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Category: Dorman Smith Switchgear Guide to Type Testing

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Dorman Smith
A Guide to Type Testing

The standard to which LV Switchboards should be manufactured is EN6043-1. The standard is non prescriptive and allows for manufacturers to be innovative whilst fully meeting the standard and, most importantly, providing the user with the equipment required. The standard details two categories of assembly, Type Tested (TTA) and Partially Type Tested (PTTA).

The definitions for these are as follows;

An Assembly: “A combination of one or more low voltage switching devices together with associated control, measuring, signalling, protective, regulating equipment etc., completely assembled under the responsibility of the manufacturer with all the internal electrical and mechanical interconnections and structural parts”.

Assemblies are likely to be produced for specific customers who may specify equipment to their own specifications and requirements. Hence the phrase “by agreement between manufacturer and user” is used throughout the standard.

Type Tested Assembly: “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”.

Partially Type Tested Assemblies: “A low voltage switchgear and controlgear assembly, containing both type-tested and non-type-tested arrangements provided the latter are derived (e.g. by calculation) from type-tested arrangements which have complied with the relevant tests”.

Why Type-Test? EN60439-1 states:

“Type tests are intended to verify compliance with the requirements laid down in this standard for a given type of ASSEMBLY.

Type tests are carried out on a sample of such an ASSEMBLY or on such parts of ASSEMBLIES manufactured to the same or similar design.

They shall be carried out on the initiative of the manufacturer”.

The standard also requires switching devices and other components to comply with their own relevant standards.

Type tests for assemblies are carried out for:

- Verification of Temperature Rise

- Verification of Dielectric Properties

- Verification of Short Circuit Withstand Strength

- Verification of the Effectiveness of the Protective Circuit

- Verification of Clearances and Creepage Distances

- Verification of Mechanical Operation

- Verification of the Degree of Protection

They are intended to:

- Prove the design capability

- Be conducted on representative samples for the design of Assembly, but are not intended to be undertaken on an Assembly which is subsequently put into service

- Be undertaken at the instigation of the manufacturer…it is recognised that it is impractical to test every conceivable configuration of circuit within an Assembly

- Be tested either in the manufacturer’s own laboratory or at an independent facility

- Have results recorded in reports or certificates that are available for examination

Explanation of Each Test

There are 7 type tests required to be carried out in order to classify an assembly as a TTA (Type Tested Assembly). This section explains the significance of each test:

(i) Dielectric Properties: The dielectric properties of a generic switchboard are tested as part of the verification process for a Type Tested Assembly. Additionally, these checks are carried out as part of the routine test sequence for every factory assembled board.

(ii) Temperature Rise: Section 7.3 of EN60439-1:1999 covers the requirements for temperature rise. In summary, there are three main areas that need to be covered:

- Temperature rise at the terminals of each device

- Temperature rise at the operating handle of each device

- Temperature rise within the enclosure

The first two in the above list are tested up to 40°C ambient as part of the type testing for the device. Providing that the maximum ambient within the enclosure does not exceed 40°C it is reasonable to assume that no further testing is required to prove these issues.

The third section can, initially and prior to any actual testing, be proven with mathematics. For the purpose of such calculations certain criteria needs to be assumed such as:

- Positioning of the Assembly. Are all panels positioned against a wall? If so, the heat can only be dissipated from three out of the four sides of the enclosure or it is a free-standing unit and heat can be dissipated out of all four sides?

- Ambient temperature around the switchboard

- Number of enclosures that classify each switchboard as. It is generally accepted that each switchboard is one enclosure (irrespective of number of sections) except in instances where the internal shielding clearly divides the unit into multiple enclosures

- If no information is available for circuit loading then a maximum loading will need to be assumed for all vertical bus-bars irrespective of the number of circuits

- Unless there is information to the contrary all devices will be calculated as carrying full load currents

The EN standard states that the maximum permissible temperature rise allowed on the external plates of an enclosure is 30°C. Typically, our calculations have shown an average maximum rise of between 12 & 13°C on the external plates of the switchboard (This is calculated from Max temp reached minus the ambient).

The temperature rise within the enclosure can be expected to be consistent with this figure.

(iii) Short Circuit Withstand Tests: It would be impractical to carry out this test sequence on all switchboards that are to be installed on site for obvious reasons. The preference within the industry is for a manufacturer to perform the more strenuous tests on a generic assembly and then adopt the same method of construction on all subsequent units.

(iv) Effectiveness of the Protective Circuit: This test is usually undertaken in two stages. The first stage is a short circuit test on the earth bar that is normally carried out during the short circuit tests on the main busbar. The second stage consists of measuring the resistance of the earth path.

(v) Clearance & Creepage Distances: These distances are measured and checked on a generic assembly prior to any electrical testing. As with the dielectric tests these checks are carried out as part of the routine test sequence for every factory assembled board.

(vi) Mechanical Operation: The mechanical operations test applies to the components used within an assembly. In accordance with EN60439-1 Section 8.2.6, no specific tests are required for the devices when positioned within an enclosure, providing that they have already been type tested in line with their own standards. All MCCBs and Fuse Combination Switches should be manufactured in accordance with their respective standards (EN60947-2 & EN60947-3).

(vii) Degree of Protection: Typically an IP test is carried out on a generic design of an assembly and then this method of construction adopted for all subsequent panels. Annex EN 60439-1 states that the IP value is subject to an agreement between manufacturer and user.

Who tests?

The tests can be carried out either in the manufacturer’s own laboratory or at an independent facility. The choice is the manufacturer’s decision.

 

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Tyco Electronics UK Limited
Energy Division
Freebournes Road
Witham
Essex
CM8 3AH

Tel : 0870 870 7500
Fax : 0870 240 5287