All Tigo EI Inverter models (3.8, 7.6, 11.4 kW) are 208V and 240V compatible. Although the EI Inverters are single-phase, 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!
The utility or inspector may have some questions about this application, but you may alleviate their concerns if the following considerations are applied.
The National Electric Code states that it is acceptable to install single phase inverters on three phase panels if the voltage imbalance between the phases is below 3%. However, check with your local utility for their requirements.
Follow these instructions to determine AC panel voltage imbalance using the following scenario. These voltages were measured by the installer.
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 does comply with the NEC directive of 3%; however, check with your local utility for their imbalance restrictions. Some utilities may be lower or higher than 3%.
If the panel imbalance is greater than 3%, the inverters must be installed so that they do not contribute 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.