**First, the Basic Introduction of Wire and Cable**
Wire and cable are typically composed of several sets of wires, with at least two wires in each group. They resemble ropes in structure, where each set is insulated from one another and often twisted around a central core. A highly insulating outer layer covers the entire assembly. These components are primarily used for transmitting or distributing electrical signals and power.
**Wire and Cable Mainly Consist of Four Parts**
1. **Conductive Core**: Made from highly conductive materials like copper or aluminum. Depending on the flexibility required, the core may be made up of a single wire or multiple stranded wires.
2. **Insulation**: The insulation material must have high resistance to ensure safety. Common materials include oil-impregnated paper, polyvinyl chloride (PVC), polyethylene, cross-linked polyethylene, and rubber.
3. **Sealing Sheath**: This layer protects the insulated core from mechanical damage, moisture, chemicals, and light. For moisture-sensitive cables, lead or aluminum extrusion is commonly used.
4. **Protective Cover**: It shields the sealing sheath from physical damage. Materials such as galvanized steel strips, steel wires, or copper wires are often wrapped around the sheath, forming an armored cable. This armor also serves as an electromagnetic shield. To prevent corrosion, these layers are often coated with asphalt, wrapped in jute, or covered with a PVC or polyethylene sleeve.
**Second, Wire and Cable Specifications**
The specifications of wires and cables refer to the number of cores and their cross-sectional dimensions. While full naming can be complex, people often use simplified terms like "low voltage cable" to describe specific types. The model numbers usually provide enough detail to identify the exact product.
**Third, Application Classification of Wire and Cable**
1. **By Insulating Material**: Examples include oil-impregnated paper-insulated cables, PVC cables, and cross-linked polyethylene cables.
2. **By Purpose**: Cables are categorized into power cables, communication cables, and control cables. They are used in power systems, information transmission, and industrial equipment.
**Power System**
In power systems, common wire and cable products include overhead bare wires, busbars, power cables (such as plastic, oil-paper, and rubber cables), branch cables, magnet wires, and cables for electrical equipment.
**Information Transmission System**
These cables are used in telephone lines, TV cables, data cables, fiber optics, and other communication systems. They transmit electronic signals and digital data efficiently.
**Mechanical Equipment and Instrumentation Systems**
This category includes power cables, magnet wires, data cables, and instrumentation cables, which are used in various industrial applications.
**Product Classification**
1. **Bare Wires and Conductors**: These have no insulation or sheathing, such as steel-cored aluminum conductors and electric locomotive wires. They are mainly processed through smelting, rolling, and stranding.
2. **Power Cables**: These feature insulated outer layers and are used for transmitting high-voltage electricity across power networks.
3. **Cables for Electrical Equipment**: This category includes a wide range of specialized cables such as fire-resistant, flame-retardant, low-smoke, and weather-resistant types.
4. **Communication Cables and Fiber Optics**: These cables are essential for data and signal transmission, ranging from traditional telephone cables to modern fiber optic cables.
5. **Electromagnetic Wires (Winding Wires)**: Used in motors, transformers, and other electrical devices.
**What Is the Difference Between Wires and Cables?**
There is no strict boundary between "wires" and "cables." Generally, a product with fewer cores, smaller diameter, and simpler structure is called a wire. If it’s not insulated, it's a bare wire. Otherwise, it's a cable. Wires with a cross-section larger than 6 mm² are considered large wires, while those below that are small. In daily use, household wiring is often referred to as a wire, and power cables as cables.
A wire usually consists of one or a few soft wires with a flexible protective layer, while a cable contains multiple insulated wires enclosed in a tough outer layer made of metal or rubber. Both cables and wires typically consist of three main parts: a core conductor, an insulating sheath, and a protective sheath.
Siren and Alarm
A siren is a loud noise-making device. Civil defense sirens are mounted in fixed locations and used to warn of natural disasters or attacks. Sirens are used on emergency service vehicles such as ambulances, police cars, and fire trucks. There are two general types: pneumatic and electronic.
Many fire sirens (used for calling the volunteer fire fighters) serve double duty as tornado or civil defense sirens, alerting an entire community of impending danger. Most fire
sirens are either mounted on the roof of a fire station or on a pole
next to the fire station. Fire sirens can also be mounted on or near
government buildings, on tall structures such as water towers,
as well as in systems where several sirens are distributed around a
town for better sound coverage. Most fire sirens are single tone and
mechanically driven by electric motors with a rotor attached to the
shaft. Some newer sirens are electronically driven speakers.
Fire sirens are often called "fire whistles", "fire alarms", or
"fire horns". Although there is no standard signaling of fire sirens,
some utilize codes to inform firefighters of the location of the fire.
Civil defense sirens also used as fire sirens often can produce an
alternating "hi-lo" signal (similar to emergency vehicles in many
European countries) as the fire signal, or a slow wail (typically 3x) as
to not confuse the public with the standard civil defense signals of
alert (steady tone) and attack (fast wavering tone). Fire sirens are
often tested once a day at noon and are also called "noon sirens" or
"noon whistles".
The first emergency vehicles relied on a bell. Then in the 70s,
they switched to a duotone airhorn. Then in the 80s, that was overtaken
by an electronic wail.
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