Welcome to the final lesson of our foundational module on motor control circuits. In our previous sessions, we have built the complete operational logic for both a Direct-On-Line (DOL) and a star-delta starter, culminating in the automated sequencing of the star-delta starter using an on-delay timer. Our circuits are now functional, but they operate silently, providing no external feedback. In any industrial environment, this is both impractical and unsafe.
This lesson bridges that gap by focusing on operator feedback. We will explore how to specify and wire the essential indication lamps that communicate the status of our motor circuits. You will learn how to add Run, Trip, and E-stop active indicators, turning your theoretical circuit into a design that can be safely monitored and understood at a glance. Mastering this completes the fundamental knowledge required before we transition into implementing these designs in EPLAN.
The Language of Lights: Status and Fault Indication
Indication lamps, or pilot lights, are the primary user interface for a control panel. They answer critical questions: Is the motor running? Has a fault occurred? Is the system in a safe state? To ensure this communication is clear and universal, we rely on standardized colors.
While local conventions can vary, the IEC 60204-1 standard provides an excellent baseline for safety and clarity. The following resource outlines these common practices.
IEC 60204-1 Wiring Color Codes and Indicator Light Standards Reference – Industrial Monitor Direct
This reference from Industrial Monitor Direct provides a concise overview of indicator light standards.
Please review the table under the heading "Symbol Reference". Pay close attention to the typical colors assigned for 'Running', 'Stopped', and 'Fault/Alarm'. Also, read the section on industry practices to be aware of real-world variations.
Based on this standard, we will adopt the following color scheme for our project:
- GREEN: Motor Running
- RED: Fault Condition (Overload Trip or Emergency Stop Activated)
- YELLOW / AMBER: Trip Condition (often used to distinguish from other faults)
- WHITE: Motor Stopped / Ready
Now, let's explore how to wire each of these lamps to reflect the circuit's true state.
Wiring the Indication Lamps
The logic for wiring an indicator lamp relies on using spare auxiliary contacts from our control components (contactors, relays, pushbuttons). An auxiliary contact is an electrical switch that is mechanically linked to the main component and changes state along with it.
The NHP Motor Control Handbook provides a good introduction to this concept.
[PDF] Motor Control Handbook - NHP
This handbook from NHP offers a practical summary of how pilot lights are used in motor control.
Read the section titled "Signalling devices" to understand the general principle. Then, review the "Note" at the end of the next section, which explicitly mentions using an auxiliary contact for signalling.
With this principle in mind, let's wire our specific indicators.
1. Trip Indication (RED or YELLOW)
The 'Trip' lamp must illuminate when the thermal overload relay detects a fault. The overload relay is designed with a special set of contacts (typically numbered 97-98) for exactly this purpose. These contacts are Normally Open (NO). In normal operation, they are open, and no current can pass. When the relay trips, they close, completing the circuit for our lamp.
The following video demonstrates this wiring practically.
Star Delta Starter Indication Lamp Wiring Explained Practically @TheElectricalGuy
In this video, "The Electrical Guy" clearly shows how to wire the trip indicator for a star-delta starter.
Watch the segment from the beginning until the trip lamp is wired. Notice how he uses the Normally Open (NO) contact of the overload relay (terminals 97 and 98) to ensure the lamp only gets power when a trip occurs.
2. Motor Stopped / Ready Indication (WHITE)
The 'Stopped' lamp should be on when the motor is not running, but is otherwise healthy (i.e., not tripped). The most straightforward way to achieve this is to use a Normally Closed (NC) auxiliary contact on the main motor contactor. When the contactor is off (motor stopped), the NC contact is closed, lighting the lamp. As soon as the contactor energizes (motor starts), the contact opens, turning the lamp off.
Star Delta Starter Indication Lamp Wiring Explained Practically @TheElectricalGuy
This next segment from the same video demonstrates the wiring for the 'off' indication lamp.
Watch the portion explaining the off indication wiring. The key is using the Normally Closed (NC) contact of the main contactor to achieve the inverse logic: the lamp is on when the contactor is off.
3. Motor Running Indication (GREEN)
This seems simple: use a Normally Open (NO) auxiliary contact on the main contactor. When the contactor energizes, the contact closes, and the 'Run' lamp turns on.
For a DOL starter, this is perfectly correct. However, for a star-delta starter, this logic is flawed and can be misleading. The main contactor can be on, but if the star or delta contactor fails to engage, the motor isn't truly running. The 'Run' lamp would give a false positive.
The correct and safe method requires interlocking. The 'Run' lamp should only light up if:
- The main contactor is ON, AND
- Either the star contactor is ON OR the delta contactor is ON.
This logic is implemented by wiring the NO contacts from the star and delta contactors in parallel with each other, and then in series with the NO contact of the main contactor. The video below provides an outstanding explanation and demonstration of this crucial detail.
Star Delta Starter Indication Lamp Wiring Explained Practically @TheElectricalGuy
This is the most critical part of the video. It explains the correct, safe way to wire a 'Run' indicator for a star-delta starter.
Watch carefully from where he explains the flaw in the simple approach and then demonstrates the correct interlocking method. Then, watch the final test where he proves the interlocking works by simulating a failed contactor.
4. Emergency Stop Active Indication (RED)
Finally, the 'E-stop Active' lamp must turn on when an emergency stop button is pressed. Like overload relays, E-stop buttons are designed for this dual function. The main NC contact breaks the control circuit, while a separate, electrically isolated NO contact is used for indication. Pressing the button opens the NC contact and closes the NO contact simultaneously.
This video clearly illustrates the component and the wiring.
How Emergency stop switch works? / How to wire an Emergency Stop Switch? / Best Explanatory Video..!
This video from Electro Academy provides a complete guide to wiring an emergency stop, including its indicator lamp.
First, observe the introduction of the components, specifically the E-stop button's contacts. Note that it has both NO and NC contacts. Next, watch how the lamp is wired using the NO terminals. Finally, see it in action during the operational test.
A Complete Picture
Now that we understand the logic for each lamp, we can visualize how they integrate into a complete control circuit. The diagram below shows a typical arrangement for a DOL starter with ON, OFF, and TRIP lamps. You can now trace the connections for each lamp and recognize the logic we've just discussed.
When we move into EPLAN, these hand-drawn circuits will be transformed into professional schematics, like the one shown in the screenshot below. You can already identify the symbols for the lamps (-H01 for Motor Running, -H02 for Fault) and see how they are connected within the larger circuit.
Conclusion
You have now completed the final piece of our motor control theory module. By adding indication lamps, you've learned to create circuits that are not only functional but also communicative and safe, providing clear visual feedback to operators.
Key Takeaways:
- Indication lamp colors are standardized for clarity: Green for Run, Red for Fault/E-Stop, and White for Stopped/Ready.
- Trip lamps are wired through the Normally Open (NO) contact of the overload relay.
- Run lamps are wired through Normally Open (NO) auxiliary contacts on the contactors. For a star-delta starter, a robust interlocking of the main, star, and delta contactors is essential for an accurate indication.
- Stopped lamps use a Normally Closed (NC) contact on the main contactor to provide an inverse status.
- E-Stop Active lamps use a dedicated Normally Open (NO) contact on the E-stop pushbutton assembly.
With this lesson, you have finalized the complete circuit diagrams for your project on paper. You now have all the foundational electrical knowledge required. In the next module, we will begin the practical portion of your project: setting up the EPLAN software and creating the digital framework for our industrial motor control panel.