1. Wiring and Grounding

2. # Power quality problems are related to wiring and grounding.
# Many power quality problems are solved just by tightening a loose connection or replacing a corroded conductor.
# Therefore, the study on wiring and grounding is necessary to evaluate power quality problems.

3. Summary of US Practices for Building Wiring and Grounding
National Electric Code (NEC) published by the National Fire Protection Association (NFPA) as ANSI/NFPA Standard 70.
A circuit conductor that is intentionally grounded is a grounded conductor.
A conductor that connects equipment or a grounded circuit to the grounding electrodes is a grounding electrode conductor.
Examples of grounding electrodes are grounded building steel, grounded water pipes and driven ground rods.

4. Transformer
Service Entrance
Black
Red
White N
Green or bare
wire or metal conduit
Hot wire insulation colors are Red and Black on 120/240 V single phase system.
Neutral always has white insulation and equipment grounding conductor is either bare or has green insulation.

5. Service Entrance Black Red N Green or Bare Bonding jumper Grounding
White N
Green or Bare
Bonding jumper
Grounding
electrode
conductor
Building
grounding
electrode
Equipment grounding
conductor

6. Discussion
Neutral will carry normal currents on 120 V circuits, but equipment grounding conductor will not carry normal currents
Hot wires carry normal load currents on 240 V circuits
Equipment grounding conductor provides a safety ground
Equipment grounding conductor may be metallic conduit or separate bare or green wire

7. Transformer
Service Entrance
White N
Green or Bare
Three-phase system, note that grounded conductor (neutral) and equipment grounding conductor (green) are bonded at service entrance.

8. Reasons for grounding Personnel safety -Dangerous touch potential
2. Grounding to assure protective device operation
3. Noise control
-Equipotential ground system

9. Typical Wiring and Grounding Problems
Problems with conductors and connectors
Missing safety ground
Multiple neutral-to-ground connections
Ungrounded equipment
Additional ground rods
Ground loops
Insufficient neutral conductor

10. Solutions to Wiring and Grounding Problems
Branch Circuit
Feeder
Service Entrance
Panel Board N G
Note that grounded conductor (neutral) and equipment grounding conductor (green) are bonded at service entrance, not at panel boards.

11. Branch Circuit
Receptacle
Service Entrance
Panel Board N G
Load
Load current return path may include the neutral but not the grounding conductors

12. Isolated Ground Receptacle
Branch Circuit
Service Entrance
Panel Board N G IG
Load
Special case: Isolated ground receptacle (orange color) can be used if induced noise is a problem

13. Transformer
Service Entrance N
Special case: separately derived system grounded to building steel or metallic cold water pipe

14. Comments
Never install a separate ground rod for the “isolated ground” but bond to ground at the service entrance or at the transformer of a separately-derived system
If noise is really a problem, use an isolation transformer (creating a separately derived system) nearby, ground to building steel

15. Building steel Isolation transformer Service Entrance Load
Isolated Ground Receptacle
Building steel

16. Summary of Wiring and Grounding Solutions
The grounding system should be designed to accomplish the following minimum objectives:
There should never be currents flowing in the grounding system under normal operating conditions. One can likely measure very small currents in the grounding system due to inductive coupling, capacitive coupling, and the connection of surge suppressors and the like. In fact, if the ground current is exactly zero, there is probably an open ground connection. However, these currents should be only a tiny fraction of the load currents.
There should be, as near as possible, an equipotential reference for all devices and locations in the system.
To avoid excessive touch potential safety risks, the housings of all equipment and enclosures should be connected to the equipotential grounding system.

17. The most important implications resulting from those objectives are:
There can only be one neutral-to-ground bond for any subsystem. A separately derived system may be created with a transformer, which establishes a new neutral-to-ground bond.
There must be sufficient interconnections in the equipotential plane to achieve a low impedance over a wide frequency range.
All equipment and enclosures should be grounded.