Power and control circuits

Power circuits deliver power to devices/loads (motors, lights, heating elements), handling high voltage and current for such devices, often having transformers, circuit breakers, fuses, switches, and heavy-duty wiring.

Control circuits manage devices operations, sending signals to control components (relays, contactors, and automation devices), often handling logic and timing of operations. It's a part of a circuit where panel switches. Limit switches and sensors connect to control a larger machine, using timers, small relays, sensing equipment, overload, interlock contacts and switches. They're often low current input and control devices, often in control cubicles. Control switches can be remote, giving the switching and control of the power circuit.

[3] Both systems manage machinery/motors/other electrical devices' operation, crucial in industrial automation, robotics, HVAC systems, and house usages.

Here, the control circuit is on the right and the power circuit, on the left, giving power to the motors.

Power and control circuits

Powering a control circuit

Overload operations

Numbering

References

Control device

A control device is an electrical component manage operation of a circuit/machine/system, acting as switches/sensors/automated controllers to start/stop/adjust electrical loads (e.g., motors, heaters, lights).

They're directly linked to control and power circuits in electrical systems. Control devices link the 2 circuits the interface between the low-power control circuit and the high-power load circuit.

Power sources

[1] Power circuits use both AC and DC and for control circuits, a control transformer, as power sources.

Notes:

Power source origin of electrical energy (raw input)
Power supply circuit/device converts, regulates, and sends power from a source to a load

Both are often interchangeable, but have subtle differences.

(A) Control Circuit (Low Voltage/Current)

Devices: Start/Stop buttons, relay coil (M), overload relay (OL) contacts.

Function: When you press Start, the control circuit energizes the M coil.

(B) Power Circuit (High Voltage/Current)

Devices: Main contacts of the M contactor, motor, fuses.

Function: The energized M coil closes the M power contacts, allowing high current to flow to the motor.

Real-world examples

Power circuit:

AC input (120V/230V) mains power from the wall outlet.
Step-down transformer converts 120V/230V AC to 12V AC.
Bridge rectifier (Diode-based, e.g., 1N4007 diodes) converts AC to pulsating DC.
Smoothing capacitor (e.g., 1000µF, 25V) reduces ripple in the DC output.
Voltage regulator (e.g., LM7812) e nsures a stable 12V DC output.
Filtering capacitors (e.g., 100nF ceramic + 10µF electrolytic) further smoothens an output.
LED strip load is a device powered by the circuit.

Ladder diagrams

Control circuits are often drawn as ladder diagrams, to troubleshoot circuits easier.

Ladder drawings use 2 vertical lines to tell common power connections.

The first rung tells the control power source, here being a transformer.

It maybe L1 and N.

Rungs 2#, 3# and so on have the control logic. Rungs' order often tells events' sequence.

Voltage

Voltage must always be highest to lowest-–down a page.

Powering a control circuit

A control circuit is a part of a circuit where a panel switches. Limit switches and sensors connect to control a larger machine, using timers, small relays, sensing equipment, overload, interlock contacts and switches. They're often low current input and control devices, often in control cubicles. Control switches can be remote, giving the switching and control of the power circuit.

The basic power circuit for many applications:

Fig 1. Power for controls is often tapped off ahead of M contacts, at ~208, 240, 480 or 600 V.

to tap off: to draw power/make a connection to a main electrical line/source for purposes like powering an equipment piece or circuit

Most common arrangement is to use a control transformer, often for either 24 or 120 V. Other voltages and arrangement are also used.

Often a control circuit is grounded and has a fuse.

2 common styles of power drawings exist for 3 phase motors--can be extended/modified if needed.

Overload operations

Numbering

As control drawing become complex, careful documentation is crucial for correct installation and maintenance, like numbering points on drawing in consistent manners.

A usual control drawing to be very familiar at.