ABB TB521-ETH After sales service is provided for the control card of the power supply device

Description

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1.2.2 Voltage drop
Type of installation Lighting
%
Other uses
%
A – Low voltage installations supplied directly from a public low
voltage distribution system
3 5
B – Low voltage installation supplied from private LV supply a 6 8
a As far as possible, it is recommended that voltage drop within the final circuits do not exceed those indicated in
installation type A.
When the main wiring systems of the installations are longer than 100 m, these voltage drops may be increased
by 0,005 % per metre of wiring system beyond 100 m, without this supplement being greater than 0,5 %.
Voltage drop is determined from the demand by the current-using equipment, applying diversity factors where
applicable, or from the values of the design current of the circuits.
In an electrical installation it is important to evaluate voltage drops from the
point of supply to the load.
The performance of a device may be impaired if supplied with a voltage different
from its rated voltage. For example:
• motors: the torque is proportional to the square of the supply voltage; therefore, if the voltage drops, the starting torque shall also decrease, making it
more difficult to start up motors; the maximum torque shall also decrease;
• incandescent lamps: the more the voltage drops the weaker the beam becomes and the light takes on a reddish tone;
• discharge lamps: in general, they are not very sensitive to small variations in
voltage, but in certain cases, great variation may cause them to switch off;
• electronic appliances: they are very sensitive to variations in voltage and that
is why they are fitted with stabilizers;
• electromechanical devices: the reference Standard states that devices such
as contactors and auxiliary releases have a minimum voltage below which
their performances cannot be guaranteed. For a contactor, for example, the
holding of the contacts becomes unreliable below 85% of the rated voltage.
To limit these problems the Standards set the following limits:
• IEC 60364-5-52 “Electrical installations of buildings. Selection and erection of
electrical equipment – Wiring systems” Annex G states that the voltage drop
between the origin of an installation and any load point should not be greater
than the values in Table 18 expressed with respect to the value of the nominal
voltage of the installation.