Table of Contents

A) CURRENT CARRYING CAPACITY and CORRECTION FACTORS Top

The CableApp uses the correction factors as defined in the Table B.52.1 of IEC 60364-5-52. This allows the user to tailor a circuit rating for their given prescribed installation. These correction factors cover the following parameters: ambient temperature (air, and ground where appropriate), soil resistivity, depth, proximity of multiple circuits for ladder, tray, direct in ground and in ducts in the ground.

a1) LV Cables to IEC 60502-1 / HD 603 S1 or similar

a2) MV Cables to IEC 60502-2 or similar

a3) MV Cables to HD 620 S2 or similar

B) BASE CONDITIONS Top

The published current ratings in IEC / HD 60364-5-52 are based on the following conditions:

The published current ratings in IEC 60502-2 are based on the following conditions:

The published current ratings in HD 620 S2 are based on the following conditions:

C) Voltage Drop Top

The CableApp executes voltage drop calculations using the formulae for voltage drop published in Appendix G of IEC 60364-5-52, for the appropriate cable and installation type. The voltage drop between the origin of an installation and any load point shall not be greater than the values below:

As far as possible, it is recommended that voltage drop within the final circuits do not exceed those indicated in installation type A

When voltage drops exceed the values shown above, larger cables (wires) must be used to correct the condition

When the main wiring systems of the installations are longer than 100 m, these voltage drops may be increased by 0,005% per meter of wiring system beyond 100 m, without this supplement being greater than 0,5%

Voltage drop is determined from the demand by the current-using equipment, applying diversity factors where applicable, or from the values of the design current of the circuits

A greater voltage drop may be accepted:
- for motor during starting periods
- for other equipment with high inrush current,
provided that in both cases it is ensured that the voltage variations remain within the limits specified in the relevant equipment standard

The following temporary conditions are excluded:
- voltage transients
- voltage variation due to abnormal operation

Voltage drop may be determined using the following formulae:

D) ENERGY CONSCIOUS SOLUTION Top

The following information provides guidance in energy efficiency, and the calculation method used to provide the Energy Conscious Solution in the CableApp

The calculation requires the end user to define some of the parameters used in the calculation, within the "Settings" menu of the CableApp

The potential savings should be considered as guidance only

According to Joules Law, whenever a conductor carries current, it will generate heat (thermal energy)

Thermal energy of a cable corresponds to the following general formulae:

Where:

If the cross-sectional area (S) of a cable is increased, there will be a corresponding reduction in the resistance (R). When carrying the same current I, there will be a reduction in the energy loss (E_P). This energy saving can be quantified both as a cost saving in electricity bills and a reduction in CO₂ emissions.

The cable itself will be more expensive because it will have a higher cross-sectional area (S) but the installer will benefit from the following:

  - Lower running costs, reduced energy bills.
  - Reduced CO₂ emissions, therefore an environmentally better proposition.
  - Extended design life for the cable because it is operating at a lower temperature.

Standard design life is based on the cable being at its maximum load (maximum operating temperature) for every hour of that defined life in years.
  - Improved short circuit capability - larger cross-sectional areas will carry higher currents in a fault condition.
  - Potential to uprate the cable to carry higher loads in the future.

As a rule, cables do not carry the same current (I) continuously. For this reason, it is advisable to consider the mean square value of the current over time or at least to make an estimate.

The CableApp will offer by default the average usage of load (I ') equal to 75% of I, but other values can be selected or defined by the user in the "Settings" of the CableApp:

Thus, the energy saved (E_A) by installing conductors of lower resistance (R₂) than (R₁) will be:

Having calculated the saved energy, the economic savings can be calculated (A£) and the savings in CO₂ emissions since we have defined the electricity tariffs (Energy Price) in RON/kWh (in the "settings") and the approximate values of CO₂ emissions (A_CO2) kg per kWh generated taking account of the country’s energy mix is defined by the CableApp (note, this value cannot be modified by the user).

Entering the value of the electricity rate and the value of CO₂ emissions per kWh will therefore give the savings achieved by installing cross-section conductors with a larger section.

E) Example of Economic / Ecologic Calculation Top

Let’s assume we want to carry out an economic and ecological calculation as follows:

System - three-phase; 130 m; 268A (dummy data)
CableApp Proposed Technical Size - 95mm² copper conductor

To calculate the savings, we must consider increasing the cross-sectional area from 95mm² to the next largest standard cross-section, which is 120mm².

Reference is made in the background of the App to the electrical resistance table (above), calculated at a given average operating temperature. The R value for the next size is selected, in this case 120mm².

For the simplicity of the calculation, both conductors are assumed to operate at the same temperature. The resistance for the larger conductor will be lower than given in the table when carrying the same load, because the larger conductor will operate at a lower temperature. The subsequent savings will be a conservative estimate.

If the calculation is undertaken for an annual usage, then the time (t) will be 365days • 24h = 8760 h.

We will assume the average usage is 75% (default value in the App, but this can be changed in the “settings” menu)

Now we can calculate the energy that can be saved in a year using 120 mm² instead of 95 mm².

We have defined the chosen installation with a tariff rate for electrical energy of 0.45 RON / kWh (remember the user should define their Tariff in the "settings").

The CableApp uses a default value for CO₂ emission equal to 0.40 kg CO₂ / kWh.