Wiring a 400 AMP meter base and a 400 AMP subpanel is a common concern for larger houses. This short guide will explain which types of cables in which sizes you should use for a 400 AMP meter base. You will also learn about when it's time to upgrade to the 400 Amp service.

The purpose of a 400 Amp Meter Base

A meter base is a glass enclosure used to protect an electric meter from contact with other components and devices, weather, or water. The electrical meter itself is a device that measures the electricity consumed by a household or other unit.

 The meter base can be located outside, on the exterior wall of your house, linking your house electrical system to the utility cables of your electrical company. You can find an additional utility meter base in some apartment buildings on your apartment's floor. 

A meter base is designed to accommodate different amperages. Thus, a 400-Amp meter base accommodates a single 400 Amp panel.

When is 400 Amp service necessary?

A 400 Amp service is a solution for a large house with a sophisticated HVAC system, significant air conditioning, and heating demands, or all-electric appliances. In addition, it makes sense for houses of different sizes that use hot tubs, saunas, or electric vehicle charging stations.

House owners tend to upgrade to 400 Amp service panels if they are planning significant house renovations and are planning to increase the electrical load with many new electric devices. While all of these are general facts that point toward your house needing a 400-amp service, the final decision should be based on performing a load calculation to determine the actual electric load of your home.

Before installing a new panel, make sure to contact your local building department to get a clear picture of local permits and requirements in your state or area.

Types of cables to use for a 400 Amp Meter Base

• Service entrance cables: Type SE cables in both copper and aluminum are a popular choice for a 400 Amp meter base above ground.
• THHN/THWN cables are a popular choice for 400 Amp meter base to be run in conduit in copper and aluminum.
• XHHW/XHHW-2 is similar to THHN/THWN, but with XLPE insulation and better moisture and heat resistance. Available in copper or aluminum.
• UF underground copper feeder cables are used if the cable from the meter base to the panel should be run underground. This cable is used for direct burial applications.

Size of the cables to use for a 400 Amp Meter Base

A 400 Amp service panel and 400 Amp meter base require a 750 kmil (750 MCM) 0r 1000 kcmil (1000 MCM) aluminum wire at 194°F or only 1000 kcmil (1000 MCM) at 167 °F. For copper wire, you will need 600 kcmil (600 MCM) copper wire for both 167 °F and 194°F.

For a 140 °F underground service, 1250 kcmil aluminum and 750 kcmil copper cables are optimal.

These sizes are relevant both for single-phase and three-phase service.

As for the grounding conductors, the minimum size is 3 AWG for copper or 1 AWG for aluminum or aluminum copper-clad. This is the minimal size of the grounding conductor, as per NEC 2020.

The final choice of the correct size depends on the local codes and regulations.