6.1.3 Electrostatic discharge (ESD)
This standard refers to the immunity of a piece of equipment to an electrostatic discharge. After a discharge of this type occurs, the piece of equipment should continue operating according to the suitability criteria set forth in the product-specific standards. The discharge occurs only at the points that can be accessed by the user, as well as identifying labels and external sides of boxes containing the equipment itself and even at terminals which lie uncovered.

6.1.4 Fast transients (burst)
In this test a fast high-voltage is applied pulse train to the equipment under test, applying those pulses through its input and out put terminals, with a severity level according to the terminal type. The equipment should continue operation after the test accordin g to the suitability criteria set up in each product-specific standard.

6.1.5 Harmonics limitation
Power supply equipment, both linear and switched, draw pulse current (see fig. 38) owing to the capacitors being charged. This waveform consists of a series of harmonics and a fundamental wave which with a frequency that equals the main frequency. Limiting the harmonics requires the power supply to have a power consumption with a limited band width which will result in a high power factor.

6.2 Safety regulation
A person exposed to an electric potential experiences a current flow through his body which may remain inadverted or pose a serious threat for his health. Safety regulations apply to all equipment featuring any electric risk and classify them in different categories or classes depending on the isolation available.

6.2.1 Classes of equipment
There are three classes of equipment depending on the isolation type and on the connection of this equipment to the electric distrib ution mains:
• Class I equipment. That equipment complies with: a) Basic isolation, b) To provide the piece of equipment with a connection with a safety earth.
• Class II equipment. Equipment that features a double isolation and may be not earthed.
• Class III equipment. This equipment does not have enough voltage to represent a risk situation.

6.2.2 Isolations
Isolation clearances necessary to consider an isolation as basic or double, as well as the material used for isolation should comply with certain rules. The isolation material should not be hygroscopic, should have the appropriate thickness and enough creepage. The minimum clearances to consider the type of isolation can be broken down in two types: clearances and creepages. The term clearance indicates the minimum direct distances between two circuits that must be isolated, while the creepage indicates the minimum distance that must exist between the two points following the intermediate isolation contour. These distances vary depending on the level, environment in which the equipment will operate and the voltage that the equipment is supposed to lock. For further information, please check the applicable standard for each type of equipment.