Electrical Insulation: Keeping different voltages and polarities separated in an electrical circuit is critical to proper operation of the product. It is also critical to keeping the product user from being “shocked” by the electrical circuit as well as helping to prevent fires started by the electric circuit. Electrical circuit separation is usually provided by a combination of through-air spacings and solid insulating materials. This whitepaper will discuss the different types of solid insulation used to protect the user from a “Risk of Shock” and comply with the applicable UL, CSA, EN, or IEC product safety standard. See whitepaper #30 for important details on Risk of Shock.
Insulation Types: There are 5 different insulation type definitions that can be found in product safety standards.
1) Operational Insulation is insulation that may be critical to proper product operation but the insulation is not relied upon for Risk of Shock protection. It may also be referred to as Functional Insulation. There are usually no requirements in the product safety standards that apply to operational insulation.
2) Basic Insulation provides one level of protection towards Risk of Shock compliance. Most standards require two levels of protection from shock hazards. Basic insulation is dielectric voltage withstand tested in the 1200 – 1500 VAC range depending on the product safety standard and the working voltage.
3) Supplementary Insulation provides one additional level of protection towards Risk of Shock compliance. Supplementary insulation is used in conjunction with Basic insulation to create a Double Insulation system. Supplementary insulation is intended to continue to provide protection in the event that the Basic insulation fails. So although most requirements for supplementary insulation are the same as that for basic insulation, there are usually some additional requirements. For example, some safety standards have a minimum thickness specification for supplementary insulation.
4) Double Insulation consists of Basic and Supplementary insulation used together to create an insulation “system” that provides two levels of Shock Hazard protection. A circuit that is “double insulated” is generally suitable for operator access (touch). Double insulation is typically tested in pieces = Basic insulation and Supplementary insulation. The manufacturer identifies which insulation is the Basic insulation and which is the Supplementary insulation, with consideration of which material can pass any additional requirements specified for Supplementary insulation. Double insulation is dielectric voltage withstand tested in the 3000 – 4000 VAC range depending on the product safety standard and working voltage.
5) Reinforced Insulation also provides two levels of Shock Hazard protection and therefore is also suitable for operator access (touch) in most product safety standards. Reinforced insulation is dielectric voltage withstand tested in the 3000 – 4000 VAC range depending on the product safety standard and working voltage. Reinforced insulation can have a minimum thickness requirement depending on the standard and usually has at least twice the creepage distance requirement as Basic insulation.
Circuit Purpose & Location: The product’s electrical schematic diagrams and layout diagrams are reviewed to identify which insulation in the product is part of the Risk of Shock protection system. Where and how the insulation is used identifies what part of the Risk of Shock protection the insulation serves. This information is then used to identify the insulation type and from that, the associated requirements, i.e. dielectric test voltage, creepage distance, and if there is a minimum thickness or number of layers requirement. Here are a few common examples:
• User accessible electrical circuits are typically required to have two levels of Risk of Shock protection = Double or Reinforced insulation
• Conductive metal enclosures that are reliably grounded typically must have one level of Shock Hazard protection = Basic insulation
• Conductive metal enclosures that are not reliably grounded typically must have two levels of Shock Hazard protection = Double or Reinforced insulation
• A plastic enclosure is usually part of the Risk of Shock protection system = the enclosure plastic serving as Reinforced insulation or as part of a Double insulation system
Conclusions: Determining Risk of Shock compliance for an electrical product is a complicated process which includes identifying where Basic, Supplementary, Double, & Reinforced insulation must be provided within the product, and then testing and measuring those materials based on their insulation type. Double and Reinforced insulation have more stringent test specifications and increased spacing requirements which translates to higher cost and fewer options when sourcing these types of insulating materials. It is therefore important that product designers minimize the areas within the product that require Double or Reinforced insulation.
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