As shown in Fig.1.39, any electrical equipment has two circuits;


Fig.1.39 Power & control circuit

Circuit breaker (Merlin Gerin), Contactor, overload relay & selector switch

(Telemecanique), Motor (Siemens)


·           The first one is the Power circuit which includes:
–   Equipment load (motor, heater, etc)
–   Circuit breaker or fuse load isolator (to protect power circuit against short circuit)
–   Power contactor (an electromechanical device that is operated by an electromagnetic coil and allows automatic or remote control for opening and closing of an electric power circuit).
–   Thermal overload relay ( a relay that responds to any extra current consumed by load and is operated at a pre-set value of overload current)
Note: ELCB (Earth leakage circuit breaker) should be included in power circuits, to protect people against electric shocks and/or motors against earth leakage. This device is either to be built-in the equipment or to be included in building distribution board feeding the equipment. In fact ELCB is an essential device for all electric kitchen equipments (check local codes), to protect operators against electric shocks especially for some equipments such as dishwashers, boilers, etc
  • The second one is the control circuit which is used to control equipment load (e.g. start / stop, interlocking elements to prevent damage or improper operation such as prevention of heater start in a wet bain-marie with no water depending on manual switch (Fig.1.40 & Fig.1.41) or automatic sensor (Fig.1.42). In general, control circuit main components are ;
–   Low voltage transformer (control circuit should have low voltage (12 or 24 Volts) for operator safety.
–   Fuse or circuit breaker to protect against short circuit.
–   Manual switch (selector switch, push-button, etc) for manually operated equipments or to start automatic control circuit.
–   Automatic sensor (thermostat, pressure switch, float switch, timer, limit switch, etc, according to equipment type).
–   Solenoid; a solenoid is a device to convert electric energy to a linear mechanical action by using of an electromagnetic coil. Solenoids are used in a wide range of commercial & industrial applications such as packing, punching, stamping, door locking & unlocking, etc.
–   Solenoid valve; one of the most common applications for solenoid is solenoid valve. Solenoid valve function is to control fluid flow (water, compressed air, steam, etc) through opening and closing valve by the use of solenoid action, or simply it’s an electric operated valve. Solenoid valves are widely used in kitchen equipments (dish washers, bain-maries, ovens, etc)
–   Safety controls such as under voltage protection, phase sequence controller, etc.
–   Accessories; such as signal lamps, sirens, panel meters, etc.

Fig.1.40 Manual control circuit with selector switch

Fig.1.41 Manual control circuit with Push – button


Fig.1.42 Automatic control circuit with selector switch & pressure switch

Fig.1.43 Interlocking between kitchen hood fans