Elements of an Electrical Installation: A Comprehensive Overview
Elements of an Electrical Installation
Introduction
This chapter provides an overview of the elements commonly found in an electrical installation. The goal is to familiarize you with the terminology and concepts that will be used throughout.
1. Service Entrance
The service entrance is the point where the utility’s electrical network connects to the user’s electrical system. It can also refer to the overhead or underground lines that connect the mains supply to the metering system. In addition to input terminals, the service entrance typically includes a disconnect switch to protect the facility and equipment from high voltage.
2. Metering Equipment
Metering equipment, owned by the utility company, is installed at the service entrance to measure energy consumption. This equipment is sealed and protected from external factors, and it’s placed in an accessible location for reading and inspection.
3. Switches
A switch is a device designed to open or close an electrical circuit, controlling the flow of current.
3.1 Main Switch
The main switch, also known as the general switch, is located between the service entrance (after the metering equipment) and the rest of the facility. It serves as a means of disconnecting and protecting the system from the utility’s network.
3.2 Branch Circuit Switch
Branch circuit switches protect and disconnect individual circuits that distribute electricity to different sections of the facility or to other panels.
3.3 Thermomagnetic Switch
Thermomagnetic switches are commonly used to protect against overloads and short circuits. They come in various sizes and can function as both a switch and a circuit breaker. They have an electrodynamic element that allows them to respond quickly to short circuits.
4. Starter
A starter is a switching device that may include magnetic or thermal overload protection, fuses, an electromagnetic contactor, and a bimetallic relay. The contactor is essentially a coil with an iron core that opens or closes a set of contacts to energize or de-energize the coil.
5. Transformer
Transformers change the supply voltage to the required voltage. Large installations may need multiple transformers (grouped in substations) to achieve different voltage levels. Some facilities may operate at the same voltage as the service entrance and therefore don’t require a transformer.
6. Panels
A panel is a metal enclosure that houses instruments, starters, switches, and/or control devices. Panels are essential for a safe, reliable, and organized electrical installation.
6.1 Main Panel
The main panel is located immediately after the transformer and contains a main switch. The transformer connects to the input of the main switch, and the output connects to bus bars that distribute power to different circuits through branch circuit switches.
6.2 Motor Control Centers (MCCs)
In industrial facilities and those with multiple motors, starters are often grouped in compact panels called motor control centers.
6.3 Distribution Panels
Distribution panels may have a main switch depending on their distance from the main panel and the number of circuits they supply.
7. Motors and Motor-Driven Equipment
Motors are located at the end of branch circuits and convert electrical energy into mechanical energy. Each motor should have its own starter.
8. Control Stations
Control stations include buttons, switches, and indicators used to control process elements such as: limit switches, torque sensors, temperature gauges, pressure sensors, and other devices. These devices typically handle low currents compared to the main power circuits.
9. Outlets for Lighting and Receptacles
Lighting fixtures, like motors, are at the end of the electrical system and convert electrical energy into light (and often heat). Receptacles provide power to various portable devices and are housed in electrical boxes.
10. Emergency Power System
Emergency power systems typically consist of an internal combustion engine coupled to an AC generator. The generator’s capacity is calculated based on the loads that must operate continuously during a power outage. These loads should be on a dedicated circuit.
11. Grounding in an Electrical Installation
A) Earth: The Earth’s potential is considered zero and is used as a reference and a sink for unwanted currents.
B) Earth Resistance: This refers to the electrical resistance of the soil at a specific location.
C) Grounding Electrode: A grounding electrode is a conductor buried in the ground with a terminal for connecting a grounding conductor.
D) Remote Earth: This refers to a grounding point that is distant from the point under consideration.
E) Grounding System: A network of electrical conductors connected to one or more grounding electrodes and equipped with terminals for connecting to the electrical system.
F) Grounding Connection: The connection between a conductor and the grounding system.
G) Solidly Grounded: When a conductor is firmly connected to a grounding system that is connected to the earth.
H) Isolated Neutral: The neutral conductor of a system that is connected to the ground through an impedance.
I) Generator Neutral: The point that serves as a voltage reference for each phase of a generator.
J) System Neutral: The reference potential of a system, which may differ from the ground potential and may not physically exist.
K) Solidly Grounded Neutral: Commonly used in low-voltage installations to protect people from electric shock.
L) Floating Neutral: The neutral of a system that is not grounded.
12. Interconnections
Wires, whether copper or aluminum, can be interconnected using various methods. They can be installed in conduits, tubes, or trays. Connections at equipment terminals must ensure proper contact and avoid defects that could reduce the conductor’s cross-sectional area. Conduits protect conductors and can be made of metal or non-combustible plastic. Square ducts or cable trays are also used. Supports for these elements must be rigid, and their placement should consider functionality, aesthetics, ease of maintenance, and cost-effectiveness.