OVC III overvoltage category in MEAN WELL power supplies

Most users of mains electrical equipment are confident that they can simply plug their device into a convenient outlet, and this device will work correctly, safely and reliably. The fact is that anywhere in the home, office, or factory where power is supplied from wall outlets, it is likely that an environment has been created in which electricity is relatively "clean", without excessive voltage transients that can damage the final equipment. However, as we gradually move back along the infrastructure wiring to the switchboard, and then further to the AC connection for the building, the likelihood of overvoltage from external events such as lightning strikes and load surges from other installations in the power grid, which pose obvious risks, increases.

The Over Voltage Category (OVC) defines the level of overvoltage caused by lightning or unstable power supply for various electrical equipment or power supply connection points. It is used to ensure that a certain transient voltage does not pass from the primary side to the secondary side, where safety must be maintained at a sufficient level.

Surge protection

The international standard IEC 60664-1 "Approval of insulation for equipment in low-voltage power supply systems" defines four categories of installations, designated from OVC I to OVC IV. By definition, OVC category I refers to powered equipment that is connected lower down the grid from a well-protected isolated power source, such as a laptop powered by direct current from a charger, while OVC category IV applies to energy company equipment connected directly to an incoming power source in a distribution cabinet. This means that most of the network equipment in buildings belongs to the OVC II and OVC III categories.

Categories of overvoltage in the power supply network

The IEC 60664-1 standard defines the following pulse voltage ratings for various OVC categories:

Normalized pulse voltage for OVC categories

The nominal transient overvoltage or pulse voltage for OVC III is 4000V, taking into account the 230V AC network (Russia). It should be noted that the values in the table are the nominal peak pulse voltage of 1.2/50 µs for the main insulation. For double or reinforced insulation, the following higher voltage category is used. For example, 300 Vrms OVC II requires a rated voltage of 4000 V. for reinforced insulation. In addition, the OVC III power supply is compatible with OVC II, I applications and environments.

OVC III overvoltage category power supplies require reinforced protective barriers. Power supplies designed for OVC III zones need improved characteristics of the withstand voltage and the gap distance between the primary and secondary sides compared to the more common types of OVC II. These requirements can be met by using a separation transformer to reduce transients to OVC II levels, a better solution is to design the power supply so that it can be directly connected to the power supply in an OVC III environment.

Connecting OVC II and OVC III power supplies to the power supply network

MEAN WELL offers a wide range of OVC III power supplies, for example, the LRS-35, LRS-50, LRS-75, LRS-100, LRS-150, RSP-75, RSP-100, RSP-150, HDR-15/30/60/100 and others series power supplies have this compliance. The Specification includes information about the overvoltage category Over Voltage Category in the Environment section (OVC III only, since all other MEAN WELL power supplies have OVC II), and information about the withstand voltage Withstand Voltage in the Safety section.:

Figure 5. Information about the OVC III category using the example of the HDR-100N2 series

Is it possible to use OVC II category power supplies in OVC III applications? Yes, but when using additional security features:

• Using an AC isolation transformer in front of the OVC II power supply to protect against interference and ensure safety.
• Using a Type 2 or Type 3 Surge Protection Device (SPD) at the input of the OVC II power supply to limit the input pulse voltage level. For example, the SPD-20-240P from MEAN WELL.

Although both solutions increase the cost and occupied space, nevertheless, it can be an acceptable solution for using an OVC II power supply in a more demanding application.

For advice or clarification of information on MEAN WELL power supplies, please contact the email address Meanwell@chipdip.ru .