Technical information

CONTROL CIRCUITS

In the definition of the individual components in a

control circuit, reference is made to a general direct

current circuit with one side connected to the

equipotent protection circuit.A distinction is made

between:

Supply: power source, in this case a power supply

unit (but also a transformer).

Overcurrent Protection: overcurrent protection, in

this example an supplementary protection 1492 –SP

(but also a fuse).

Internal conductors/cables inside the panel

Terminal: interface terminal between the panel and

on the machine

Load: load, in this example a solenoid valve (but also

a coil or something else)

External: conductors/cables outside the panel

1.3.1 Load

The UL508A definition of the control circuit is an “electrical circuit that

commands a control element (e.g. a contactor) and that does not f

eed pow er

loads”.

In paragraph 46 the standard lists the main loads that can be inserted in a control

circuit: coils (of the contactors), solenoid valves, general meters, sounders and

light signals.The solenoids, i.e. the coil of non contactors, should be assessed case

by case.

Motors, lighting and resistors are never control loads. In reality,under certain

conditions, panel maintenece lights and panel cooling fans can be considered as

control circuit.

If one side of the control circuit is connected to the equipotent protection

conductor,it is compulsory to connect one of the load connection terminals

directly to this side.