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Electrical Cable Sizing Chart

 

• Step 1. DC Amps: Locate the flow of current in amps of your circuit along the top of the chart below.
  
   
• Step 2. Circuit Type: Select the correct type of circuit. Examples of Non Critical circuit are bait pumps,
  windlasses, general lighting, general appliances. Examples of Critical circuits are bilge blowers, panel main feeders, navigation lights, electronics.
  
   
• Step 3. Cable Length: Find the correct length range of cables. Please note that the length is the total length of the positive and negative wires. I.E. Distance from battery to appliance multiplied by 2.
  
   
• Step 4. Correct Cable Size: Intersect the DC Ampere with the cables length range to identity the correct coloured symbol.
  
  
   

Cables impedance calculation

 

Impedance is calculated by below formula:

This method calculates the impedance when the cable and load power factor is the same, this scenario is worse case power factor.

cable sizing calculator uses the resistance Rc from Table 35 in AS/NZS 3008-2017. The reactance for single core cables is selected from the flat

Loop impedance calculation

The maximum loop distance is calculated by below formula:

 

Where:

• V_1Φ is the single phase voltage.
• I_min is the minimum alowable tripping current of the MCB or other protection device.
• Z_c is the cable impedance in Ohm/km.

Voltage drop calculation

The three phase AC voltage drop is calculated as below

The single phase AC voltage drop is calculateda as below

Where I is the load current, L is the distance, and Z_c is the cable impedance in Ohm/km.

Short circuit calculation

The short circuit capacity of the cables is calculated according to AS/NZS 3008-2017