question: Why does connecting an electrical circuit without an appliance on it cause fires/explosions?
comment: The amount of current that flows is inversely proportional to the resistance. So if you drastically reduce the resistance, you drastically increase the current. Normally this will just trip your circuit breaker, since that's exactly what circuit breakers are for. Without one, it would heat up the wires so much it would start a fire.
passages: Section::::Operating and design principles.
  
  In normal use, electrical equipment often creates tiny electric arcs (internal sparks) in switches, motor brushes, connectors, and in other places. Compact electrical equipment generates heat as well, which under some circumstances can become an ignition source.
   Sparks are an ignition source in combustible environments that may lead to catastrophic explosions in concentrated fuel environments. Most explosions can be traced back to a tiny electrostatic discharge, whether it was an unexpected combustible fuel leak invading a known open air sparking device, or an unexpected spark in a known fuel rich environment. The end result is the same if oxygen is present and the three criteria of the fire triangle have been combined.
  
  Section::::Damage prevention in electronics.
   BULLET::::- All power mains outlets should have a wall cover to avoid accidentally touching the electrified sides between the wall and outlet. This is especially important for children, as their small fingers can easily reach into this gap along the sides.
  
  BULLET::::- Using AC electrical appliances around bathtubs, swimming pools, hot tubs, etc. with the risk that the appliance may fall into the water and cause electrocution. Only battery-operated devices are safe.
  
  BULLET::::- Failure to use child safety plugs in all outlets, and keeping children away from electrical cords.
   The introduction of electrical apparatus for signaling or lighting in coal mines was accompanied by electrically-initiated explosions of flammable gas and dust. Technical standards were developed to identify the features of electrical apparatus that would prevent electrical initiation of explosions due to energy or thermal effects. Several physical methods of protection are used. The apparatus may be designed to prevent entry of flammable gas or dust into the interior. The apparatus may be strong enough to contain and cool any combustion gases produced internally. Or, electrical devices may be designed so that they cannot produce a spark strong enough or temperatures high enough to ignite a specified hazardous gas. Integrating these types of motors can ensure that equipment, facilities, and workers stay protected and machinery is not damaged.
   Section::::Electrical ignition hazard.
  
  A household light switch may emit a small, harmless visible spark when switching. In an ordinary atmosphere this arc is of no concern, but if a flammable vapor is present, the arc might start an explosion. Electrical equipment intended for use in a chemical factory or refinery either is designed to contain any explosion within the device or is designed not to produce sparks with sufficient energy to trigger an explosion.
   In electrical equipment in hazardous areas, if two electrical enclosures are connected by a conduit, an explosion of a gas in one of the compartments travels through the conduit into the next enclosure. The pressure of the 'primary' explosion together with the pressure from the 'secondary' explosion in the other compartment produces one huge explosion that the equipment cannot handle. Heat, arcs or sparks escape from the equipment and ignite any gas or vapour that may be around.
   In an improper installation, the overcurrent from a short circuit may cause ohmic heating of the circuit parts with poor conductivity (faulty joints in wiring, faulty contacts in power sockets, or even the site of the short circuit itself). Such overheating is a common cause of fires. An electric arc, if it forms during the short circuit, produces high amount of heat and can cause ignition of combustible substances as well.
   The German Wiring rules VDE 100, recommend AFDDs for high risk situations, and lists old peoples care homes, community centres and Kindergartens as examples.
  
  Section::::Limitations.
   In Europe, "electrical fires" are no longer recognized as a separate class of fire as electricity itself cannot burn. The items around the electrical sources may burn. By turning the electrical source off, the fire can be fought by one of the other class of fire extinguishers.
  
  Section::::Metal.
  
  Class D fires involve combustible metals - especially alkali metals like lithium and potassium, alkaline earth metals such as magnesium, and group 4 elements such as titanium and zirconium.
   Each chemical gas or vapour used in industry is classified into a gas group.
  
  Group IIC is the most severe Zone system gas group. Hazards in this group gas can be ignited very easily indeed. Equipment marked as suitable for Group IIC is also suitable for IIB and IIA. Equipment marked as suitable for IIB is also suitable for IIA but NOT for IIC. If equipment is marked, for example, Ex e II T4 then it is suitable for all subgroups IIA, IIB and IIC
   BULLET::::- "Defective appliances": If a property fire was caused by an appliance which had a manufacturing or design defect (for example, a coffee maker overheating and igniting), making it unreasonably hazardous, the insurance company might attempt to collect the cost of the fire damage ("subrogate") from the manufacturer; if the fire caused personal injury or death, the injured party might also attempt an injury lawsuit against the manufacturer, in addition to the carrier of health or life insurance attempting subrogation.
   Cases also exist where the ignition factor is not the activation energy. For example, a smoke explosion is a very violent combustion of unburned gases contained in the smoke created by a sudden fresh air input (oxidizer input). The interval in which an air/gas mix can burn is limited by the explosive limits of the air. This interval can be very small (kerosene) or large (acetylene).
  
  Water cannot be used on certain type of fires:
  
  BULLET::::- Fires where live electricity is present – as water conducts electricity it presents an electrocution hazard.
   BULLET::::- Ex nA II T3 X (Type n, non-sparking, Group 2 gases, Temperature class 3, special conditions apply).
   When plugging a device into a power strip, a buildup of carbon or dust can cause sparking to occur. This generally doesn’t pose much of a risk in a non-explosive atmosphere, but explosive atmospheres (for example, near a gasoline refueling station or a solvent cleaning facility) require specialized explosion-proof sealed electrical equipment.
  
  Section::::Safety.:US regulations.
  
  BULLET::::- Underwriters Laboratories standard 1363 contains requirements for "relocatable power taps". Included in the scope section of the standard is the statement:
  
  BULLET::::- National Electrical Code recognizes power strip as Multioutlet Assembly in Article 380.
  
  Section::::Safety.:EU and UK regulations.
   BULLET::::- Not following manufacturer safety instructions for electrical appliances. This includes not using and immediately unplugging any appliance with a damaged electrical cord. If this cannot be done safely (i.e. damage is too close to the plug), the circuit breaker should be turned off beforehand.
  
  BULLET::::- Touching metallic areas of an AC electrical appliance while also simultaneously touching faucets, water pipes, another metallic AC appliance, or being even partly immersed in water (including wet feet). This could ground the body through metal or water, with the risk that a faulty appliance is electrically "hot" on its outside cover or chassis.
   In the USA, arc faults are one of the leading causes for residential electrical fires. Each year in the United States, over 40,000 fires are attributed to home electrical wiring. These fires result in over 350 deaths and over 1,400 injuries each year.
   Canada has a similar system with the Canadian Electrical Code defining area classification and installation principles. Two possible classifications are described in Canadian Standards Association (CSA) C22.1 Canadian Electrical Code (CEC) Section 18 (Zones) and Appendix J (Divisions).
  
  Section::::Division and Zone classification systems.:Explosive gas area classifications.
  
  Typical gas hazards are from hydrocarbon compounds, but hydrogen and ammonia are common industrial gases that are flammable.
   Section::::Explosion hazard.
  
  Even voltages insufficient to break down air can be associated with enough energy to ignite atmospheres containing flammable gases or vapours, or suspended dust. For example, hydrogen gas, natural gas, or petrol/gasoline vapor mixed with air can be ignited by sparks produced by electrical apparatus. Examples of industrial facilities with hazardous areas are petrochemical refineries, chemical plants, grain elevators, and coal mines.
  
  Measures taken to prevent such explosions include:
  
  BULLET::::- Intrinsic safety by the use of apparatus designed not to accumulate enough stored electrical energy to trigger an explosion
   Section::::Electrical.
  
  Electrical fires are fires involving potentially energized electrical equipment. The US system designates these "Class C"; the Australian system designates them "Class E". This sort of fire may be caused by short-circuiting machinery or overloaded electrical cables. These fires can be a severe hazard to firefighters using water or other conductive agents, as electricity may be conducted from the fire, through water, to the firefighter's body, and then earth. Electrical shocks have caused many firefighter deaths.
   For parts of a distribution system, fuses are capable of both sensing and disconnecting faults
  
  Failures may occur in each part, such as insulation failure, fallen or broken transmission lines, incorrect operation of circuit breakers, short circuits and open circuits. Protection devices are installed with the aims of protection of assets and ensuring continued supply of energy.
   Homemade devices may fail to include safety features and can provide numerous hazards, including:
  
  BULLET::::- A firing circuit using high-power, non-isolated AC line voltage can be a shock hazard to the operator and bystanders.
  
  BULLET::::- The use of high-current fuses as ignitors can cause main circuit breakers and fuses to trip, due to the sudden inrush of hundreds of amperes through a dead-shorted circuit. Switches used to control ignition may be damaged from the high-current surges.
   A high current electrical fault can create an 'electrical explosion' by forming a high energy electrical arc which rapidly vaporizes metal and insulation material. This arc flash hazard is a danger to persons working on energized switchgear. Also, excessive magnetic pressure within an ultra-strong electromagnet can cause a "magnetic explosion".
  
  Section::::Causes.:Mechanical and vapor.
  
  Strictly a physical process, as opposed to chemical or nuclear, e.g., the bursting of a sealed or partially sealed container under internal pressure is often referred to as an explosion. Examples include an overheated boiler or a simple tin can of beans tossed into a fire.
   Where wiring, or raceways that hold the wiring, must traverse fire-resistance rated walls and floors, the openings are required by local building codes to be firestopped. In cases where safety-critical wiring must be kept operational during an accidental fire, fireproofing must be applied to maintain circuit integrity in a manner to comply with a product's certification listing. The nature and thickness of any passive fire protection materials used in conjunction with wiring and raceways has a quantifiable impact upon the ampacity derating, because the thermal insulation properties needed for fire resistance also inhibit air cooling of power conductors.
   In the case of non-permanently connected domestic equipment, a BS 1363-2 socket rated at 13 A is attached to the ring circuit, into which a fused plug may be inserted. (Note, it is not intended that the fuse should protect the appliance itself, for which it is still necessary for the appliance designer to take the necessary precautions.) Multiple socket accessories may be protected with a fuse within the socket assembly.
  
  Section::::Residential wiring.
  
  Section::::Residential wiring.:Cable types.
  
  In domestic wiring, the following cable types are typically used:
  
  Section::::Residential wiring.:Cable types.:Internal wiring.
  
  BULLET::::- Twin and earth polyvinyl chloride-insulated and -sheathed cables, or
   The flow of granules of material like sand down a plastic chute can transfer charge, which can be easily measured using a multimeter connected to metal foil lining the chute at intervals, and can be roughly proportional to particulate flow. Dust clouds of finely powdered substances can become combustible or explosive. When there is a static discharge in a dust or vapor cloud, explosions have occurred. Among the major industrial incidents that have occurred are: a grain silo in southwest France, a paint plant in Thailand, a factory making fiberglass moldings in Canada, a storage tank explosion in
  
presuppositions: Connecting an electrical circuit without an appliance on it causes fires or explosions.
corrections: Connecting an electrical circuit without an appliance on it will cause a fire only if you don't have a circuit breaker.
raw_presuppositions: Connecting an electrical circuit without an appliance on it causes fires or explosions. Connecting an electrical circuit without an appliance on it causes fires/explosions.
raw_corrections: Connecting an electrical circuit without an appliance on it will cause a fire only if you don't have a circuit breaker. Connecting an electrical circuit without an appliance on it usually just trips your circuit breaker.