Improvements in IEC 61439 series compared to IEC 60439 series.
The new document structure:
Readability of the IEC 61439 has been improved compared to the IEC 60439 by implementing the
new structure of the clauses:
a) Clauses for normative reference and definitions are separated;
b) Newly introduced in clause 4 is a table with all the typical units for LV systems;
c) Also n important change is the separation the constructional requirements (clause 8) and the
performance (electrical) requirements (clause 9);
d) Design verification in clause 10 has been detailed, with more guidance and rules for the
various verification methods;
e) Routine verification in clause 11 has been separated from the design verification.
These improvements acknowledge that the assembly manufacturer/designer focuses on the
constructional and performance requirements and less bothers with de design verification which is for
the laboratories to address.
Introduction of designated design verification methods
A significant change in the new LV Assembly standard is the introduction of three methods of design
verification to replace TTA and PTTA (Type Tested Assembly and Partially Type Tested Assembly).
Where TTA in principle required complete testing of all assemblies or modular LV assembly systems,
the new standard acknowledges that assemblies or modular LV assembly systems may be
manufactured in various similar arrangements that can be sorted in variants. IEC 61439 requires
design verification of the critical variants only. To sort the critical variants a number of rules are
provided in order to avoid superfluous testing.
Where PTTA allowed calculation (that was applied to the discretion of the assembly manufacturer) for
some verifications the new standard introduces concrete rules for this method. In essence these rules
limit the loading of parts and conductors to values that are considered safe in case no true test is
performed. Note that verification of temperature rise is limited to assemblies with a total current of
1600 A, above that one is obliged to test with current.
The new standard allows the manufacturer to combine the different methods for verification as long as
it is indicated in the test report which method was used for the individual design verification.
Better or worse?
In general the new standard is better, due to the new structure, the new introduced clear methods of
verification and abandoning the vague terms TTA and PTTA.
It is worse where it bothers laboratories to verify the constructional requirements regarding the
incorporation of switching devices and components, wiring and terminals, information that is not
always easy to come by. Probably only half of the verifications in this area are useful. Many of the
items are subject to an agreement between user and manufacturer and therefore may vary for each
one-off assembly.
Written for Eaton MCC Forum
Bas Bouman
Applications and Standards LV Systems
Eaton Electric B.V.
Hengelo The Netherlands.
12 May 2010
