Electrical service grounding, Chapter 1: building and service entrance grounding, Fig. 1-21 – ERICO Practical Guide to Electrical Grounding User Manual

Page 17

Advertising

Grounding conductors shall be protected against physical
damage wherever they are accessible (Fig. 1-21).
Grounding conductors installed as separate conductors in
metal raceways always must be bonded at both ends to
ensure that current flow is not choked off by the inductive
element of the circuit. See page 15 for a discussion of how
to accomplish the required bonding.

ELECTRICAL SERVICE GROUNDING

Article 230 of the NEC contains the requirements for
installing electrical services for buildings and dwellings.
Contractors, however, should keep in mind that local
authorities, including local electrical utilities, often have
requirements which supersede or augment the NEC.
Contractors should contact the local authorities and
determine if requirements for electrical services exist which
differ from the NEC.

The requirements for grounding electrical services are
contained in Article 250 of the NEC. Section 250-23(a)
requires that a grounded electrical system, which supplies a
building or structure, shall have at each service a grounding
electrode conductor connected to the grounding electrode
system. In addition, the grounding electrode conductor
shall also be connected to the grounded service conductor.
This connection may occur at any accessible point from the
load end of the service drop or service lateral to the
grounded conductor (neutral) terminal block in the service
disconnecting means. (Fig. 1-22 and Fig. 1-23) Keep in
mind that the service disconnecting means is often the heart
of the electrical system. This is frequently the point at
which the required grounding connections occur
(Fig. 1-24).

Chapter 1: Building and Service Entrance Grounding

Plastic Conduit
Protection

Fig. 1-21

To Electrical

Service

A B C

Service Equipment
Enclosure

Grounded Circuit
Conductor

MBJ
250-53(b)

Grounded
Neutral Bar

EGC
250-50(a)

To Branch
Circuit Load

Grounding
Electrode
Conductor
250-92

Grounded
Electrode
250-81

Fig. 1-24

Grounding Of AC Power Per NEC 250-23

Fig. 1-22

Grounding Of AC Power Per NEC 250-23 Exception 5

Fig. 1-23

GROUND

Phase Conductors

Main
Bonding
Jumper

Grounding
Electrode
Conductor

Conductor Size
per NEC 250-94

Electrode System
NEC 250-81 or 83
May consist of:

Water Pipe
Structural Steel
Ring Ground
Concrete Electrode
Rod or Pipe

P
H
A
S

N
E
U

R
A

Service
Entrance
Cabinet

Grounded Conductor (Neutral)

Power

Company

Transformer