Product Selection, Project Engineering and Modification
10
303049 / 825060300230
2022-05-30·BA00·III·en·00
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Ex d enclosure made of aluminium/flameproof enclosure
8250/0 series empty enclosure,
8250/1 series terminal box,
8250/5 series control panel/control station
5.3
Internal Built-In Components
(Conductors, Terminals)
Ascertaining the maximum number of conductors
5.3.1 Ascertain the Number of Conductors using the Table from the EU Type Examination
Certificate
▶
Refer to the specifications in the EU Type Examination Certificate for the maximum
permitted number of conductors in relation to the current load and conductor
cross-section.
Taking enclosure 8250 as an example: The maximum permitted number of conductors can
be ascertained using the following tables "Maximum number of terminals".
Explanations of the table:
Each inserted conductor and each internal connection conductor must be counted.
Jumpers and protective conductors do not count.
Uncritical area (light area of table)
The light area is non-critical in terms of enclosure heating. Electrical circuits classified as
being in this area can be incorporated in the enclosure in any number.
Critical area (labelled area of the table)
This part of the table shows the maximum permissible number of conductors considering the
conductor cross-sections and the continuous current loading. When using this table,
simultaneity factors and load factors may be accounted for. Mixed assemblies with electrical
circuits of different cross sections and currents are possible; in this case the proportion of the
load from the individual circuits should be taken into account. If a terminal box is fully loaded
according to the criteria in the dark part of the table, then any number of electrical circuits
from the non-critical area (light part of the table) may be added.
Dangerous (dark area of the table)
Terminal boxes which are designed according to this area require an additional
temperature-rise test.
Example calculation (general):
▶
Ensure that operating temperatures – particularly low temperatures – for the terminal
boxes correspond to the selected electrical lines.
Heat develops due to contact resistance at the clamping units and due to the conductors
installed in the enclosure. In order to ensure that the maximum permissible temperature
of the enclosure is not exceeded, the current load of the electrical circuits in the enclosure
must not be too large!
Cross section [mm
2
] Current [A]
Number of conductors Proportion
2.5
20
8 (of 20)
= 40%
4
25
6 (of 22)
= 27%
6
35
4 (of 17)
= 24%
= 91% < 100%