5 ways to fail Low Voltage Directive (LVD) testing

This post is by Chris Rouse, Safety Product Manager, TRaC

Although Low Voltage Directive (LVD) safety testing is perceived as much simpler than EMC or environmental testing, it should not be ignored during CE certification.

If a product is unsafe, it can pose a potentially very serious risk to health, along with the possibility of fire or explosion should a product be electrically unsafe. Considering the LVD as an easy touch is certainly a risky game to play!

In fact it’s quite “easy” to fail certification: of the hundreds of products per year I see at the TRaC safety laboratory, at least 80% fail first time round. This is a scary figure given that on occasions products are close to release or may even already be on the market!

For a majority of the products which fail, some kind of modification or additional qualification of documentation is required to enable the product to be considered as compliant.

Often the problem is quite simple to solve, so I thought it would be useful to list the five most common causes of failure during LVD testing to help ensure your next product isn’t another statistic:

1) Single fault testing: Insufficient or incorrect protection of electrical circuitry such that overheating, fire or breakdown of insulation occurs during single fault testing

2) Temperature rise: Insulation on components, such as isolation transformers, PCBs or main component are found to be operating in excess of the allowed limits of the test standard or the particular component standard. This could result in a derogation of insulation property over a period of time which could in turn cause an electric shock hazard.

3) Protection of batteries (in particular lithium cells): Often lithium cells are required to be protected from over-charge and over-discharge and these protection components are either missing or insufficient for the battery capacity

4) Component approval: All safety standards assume safety critical components and carry their relevant third party approval, normally against an EN or IEC standard. Often this information is lacking, expired or the test specification withdrawn.

5) Marking and instructions: Incorrect or insufficient electrical ratings and warning marks on equipment along with insufficient information or technical explanation as to how the equipment should be used, installed and serviced.

 

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1 Comment

  1. January 07, 2014 11:02

    I would add another item:
    6. Creepage and clearance: PCB designers often get the primary side right, but seem to forget about the secondary (i.e. after the transformer), assuming that there is no danger involved, due to the low voltages present. However if the circuit is controlling something on the mains side i.e. a motor or a heater via a relay/optocoupler the C&C’s become quite critical.

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