Chilicon Power.
(310) 800-1396
15415 Sunset Blvd, Suite 102, Pacific Palisades, CA 90272
TBT8-R2001
TECHNICAL BULLETIN
Voltage Rise Calculation
Date: 2/27/2020
Chilicon Power microinverters require a minimum design effort compared to
conventional optimizer/string based systems. In addition to maximum branch
sizing determination*, the only other calculation needed to ensure that all
micros operate within code defined limits is that of voltage rise. However, as
Chilicon Power uses #10 AWG wire in our cabling, voltage rise values are
modest compared to competing microinverter systems.
Voltage Rise: Any time a current flows through a device with internal resistance, Ohm’s
Law states that a voltage change will result. As each microinverter acts as a current source,
the voltage along a chain will increase with the largest voltage present at the furthest
microinverter on the circuit. Residential grids should supply 240V at the service panel, with
the microinverters allowed to operate up to 264V (229V for 208V systems).
The total voltage rise is the sum of the voltage rises from 1) the trunk cable
individual subcircuits, 2) the subcircuit lines connecting to the subpanel, and 3)
the line connecting the subpanel to the main service panel.
1) To calculate the expected voltage rise at the last microinverter, use the
tables in this document to find the appropriate value of either voltage increase
or percentage increase based on the number of microinverters in the circuit,
the cable lengths deployed, and the grid voltage. If using a mixture of cable
lengths, choosing the value associated with the longest length will give a worst
case scenario for voltage rise. A rule of thumb is that the total voltage rise
percentage to the main panel should not exceed 2%.
2) Next, calculate the voltage rise associated with the total length and wire size
of the cabling from the subpanel to each of the subcircuits. Use the maximum
potential current of each microinverter for this calculation. If the microinverter is
current limited, use the current limited value.
V
rise
= (Micros in branch x current per micro) x (resistance in
Ω
per unit length) x (length x2)
For #10 AWG THWN-2 CU resistance = .00129
Ω
/ft (0.00423
Ω
/m)
A number of programs are available to assist with this calculation such as:
https://www.calculator.net/voltage-drop-calculator.html