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SECTION VI WIRING METHODS 2/03

32
SECTION VI
WIRING METHODS

6.01 GENERAL
A. The customer's service entrance wiring from the service head to
the service equipment shall (except on underground and bus duct
installations) be either approved Type SE 3-wire service-entrance cable, or
a minimum of three individual conductors enclosed in aluminum rigid
conduit, galvanized rigid steel conduit, intermediate metallic conduit or
Schedule 80 electrical grade PVC conduit. Only rigid galvanized conduit
shall be used to support the service drop. EMT shall not be used for
service entrance conductors. Bus duct shall be totally enclosed with no
plug-in openings, shall be protected against mechanical damage and
dust accumulation, and shall be weatherproof where installed outdoors or
in wet locations.

B. No other conductors will be installed in the same raceway with
service-entrance conductors. A grounded electrode conductor or bonding
conductor is not allowed.

C. Unmetered wires will not be permitted in any conduit, wiring
raceways, pull box, distribution cabinet or other similar device containing
metered wires.

D. The opening through which a service-entrance cable enters a
building or structure shall be protected at that point with an aluminum plate
and suitable waterproof material to effectively seal the opening against
moisture and insects.

E. Service-entrance conductors should be without splice, except as
permitted in the latest version of the National Electrical Code. On a multiple
switch or circuit breaker installation, taps for multiple-service equipment
may be made to the main conductors in the service equipment, channel, or
junction box, provided such equipment is at the same location and
interconnected with conduit. The Company however, recommends the use
of a bussed multiple switch or breaker service-entrance panel in order to
avoid the hazardous and difficult taps to the service-entrance conductors. 2/03

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F. The line side of a service installation, up to the metering facilities,
shall not contain a junction box, wiring trough or outlet fittings.

Exception: A wiring trough or junction box may be installed if the facilities
are:

1) Capable of being sealed with a Company seal.
2) Deemed to be necessary by the Company.
3) Specifically approved by the Company.

G. Conduit fittings, with provisions for sealing, may be used only
when it is impractical to install conduit bends in the service either outdoors
or indoors. Where the Company's metering equipment is located on the
line or source side of the service equipment, the customer may, where
necessary, install a junction box or wiring trough at the service equipment.

H. All meter installations will be connected with a meter-switch-fuse
sequence except where specifically approved by the Company. A switch-
fuse-meter installation may be approved for multiple meter installations.

I. Only one conductor per lay-in lug or lug barrel shall be permitted
unless the lug is designed and UL approved for more than one conductor.

6.02 CONDUCTORS
A. Where a single main line switch or circuit breaker, of 800A
capacity or less, constitutes the service equipment and the ampacity of the
ungrounded conductors does not correspond to a standard size switch or
circuit breaker, the next larger standard size switch or circuit breaker may
be used; otherwise, the conductors and the switch or circuit breaker shall
have equal ampacity ratings. If the rating of a standard size switch or
circuit breaker is more than 800A, the ampacity rating of the conductor(s)
must be equal to or greater than the rating of the switch or circuit breaker.
(See Tables 6.1 and 6.2 for conductor size required for typical single
switch installations.) 2/03

34
B. Where multiple switches or circuit breakers in separate
enclosures constitute the service equipment, the main ungrounded service-
entrance conductors shall have an ampacity of not less than 100% of the
sum of the rating of all the switches, but not to exceed six total switches or
circuit breakers. Tap conductors to each main switch or circuit breaker
shall be sized according to 6.02A. Conductors at all times shall have
adequate ampacity for the load calculated in accordance with the latest
edition of the National Electrical Code.

C. Where multiple switches or circuit breakers in a single enclosure
constitute the service equipment, the ampacity of the service-entrance
conductors shall be equal to or greater than the main bus rating of the
enclosure. Modular meter devices shall comply with this provision.

D. Where two to six service disconnecting means in separate
enclosures are grouped at one location and supply separate loads from
one service drop or lateral, one set of service-entrance conductors shall be
permitted to supply each or several equipment enclosures.

E. A maximum of two sets of conductors will be permitted for single-
phase, self-contained metering greater than 200A. The minimum allowed
switch size will be 100 ampere. Total combined ratings not to exceed 400
ampere.

F. When service entrance conductors of 500 kcmil copper or larger
are required, parallel runs of service-entrance conductors may be installed
in separate raceways. Aluminum or copper conductors, comprising each
phase or neutral, will be permitted to be connected in parallel (electrically
joined at both ends to form a single conductor) only if all of the following
conditions are met: all of the parallel conductors of each phase (or neutral),
but not necessarily all phases are; of the same length, of the same
conductor material, same circular-mil area, same insulation type,
terminated in the same manner. Separate raceways will have the same
physical characteristics. Each set of conductors of a parallel service shall
include each phase conductor and a neutral. Minimum size of conductor to
be used for parallel operation is 1/0. The Companys concern in the use of
paralleled circuits is that the conductors in parallel per phase (or neutral)
will evenly divide the load current. 2/03

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G. Copper conductors are recommended for all service entrances.
However, aluminum conductors are approved for most service
entrances provided the aluminum conductors are thoroughly
cleaned and coated with NO-OX-ID Grease, or equivalent, before
clamping at all connections.

H. Maximum allowed amperage of conductor is based on 75 degrees
Centigrade temperature rise and 30 degrees Centigrade ambient.

TABLE 6.1
RESIDENTIAL
120/240 VOLT, 3-WIRE, SINGLE-PHASE

Ampere
Rating of
Single
Main
Disconnect

Size of
Phase Conductors

Minimum
Neutral Size
Copper Aluminum Copper Aluminum
100
4 AWG
2 AWG
6 AWG
4 AWG
200
2/0 AWG
4/0 AWG
1/0 AWG
2/0 AWG
400
400 kcmil
600 kcmil
300 kcmil
400 kcmil 2/03

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TABLE 6.2
COMMERCIAL SINGLE-PHASE AND
THREE-PHASE AND
RESIDENTIAL THREE-PHASE

Ampere Rating of
Single Main
Disconnect
Minimum Required
Phase & Neutral
Conductors
Copper Aluminum
100
200
225
400
600
800
1000
1200
3 AWG
3/0 AWG
4/0 AWG
500 kcmil
2-300 kcmil
2-500 kcmil
3-400 kcmil
3-600 kcmil
1 AWG
4/0 AWG
250 kcmil
800 kcmil
2-400 kcmil
2-800 kcmil
3-600 kcmil
4-500 kcmil
NOTE 1: Tables 6.1 and 6.2 show the minimum copper and aluminum conductor sizes
recommended for standard-size service entrances. These tables are based on not more
than three phase conductors in a raceway at 75º C (167º F) in a wet location.
NOTE 2: Tables 6.1 and 6.2 are not applicable to multiple switch installations.
NOTE 3: Table 6.2 shows the neutral conductor to be full sized. Due to present day
loading, there may be harmonic currents present in the neutral conductor, and the neutral
conductor shall be considered to be a current-carrying conductor. 2/03

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TABLE 6.3
Allowable Amperage of Insulated Conductors
Rated 0 through 2000 Volts, 75
°
C (167
°
F)
Not More Than Three Current-Carrying Conductors in Raceway or Cable or
Earth (Directly Buried) Based on Ambient Temperature of 30
°
C (86
°
F)
Size
Wire Type
Wire Type
AWG
kcmil
FEPW, RH, RHW,
THHW, THW,
THWN, XHHW,
USE, ZW
RH, RHW, THHW,
THW, THWN,
XHHW, USE
COPPER ALUMINUM
8
6
4
3
50
65
85
100
40
50
65
75
2
1
1/0
2/0
115
130
150
175
90
100
120
135
3/0
4/0
250
300
200
230
255
285
155
180
205
230
350
400
500
600
310
335
380
420
250
270
310
340
700
750
800
900
460
475
490
520
375
385
395
425
1000
1250
1500
1750
2000
545
590
625
650
665
445
485
520
545
560
Reference: 1999 National Electrical Code, Table 310-16