Electric shock with the air conditioner and the personal computer

Earth of the appliance is very effective in the prevention of the electric shock. Do not it ground (earth) by an appliance not out of order and have not it gotten an electric shock?Because I had gotten an electric shock by yucky while detaching the air conditioner of Sharp, the cause was investigated.

An appliance not out of order is gotten an electric shock.

The second side of the transformer on the utility pole in this figure and the core of the transformer are grounded in the place in the utility pole (earth).

As for a recent inverter air conditioner, the noise filter circuit is used as shown in left figure. Coil L is a coil in the ferritic core that cancels and is rolled. The low-pass filter is composed of this L, C1, C2, and C3.

Capacitor C1 and C2 are connected with the metal the exterior part of the air conditioner. There is considerably a thing that is might not in the upper floor in the apartment house etc. the ground terminal though it is common sense in a usual air conditioner to ground this metal department (earth), and not grounded either.

The voltage of about 50V hangs in the human body for C1=C2. C3 is irrelevant to the electric shock.

Electric shock with capacitor of noise filter

This figure is an explanation of the electric shock with the capacitor of the noise filter of the air conditioner.

The equivalent circuit is shown in left figure by the law of Otori and [tebunan]. The edge of open voltage of not the electric shock but the metal the exterior part becomes 50V of the half of 100V power supply. Power supply..short-circuit..exterior..metal..power supply..impedance..become.

It doesn't limit to the air conditioner, and the personal computer and the refrigerator use the inverter and the switching regulator recently. The number of products that use the noise filter for this noise prevention (unnecessary radiation measures) has increased. There is something from which a big capacitor of capacity is comparatively used for this circuit recently. These products are easily imagined similarly getting an electric shock.

In this case, it is needless to say to the prevention of the electric shock ..the best... ground it (earth)Grounding it is effective also in the noise prevention.

Measurement of noise filter capacitor and calculation of electric shock current

For Sharp air conditioner AY-S22BE1

The actual measurement value in Sharp air conditioner AY-S22BE1 that I had gotten an electric shock is C = C1+C2 = It became 0.016μF. (The measurement used the capacity measurement function of the capacitor with M-3860M of METEX. )

The reactance of this capacitor C When you calculate Z
Z = It   becomes 1/2πfC ≒ 166kOHM. (f = 60Hz)

The maximum current that flows to the human body disregarding the human body and the ground resistance When you calculate I
I = It     becomes 50/Z ≒ 0.3mA.

It is sure to be felt that it is yucky with dindling if it is said 0.3mA. It is time when the electric shock situation when the air conditioner is detached felt after the outdoor machine of 3F of the apartment house by bare-handed. One's feet was only socks without putting on slippers with concrete. Socks were a little damp by the sweat. The air conditioner had not grounded it.

Because the air conditioner was not able to be detached in such a state because it was yucky, it put on slippers. Gloves must be good insulation.

For the assembly personal computer

Two capacity of the noise filter capacitor in the power supply part of an assembly personal computer on hand was measured. C = C1+C2 = There were the   one of 0.0154μF and the   one of 0.0074μF. ..certain.. I see. the one of the personal computer in this gotten an electric shock

If it is an air conditioner, the personal computer doesn't usually ground it though grounding it because it is the one set up in outdoor to which rain sets in is common sense. I think that it is a problem that gets an electric shock with the personal computer.