A burning issue?

Changes to the regulations mean manufacturers must reassess the fire-resistance and assembly safety of the components they use - industrial customers should also take note, says Terry Spriggs.

2008 will see an ever-growing range of domestic appliances available on the market and all products will have to conform to EN60335-1, 2002 and, if applicable, the latest relevant device specific part 2 of the standard.

Any manufacturers still operating to the 1995 standard will not obtain product approval so conformance to the ever more stringent requirements is essential.

One of these changes could literally mean the difference between life-and-death so industry needs to be aware that the regulations applying to domestic goods are there for a good reason, and could soon be expected of industry - a fire started by a substandard terminal block or electrical fitting for example could be avoided if manufacturers took heed of some of these changes.

In 2005, the updated EN60335-1 standard for the safety of household appliances came into full force.

The first major update of the domestic appliance safety regulations since 1995, the new rules required manufacturers to adopt more stringent fire safety and electrical isolation standards.

A failure to properly understand these standards by OEMs can now lead to costly delays in bringing products to market for domestic goods, yet selecting the right components and designs to ensure compliance need not be costly or challenging for domestic goods manufacturers, or for industry.

One of the essential changes to the regulations concerns the fire resistance of components.

All electrical components must be able to withstand exposure to a 750C glow wire, with any flame that occurs as a result of this exposure being self-extinguished within 2s.

This is a far tougher test than the outgoing standard, which allowed a 30s period for any flame to be extinguished.

That 2s permissible burn time is a particularly demanding requirement, essentially meaning that components must produce no flame at all, since it is difficult for self-extinguishing materials to act effectively in such a short time.

To add to the challenge of compliance, components must also be halogen-free and low-smoke.

Components likely to be affected by the new flammability rules are any where that plastic materials come into contact with conductors, including enclosures, switches and terminal blocks.

In order to comply with the new regulations, manufacturers of these products are having to adopt new materials in their designs.

Ceramic materials give the highest degree of heat and flame resistance, but their high cost makes them unsuitable for many price sensitive high volume applications.

Fortunately for appliance manufacturers, there are cost effective alternatives available.

Modern nylon-based materials can deliver appropriate performance at a relatively small price premium over noncompliant materials.

Although a supplier of many different components to a variety of industries, bulk supplier of approved and tested components such as UK market leader Hylec-APL now recommends the use of components that pass the stringent domestic regulations for safety reasons.

Items typically include PCB mounted terminal blocks, nylon pillar terminal blocks and domestic appliance connectors from manufacturers such as: Metalluk, ITW Elettro-Gibi, and microswitches from Cherry.

The new EN 60335-1 standards also include revised tables for creepage and clearance limits.

Clearance distances refer to insulation distances through air - the shortest distance between to conductive elements.

Creepage distances are measured along the insulated surface between the two conductors.

With the new, more stringent limits, designs become far more sensitive to small manufacturing errors.

Inserting a wire too far into a terminal block can lead to the conductor protruding from the other side, potentially breaching clearance limits.

Tight quality control during assembly is one strategy to avoid falling foul of issues like these, but there are also component selections that can help to prevent these problems occurring.

Barrier inserts are a simple way to completely eliminate over-insertion of conductors into terminal blocks, ensuring that clamping always occurs on the conductor and that nothing protrudes through the rear of the block.

Barrier inserts also help to cut manufacturing costs by increasing assembly speed.

These changes are the most significant in domestic appliance safety for some time.

Failure to comply with any applicable rules could be extremely costly - although the corrective action required may be relatively simple, manufacturers will not be allowed to sell their products until the work is complete and testing repeated, potentially loosing weeks or months of sales during the crucial product launch period.

Designers should take the time now to study the new regulations and make sure all components they are sourcing themselves - and all those coming in from overseas suppliers - comply with the new rules.

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