A succession of severe winters has had the result of establishing the practice of thawing frozen water mains and service pipes by means of electricity. In some sections during the winter of 1903-4 water mains 7 ft. underground were frozen, and the old method of digging up the frozen ground to expose the affected pipe was found to be a matter of great expense, especially as several thousands of freeze-ups occurred in some of the large cities.
The principle upon which this method works is the fact that an electric current, in passing through a conductor which offers considerable resistance to its passage, develops a great amount of heat in the conducting material.
Plate LII. Thawing Underground Water Pipes By Electricity
Thawing of Water Mains & Services by Electricity
In passing an electric current through a frozen water pipe there is sufficient resistance encountered to generate the heat necessary to thaw the pipe. The ice itself offers great resistance, it being a poor conductor, while the pipe, especially at its joints, offers a considerable amount also. With this principle to work upon, the thawing of pipes may be accomplished if the means are at hand for providing a large enough current, in this work the securing of a large amount of current being of most importance, just as in the use of water for some purposes, the volume which may be obtained is of greater importance than the pressure which it is under.
Many different and successful methods have been made use of in supplying the electric surrent. In sizable towns and in cities, the most convenient source of electricity for this work has been the electric-lighting mains, most of which are now alternating circuits.
In employing alternating currents it is necessary to use what is known as a step-down transformer. Such a device consists essentially of two coils of wire adjacent to each other, but not connected together in any way. The ends of the primary coil are connected to the lighting mains, and the passage of the current through this coil induces a current in the secondary coil. The step-down transformer takes a current from the mains at a high voltage or pressure and delivers it through the secondary coil under a much lower voltage.
Currents under various voltages, up to several thousand in amount, have been used on the primary and transformed generally to about 50 volts on the secondary.
An electric circuit is made up of three factors - current in amperes, voltage, and resistance. As the resistance increases, the amount of current decreases, and vice versa.
The thawing apparatus is generally placed upon a wagon or sled, and consists principally of the transformer and what is known as a water resistance. The latter is usually in the form of a small barrel filled with salted water, in which two copper plates are immersed, each being connected to a wire.
After this apparatus has been taken to the place where the thawing is to be done, the primary leads are connected to the electric-light mains, proper fuses and an ammeter for measuring the current being provided.
The secondary leads or connections are then attached at either end of the frozen section, and the water resistance placed at any point in the secondary circuit, with the copper plates far apart. When in this position the resistance is great, and the amount of current small. When it is seen that a larger amount of current is necessary, it may be obtained by reducing the resistance, that is, by moving the plates closer together. Various amounts of current are required, depending on the conditions of each individual piece of work. For service pipes, which are naturally more often affected than the mains, currents of an amount between 200 and 300 amperes are generally used.
Long leads are used on this work, and when possible the connection may be made most easily by attaching one of the secondary leads to the nearest hydrant, and the other to a faucet or to the piping inside the house, the current thus being allowed to pass through the frozen section. Attention should be given to making as good connections to the hydrant and faucet as possible, as a poor contact at either place may result in burning the metal.
When there is no hydrant conveniently located, connection may be made to the piping of an adjacent house, and if the latter is too far distant it sometimes becomes necessary to dig down to the pipe to make the connection.
When the service pipes of two or more adjacent houses are to be thawed, the several water services may be connected in series, and a single application of the current answer for thawing all of them.
By using long secondary leads, frozen service pipes of several houses may often be thawed without changing the primary connections to the lighting mains.
So universal has the practice become of thawing frozen mains and service pipes by electricity, that apparatus designed especially for such work may now be procured of manufacturers of electrical apparatus.
In some cases, where it was impossible to use lighting or power circuits, portable outfits have been used in this work, consisting of a steam or gas engine connected to an electric generator. Storage batteries have also been made use of. The time used in thawing pipes depends so largely on conditions, size of pipe, length of frozen section, amount of current available, etc., that it is difficult to make any estimate of it. Under favorable conditions, however, service pipes of different sizes have been thawed out in from ten to twenty minutes, and long lines of water mains, as large as 10 in. in size, in two or three hours.
The plumber, being ordinarily unacquainted with electrical work, should always seek the advice or the services of competent electricians before attempting this class of work, as errors in connections on his part might result seriously.
The workman inexperienced in electrical work might easily make a mistake which would not only result in considerable damage to apparatus, but which might also affect the lighting circuit to such an extent as to render it useless until repaired. In addition, there is the danger of serious or fatal injury to the workman.
The matter of caring for frozen mains and services has in many cities been taken over by the city water department, the thawing operations being performed by them, in combination with the electric-lighting companies. This would appear to be by far the best method under the circumstances.