Circuits
33 Three-Wire Circuit With Pilot Lights
Motors are often installed in loud environments or at remote locations, and so simply relying on the sound of a running motor to tell an operator its status is unreliable. To aid with this, we can connect pilot lights in our control circuit to indicate the running status of a motor. Pilot lights that are installed in the control circuit in parallel with the motor starter will be energized when the motor is energized. These are often referred to as motor running lights.
Pilot lights must NEVER be installed in series with motor starters; the motor starter might not have enough voltage to pull in, and if the filament in the pilot light burns out, it will create an open in series with the rest of the circuit.
Motor starters often come with auxiliary contacts beyond the normally open 2-3 holding contacts, and if not, many starters can have additional auxiliary contacts added to them.
If a motor starter has a set of normally closed contacts these can be wired in series with a pilot light. As long as the motor starter is not energized, the contacts will remain closed and the light will be on. This can indicate to an operator that a motor is in the off or de-energized condition.
A small lamp connected in the control circuit to indicate the status of a motor or other situation.
In contrast to the Power Circuit, the Control Circuit consists of inputs, in the form of switches, pushbuttons or pilot devices, which when activated, can either directly, or through a magnetic motor starter, energize a load. The Control Circuit often operates at a lower voltage than the Power Circuit for safety and ease of installation.
In electrical terms, refers to a connection where current has more than one path to flow.
Loads connected in parallel will experience the same potential difference (voltage), but may draw different values of current depending upon their individual resistance.
In electrical terms, refers to a connection where current has only one path to flow.
Loads connected in series will have the the same value of current flowing through them, and share the total voltage between them. Switches and overcurrent equipment is connected in series with equipment to control and protect it.
The difference in electric potential between two points, which is defined as the work needed per unit of charge to move a test charge between the two points. It is measured in volts (V).
Contacts on a magnetic starter that are not Horsepower rated. Can come as either normally-open or normally-closed and can be used as maintaining contacts, electrical interlocks or control for pilot lights.
A contact that under normal conditions does not have continuity through it. When the contact changes its state it permits the flow of current by closing its contacts. Can be associated with pushbuttons, pilot devices or magnetic contactors.
Also known as a "maintaining" contact, these are the normally open contacts of a magnetic starter that are connected in parallel with the start button in a three-wire control circuit. When using the conventional NEMA numbering system, they get wire numbers "2" and "3."
A contact that under normal conditions has continuity through it. When the contact changes its state it interrupts the flow of current by opening its contacts. Can be associated with pushbuttons, pilot devices or magnetic contactors.
