Battery & DC Systems
DC Bus & Cable Sizing
Size DC cables for battery systems, PV and DC switchgear based on current, voltage drop and temperature.
Units:
DC voltage drop is more critical than AC: in a 24V system, 2% drop = 0.48V which can cause relay dropout or PLC faults. Size DC cables for max 1% voltage drop for control circuits.
deltaU = 2 x rho x L x I / A | A_min = 2 x rho x L x I / deltaU_max
Input
DC current I iMaximum DC current in Amperes.
A
One-way cable length iOne-way cable length. Return path doubles effective length.
m
System voltage iDC bus voltage: 12, 24, 48, 110 or 220V DC.
V DC
Max voltage drop iRecommended: 1% for DC control circuits, 3% for power circuits.
%
Conductor material iCopper: rho=0.0175, Aluminium: rho=0.028 Ohm.mm2/m.
Result
Max voltage drop [V]
—
Minimum conductor area [mm2]
—
Recommended standard size [mm2]
—
Actual drop (std size) [V]
—
Actual drop (std size) [%]
—