Residential Electrical Inspector (CAE)

Parallel Conductors

Lesson 10

Based on the 2014 OESC

Updated: January 2017

2

Code Sections used in this Module

110.3(B) Install per manufacturers instructions

110.14 Temperature and termination adjustment

310.10 Parallel conductor installation

Table 8 Chapter 9

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Parallel Conductors

What is the purpose of using parallel conductors?

Generally, paralleling is used to reduce costs and

installation difficulties associated with large

conductors and raceways. The parallel conductors

can be run in the same raceway or separate

raceways. When 2 conductors of the same size are

paralleled, their ampacity doubles.

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5

Circuit

Breaker Load

Two conductors supplied from a common overcurrent

device to a common load are treated the same as one large

conductor. For example, (2) 3/0 AWG conductors can carry

400-amps

3/0

3/0

A single 350 Kcm conductor is needed to carry 400-amps

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6

A 3/0 AWG conductor has

167,800 circular mils, 2 of

the conductors = 335,600

circular mils. These two

conductors in parallel can

carry 400-amps. A single

350 Kcm conductor can

carry 400-amps but is

350,000 circular mils in

size.

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Parallel Conductors

On most installations, paralleled conductors are

generally not used until 400-amp or larger services

are installed. Section 310.10(H) governs the use of

parallel conductors. Generally, the conductors are

sized at a minimum of 1/0 AWG before they are

allowed to be used in parallel. A 400-amp panel will

generally have (2) 4/0 aluminum or (2) 3/0 copper

conductors per phase.

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Conductors run in parallel are required to be the

same size, length, insulation, material and

terminated in the same manner, 310.10(H)(2). If the

parallel conductors are in the same raceway, conduit

fill and de-rate for current-carrying conductors can

apply. Separate raceways require each raceway to

have a full size EGC installed in each raceway. The

following slides show common installations, some

with code violations.

The principal for parallel runs is the same for single-

phase or three-phase loads. 8 of 29

Verify that all

the lugs are

rated for

multiple

conductors.

110.3(B)

110.14(A)

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This slide shows a violation of 310.10(H)(3). Each

conduit should have the same number of conductors

and a full size EGC

6 conductors

80% de-rate 3 3 3

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Services grouped at

one location.

230.72(A)

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Services

grouped, proper

routing of GEC

to electrode

230.72(A),

250.64(D)

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Proper routing

of GEC and

taps per

250.64(D)

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Lugs are rated for

only one

conductor, main

bonding jumper

not installed

correctly.

250.28, 110.3(B)

200.2(B)

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Improper

GEC

connection to

electrode.

Removal of

the left panel

removes the

connection to

the

grounding

electrode

system.

250.64(D) 15 of 29

Two conductors under

lug rated for a single

conductor

110.14(A)

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310.10(H) Conductors in Parallel.

(1) General. Aluminum, copper-clad aluminum, or

copper conductors, for each phase, polarity, neutral,

or grounded circuit shall be permitted to be connected

in parallel (electrically joined at both ends) only in

sizes 1/0 AWG and larger where

installed in accordance with 310.10(H)(2) through

(H)(6).

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310.10(H)(2) Conductor and installation

Characteristics.

The paralleled conductors in each phase, polarity,

neutral, grounded circuit conductor, equipment

grounding conductor, or equipment bonding

jumper shall comply with all of the following:

(1) Be the same length

(2) Consist of the same conductor material

(3) Be the same size in circular mil area

(4) Have the same insulation type

(5) Be terminated in the same manner

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310.10(H)(3) Separate Cables or Raceways.

Where run in separate cables or raceways, the cables

or raceways with conductors shall have the same

number of conductors and shall have the

same electrical characteristics. Conductors of one

phase, polarity, neutral, grounded circuit conductor,

or equipment grounding conductor shall not be

required to have the same physical characteristics as

those of another phase, polarity, neutral, grounded

circuit conductor, or equipment grounding

conductor.

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(4) Ampacity Adjustment. Conductors installed in

parallel shall comply with the provisions of

310.15(B)(3)(a).

(5) Equipment Bonding Conductors. Where

parallel equipment bonding conductors are used, they

shall be sized in accordance with 250.122.

(6) Bonding Jumpers. Where parallel equipment or

supply-side bonding jumpers are installed in

raceways, they shall be sized and installed in

accordance with 250.102.

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250.122(F) Conductors in Parallel. Where

conductors are installed in parallel in multiple

raceways or cables as permitted in 310.10(H), the

equipment grounding conductors, where used, shall

be installed in parallel in each raceway or cable.

Where conductors are installed in parallel in the same

raceway, cable, or cable tray as permitted in

310.10(H), a single equipment grounding conductor

shall be permitted.

Each equipment grounding conductor shall be sized

in compliance with 250.122.

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Incorrect marking

of conductors on

transfer switch

for generator.

Only grounded

(neutral)

conductors can

be marked white.

200.7

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200.7 Use of Insulation of a White or Gray Color

or with Three Continuous White or Gray Stripes

(A) General. The following shall be used only for

the grounded circuit conductor, unless otherwise

permitted in 200.7(B) and (C):

(1)A conductor with continuous white or gray

covering

(2)A conductor with three continuous white or gray

stripes on other than green insulation

(3) A marking of white or gray color at the

termination

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GEC for

second

panel fed

thru first

panel.

250.64(D)

GEC

runs to

other

panel

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(D) Building or Structure with Multiple

Disconnecting Means in Separate Enclosures.

For a service or feeder with two or more

disconnecting means in separate enclosures

supplying a building or structure, the grounding

electrode connections shall be made in

accordance with 250.64(D)(1), (D)(2), or (D)(3).

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Lesson 9 and Lesson 10 Questions

will be sent to you

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