Low-voltage high rupture capacity (HRC) fuses are used in the area of main distribution boards in low-voltage networks where there is a high prospective short circuit current. Even currents too low to induce tetanus are often able to scramble nerve cell signals enough that the heart cannot beat properly, sending the heart into a condition known as fibrillation.
Make sure the situation is safe for you to step into, or else you will be the next victim, and nobody will benefit from your efforts. Wiring regulations usually define a maximum fuse current rating for particular circuits. If a wire inside the appliance accidently comes in contact with the case, there is no danger presented to the user of the appliance. More on these devices in a later section of this chapter. Given the many causes of ground faults, they tend to be unpredicatable. The National Electrical Code requires that special shock-detecting receptacles called Ground-Fault Current Interrupting (GFI or GFCI) be installed in wet and outdoor areas to help prevent shock incidents. It is too poor of a conductor to support continuous current for powering a load.
The appliance will still function properly, but if there is an internal fault bringing the hot wire in contact with the case, the results can be deadly. Asphalt, for instance, being oil-based, has a much greater resistance than most forms of dirt or rock. The "Hot" side of the circuit, named for its potential for shock hazard, will be dangerous to touch unless voltage is secured by proper disconnection from the source (ideally, using a systematic lock-out/tag-out procedure). The speed at which a fuse blows depends on how much current flows through it and the material of which the fuse is made. Current will affect whatever muscles are in its path, and since the heart and lung (diaphragm) muscles are probably the most critical to one's survival, shock paths traversing the chest are the most dangerous. Even with a good lock-out/tag-out safety program in place, there is still need for diligence and common-sense precaution. A standard fuse may require twice its rated current to open in one second, a fast-blow fuse may require twice its rated current to blow in 0.1 seconds, and a slow-blow fuse may require twice its rated current for tens of seconds to blow. Ideally, of course, you don't want either wire accidently coming in contact with the conductive case of the appliance, but there are usually ways to design the layout of the parts to make accidental contact less likely for one wire than for the other.
Thankfully, nothing bad happened, but had the engine been running and the shock felt at my hand instead of my leg, I might have reflexively jerked my arm into the path of the rotating fan, or dropped the metal wrench across the battery terminals (producing large amounts of current through the wrench with lots of accompanying sparks). Fuses are widely used for protection of electric motor circuits; for small overloads, the motor protection circuit will open the controlling contactor automatically, and the fuse will only operate for short circuits or extreme overload. The combination of firm contact with metal and my sweaty skin made it possible to feel a shock with only 12 volts of electrical potential.
There are two styles of fuse base that can be screwed into these units: one designed for rewirable fusewire carriers and one designed for cartridge fuse carriers.
Timeline (from "Stargazers") Therefore, a person standing on the ground between those two points will be in danger of receiving an electric shock by intercepting a voltage between their two feet! First, you check your meter on a known source of voltage to see that its working properly. This is important on jobsites, where many people share the same equipment, and not all people there may be aware of the hazards. Voltage drop often is not significant in more traditional wire type fuses, but can be significant in other technologies such as resettable (PPTC) type fuses. If this is done, there will be no grounding of the appliance case to keep the user(s) safe. For example, fuse holders for North American class RK fuses have a pin that prevents installation of similar-appearing class H fuses, which have a much lower breaking capacity and a solid blade terminal that lacks the slot of the RK type. So-called self-resetting fuses use a thermoplastic conductive element known as a polymeric positive temperature coefficient (PPTC) thermistor that impedes the circuit during an overcurrent condition (by increasing device resistance). Automotive fuses can be classified into four distinct categories: Most automotive fuses rated at 32 volts are used on circuits rated 24 volts DC and below. Only the insulators which hold those wires need to resist a higher voltage--e.g by shaping them as a long stack of ceramic plates which sheds off rainwater. Fuses are selected so that the minor, branch, fuse disconnects its circuit well before the supplying, major, fuse starts to melt. Similar appearing fuses may have significantly different properties, identified by their markings.
For example, UL 248-19 allows photovoltaic fuses to be rated up to 1500 volts, DC, versus 1000 volts under the general requirements. In automobile alternators and central power station generator plants, voltage regulators control the output of the plant.
Another item that could be used to safely drag a "frozen" victim away from contact with power is an extension cord. Fuses have the advantages of often being less costly and simpler than a circuit breaker for similar ratings. In electronics and electrical engineering, a fuse is an electrical safety device that operates to provide overcurrent protection of an electrical circuit. While glass fuses have the advantage of a fuse element visible for inspection purposes, they have a low breaking capacity (interrupting rating), which generally restricts them to applications of 15 A or less at 250 VAC. In the Bussmann handbook, the table is appropriately entitled Deleterious Effects of Electric Shock, and credited to a Mr. Charles F. Dalziel. A lock-out/tag-out procedure works like this: all individuals working on a secured circuit have their own personal padlock or combination lock which they set on the control lever of a disconnect device prior to working on the system.
Its essential component is a metal wire or strip that melts when too much current flows through it, thereby stopping or interrupting the current.
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