Cable sizing calculator IEC 60364 and HD 60364

The cable sizing calculator considers current rating, voltage drop and short circuit current according to the IEC 60364 and HD 60364 standards.

Description

The cable sizing calculator calculates the cable size based on current rating, voltage drop and short circuit current according to IEC 60364 and HD 60364 standards. IEC 60364 -Electrical Installations for Buildings, is a harmonized standard that has been adopted by many countries in the world. For example, European Union adopted the IEC 60364 standard and published it as HD 60364.

Paremeters for the Cable sizing calculator (IEC 60364 and HD 60364)

• Voltage (V): Specify the voltage and select the phase arrangement: 1 Phase AC or 3 phase AC. Currently supports AC only.
• Load (kW, kVA, A, hp): Specify the the load in kW, kVA, A, or hp. Specify cosΦ (load power factor) when load is specified in kW or hp.
• Maximum volt drop (%): The maximum allowable voltage drop.
• Distance (m, ft): The estimated cable or wire length in meters of feet
• Short circuit current and time (kA, ms): The short circuit current and clearing time for the protection device.
• On low voltage circuits the let-through current is typically used, i.e. downstream of the protection device (fuse, MCB, or MCCB).
• On high voltage circuits the prospective fault current and back-up protection time is typically used i.e. the fault current on the primary side of the circuit breaker, contactor or fuse.
• Cable type: The number of cores in the cable. Ignore the neutral and earth conductor in three phase cables.
• Insulation type: The type of insulation. Typically Thermoplastic (PVC) or Thermoset (XLPE). The important part is to select the correct temperature rating.
• Number of parallel cables: Typically only one cable. More than one cable may be selected for high load scenarios. If the cable type is single core, this parameter means sets of cables, . In other words, six cables will be considered if two parallel cables for a “Three single-cores” type cable is selected.
• Cable installation: How the cable in installed. Consider the worse case section of the cable installation.

Current rating:

• The current rating is selected from Tables B.52.2 to B.52.13 to 21 in IEC 60364-5-52.
• The cable ratings in are based on an ambient temperature of 30°C and a ground temperature of 20°C.
• The current rating is based on the cable type, the insulation type and the cable installation method.
• The cable sizing calculator conductors only. Aluminum and flexible cables are not supported yet.

Derating

• No derating is currently applied to the current rating from Tables B.52.2 to B.52.13 to in IEC 60364.
• It is assumed that the maximum ambient temperature is 30°C and the maximum ground temperature id 20°C. For higher temperatures, a derating will have to be applied according to B.52.14 in IEC 60364.
• It is also assumed that the cable is installed as specified in Tables B.52.2 to B.52.13 in IEC 60364. to avoid derating, and there there is only one circuit. For groups of circuits, the cable will have to be derated according to tables 22 to 26.
• How to use the derated factors in the calculator: Divide the load by the derating factor from tables B.52.17 to B.52.21, and enter the new load value in the calculator.

How to calculate voltage drop with IEC 60364

• The single phase AC voltage drop is calculated as:
• $$V_{d1\phi}=\dfrac{I L (2 Z_c)}{1000}$$, where I is the load current, L is the distance, and $$Z_c$$ is the cable impedance in Ω/km.
• The three phase AC voltage drop is calculated as:
• $$V_{d3\phi}=\dfrac{I L (\sqrt{3}Z_c)}{1000}$$.
• The impedance is calculated as: $$Z_c = \sqrt{R_c^2 + X_c^2}$$. This method calculates the impedance for the worse case power factor, i.e. when the cable and load power factor is the same.
• The resistance is calculated according to Annex G in IEC 60364-5-52 as $$R_c= =\dfrac {0.0225\cdot L}{s}$$, where s is the cross-sectional area of the conductors in mm2, and L is the length of the conductor in meters.
• A reactance $$X_c$$ of 0.08 mΩ/m is used for all cables, according to Annex G in IEC 60364-5-52.

How to calculate short circuit rating with IEC 60364

The short circuit capacity of the cables is calculated according to AS/NZS 3008 as: $$I^2t = K^2S^2$$, where,

• I is the short circuit current in amperes,
• t is the short circuit duration in seconds.
• S is the cross sectional area of the conductor.

And K is calculated according to IEC 60364-5-54 as:

$$K=226\sqrt{\ln\bigg(1+\dfrac{\phi_f-\phi_i}{234.5+\phi_i}\bigg)}$$

Where here $$\phi_f$$ and $$\phi_i$$ are the final and initial conductor temperatures, which is based on the insulation material, initial conductor temperature and final conductor temperature.

The calculator assumes that the initial conductor temperature is the maximum allowable operating temperature for the insulation type, i.e. 70°C for PVC and 90°C for XLPE. The maximum allowable short circuit temperature from Table 53 in AS/NZS 3008 is used as the final conductor temperature i.e. 160°C for PVC and 250°C for XLPE.