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Chapter 5

400 A self-contained services

The meter base/socket required for a 120/240 V, 400 A service is called a Class
320 meter base/socket (see Figures 30 and 31). It is larger than the 200 A meter
base/socket, but it is still a self-contained meter base/socket. It can be installed on
residences where the continuous current rating is 320 A or less.
NOTE: If your structure requires more than 320 A of continuous current, you are
required to install a CT service (refer to the 400 A current transformer (CT) services
section in this chapter).

Underground In addition to the meter base/socket requirements listed earlier in this chapter,
Class 320 meter bases/sockets for 400 A underground services shall:
• Be rated for 120/240 V and 320 A continuous current.
• Contain four meter jaws and one connection point for the neutral conductor.
• Contain a Class 320 manual block bypass (see Figure 30).
• Have lugs that will accept 350 MCM aluminum wire.
• Accept 3-inch steel or Schedule 40 or 80 conduit through a knockout in the
bottom left corner or center of the enclosure.
• Have at least an 8-1/2-inch clearance between the bottom of the lugs and the
bottom of the enclosure (see Figure 30).

Figure 30 Typical arrangement of service conductors for underground class 320 meter base/
socket

METER
BASE/SOCKET
MUST BE
GROUNDED
PER NEC.

BYPASS STUDS BYPASS STUDS
LOAD
LUGS
LINE LUG LINE LUG

NEUTRAL BLOCK
8-1/2"
MIN
CUSTOMER
WIRES

3" RIGID STEEL OR PVC FOR 320 A
RESIDENTIAL, CUSTOMER PROVIDED
(MAY BE LOCATED IN THE BOTTOM
PSE’S 4/0 OR CORNER OPPOSITE THE NEUTRAL
BLOCK OR CENTER OF THE ENCLOSURE)
350 CABLE

Electric Service Handbook 2017 — Single-Family Residential Projects 51