Many companies in the mining, automobile, textile and paper industry have to pay an additional charge over and above the normal charge for units of electricity consumed as maximum demand charge. This charge often forms a large part of the bill which can be tracked at times to only one 30 minute instance of high power usage. This is because the utility company charges a penalty when the factory draws more power than the contracted maximum demand. The maximum power consumed in factories over a calculated period of time, which is normally anywhere between 8 to 30 minutes is known as maximum demand. In many countries, 15 minutes is considered as the most common time period.