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The maximum admissible current in conductors is specified namely  by the IEC recommendations.

The limits are due to temperature, and related to the dissipation of the joule heat,  and therefore depend on the layout (environment of the wire, grouping of several wires, etc).

PVsyst takes the minimum sections for the nominal currents into account, supposing the less constraining layout, i.e. "C" mounting mode, wires in a duct at free air.

It is your responsibility to check the compatibility of the proposed sections with the specific layout conditions of your system.  For example, ducts exposed at sun may encounter high temperatures, and should be sized as if the environmental temperature  were 70°C. This may lead to a reduction .of admissible current of the order of 40%.

For more information about cable installation, please consult for example   http://www.electrical-installation.org/enwiki/General_method_for_cable_sizing

The Current limit in PVsyst is calculated according to the  norm  IEC 364-5-523 (1983), following the formula:

  Imax  =  ImaxRef  *  Section[mm²] ** Esect               (where  **  means Power)

where:

   Copper:              ImaxRef  =  13.5 A/mm²

   Aluminum:        ImaxRef  =  10.5 A/mm²  

   Exponent :          Esect      =  0.625  

 

 

 

Very high currents

We can observe that for high sections, the specific current becomes very low (of the order of  1.6 A/mm²  for 300 mm², i.e. a diameter of 20 mm).

For still higher sections the exponential behavior leads to very low and unrealistic values.  

For very high currents we can admit that the conductors will no more be round, but become flat bus bars or sets of several bars in parallel, which will have different heat removal properties.

Therefore we have put a limit to the specific current, i.e. set a limit section from which the specific current will remain constant.

This limit has been fixed to 300 mm2, but may be modified in the hidden parameters.

Installation mode correction

We have also defined a modifying parameter in the hidden parameters, allowing to modify the maximum current according to some Installing configuration specificity. This parameter is set to 1 by default.