Q & A

1. How to test the switch plug panel and insulation material?

A: To ignite the insulation material with cigarette-lighter, to remove the cigarette-lighter from the insulation material 5-10S, the material is able to preserve the fire and cut off it, thus identify the insulation material has reached the VO grade.

2. What are the advantages of the pure silver contact?

A: Little electric arc produced, good electric conductivity.

3. Why should border a piece of pure silver or silver alloy on the contact?

A: The contact surface of the contact will be oxidized while it contacts with the atmosphere. If the copper is oxidized, its surface will produce a kind of membrane of CUO or Cu₂O. The electric conductivity of the oxidized membrane of the copper is rather bad; its resistance is 1016 times more than the resistance of the pure copper. Therefore the resistance of the oxidized copper contact is very great, while the electric current passes such contact, it will bring intolerable high temperature. Though the resistance of the oxidized membrane of the silver is rather great, to compare with the oxidized membrane of the copper, the resistance of the silver is 1/1012 times less than it of the copper. Meanwhile, the membrane of the silver will be broken to pieces and split, therefore, the silver contact is much better than the copper one.

Take the little tolerance of electric arc, resistance to electric grind and weld of the pure silver into consideration, silver alloy (like silver-nickel, silver-wolfram, silver-oxidized cadmium, silver-oxidized tin etc.) contacts are widely used by the way of drilled welding onto the connect panel while the working electric current is greater than 40A. Sometimes the contacts made of precious metals like gold, molybdenum, platinum etc. are used among the weak electric relays.

In view of the facts mentioned above, you’ll get to know the reason why the worn out contacts are not allowed to word any longer.

4. Why should there plate the silver or tin on the join point of the electric equipment?

A: The join point of the electric equipment is of copper, which is easy to be oxidized, and its resistance of the oxidized membrane is quite great, its resistance is over ten grades greater than the resistance of the copper. In the meantime, it is difficult to get rid of the oxidized membrane of the copper. But the connection of the join point and the bus is static, there is not any relative motion between them, therefore, it can’t be dispersed once the oxidized membrane appears. The existence of the oxidized membrane of the copper makes the resistance much greater, so that the temperature is very high, the power wastage is also very great. Moreover, in view of the creep of the material under the high temperature, the screw connection may be loosen so that the resistance will get much greater. Sometimes, it may result in spark somewhere in the equipment. Thus a vicious circle occurs. If the copper join connects with the aluminum bus, there will be electricity corrosion chemical reaction between the copper and aluminum. It is worse that a vicious circle forms between the mentioned corrosion and the high temperature. In order to solute the above problem, the usual practice is to plate silver or tin, or smear tin on the contact, in case to avoid the copper and aluminum from electricity corroding so as to low the connection resistance and power wastage and stabilize the connection resistance. As usual, smearing tin is widely adopted because the cost of smearing tin is lower than that of plating silver.

5. Why should restrict the altitude of the using environment of the electric equipment?

A: The altitude of the using environment has the influence to the heat raising and resistance and cutting off of the electric equipment. Because when the altitude is higher, the air is thinner, thus troubles the heat dispersing condition, and the putting out electric arc of the relay. It is stipulated in the national standard that the altitude of the using environment of the electric equipment is not higher than 2000m. Therefore, if the electric equipment is needed to work in above the 2000m high, the resistance of the equipment should get greater, and the demand of power cutting off should be not so stern.

6. Is the 50Hz electric equipment able to be used in a 60Hz electrified wire fence?

A: Actually, it is the problem whether the electric power frequency has the influence to the function of electric equipment. We’d like to discuss it as follows: