Basic knowledge IEC / UL

What does IEC mean?
The abbreviation IEC stands for “International Electrotechnical Commission“. The commission is based in Geneva.

• International voting on the content of standards for worldwide standardisation. Each member body country may submit proposed modifications of existing standards and request for new standards.
• Germany is one of the few industrial countries that are leading in the field of standardisation.
• After acceptance of the standard by the member countries, each country is allowed to harmonise it in a national version.

Thus, in Europe the national standard DIN EN 60439-1 with same content results from the international standard IEC 60439-1. This also conforms to the national VDE 0660 part 500.

Testing to DIN EN 60439-1
For a safety function of low-voltage switchgear combinations it is necessary to match the different features of the individual components - the technical details to be considered are described in standard IN EN 60439-1(“Low-voltage switchgear combinations; part 1: Type-tested and partially type-tested assemblies“).

The proof of requirements for fulfilling the basic legal principles for low-voltage switchgear assemblies may be provided in line with the declaration of conformity and CE labelling by applying the standard mentioned above. The manufacturer must observe the relevant standards at the planning stage as well as in manufacturing, assembly and plant documentation.

This basically means for the manufacturer that there are the following variant options according to the above mentioned standard:

• Variant 1:
  type-tested assemblies (TTA)
• Variant 2:
  partially type-tested assemblies (PTTA)

The first variant comprises the testing of a ready-to-use system in an accredited testing laboratory. The test equipment must correspond to the technical scope and features of the system that will be installed on-site.

In accordance with DIN EN 60439-1 (table 7) the following tests must be carried out with the test piece:

» Show tables

The scope of the TTA tests results in high costs. For this reason it is not worthwhile for the switchgear manufacturers to test individual installations. For customisation and individual installations the cost input is just not proportional to the value. Only for larger quantities (mass production) will these costs amortise.

In addition to the testing costs there will be construction, material, labour, installation, and transport costs for the test piece itself. Often costs for maintenance and at worst for destroying the assembly during testing are not taken into consideration. The short-circuit test often result in a destruction of the test piece so that it cannot be used as a ready-for-sale plant to an end customer.

The second variant (PTTA) enables the equipment manufacturers to produce state-of-the-art equipment without additional tests or peripheral costs.

• Type-tested and not type-tested assemblies are used for the equipment construction.
• The last ones can be proven e.g. by calculation based on type-tested components.
• In comparison with the type-tested equipment it is necessary to provide overall proof by means of tests or calculation based on tests carried out.

For the exact amount of testing for both variants as well as the exact standard references that are necessary to meet the requirements see table 7 of DIN EN 60439-1.

Testing under accidental arc conditions

In addition to this testing procedure voluntary testing under accidental arc conditions may be carried out.

IEC 61 439: New standard for low-voltage switchgear and controlgear assemblies
The new IEC 61 439 lays down the definitions and states the service conditions, construction requirements, technical characteristics as well as verification requirements and will replace IEC 60 439. The standard IEC 61 439 is structured as follows:

• IEC 61 439-1 (replaces IEC 60439-1):
  General rules
• IEC 61 439-2 (replaces IEC 60439-1):
  Power switchgear and controlgear ASSEMBLIES
• IEC 61 439-3 (to supersede IEC 60439-3): Distribution boards
• IEC 61 439-4 (to supersede IEC 60439-4): ASSEMBLIES for construction sides
• IEC 61 439-5 (to supersede IEC 60439-5): ASSEMBLIES for power distribution
• IEC 61 439-6 (to supersede IEC 60439-2):
  Busbar trunking systems
• IEC/TR 61 439-0 (new): Specifier's guide

What does UL mean?
UL or Underwriter Laboratory was founded in 1894 as a non-profit-making organisation for testing and certification. UL operates five testing laboratories in the United States and subsidiaries worldwide, with an emphasis on product testing aimed at general safety.

• International regulations and standards such as NEMA and IEC are used as a basis by manufacturers for product development and subsequent testing.
• Nationally recognised testing laboratories confirm and certify that a product meets specific standards.
• In North America, this is carried out by organisations such as UL or CSA (Canadian Standard Association).

For many applications, only UL and/or CSA-approved products are acceptable. It is therefore advisable to ensure that electrical control systems intended for use in North America are designed with UL-approved components.

UL product labelling:
What does “UL listed“ or “UL recognized“ mean?

When labelling UL-approved products, a general distinction is made between Recognized Components and Listed Components:

Recognized Components
This label is used on products that are not complete in terms of their application.

• These products are listed in the UL’s “yellow component database”.
• The correct use of such components must make due allowance for the “Conditions of Acceptability”, listing the framework conditions and application parameters approved by the UL.
• These may be deratings, application/use specifications in conjunction with additional active/passive components, as for example specific fuse types.
• Furthermore, the application field of “branch circuits“ or “feeder circuits“ of the component is determined by the COAs.
  
  

Listed Components
This symbol is used in products that offer a complete function in themselves. Without consideration of the COAs.

• These products are listed in the UL’s “green component database”.

They may be used without restriction in accordance with the tested rating. For this all technical data must be visible on the type plate. Separate assembly instructions must be directly attached to the device or allocated to the product on a package insert.

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What is the difference between UL 508 und UL 508A in application?
UL 508 describes the standard for Industrial Control Equipment like Rittal busbar systems, SV components, switchgear etc. In addition the UL 508 is divided in sections A,B,C ... to classify the application field of the tested devices:

• A - Magnetic, manual and solid starters
• B - Thermal, magnetic, and solid overload relays
• C - Push buttons, selector switches and pilot lights
• D - Control circuit switches and relays

UL 508A is the standard for the assembly of switchgear for Industrial Control Panels that must be observed by the plant engineers. UL 508A combines all necessary UL standards including UL 508 which are necessary for switchgear construction.

For example, this standard contains information on:

• Machine controllers
• Elevator controllers
• Crane controllers
• Equipment for heating, air-conditioning and ventilation systems
  

Both standards describe control systems for general industrial applications with a rated voltage of up to 600 V. The maximum permissible ambient temperature is 40°C.

How does the US acceptance procedure for electrical plants work?
Every piece of electrical equipment (machine/plant) is tested by the competent local inspector (AHJ = Authority Having Jurisdiction) prior to commissioning. The AHJ has the final say with regard to commissioning.

• All AHJs use Standard NFPA 70 (NFPA = National Fire Protection Association) as a basis, which is generally regarded as the NEC (National Electrical Code).
• The AHJ considers the use of UL-recognized or UL-listed components an important indication that a system complies with the safety requirements to NFPA 70.
• This saves time and money during construction and commissioning of the equipment, as the UL symbol indicates that testing of the components and/or of the system did not reveal any foreseeable risks with regard to fire, electric shock and associated dangers.

For appliances with recognized labelling, the UL inspector inspects the COAs he can see in the UL-file.

Glossary of commonly used UL directives for low-voltage distributors (switch-/controlgears)

• UL 248 Low-Voltage Fuses
• UL 486 Equipment Wiring Terminals for use with Aluminium and/or Copper Conductors
• UL 489 Molded-Case Circuit breakers, Molded-Case Switch and Circuit-Breaker Enclosures
• UL 508 Industrial Control Equipment
• UL 508A Industrial Control Panels
• UL 512 Fuseholders
• UL 845 Motor Control Centers (MCC`s)
• UL 891 Switchboards

The scope of testing nearly corresponds to the content of the IEC testing (point 1-5). The most striking differences are, for example, in the field of short-circuit testing with the adjustment of phase sequence and the documentation of test results. The root mean square value (RMS) is preset by UL at the testing equipment.

• The oscillogram shows the surge short-circuit current at the beginning of the short-circuit current, however it will not be considered closer in contrast to IEC testings.
• The test time is limited to 3 cycles, this corresponds to 60ms. IEC test a value of 1000ms or according to manufacutere's specifications.
• Merely the end value is changed for the temperature limits admissible. The required creepage distances and clearances are divided into feeder and branch circuits.
  
  
• In short: Feeder-circuits are the infeed and main busbar area where increased creepage distances and clearances are valid. For 600 V AC this is 25.4 mm clearance und 50.8 mm creepage distance in accordance with UL 508A. (compared to IEC: For 600 VAC industrial applications; 8 mm clearance und 11 mm creepage distance)
  
  
• Branch circuits are in simple terms control circuits and outputs for electric motors with decreased creepage distances and clearances. For 600V AC this means in accordance with UL 508A 9.5 mm clearance and 12.7 mm creepage distance.
  (compared to IEC: For 600V AC industrial applications; 8 mm clearance and 11 mm creepage distance)
  

The application field used is classified according to the last „Over Current Protection Device“(listed component to UL 489/248, power circuit-breaker or fuse). After the last protective device of a current path with the above described features the branch circuit starts with reduced creepage distance and clearances. Everything before the protective device corresponds to feeder circuits.