elec calc DC, the Module for Direct Current

June 22, 2020

The DC module “Direct current” is an additional module of elec calc. It allows the design and sizing of low voltage electrical installations in direct current, up to a voltage of 1500 VDC. Completely integrated into the elec calc software, it maintains all of its functionality and ergonomics and allows the creation of installations mixing DC and AC parts.

It meets the sizing needs of auxiliary networks (control and command) and general distribution, excluding those relating to specific standardization or regulations (photovoltaics, rail traction, etc…).


Being part of low voltage networks, the applicable electrical installation standards are identical to those of AC networks, mainly those of the IEC 60364 series or their national versions. For the calculation of short-circuit currents, reference should be made to the series of standards IEC 61660.


The following DC sources are managed for a 2-wire power supply with TNC, TNS, or IT earthing system:

  •   –  Rectifier only: the essential input data are nominal power, cos ϕ, efficiency, output voltage, maximum short-circuit current, and its holding time.
  •   –  Battery: the essential input data are the output voltage and the maximum short-circuit current. Capacity can be indicated for information.
  •   –  Rectifier/battery assembly: the input data is a combination of that of the two constituent elements.

The following receivers are managed in the DC module:

  •   –  Plugs/sockets (single or multiple)
  •   –  Lighting (single or multiple)
  •   –  Resistive loads (single or multiple)
  •   –  Generic receivers

The following switching and protection devices are managed in the DC module:

  •   –  Switches
  •   –  Contactors
  •   –  Fuses
  •   –  Thermal magnetic circuit breakers
  •   –  Magnetic only circuit breakers


The following calculations are carried out like for AC installations in accordance with the aforementioned reference documents:

  •   –  Design currents and power balance
  •   –  Cable sizing
  •   –  Calculation of short-circuit currents
  •   –  Sizing of overload and short-circuit protections
  •   –  Calculation of voltage drops
  •   –  Calculation of thermal stresses

elec calc performs all the verifications which guarantee compliance with the reference documents and reports, where applicable, the alert or non-compliance points detected.


The switching and protection devices used in direct current have different characteristics from those used in alternating current. In addition, for multiple switches and circuit-breakers, it is necessary to manage the different cablings of the poles in order to have the relevant data. Note also that the breaking capacity of circuit-breakers is dependent on the network time constant (L / R ratio) which must, therefore, be known.

elec calc provides users with specific manufacturer catalogs for the switching and protection devices used in DC. The user can also manage his own catalogs as for the other components.

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