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Safety testing limits risk of shock, fire, and injury, Part 1

-March 01, 2013

Electricity is like the genie in a bottle. When it is contained and properly harnessed, its power is endless. However, when it escapes in an uncontrolled manner, electricity has the potential to cause harm. In addition to electric shock, electrical products can cause fires, burn injuries, explosions, or other harm (see Figure 1). Making a product safe requires an understanding of the hazards that exist for electrical products and the safety tests required to meet product safety standards. Safety testing is performed to help ensure that electrical products do not harm the user, product, and surroundings.



Figure 1   Hazards posed by electrical products

Product safety standards are used to test and evaluate products for safety compliance. It is important to use the appropriate standard. The relevant safety standard for test and measurement equipment (TME) is IEC 61010-1 and for information technology equipment (ITE) the standard is IEC 60950-1. Limits can differ between safety standards. The most common voltage limits are 30 Vrms, 42.4 Vpk and 60 VDC (ITE).

There are numerous safety tests with over fifty tests in the TME standard and over sixty tests for the ITE standard. The actual number of required tests is dictated by the design, rating, use environment, and potential hazards of the product, as well as by the applicable product safety standard. Examples of product safety tests include dielectric voltage withstand, temperature, leakage current, and impact.

This article describes the importance of safety testing. It also presents a step-by-step guide about performing safety tests with pass/fail criteria for each test. This article introduces important product safety tests, known as Type tests, which are performed for safety design verification. It also describes production tests, known as Routine tests, which are important product safety tests performed during the manufacturing process to uncover production related safety defects.

Part 1 of this article will cover the following electrical product safety tests:
  • Dielectric Voltage Withstand Test – Hipot
  • Grounding Continuity Test
  •  Input Power Test
  • Limit Values for Accessible Parts Test
  • Leakage Current Test

Part 2 of this article will cover the following mechanical safety tests as well routine, production, safety testing:
  • Temperature Test
  • Cooling Abnormal Test
  • Component Abnormal Test
  • Impact Test – Dynamic Rigidity
  • Routine Tests  – Withstand and Continuity

The following safety terms and definitions apply for the purposes of this article:
  • Hazard—Potential source of harm, such as electric shock, burn, fire, explosion, and others.
  • Type Test—Test of one or more products, test samples, to show the design meets safety standards.
  • Routine Test— Test of each product in manufacturing, typically at the end of the production process.
  • Hazardous LIVE Voltage—Voltage > 30 Vrms, 42.4 Vpk and 60 VDC; risk of shock, burn, or fire. Note: Voltage limits can differ between safety standards. The most common limits are 30 Vrms, 42.4 Vpk and 60 VDC (ITE, others).
  • Extra-low Voltage (ELV)—Voltage ≤ 30 Vrms, 42.4 Vpk and 60 VDC; no risk of shock.
  • Hazardous Energy—Power > 150 VA (TME) and > 100 VA (ITE); risk of burn or fire.
  • MAINs—AC or DC power distribution system to which the product is intended for connection to power.
  • Single Fault (Abnormal)—One fault present, such as a component short, which could cause a hazard.
  • Rating—Set of rated values and operating conditions, such as voltage, current, and temperature.
  • Normal Use Condition—Operation according to product ratings and instructions; maximum loading for tests.
  • Extended Use Condition—Operation according to extended ratings, such as above 40 ºC environment (TME).
  • Insulation—Safety isolation required to protect against shock, such as Basic, Supplemental, and Double/Reinforced.
  • Protective Earth (PE)—A main PE terminal of a product that is required to be earthed, grounded, for safety purposes.

Note: This article is an introduction and overview of product safety testing. Product safety standards take precedence over any information presented in this article. Refer to the relevant product safety standards for the specific testing requirements. Product safety design is addressed in the standards and other articles (see Related Articles).

Dielectric voltage withstand test

A shock or fire hazard can exist when a product operates at hazardous LIVE voltage, such as when the power is derived from a wall outlet of 120 VAC/60 Hz in North America or 230 VAC/50 Hz in Europe. The operational, rated, voltage of the product can be a continuous input or output voltage.

Continue reading page two (on tmworld.com)

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