Cable Size for 55kW Motor Calculator

Cable Size Formula:

\[ A = \frac{I \times L \times 2 \times \rho}{Vd} \] \[ I = \frac{55,000}{\sqrt{3} \times V \times PF \times \eta} \]

Voltage (V):

Power Factor (PF):

Efficiency (η):

Cable Length (L):

meters

Resistivity (ρ):

Ω·m

Allowed Voltage Drop (Vd):

Current (I):

Cable Cross-Section Area (A):

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1. What is the Cable Size Calculation?

The cable size calculation determines the appropriate cross-sectional area of electrical cable needed for a 55kW motor, considering current requirements and acceptable voltage drop over the cable length.

2. How Does the Calculator Work?

The calculator uses two main formulas:

\[ A = \frac{I \times L \times 2 \times \rho}{Vd} \] \[ I = \frac{55,000}{\sqrt{3} \times V \times PF \times \eta} \]

Where:

\( A \) — Cable cross-section area (mm²)
\( I \) — Current (A)
\( L \) — Cable length (m)
\( \rho \) — Resistivity of conductor material (Ω·m)
\( Vd \) — Allowed voltage drop (V)
\( V \) — System voltage (V)
\( PF \) — Power factor
\( \eta \) — Motor efficiency

Explanation: The first formula calculates the required cable size based on current, length, and allowed voltage drop. The second formula calculates the current drawn by the motor.

3. Importance of Proper Cable Sizing

Details: Correct cable sizing ensures safe operation, prevents overheating, maintains proper voltage levels, and complies with electrical codes.

4. Using the Calculator

Tips: Enter system voltage (typically 400V for industrial motors), power factor (usually 0.8-0.9), motor efficiency (typically 0.9-0.95), cable length, conductor resistivity (0.0000000172 Ω·m for copper), and allowed voltage drop (typically 3-5% of system voltage).

5. Frequently Asked Questions (FAQ)

Q1: Why calculate cable size?
A: Undersized cables can overheat and cause fires, while oversized cables are unnecessarily expensive.

Q2: What's typical resistivity for copper?
A: 0.0000000172 Ω·m (or 17.2 nΩ·m) at 20°C for pure copper.

Q3: What voltage drop is acceptable?
A: Generally 3-5% of supply voltage (12-20V for 400V systems).

Q4: Does cable type affect the calculation?
A: Yes, different insulation types have different current carrying capacities at various temperatures.

Q5: Should I round up the calculated size?
A: Yes, always select the next standard cable size above the calculated value.