[LazyPup]

DEAN

The two internally lined nipples are dielectric nipples. Do not confuse electrical continuity with dielectric continuity.

Whenever two dissimilar metals are in direct contact, and the junction between the metals is reacted upon by the application of heat energy or a chemical electrolyte a very small electrical current is generated.

We see a helpful application of a dielectric current in the case of a thermocouple. A Thermocouple uses two dissimilar metals, normally nickle and copper and as it is heated in the flame of a gas pilot light it generates a current. The current is then passed through a coil of copper wire inside the gas control, which forms an electro-magnetic field to hold the gas valve open. If the pilot flame should happen to go out, the by-metal contact cools and stops generating the current, which would then stop energizing the copper electro-magnetic coil and the gas valve is closed by an internal spring. During this process electrons transfer from one metal to the other to generate the current. In time enough molecules will be transferred to physically break down the contact between the two metals which explains what happens when a thermocouple burns out.

There is another very interest property of dissimilar metal contact. While the application of heat will generate a current we can reverse the process. The external application of electrical energy to a dissimilar metal junction with either generate heat or remove heat energy from the point of contact depending upon the polarity of the applied electrical current. Thus if a battery were applied to a thermocouple the tip of the thermocouple would get warm and if the battery polarity was reversed the tip would get cold. In recent years we have seen portable ice chests for automobiles that can either heat or cool. The actual heating or cooling unit in those products is simply a large Bi-Metal plate with heat sink fins. When the automotive electrical energy is applied in one direction the plate temperature increases which then heats the container. Reversing the polarity will cause the bi-metal plate to cool, thus cooling the container.

The entire process is similar to the production of electrical energy in a dry cell battery. Voltage is the measurement of the flow of electrons from on point to another. In a dry cell battery the the electrolite is the catalist that causes the reacton. The flow of electrons is from a zinc anode to a carbon cathode. The flow of electrons continues until the zinc anode is consumed, at which point we say the battery is dead. (Properly a flashlight battery should be called a cell. A battery is a combination of two or more cells.)

In a water pipe the water serves as the electrolite, and in the case of water heaters we also have the addition of heat which further enhances the process. Electrons are drawn out of the copper and carried by the water until they are deposited on the iron. The introduction of a plastic lined nipple is sufficient to keep the two dissimilar metals separated far enough that the electrical resistance of the water is sufficient to prevent the flow of electrons from the copper to the iron in the electrolite path, thus, while the plastic lined nipples would have a direct electrical continuity, they do not have an electro-chemical continuity in the electrolytic path.