Occurrence of Freezing Problems
Since freeze-ups occur in most municipal systems in Ontario, the services of thawing crews are required during the winter months. Apparently, as long as a favorable balance of heat is maintained in the pipeline, freezing conditions will not develop. Frozen services are more common than frozen mains. Less water and longer periods of no motion can cause this. Insulation protects pipes from freezing. Another protection is to bury the pipes below the frost line.
Electrical Thawing of Watermains and Services
The passage of electrical current through a conductor, whether it is a wire or a pipeline, encounters resistance. This resistance creates heat, the intensity depending upon the characteristics of the conductor. This is the principle behind the electrical thawing of pipes. The low melting point of lead indicates the danger of melting lead surface pipes with high currents. Iron lines heat most readily, while copper heats slowly. Whenever lead goose-necks are used, low currents should be employed.
Thawing Procedure
- Locate the frozen section of pipe.
- Include the frozen section in an electrical circuit by connecting cables from the source of energy to the closest convenient points in the piping system (hydrants, curb service boxes, etc., or, for service connections, exposed pipes in the house and the service shut-off)
- Ensure that good electrical connections are made. Remove rough scale at the point where the clamp is to be fastened to the pipe or arcing may cut holes in the pipe.
- If a house service is involved, remove the water meter from the circuit to break the connection between the service pipe and the house piping.
- Remove the ground clamp from the water pipe to prevent stray electrical currents getting into the neutral wire and wiring system of the house.
- Proceed with the thawing.
Removal of the meter alone or disconnection of the ground clamp alone is not enough to keep the current from feeding into the house wiring circuits. Use caution. Underground contact of metal pipes or some other circuit may occur.
Some Do’s and Don’ts on Thawing Frozen Watermains
- Use the least current possible to do the job. The lower the voltage, the less the chance of injury to persons or property, including piping.
- Avoid connections which might waste current and prolong thawing. Use only generator sets equipped with meters to determine the exact amount of current used. If the meter does not indicate a current flow, this may be caused by poor connections or bad joints in the pipe, or connections which have been made to different pipe systems. Make sure that the frozen length of pipe is included in the circuit.
- Avoid the possibility of shorts or ground. Current may be fed back through gas services by the water heater. No gas pipes or furnace support wires should be in contact with the pipe being thawed. Radio ground wiring should be detached. Heat may be detected by placing a hand on the meter couplings. To play safe, the main switch should be disconnected.
- Make certain of the pipe material in use and make allowances in the current applied.
- Make sure the wires from the energy sources are adequate and that a good electrical contact is made. Scraping the pipe surface may be necessary. Distance between the connections should be as short as possible and limited to the frozen piece of pipe.
- Open pipe before thawing. This will let you know if water is beginning to flow. It also avoids the possibility of steam pressure developing and doing more damage than the frozen line.
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