Pre-Requisites for Design

Before designing a Powerwall 3 system with three or more Powerwall 3 units:

• AC line impedance must be measured at the installation site to ensure the utility grid connection is able to support the desired quantity of Powerwalls. If the required grid impedance is too high, the Powerwalls may not connect to the grid, resulting in undesirable operation. See Impedance Requirements for Multi-Powerwall 3 Systems for maximum impedance values.
• To minimize impedance:
  • Install the Powerwalls as close as possible to the point of interconnection with the grid. The recommended maximum wire length is 10 m.
  • Install wires larger than required by code between the Powerwall generation panel and the point of interconnection with the grid. For example, if the design requires 95 mm² wire, use 120 mm² wire.
• Designers must properly size overcurrent protection and loads to account for the full power potential of multiple Powerwalls. For example, a 4-Powerwall system is capable of discharging up to 46 kW of power.
• Multi-Powerwall installations may require larger Powerwall communication wire between the Backup Gateway and the Powerwall units. Please refer to Required Supplies for communication cable requirements, as your install may require up to 1.5 mm² wire.

Service Type and Capacity Requirements

Up to (4) Powerwall 3 units can be installed on a single site, but the maximum number of Powerwalls may be limited by the site electrical service, utility grid infrastructure, or local requirements; therefore an impedance test is required to confirm.

Line Impedance Requirements

The sensitivity of the system to line impedance increases with the number of Powerwalls in the system. (See Impedance Requirements for Multi-Powerwall 3 Systems for the maximum allowable impedance as it relates to number of Powerwalls.)

If grid impedance at a site exceeds the maximum allowable value, do either of the following:

• Decrease the impedance of the site grid connection. This may require coordinating with the local electrical utility. See “Minimize Impedance” in Pre-Requisites for Design for suggestions.
• Reduce the quantity of Powerwalls installed at the site to meet the maximum allowable impedance value.

If impedance values exceed the requirement for the installed number of Powerwalls, the system may not function properly.

Measuring Line Impedance

To determine the line impedance at a site, measure between Line and Neutral where the Powerwalls will be interconnected to the site electrical system with testing equipment such as the following:

• Fluke 1660 Series Installation Tester (1662, 1663, or 1664)
• Metrel-MI3000 Multifunction Tester
• Megger LTW315 Loop Impedance Tester

Example Line Impedance Test Instructions

For details on line impedance testing, refer to the test equipment manufacturer’s instructions. The steps below are general guidelines only.

Table 1. Recommended Interconnection Point for Large Multiple Powerwall Systems

1	Service Entrance
2	Meter
3	Main Switch
4	Main Panel