Rockwell Automation Low-Voltage Switchgear and Controlgear - Manual (Page 14)

1.2 Electrical heating devices
Electrical heating devices are for example used for heating rooms, industrial resistance furnaces
and air-conditioning plants.
In the case of wound resistance elements, the making current can be 1.4 times the rated
current. In the selection of switchgear devices it should be noted with respect to the rated
operational current that (in contrast to the motor) the current consumption increases when the
mains voltage increases. When contactors are used, utilization category AC-1 should be used
as a basis for alternating current and DC-1 for direct current. For manual switching, a load-
switch with corresponding load-switching capacity (AC-21) is sufficient.
Furthermore, if the ambient temperature is very high this must be taken into account.
Heating circuits are often single pole circuits. Usually multi-pole switchgear devices with poles
connected in parallel are used, which enables to increase the permissible load current. For the
load-carrying capacity of switchgear units with poles connected in parallel, see section
2.4.1.1 .
1.3 Lamps and illumination equipment
The illumination devices are subject to constant change due to developments in energy
efficiency and electronics. For the choice of associated switching (e.g. contactors) and protec-
tive equipment (e.g. miniature circuit breakers and circuit breakers) not only the type of lighting
equipment itself should be taken into account but also the kind of control circuit. Particular
attention should be paid to inrush currents caused by compensation capacitors and charging of
electronic control devices. This loading may be reduced by the attenuating effect of long lines.
The startup and operational current loads should be obtained from the respective manufactur-
ers. The below descriptions relate to the basic characteristics. Also see
Tab. 1.3-1 .
In general it is recommended to utilize a max. of 90 % of the current capacity of the switchgear
as the current consumption of lighting equipment typically increases when the voltage in-
creases.
1.3.1 Incandescent lamps
The filaments of incandescent lamps have a very low ohmic resistance when cold. This creates
a high current peak when they are switched on (up to 15 · l
e
). The making capacity of the
switchgear must thus at least correspond to this value (utilization category AC-5b). Upon
switching off, only the rated current has to be disconnected due to the high resistance of the hot
filaments.
1.3.1.1 Halogen lamps
Halogen lamps are actually a version of incandescent lamps and their behavior is basically the
same as the latter. The lamps are often designed for low voltages and powered via a trans-
former or electronic mains adapter. Their inrush currents should be taken into account for
switching on.
1.3.2 Discharge lamps
Discharge lamps such as fluorescent tubes, energy saving lamps, mercury vapor lamps,
halogen metal vapor lamps or sodium vapor lamps require both a starting circuit and a current
limitation device. These devices may be conventional or electronic. Discharge lamps with
electromagnetic series chokes have a low power factor and are therefore usually compensated.
The compensation capacitance leads to high inrush currents that must be taken into account
when the switchgear is selected.
Most electronic series devices have a high power factor (e.g. cos φ ≈ 0.95), nevertheless during
switching on there occurs a charging current surge that loads the switchgear accordingly.
When selecting the switchgear for high in-rush currents, the permitted rated power for the
switching of capacitors should be taken into account as per utilization category AC-6b. In order
to prevent undesired release of miniature circuit breakers with the simultaneous activation of a
number of fluorescent tubes, information is provided by the tube manufacturers on the maxi-
LVSAM-WP001A-EN-P - April 2009 1-4