About an electric shock and a grounding

Necessity of grounding    

grounding is

  The literal meaning of a ground (Earth) is the earth. It is connecting grounding (grounding) with the earth. Since the earth has a very big form and potential is very stable, if it connects with the earth by low resistance, potential of the connected thing will be stable.
  Ground resistance is resistance from a ground electrode (earth electrode) to the depths of the earth.

  Why is grounding of electrical appliances required?

  Although this page has considered whether a ground is mainly required because of safety, it may be required because of stability of apparatus of operation, prevention of unnecessary radiation of electromagnetic waves, etc. besides it.

Necessity of earth of transformer on pillar

The high voltage of 6600V has been converted into 100V or 200V of the domestic use with the transformer on the utility pole in left figure. The second side of this transformer and the core of the transformer are grounded.   It thinks about the case without this earth. When the insulation of this transformer worsens, the leak of an electric product becomes hanging of 6600V of the first side to 100V/200V circuit of the second side, and ..certain.. not related of ..it is.. very at risk.   If the second side is grounded at this time, the high pressure can be prevented from the current's flowing to the earth through the earth of the transformer on the pillar when the insulation of the transformer worsens, and hanging to the second side of the transformer on the pillar.   What is the reason to ground (white)?Even if a part of 200V(for instance, red) is grounded, the above-mentioned purpose can reach. However, the voltage of ground becomes 200V in this case in a black line as for 100V circuit. If it is an earth of the neutral point, the voltage of ground is 100V in 200V circuit. It can be said as dangerous when getting an electric shock low that the voltage of ground is low.   It is necessary to ground the transformer on the pillar absolutely for safety like this.   (The voltages discussed here are the effect all values. The peak value becomes these about 1.41 times. )

Necessity of earth of electric product

  When there is a ground of a pillar top transformer, the airraid voltage 100V occurs to domestic one side of 100V, and the both-ends child of 200V. That is, if people touch a part for the metal department of the exterior when insulation of an electric product worsens like the upper drawing and 100V has started a part for the metal department of the exterior of a product (that is, when electric products have leaked), an electric shock will be received. At this time, if the step which stands for people is moist, much current (current leakage) may flow, and people may die.
  In this case, if there is a ground good for electric products, even if people will touch a part for the metal department of the exterior, electricity flows into the direction of a ground and the human body is safer. Moreover, when this ground current (current leakage) flows, the short circuit breaker of a switchboard works and electricity is stopped.
  Thus, grounding is very important for the electric product used at a humid place.
  Then, even if it uses a microwave oven at dry place, why does it need to be grounded? It is because the electric power treated by high voltage is large, so a microwave oven may require high voltage for a part for the metal department of the exterior depending on how to break when it breaks down (about 500W-1000W). Moreover, since the electric power to treat is large when it becomes so, people's possibility of dying is large. It is said that it sometimes passes away during repair of a microwave oven although it is rare.

When there is no necessity for a ground

A ground is not required for all electric products. When as follows, the ground may not have the danger of an electric shock few.

• When instituting at the place which dried what working voltage uses in the direct current 300V or the circuit not more than exchange airraid voltage 150V --- (a ground is unnecessary if television, video, etc. are the places which also dried the apparatus of the single phase 200V)
• When the machine instrument of double insulation structure to which Electrical Appliance and Material Safety Law is applied is instituted --- (power tool etc.)
• The circuit which supplies electricity to the machine instrument for low voltage instituted in addition to a moist place When a high sensitivity high-speed type earth leakage breaker (it restricts to the thing of 15mA or less of rated sensed current and the current operation type not more than operating time 0.1 second) is instituted --- (a ground is required even if it uses this earth leakage breaker, since it is difficult to install a washing machine in a dry place)
• In addition, although it is, it omits.

Kind of earth construction

*1:  The line earth fault current of I = high voltage circuit[A]
In D kind grounding, the ground resistance of ordinary electric products is 100ohms or less, and a grounding electric wire is more than Dia.1.6mm.

The electrical work person does the earth construction.

  Because the earth construction is very important for safety like this, the amateur is supposed not to be able to do the earth construction. Request it to the electrical work person.
  As for the earth construction below the earth resistance 100Ohm, even the specialist might be very difficult according to the place. It is likely to become considerably large scale construction. Moreover, the earth ohmeter is needed for the measurement of the ground resistance.

Color of earth cable (earth electric wire)

  The color of the earth cable (earth electric wire and groundline) has been decided the line of stripes pattern green/yellow by International Standard IEC60227. It is decided that a green sign is put up by the extension regulations in the line of stripes pattern green or green/yellow or other lines in Japan.

"The earth is taken" is a dirty word.

  This is from a safety side to the dirty word by the way though it might be said, "The earth is taken" to connect the earth cable. It is because it is indefinite whether to connect the earth or to take the earth cable (In a word, remove). The dead seem to have gone out by a misunderstanding ..this...

Electric shock and dangerous current value

  Even a little current might not only be felt an unpleasant current by the electric shock but also dies when passing over an important part of the body of the heart etc.
  There are a lot of cardiac standstills (ventricular fibrillation) and respiratory arrests in the cause of the death by the electric shock by the low voltage, and is a burn by generating heat because of the current that flows in the arc heat and the human body by the electrical discharge in addition to it in the electric shock accident by a high voltage. Because the current passes the depth of the body, the burn by the electric shock is very dangerous.
  How to feel the electric shock is different by direct current and the exchange. It goes into convulsions in the exchange as the muscle trembles while direct current shrinks the muscle and stiffens. It is said that about 1000V of direct current is very dangerous because of the muscle's stiffening gripping the electric wire when it touches the electric wire by the hand and not parting.
  When fiddling with the transmitter of the vacuum tube type (It was a power supply of 500-1000V in direct current), it was written that not working alone in the middle of the night was important in old times in a wireless magazine. It decided not to touch in the transmitter of the vacuum tube type alone in the middle of the night after this had been seen.

  It gets an electric shock even if the leak breaker has adhered and there is a considerable impact in the translation where the current of about 30mA flows to the human body for about 0.1 seconds if Cara currents in the matrix flow. It makes it to Zotsu when thinking of the thing if the leak breaker has not adhered though I experience such an electric shock accident, too.