To what extent does low voltage increase firing time?
When your kiln takes too long to fire, it is not always because of worn heating elements. Low voltage can double firing time.
Electrical current in most of the United States is so reliable we take it for granted. Voltage levels rise and fall regularly, though usually not enough to matter. When it drops too low, however, problems arise.
Some power companies do not have enough generating capacity to correct low voltage. In those cases, changing the power transformer won't help. A maintenance supervisor of a school called us because his Paragon kilns were not reaching firing temperature. Voltage was low. Yet the kilns were the least of his problems. "What I'm worried about are the motors that keep burning up around here," he said. His local power company did not have enough generators to raise voltage.
Voltage commonly drops during periods of heavy electrical demand, such as summer. In Dallas, voltage drops during summer days between 4:30 and 8:30 p.m. This is when people come home from work and turn on air conditioners. During these hours, voltage can drop from 240 to as low as 190.
Utility companies kick in extra generators during peak periods to raise voltage. To help further, some high-rise buildings cut back air conditioning during summertime peak demand. Air conditioners in the building are timed to turn on in rotation. One will stay on for, say, fifteen minutes while the others are shut down. When that one shuts off, another will turn on. This keeps the temperature at a tolerable level throughout the building.