Grounding Terminal In Electrical Plugs: Protection or Risk?

[Bararontok]

What is the purpose of the grounding terminal in the plugs of some electrical appliances? Is it designed to act as an arrestor for unwanted electrical charge coming from lightning, static electricity, power fluctuations, and electrical arcs, sending the excess current to a grounding wire installed in the building which is plugged into the ground? If the grounding terminal is connected to the circuitry of the electrical appliance, will that not cause the electrical power from the grid to be conducted into the grounding terminal and damage electrical wiring? Or is there an automatic relay that uses a sensor to measure abnormal changes in electrical activity in the device circuitry so that only then will the relay switch on the connection to the ground line so that the ground can absorb the excess electrical charge?

 

[jedishrfu]

Check out Earthing system in Wikipedia for a full explanation. The gnd wire connects all nonconducting metal parts of a device to gnd so that should you touch them you won't get shocked. Also the circuit breaker is placed in the mix to trip should current flow thru the parts to gnd. The breaker doesn't trip so easily should you touch the hot ends and that's why some people still get lethal electrical shocks. The sixty cycle standard is a harmonic of your heart beat and so a shock can stop your heart by canceling out the beat.

 

[Bararontok]

So that means that the ground is designed to absorb electrical charge that flows into the metallic parts that are not used in the electrical circuitry such as a metal case or metal heat sinks. Since the ground is not connected to the electrical circuitry, there will not be a possibility that current in the circuitry will be diverted to the ground line. And the ground line also serves the purpose of diverting current from the metallic parts not meant to be used in the circuitry in case a breakage in electrical continuity causes parts of the circuit to come in contact with the non-electrical metallic parts so that a person touching those parts will not be electrocuted.

 

[NascentOxygen]

in case a breakage in electrical continuity causes parts of the circuit to come in contact with the non-electrical metallic parts

With any luck, under these circumstance such a high current will flow [to ground] that a fuse in the power circuit will quickly blow.

 

[Bararontok]

That is correct. The fuse really is the first line of defense in electrical devices. It is quite interesting to note that some power supply devices used for electronics do not have screws in their case and are sealed by adhesives, making the fuse difficult to replace should it be destroyed, while some devices have a special capsule with a screw and a dial protruding out of the device's case that can be unscrewed so that the fuse inside can be quickly replaced. Why not put this type of feature on all devices? Is it to force consumers to buy new power supplies costing tens of dollars rather than just replacing a fuse which only costs cents?

 

[NascentOxygen]

some devices have a special capsule with a screw and a dial protruding out of the device's case that can be unscrewed so that the fuse inside can be quickly replaced. Why not put this type of feature on all devices? Is it to force consumers to buy new power supplies costing tens of dollars rather than just replacing a fuse which only costs cents?

They probably figure that if the fuse blows, it's because there is a fault in the device. There would be no point in replacing the fuse without first troubleshooting the problem and fixing it. ‡‡ With many devices "containing no user-serviceable parts" and the cost of repairmen being prohibitive, it becomes another disposable consumer product, cheaper to replace than repair.

‡‡ Should the fuse blow when replaced, consumers may try a higher current fuse, or even a paperclip, so making the fuse non-accessible could be construed as another level of protection (of the consumer from himself).

 

[MATLABdude]

That is correct. The fuse really is the first line of defense in electrical devices. It is quite interesting to note that some power supply devices used for electronics do not have screws in their case and are sealed by adhesives, making the fuse difficult to replace should it be destroyed, while some devices have a special capsule with a screw and a dial protruding out of the device's case that can be unscrewed so that the fuse inside can be quickly replaced. Why not put this type of feature on all devices? Is it to force consumers to buy new power supplies costing tens of dollars rather than just replacing a fuse which only costs cents?

In addition to what NascantOxygen says (the blown fuse usually just being a by-product and not the root problem), over currents aren't the only failure mode for power supplies, nor are fuses the only way to do anything about it.

 

[Bararontok]

Yes that is true, some consumers do not follow the instruction manual that says to only use the fuse with the correct maximum current rating and instead insert a higher current fuse or a paperclip that permits higher currents to enter the circuitry, eliminating the overload protection given by the previous fuse.

 

[psparky]

There's a ton of other threads that describe this. Use the search feature.