Tyco Electronics - Tyco Dorman Smith Switchgear
Dorman Smith Switchgear - 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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