How high can internal voltages reach in electronic air cleaners?

In electronic air cleaners, internal voltages can indeed reach levels as high as 5000 volts. This high voltage is crucial for the operating principle of an electronic air cleaner, where particles in the air are charged and then collected on oppositely charged plates, effectively removing pollutants from the air. The application of high voltage increases the efficiency of the ionization process, enhancing the cleaner's ability to capture small particles, including dust, smoke, and allergens.

The other options represent voltages that are either insufficient or uncommon for electronic air cleaners. For instance, while 1200V and 2500V may be used in some other electrical applications, they typically do not provide the same level of performance in the context of air purification. The 8000V also exceeds standard operational requirements, as most electronic air cleaners operate effectively at around 5000V, making it unnecessary and potentially unsafe to operate at higher voltages. Therefore, the correct choice reflects the standard high voltage that balances efficiency and safety in electronic air cleaners.