Figure: High Touch Voltage Created by Improper Grounding

UNIT V: WIRING AND GROUNDING
Reasons for Grounding, wiring and grounding problems and solutions

INTRODUCTION : Any power quality variations that occur within customer facilities are
related to wiring and grounding problems. It is commonly stated at power quality
conferences and in journals that 80 percent of all the power quality problems reported by
customers are related to wiring and grounding problems within a facility.
GROUNDING : A conducting connection, whether intentional or accidental, by which an
electric circuit or equipment is connected to the earth.
REASONS FOR GROUNDING
The most important reason for grounding is safety. Two important aspects to grounding
requirements with respect to safety and one with respect to power quality are
1. Personnel safety. Personnel safety is the primary reason that all equipment must have a
safety equipment ground. This is designed to prevent the possibility of high touch voltages
when there is a fault in a piece of equipment (Fig. ).
2. Grounding to assure protective device operation. A ground fault return path to the point
where the power source neutral conductor is grounded is an essential safety feature.
Figure : High touch voltage created by improper grounding.

3. Noise control. Noise control includes transients from all sources.This is where grounding
relates to power quality.
Typical Wiring and Grounding Problems

 Problems with conductors and connectors
One of the first things to be done during a site survey is to inspect the service entrance, main
panel, and major subpanels for problems with conductors or connections.
 Missing safety ground
If the safety ground is missing, a fault in the equipment from the phase conductor to the
enclosure results in line potential on the exposed surfaces of the equipment. No breakers
will trip, and a hazardous situation results (see Fig. 10.2).
 Multiple neutral-to-ground connections
Unless there is a separately derived system, the only neutral-to-ground bond should be at
the service entrance. The neutral and ground should be kept separate at all panel boards and
junction boxes. Downline neutral-to-ground bonds result in parallel paths for the load return
current where one of the paths becomes the ground circuit. This can cause misoperation of
protective devices. Also, during a fault condition, the fault current will split between the
ground and the neutral, which could prevent proper operation of protective devices (a
serious safety concern). This is a direct violation of the NEC.
 Ungrounded equipment
Isolated grounds are sometimes used due to the perceived notion of obtaining a “clean”
ground. The proper procedure for using an isolated ground must be followed (see Sec.
10.5.5). Procedures that involve having an illegal insulating bushing in the power source
conduit and replacing the prescribed equipment grounding conductor with one to an
“isolated dedicated computer ground” are dangerous, violate code, and are unlikely to solve
noise problems.
 Additional ground rods
Ground rods should be part of a facility grounding system and connected where all the
building grounding electrodes (building steel,metal water pipe, etc.) are bonded together.
 Ground loops
Ground loops are one of the most important grounding problems in many commercial and
industrial environments that include data processing and communication equipment.
 Insufficient neutral conductor
Switch-mode power supplies and fluorescent lighting with electronic ballasts are widely used
in commercial environments. The high third harmonic content present in these load currents
can have a very important impact on the required neutral conductor rating for the supply
circuits.
SOLUTIONS TO WIRING AND GROUNDING PROBLEMS
1.Proper grounding practices
Figure illustrates the basic elements of a properly grounded electrical system. The important
elements of the electrical system grounding are described in following Secs.
Figure Basic elements of a properly grounded electrical system.

2. Ground electrode (rod)
The ground rod provides the electrical connection from the power system ground to earth.
The item of primary interest in evaluating the adequacy of the ground rod is the resistance of
this connection. There are three basic components of resistance in a ground rod:
■ Electrode resistance. Resistance due to the physical connection of the grounding wire to
the grounding rod.
■ Rod-earth contact resistance. Resistance due to the interface between the soil and the rod.
This resistance is inversely proportional to the surface area of the grounding rod (i.e., more
area of contact means lower resistance).
■ Ground resistance. Resistance due to the resistivity of the soil in the vicinity of the
grounding rod. The soil resistivity varies over a wide range, depending on the soil type and
moisture content.
3. Service entrance connections
The primary components of a properly grounded system are found at the service entrance.
The neutral point of the supply power system is connected to the grounded conductor
(neutral wire) at this point.
4. Panel board
The panel board is the point in the system where the various branch circuits are supplied by
a feeder from the service entrance. It is important to note that there should not be a
neutral-to-ground connection at the panel board.
5.Isolated ground
The noise performance of the supply to sensitive loads can sometimes be improved by
providing an isolated ground to the load. This is done using isolated ground receptacles,
which are orange in color
6.Grounding techniques for signal reference
Most of the grounding requirements previously described deal with the concerns for safety
and proper operation of protective devices.
Grounding is also used to provide a signal reference point for equipment exchanging signals
over communication or control circuits within a facility.
Summary of wiring and grounding solutions

The grounding system should be designed to accomplish these minimum objectives:
1. There should never be load currents flowing in the grounding system under normal
operating conditions.
2. There should be, as near as possible, an equipotential reference for all devices and
locations in the system.
3. To avoid excessive touch potential safety risks, the housings of all equipment and
enclosures should be connected to the equipotential grounding system.
The most important implications resulting from these objectives are:

1. There can only be one neutral-to-ground bond for any subsystem.
2. There must be sufficient interconnections in the equipotential plane to achieve a low
impedance over a wide frequency range.
3. All equipment and enclosures should be grounded.

Figure: High Touch Voltage Created by Improper Grounding

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UNIT V: WIRING AND GROUNDING

Reasons for Grounding, wiring and grounding problems and solutions

Figure : High touch voltage created by improper grounding.

Typical Wiring and Grounding Problems

Figure Basic elements of a properly grounded electrical system.

Summary of wiring and grounding solutions

The most important implications resulting from these objectives are:

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