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In engineering, a fail-safe is a design feature or practice that, in the event of a specific type of failure, inherently responds in a way that will cause minimal or no harm to other equipment, to the environment or to people. Unlike inherent safety to a particular hazard, a system being "fail-safe" does not mean that failure is impossible or improbable, but rather that the system's design prevents or mitigates unsafe consequences of the system's failure. That is, if and when a "fail-safe" system fails, it remains at least as safe as it was before the failure. Since many types of failure are possible, failure mode and effects analysis is used to examine failure situations and recommend safety design and procedures.
An uninterruptible power supply (UPS) or uninterruptible power source is a type of continual power system that provides automated backup electric power to a load when the input power source or mains power fails. A UPS differs from a traditional auxiliary/emergency power system or standby generator in that it will provide near-instantaneous protection from input power interruptions by switching to energy stored in battery packs, supercapacitors or flywheels. The on-battery run-times of most UPSs are relatively short but sufficient to "buy time" for initiating a standby power source or properly shutting down the protected equipment. Almost all UPSs also contain integrated surge protection to shield the output appliances from voltage spikes.
A power supply is an electrical device that supplies electric power to an electrical load. The main purpose of a power supply is to convert electric current from a source to the correct voltage, current, and frequency to power the load. As a result, power supplies are sometimes referred to as electric power converters. Some power supplies are separate standalone pieces of equipment, while others are built into the load appliances that they power. Examples of the latter include power supplies found in desktop computers and consumer electronics devices. Other functions that power supplies may perform include limiting the current drawn by the load to safe levels, shutting off the current in the event of an electrical fault, power conditioning to prevent electronic noise or voltage surges on the input from reaching the load, power-factor correction, and storing energy so it can continue to power the load in the event of a temporary interruption in the source power.
A short circuit is an electrical circuit that allows a current to travel along an unintended path with no or very low electrical impedance. This results in an excessive current flowing through the circuit. The opposite of a short circuit is an open circuit, which is an infinite resistance between two nodes.
A circuit breaker is an electrical safety device designed to protect an electrical circuit from damage caused by overcurrent. Its basic function is to interrupt current flow to protect equipment and to prevent the risk of fire. Unlike a fuse, which operates once and then must be replaced, a circuit breaker can be reset to resume normal operation.
A surge protector (or spike suppressor, surge suppressor, surge diverter, surge protection device or transient voltage surge suppressor is an appliance or device intended to protect electrical devices from voltage spikes in alternating current circuits. A voltage spike is a transient event, typically lasting 1 to 30 microseconds, that may reach over 1,000 volts. Lightning that hits a power line can give a spike of over 100,000 volts and can burn through wiring insulation and cause fires, but even modest spikes can destroy a wide variety of electronic devices, computers, battery chargers, modems and TVs etc, that happen to be plugged in at the time. Typically the surge device will trigger at a set voltage, around 3 to 4 times the mains voltage, and divert the current to earth. Some devices may absorb the spike and release it as heat. They are generally rated according to the amount of energy in joules they can absorb.
A power strip is a block of electrical sockets that attaches to the end of a flexible cable, allowing multiple electrical devices to be powered from a single electrical socket. Power strips are often used when many electrical devices are in proximity, such as for audio, video, computer systems, appliances, power tools, and lighting. Power strips often include a circuit breaker to interrupt the electric current in case of an overload or a short circuit. Some power strips provide protection against electrical power surges. Typical housing styles include strip, rack-mount, under-monitor and direct plug-in.
In electronics and electrical engineering, a fuse is an electrical safety device that operates to provide overcurrent protection of an electrical circuit. Its essential component is a metal wire or strip that melts when too much current flows through it, thereby stopping or interrupting the current. It is a sacrificial device; once a fuse has operated it is an open circuit, and must be replaced or rewired, depending on its type.
A kill switch (informal) also known more formally as an emergency brake, emergency stop (E-stop), emergency off (EMO) and as an emergency power off (EPO), is a safety mechanism used to shut off machinery in an emergency, when it cannot be shut down in the usual manner. Unlike a normal shut-down switch or shut-down procedure, which shuts down all systems in order and turns off the machine without damage, a kill switch is designed and configured to abort the operation as quickly as possible (even if it damages the equipment) and to be operated simply and quickly (so that even a panicked operator with impaired executive functions or a bystander can activate it). Kill switches are usually designed to be noticeable, even to an untrained operator or a bystander.
Appliance classes specify measures to prevent dangerous contact voltages on unenergized parts, such as the metallic casing, of an electronic device. In the electrical appliance manufacturing industry, the following appliance classes are defined in IEC 61140 and used to differentiate between the protective-earth connection requirements of devices.
The prospective short-circuit current (PSCC), available fault current, or short-circuit making current is the highest electric current which can exist in a particular electrical system under short-circuit conditions. It is determined by the voltage and impedance of the supply system. It is of the order of a few thousand amperes for a standard domestic mains electrical installation, but may be as low as a few milliamperes in a separated extra-low voltage (SELV) system or as high as hundreds of thousands of amps in large industrial power systems.
In an electric power system, a switchgear is composed of electrical disconnect switches, fuses or circuit breakers used to control, protect and isolate electrical equipment. Switchgear is used both to de-energize equipment to allow work to be done and to clear faults downstream. This type of equipment is directly linked to the reliability of the electricity supply.
In electronics, a shunt is a device that creates a low-resistance path for electric current, to allow it to pass around another point in the circuit. The origin of the term is in the verb 'to shunt' meaning to turn away or follow a different path.
A crowbar circuit is an electrical circuit used for preventing an overvoltage or surge condition of a power supply unit from damaging the circuits attached to the power supply. It operates by putting a short circuit or low resistance path across the voltage output (Vo), like dropping a crowbar across the output terminals of the power supply. Crowbar circuits are frequently implemented using a thyristor, TRIAC, trisil or thyratron as the shorting device. Once triggered, they depend on the current-limiting circuitry of the power supply or, if that fails, the blowing of the line fuse or tripping the circuit breaker.
A fan heater, also called a blow heater, is a heater that works by using a fan to pass air over a heat source. This heats up the air, which then leaves the heater, warming up the surrounding room. They can heat an enclosed space such as a room faster than a heater without fan, but like any fan, creates audible noise.
An arc flash is the light and heat produced as part of an arc fault, a type of electrical explosion or discharge that results from a connection through air to ground or another voltage phase in an electrical system.
In an electric power system, overcurrent or excess current is a situation where a larger than intended electric current exists through a conductor, leading to excessive generation of heat, and the risk of fire or damage to equipment. Possible causes for overcurrent include short circuits, excessive load, incorrect design, an arc fault, or a ground fault. Fuses, circuit breakers, and current limiters are commonly used overcurrent protection (OCP) mechanisms to control the risks. Circuit breakers, relays, and fuses protect circuit wiring from damage caused by overcurrent.
Capacitors have many uses in electronic and electrical systems. They are so ubiquitous that it is rare that an electrical product does not include at least one for some purpose. Capacitors allow only AC signals to pass when they are charged blocking DC signals. The main components of filters are capacitors. Capacitors have the ability to connect one circuit segment to another. Capacitors are used by Dynamic Random Access Memory (DRAM) devices to represent binary information as bits.
A high-resistance connection (HRC) is a hazard that results from loose or poor connections in traditional electrical accessories and switchgear which can cause heat to develop, capable of starting a fire.
Overheating is a phenomenon of rising temperatures in an electrical circuit. Overheating causes damage to the circuit components and can cause fire, explosion, and injury. Damage caused by overheating is usually irreversible; the only way to repair it is to replace some components.
References
- 1 2 AOP-38, Allied Ordnance Publication 38, Edition 3, Glossary of terms and definitions concerning the safety and suitability for service of munitions, explosives and related products, April 2002.
- ↑ French, Francis; Burgess, Colin (2007). In the Shadow of the Moon: A Challenging Journey to Tranquility, 1965–1969. Outward Odyssey: A People's History of Spaceflight. University of Nebraska Press. ISBN 978-0-8032-0984-8.
Before we go into any critical phase in Mission Control, we always go into 'Battle Short.' The Flight director makes the call, we lock the circuit breakers and bolt the doors, and nobody can get in or out.
- ↑ Sullivan, Bryan (January 2013). "Honeysuckle Creek: Apollo Tracking Operations, How it all worked" . Retrieved 2019-01-02.
Each computer, being of the militarized type, was fitted with a special control panel switch labeled 'battle short'. When selected, the battle short function bypassed all of the safety features such as under voltage, over voltage, high temperature, and cooling fan failure conditions. The battle short switches were used for very short time periods during certain Apollo mission critical events or maneuvers e.g. Apollo 8 Lunar Orbit Insertion (LOI).