Yes – Air is an Insulator: When the term “electrical insulation” is used, most people picture a tangible material. However, the most frequently used electrical insulation is air.
What Insulation Type is Air? In Whitepaper #86, we detailed the different types of electrical insulation = operational, basic, supplementary, reinforced, and double insulation. Different insulation types are used throughout an electrical product to protect the user from a “Risk of Shock”. Electrical circuit separation is usually provided by a combination of thru-air spacings and solid insulating materials. Thru-air spacings relied upon for Risk of Shock compliance use air as the electrical insulation. When used for shock hazard protection, air can serve as any of the defined types of insulation = operational, basic, supplementary, reinforced, or double insulation.
Benefits of Air Insulation:
a) Free: Of course there is no direct cost for “air” insulation.
b) Known Performance Properties: The insulating properties of air are known and can be relied upon for repeatable performance.
c) No Damage: Air has no manufacturing imperfections and cannot be physically damaged during the product production process.
d) Auto-Replacement: In the case where a breakdown occurs between live parts (breakdown of a thru-air spacing), the insulation is automatically replaced/replenished as soon as the overvoltage events subsides (i.e. transient voltage). No repair of the equipment is necessary.
Drawbacks of Air Insulation:
1) Size: Thru-air spacings cannot be reduced below the limits in the standard meaning that the overall product size will be partially dictated by the thru-air electrical spacings within the product. Increased size = increased product cost, packaging cost, and shipping cost.
2) Cannot Improve the Insulating Properties: Tangible insulating materials can be used that have improved properties that allow for reduced electrical spacings. Unfortunately we cannot improve the insulation properties of air to allow for reduced thru-air electrical spacings. Air has fixed properties that cannot be improved.
Summary: As manufacturers continue to develop smaller products, being aware of where air insulation is being relied upon for shock hazard protection is critical. One of the first steps in product size reduction is to reduce the free air space. Knowing where the air must be replaced with a superior insulating material is an important part of this process.
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