All Tigo EI Inverter models (3.8, 7.6, and 11.4 kW) are compatible with 208V and 240V systems. Although the EI Inverters are single-phase (split-phase, 120/240V), they can be used on a three-phase 208V AC panel. Pick two phases for the inverter two-pole breaker, and you are good to go!
AC Service Compatibility
The utility or inspector may have some questions about this application, but you can alleviate their concerns by applying the following considerations.
The National Electric Code permits the installation of single-phase inverters on three-phase panels, provided the voltage imbalance between phases is less than 3%. However, check with your local utility for their requirements.
Follow these instructions to determine AC panel voltage imbalance using the following scenario. The installer measured these voltages.
Phase A – B = 208V
Phase B – C = 203V
Phase A – C = 210V
Enter these values into the voltage imbalance formula.
Voltage Imbalance = 100 x (Max Voltage Deviation from Average / Average Voltage)
Step 1. Calculate the average voltage
- Average Voltage = 208 + 203 + 210 / 3 = 207
Step 2 Calculate the deviation voltage from the average voltage.
- Max Voltage Deviation from Average = 207 – 203 = 4
Step 3 Calculate the total imbalance.
- Voltage Imbalance = 100 x (4 / 207) = 1.9%
This panel complies with the NEC directive of 3%; however, please check with your local utility for their specific imbalance restrictions. Some utilities may be lower or higher than 3%.
Note: Typically, a deviation greater than 6V will equate to a greater than 3% imbalance.
If the panel imbalance exceeds 3%, the inverters must be installed to prevent contributing to the existing imbalance. If the Tigo inverters are installed in groups of three, they will not contribute to an existing imbalance. However, if the total number of inverters on site is not divisible by three, the extra inverters must be installed on the phases with the lower voltage. This will help stabilize the panel voltage.
Please contact Tigo Sales Engineering if you have questions about using Tigo inverters in three-phase applications.