FEATURE MACHINE BUILDING, FRAMEWORKS & SAFETY
UNDERSTANDING UL standards
An apparent lack of understanding about the use of UL
standards could lead to the loss of major export orders for OEMs, warns Ian Gibson, technical director of Flexicon
U
nderwriters Laboratories is a major force in the world of standards. You
will need to meet its standards if you want to export to an increasing number of large markets, not least the USA. In addition, UL operates a very transparent system for product approval. Anyone can log onto
www.ul.com and search under ‘online certifications directory’ to find the approvals held by a manufacturer. This means that if someone suspects that equipment or the components within it do not comply, they can report it – and UL inspectors will then check. UL representatives also visit and audit factories on a regular basis and take samples from production at random for testing. The ethos of UL is to work right down the supply chain, so that each component in a product complies. This detail and complexity, however, means that mistakes can and do occur.
LISTED AND RECOGNISED There are two types of UL approvals: UL Listed applies to a finished product and UL Recognised is for a component or a raw material that is incorporated into equipment that will itself be UL listed. Depending on the application, suppliers
Ian Gibson
to the OEM may fall into either or both UL categories. A clear example is seen
with the use of flexible conduit to protect power and data cabling. For exporters to North America it is the UL Recognised mark that is normally required for flexible conduit systems as they are likely to be incorporated into
equipment that may end up there. If, however, the cabling is to be connected to an external power or data source, then the conduit used for cable protection will need to be UL Listed. There are different UL standards
There are different UL standards applicable to flexible conduits and the standard itself will specify whether the approved product will carry the UL Listed mark or the UL Recognised mark
applicable to flexible conduits and the standard itself will specify whether the approved product will carry the UL Listed mark or the UL Recognised mark. This complexity and the methodology
for applying standards means that there are pitfalls that you need to be aware of – as illustrated by the different standards used for flexible conduit systems below:
UL 1696 – NON-METALLIC PROTECTION TUBING This is a system standard that incorporates conduits and fittings to provide a UL Recognised system for equipment that could end up being UL Listed. Typically the standard covers corrugated polyamide and spirally reinforced PVC and is harmonised for both the USA and Canada. The UL mark for this standard is cUus.
UL 1660 This is the standard for liquid tight, non-metallic, flexible conduit. Two types of conduit from this standard are commonly used: corrugated conduit (known as type C) and integral conduit (known as type B), which has a smooth inner and outer tube. It prescribes inside and outside
diameters so it is quite common for suppliers to provide conduit only or fittings only for the type B system. This approach only works because UL514B specifies that fittings must be
12 DEC/JAN 2016 | DESIGN SOLUTIONS
of a compression type that can cope with a wide tolerance. Unfortunately the performance of the system is often dependent on the fitting to conduit joint, particularly for the IP rating, pull off strength and the electrical continuity. Note, in particular, that the water ingress protection test in UL514B is similar to IPx4 and IPx5, so the resulting system may not even be liquid tight! In contrast Flexicon’s liquid tight conduit systems, incorporating both conduit and the fitting, achieve IP66, 67, 68 and 69. Conduit can be UL listed to this standard and fittings can be UL listed to the standard UL514B. The UL mark is cULus for both UL 1660 and UL 514B, showing approval for both the USA and Canada.
UL 360 This is the standard for galvanised steel, PVC sheathed, flexible liquid tight conduit. Like UL 1660, it prescribes inside and outside diameters for the conduit, so a different manufacturer can supply the fittings that meet UL 514B, which, as above, could negate the system’s liquid tight properties. In addition, UL360 requires a copper
bonding wire in the wall of the conduit for sizes up to 40mm since American regulations allow flexible conduit to be used as the earth conductor. This is quite different to the European wiring regulations that prohibit the use of flexible conduit as the earth conductor.
CORRECT SPECIFICATION While the UL standards aim to ensure a minimum quality standard down the supply chain, this approach is not without its problems. The onus is on the specifier to understand the difference between UL Listed and UL Recognised and apply it correctly to their suppliers; and to check that the system itself actually meets certain performance criteria. Mistakes do, however, occur. We have
come across cases where the flexible conduit supplier is using the wrong standard or an out of date approval. Another common error is for a supplier to claim blanket approval across an entire product range, whereas UL requires that every sized variant is individually listed or recognised. Get it wrong and the chances are
that UL will find out as they take policing of their standards very seriously. This places extra pressure on the OEMs to get it right or face what could be an expensive consequence. Our best advice is to work with suppliers who can offer you proper support on approved products.
Flexicon
www.flexicon.uk.com/en/
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