Introduction to Type-Tested and Partially Type-Tested Assemblies

IEC 60439-1-1999-09, EN60349-1 and BS EN60439-1 is Part 1 of the 439-series of standards and is the main part covering the general requirements for type-tested and partially type-tested assemblies. Parts 2, 3, and 4 of the standards deal with the particular requirements for certain specialised forms of assemblies (see below).

Low-voltage switchgear and controlgear assemblies

• -439-1: Specification for type-tested and partially type-tested assemblies.
• -439-2: Particular requirements for busbar trunking systems.
• -349-3: Particular requirements for assemblies intended to to be installed where unskilled persons have access to their use.
• -439-4: Particular requirements for assemblies for construction sites.
  

The need to conform to standards.

Low-voltage switchgear and controlgear come under the EU Low Voltage Directive, and since January 1st 1997, all new assemblies intended for use within the EU member states must be CE - marked to indicate that they conform with the essential safety requirements of this Directive.

The Directive requires electrical equipment to be safe and constructed in accordance with the principles generally accepted within the member states of the EU as constituting good engineering practice in relation to safety matters. It requires that the electrical equipment (assembly), together with its components, is made in a way that ensures it can be safely and properly assembled and connected.

It also requires that measures are taken to ensure that protection is assured against various hazards which might arise from the electrical equipment or by external influences on it.

Some of the hazards listed by the Directive include:

• Direct and indirect contact with live parts
• Dangerous temperatures, arcs or radiation
• Overloading
• Insulation failures
• Mechanical failures
• Expected environmental conditions
• Non-electrical dangers caused by the assembly
  

There is, of course, the proviso that an assembly is used in an application for which it was made, and that it is properly installed.

TYPE-TESTED ASSEMBLY (TTA) IEC 60439-1-1999-09 CLAUSE 2.1.1.1

A low-voltage switchgear and controlgear assembly conforming to an established type or system without deviations likely to significantly influence the performance, from the typical assembly verified to be in accordance with this standard.

Notes:
For various reasons, for example transport or production, certain steps of assembly may take place outside the factory of the manufacturer of the TTA. Such an assembly is considered as a TTA provided the assembly is performed in accordance with the manufacturers instructions in such a manner that compliance of the established type or system with this standard is assured, including submission to applicable routine test.

PARTIALLY TYPE-TESTED LOW-VOLTAGE SWITCHGEAR AND CONTROLGEAR ASSEMBLY (PTTA) IEC 60439-1-1999-09 CLAUSE 2.1.1.2

A low-voltage switchgear or controlgear assembly, containing both type-tested and non-type-tested arrangements provided that the latter are derived (e.g. by calculation) from type tested arrangements which have complied with the relevant tests. (see table section 4.5.4)

Internal Form of Separation

IEC 439-1, Amendment 2 1996-11 gives the following guidelines for the different separation types.

One or more of the following conditions can be obtained by dividing ASSEMBLIES by means of partitions or barriers (metallic or non-metallic) into separate compartments or enclosed protected spaces:

• Protection against contact with hazardous parts belonging to the adjacent functional units. The degree of protection shall be at least IPXXB.
• Protection against the passage of solid foreign bodies from one unit of an ASSEMBLY to an adjacent unit. The degree of protection shall be at least IP2X.
  

Unless otherwise stated by the manufacturer, both conditions shall apply.
NOTE: The degree of protection IP2X covers the degree of protection IPXXB

The following are typical forms of separation by partitions:

FORM 1 No separation.

FORM 2A Separation of busbars from the functional units. The terminals for external conductors do not need to be separated from the busbars.

Degrees of protection

The system has been tested according to the guidelines as described in IEC 60529 and passed the test conditions for the IP 54 protection as laid down in Sub-clause 7.5 (first characteristic numeral) and Sub-clause 8.4 (second characteristic numeral).

The following is an extract from the Standard.

DEGREE OF PROTECTION

Rated Currents and Short-Circuit Currents of 3-phase Transformers

The current ratings above are based on a voltage of 450V. The short-circuit currents shown in this table are higher than actual as they assure infinite power on the supply side and do not take into account impedance of cables, busbars and connections to breakers.