The 3D-printed wire markers provide a learner-friendly way to reinforce the relationship between physical wiring and abstract wire diagrams. The wire markers are especially useful because they reveal formative errors in a learner’s understanding of electrical nodes.
Figure 1 shows the markers used in an elementary circuit. The associated wire diagram is included as Figure 2. Notice that both the circuit and the associated wire diagram contain node identifiers such as +24 VDC, Rung 1 Node 1 (R1N1) and the 24 VDC supply return (RET).
Download the STEP file for the 22 AWG wire markers here. Thank you @AaronRollens for designing and printing this solution. Cable Label.step (22.4 KB)
This introductory article describes the technique associated with the 3D-printed wire markers. The working lessons concerning nodes are contained in articles such as:
- Building Logic Gates Using Industrial Switches
- Introduction to Relay-Based Ladder Logic for Industrial Control Panels
This article is part of the DigiKey Field Guide for Industrial Automation
Location: Understand It → Relay Logic → Fundamentals
Learning Pathway: Industrial Automation Technician → Fundamentals
Difficulty: 
Student — difficulty levels explained
Author: Aaron Dahlen | MSEE | Senior Applications Engineer, DigiKey
Last update: 28 Jul 2026
Figure 1: 3D-printed wire markers used on an elementary circuit.
Key Takeaways
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The 3D-printed markers bridge the relationship between the real-world circuit and the abstraction represented by the wire diagram.
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A marker can be slid along the wire, providing visual and tactile feedback that reinforces the natural movement of the learner’s pencil on the wire diagram.
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The markers can be changed on the fly, allowing the nodes to reflect the learner’s evolving understanding of the circuit. They were designed for 22 AWG wire and ferrules.
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Switch to conventional wire label methods when the learner can identify shared nodes, choose equivalent voltage test points, and reason about branch current without relying on the physical label.
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Node-based thinking gives learners a clear common language from which to explore abstract electrical concepts.
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When included, node-based thinking reinforces the purpose of terminal blocks as wires on both sides of the terminal block are still the same electrical node. This is a fundamental skill required to troubleshoot electrical circuits.
Why Use Node Labeling on the Wires?
By definition, an electrical node is the complete set of electrically connected components and conductors. This is easy to say but hard to visualize, especially in an industrial control panel where some nodes end up looking like a spider’s web of wires. On day one the learner is challenged to “see the forest for the trees” by understanding that nodes are composed of wires and terminal blocks.
Node labeling serves as scaffolding to help the learner differentiate between wires and nodes. Wire-based thinking is fragile as learners narrowly focus on the wire attached to the component such as a relay coil. Node-based thinking is robust as technicians learn to view wires and component terminals as the same equipotential node. In operational terms, technicians will have many places to probe the equipment to observe the same voltage.
Importance of Node-Based Thinking in Early Lessons
During many years of teaching, I have seen students struggle with control circuitry and especially relays. You wouldn’t think it, but the logic function embodied in Figure 1 is just as hard as breadboarding 74-series logic for the first time. In this case, the closed-loop circuit shown in Figures 1 and 2 performs the F = A & B & NOT C operation.
The electrical node is closely associated with the concept of a closed loop. From a practical perspective, the student must be able to trace the current flow from the positive rail to the return rail by transitioning across each rung of a ladder diagram. Clear node identification is like a roadmap that allows us to identify where we are on both the wire diagram and in the hardware.
As an example, consider what it takes to troubleshoot the circuit shown physically in Figure 1 with the accompanying wire diagram in Figure 2. Let’s assume the multimeter’s black test lead is attached to the return node. The learner would naturally think in terms of nodes by checking for:
- Voltage between the +24 VDC node and the return node.
- Voltage between Rung 1 Node 1 (R1N1) and the return node.
- Voltage between Rung 1 Node 2 (R1N2) and the return node.
- Voltage between Rung 1 Node 3 (R1N3) and the return node.
In all cases, the concept of voltage is reinforced as a property that is measured between two nodes.
Figure 2: Wire diagram for the circuit shown in Figure 1.
Linking Physical Wiring to the Wire Diagram
The 3D-printed wire markers solve a long-standing problem of linking the physical wires to the wire diagram abstraction. One of the most important distinctions is that the marker can be slid along the wire, providing both visual and tactile feedback. For example, a marker can be slid from the output of a switch to the input of the PLC. This mimics the natural movement of the learner’s pencil on the wire diagram.
There are several other advantages:
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True industrial wire labels focus on the wire or terminal block. This is highly desirable for the finished control panel but hides the concept of node. It’s a situation where the correct tool interferes with the elementary lessons.
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True industrial wire markers are time consuming to install and unforgiving when modifications are required. The 3D-printed markers can be quickly added by sliding them over the existing 22 AWG wire ferrules. This allows the markers to fluidly be changed as the learner’s understanding of the circuit changes.
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The 3D-printed markers are relatively inexpensive and can be produced in large quantities on a conventional 3D printer.
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The marker can be reused. Use of a sticker could increase the marker’s service life as opposed to directly writing on the marker. An alternative is to write the node designation on white electrical tape as shown in this article’s examples.
Example 1: Use of the Marker with Single and Daisy-Chained Wires
Figure 3 shows the node identifiers used with dual wire ferrules in a daisy chain configuration. This is a foundational example showcasing the difference between wires and nodes. In this example, all daisy-chained wires share a common node.
Errors in student thinking are revealed if each wire receives a new consecutively numbered node marker. Stated another way, the example shows how a single node can extend horizontally across many physical wires. In Figure 3, all wires are associated with the +24 VDC node.
Figure 3: Node markers used in a daisy chain of the +24 VDC supply to a PLC.
Example 2: Pushbutton-Based Exclusive OR Gate
Figures 4 and 5 present an exclusive-or (XOR) gate constructed using two pushbuttons. This example uses two independent rungs. Depending on the state of the pushbuttons, each rung may provide continuity, thereby turning on the green panel lamp.
This example exposes the concept of the vertical extent of a node up and down both the wire diagram and physical wiring. Observe that Rung 2 Node 1 (R2N1) is the only independent node on Rung 2. All other nodes are either connected to the +24 VDC supply node or to R1N2. The primary lesson is that nodes from upper rungs can “reach down” to other rungs.
Figure 4: A pushbutton-based XOR gate with node markers.
Figure 5: 3D-printed markers used for an XOR gate constructed from pushbuttons.
Example 3: Start/Stop Latch
The wire diagram for a start/stop latch is shown in Figure 6. This is a counterexample to the XOR gate developed in the previous section. It demonstrates that we can have components on Rung 2 that have no independent Rung 2 nodes. In this case, the Rung 2 M1 latch is connected using the R1N1 and R1N2 nodes.
Figure 6: Wire diagram for the start/stop latch with node markers.
Frequently Asked Questions
What are the alternatives to node-based wire labeling?
There are two common options:
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Avoid wire labeling altogether. This is like learning to write computer code without using comments. You can do it, but it misses the opportunity to name the wiring abstraction. Perhaps more importantly, you as the instructor can instantly see errors in student thinking. The daisy chain is a perfect example. Different labels for wires on the same node indicate that the learner is conflating wire identification and node identification.
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Teach wire labels first. This is a perfectly reasonable approach as the preferred wire identification scheme can be taught on day one. However, there will be frustration as students do not yet understand the operation of the circuit. Remember the purpose of the lab is to form student thinking. This includes room for experimentation where students naturally make mistakes. As a result, the wire labels will be added only after the circuit is operational. It is a missed opportunity as wire labeling is not part of the holistic learning process.
Changing node wire labels as the experiment progresses is preferred. This is especially true if the learners are talking amongst themselves about the meaning and boundaries of the nodes.
When should the learner switch to another wire label method?
This is like asking when we should take off the training wheels. We switch methods when the lessons are internalized such that assistance is no longer required. In this case, we look for behaviors that suggest mastery of node-based thinking:
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Without error, the learner will use the same name for all wires in a node. The error will most likely show up in a daisy-chained connection such as when +24 VDC is used for all pushbuttons and switches in a control panel.
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Meter placement to measure voltage is a good gauge, albeit hard to observe. The successful learner will fluidly troubleshoot the circuit. The rigid instance of always moving both meter probes disappears.
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The learner is able to identify the goes-into and goes-out-of the node by proper placement of an ammeter.
If we think in terms of course progression, the switch occurs sometime after control transformers are introduced. At this point the learner should have developed the mental model and had time to reinforce it through Kirchhoff’s voltage law and Kirchhoff’s current law.
Continue Exploring Industrial Control Systems
If this discussion was helpful, you may also want to explore:
DigiKey Navigation
- Full Catalog: Industrial Control & Automation
Related Foundational Articles
Use of an Interposing Relay for Increased Contactor Speed- The Demise of Ladder Logic and the Blue Relay
About This Author
Aaron Dahlen, LCDR USCG (Ret.), is a Senior Applications Engineer at DigiKey in Thief River Falls. His background in electronics and industrial automation was shaped by a 27-year military career as both technician and engineer, followed by over a decade of teaching.
Dahlen holds an MSEE from Minnesota State University, Mankato. He has taught in an ABET-accredited electrical engineering program, served as coordinator of an electronic engineering technology program, and instructed military technicians in component-level repair.
Today, he has returned to his home in northern Minnesota, completing a decades-long journey that began with a search for capacitors. Read his story here.