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Chapter 5

400 A current transformer (CT) services

120/240 V, 400 A CT services are available at an additional charge. This service
requires a different meter base (see Figure 32). It also requires additional equipment
(current transformer (CT) enclosure, conduit, CT mounting bracket, etc.). The CT
enclosure must be located on the outside of the structure that it serves. Contact your
CCS Representative for more information.
NOTE: The CT enclosure cannot be used as a junction box or bus gutter.

Figure 32 Instrument-rated (CT) meter bases/sockets

DIAGRAM A DIAGRAM B
120/240V SINGLE-PHASE METER BASE/SOCKET THREE-PHASE SINGLE METER BASE/SOCKET

9" 9"

20" 20"
MIN
MIN
TO CT CAN 1 TO CT CAN 1 11"
11" TEST SWITCH
TEST SWITCH SPACE
SPACE
4" MIN 1-1/4" MIN 4-1/2" MIN
1" MIN 12" CONDUIT DIAMETER 12"
CONDUIT DIAMETER MIN MIN

1
NOTE : NO MORE THAN FOUR 90˚ BENDS DIAGRAM B:
50 FEET MAX LENGTH 120/208 V, 4-WIRE WYE
NO CONDULETS IN THE RUN 277/480 V, 4-WIRE WYE
ALL DIMENSIONS ARE MINIMUM

Services over 400 A

All 120/240 V services over 400 A (320 A continuous current) require CT metering.
Figure 33 shows a CT mounting base. Please contact your CCS Representative for
more information. Table 7 describes minimum CT enclosure dimensions.

Table 7 Current transformer (CT) enclosure dimensions (minimum)

Switch No. of
Phase Width Height Depth
Ampacity Transformers
1 * 400-800 2 24" 48" 11"

3 * 201-800 3 36" 48" 11"

3 ** over 800 3 **

* When enclosure dimension is greater than 24" x 48", a single side-hinged door is
required.
** Services over 800 A require a switchboard designed to EUSERC specifications.
Services from 201-800 A may be switchboard designed to EUSERC specifications.

Electric Service Handbook 2017 — Single-Family Residential Projects 53