces
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• Two cables laid in the cable shaft underground
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• Three cables laid underground in the cable shaft

The current carrying capacity is greatest for solar cables that have been laid freely and becomes smaller the more “constricted” the cable is – bundled cables heat each other up.

Material in the cable

Different materials can be used for the solar cables. 

• Copper: At approximately 56 MS/m, it has a higher conductivity than aluminum (approx. 36 MS/m) and carries electricity faster.
• Aluminum: Is lighter and cheaper than copper. However, to achieve the same conductivity as copper, a larger cross-section is required.

Ambient temperature

At high temperatures (e.g., on roofs), the current carrying capacity decreases. Therefore, PV cables must be UV-resistant and designed for temperatures between -40 °C and +90 °C.

Note: If the ambient temperature of your solar cable differs from that of the manufacturer, you must include a correction factor or conversion factor when calculating the current carrying capacity.

Application of the standard IEC 60364-5-52

For the installation of multiple solar cables, conversion factors (=reduction factors) for the current carrying capacity according to IEC 60364-5-52 must be used.

When laying the cable underground, IEC 60364-5-52 Table B52-3 or B52-5, Column 7, must be used. The current carrying capacity values ​​from Column 7 apply to the installation of the cable in a cable duct in the ground.

The cables are buried directly in the ground in cable ducts with a diameter of at least 100 mm, made of plastic, earthenware, or metal. The soil must have a specific soil resistance of 2.5 K * m/W and the installed cable duct must be 0.7 m deep.

If the cable is laid directly in the ground, the current-carrying capacity according to IEC 60364-5-52 is approximately 10% higher than the values ​​in column 7.

Furthermore, IEC 60364-5-52 must be used if the following deviations occur:

1. Ambient temperatures of the ground deviate from 20 °C
2. Thermal resistance of the soil deviate from 2.5 K∗m/W
3. The number of loaded conductors/circuits deviates

Tips for selecting the right solar cable for optimal current carrying capacity

1. The solar cable must be suitable for PV systems.

At KBE-Elektrotechnik you will find a wide range of solar cables that have been specially designed for use in PV systems.

2. The solar cable must be certified. 

KBE-Elektrotechnik's solar cables are triple-certified according to the European standard EN 50618 (H1Z2Z2-K), the international solar cable standard IEC 62930 (IEC 131), and the standard 2Pfg 1169 /10.2019 (PV 1500-K). This guarantees excellent technical properties, high safety, and a long service life of at least 25 years.

3. Dimension the cable cross-section correctly

A solar cable with a cross-section of 6 mm² releases less heat than a cable with 4 mm² and the risk of overheating is reduced.

4. Use current carrying capacity tables

Here you will find the appropriate tables for determining the current carrying capacity of KBE Elektrotechnik solar cables. 

KBE Solar DB+

KBE Solar DB

5. Laying solar cables professionally

Proper installation also includes using the right connectors. Do you need help installing your solar cable? You'll find many practical tips in our guide "Correct Installation of Solar Cables."

FAQ – Frequently asked questions about current carrying capacity

What happens if the current carrying capacity is exceeded?

Permanently exceeding the current carrying capacity can lead to overheating, insulation damage, fire hazard and up to 5% power loss per meter of cable.

Can I use a normal NYY cable for PV systems?

No! Conventional cables are often not UV- or DC-resistant. For PV systems, you may only use designated solar cables.

What effect does a high ambient temperature have?

For every 10 °C above 30 °C, the load capacity decreases by approximately 5%.

Can I extend solar cables on a PV system?

Yes, but only with suitable connectors and cables with the same cross-section.