Intermittent 'Network Cable Unplugged' Under Heavy Load: Failing Power Supply
A technician is troubleshooting a workstation that intermittently loses network connectivity. The workstation has an integrated Gigabit Ethernet NIC. During an outage, the technician checks the network adapter status in the operating system and sees 'Network cable unplugged' even though the cable is securely connected to both the workstation and the switch. The technician has already replaced the Ethernet cable, the switch port, and the NIC driver. The issue occurs more frequently when the workstation's power supply is under heavy load (e.g., during gaming). Which of the following is the MOST likely cause?
Quick Answer
The answer is a failing power supply unit (PSU) that cannot deliver stable voltage to the motherboard under heavy load. When the PSU struggles during high-demand tasks like gaming, the integrated Gigabit Ethernet NIC’s physical layer transceiver loses its clean power rail, causing the link to drop and the operating system to report “Network cable unplugged” even with known-good cables and switch ports. On the CompTIA A+ Core 1 220-1101 exam, this scenario tests your ability to differentiate between layer 1 issues (cables, ports) and power-related failures that mimic connectivity problems—a common trap is replacing the cable or driver first. The key clue is the symptom’s correlation with PSU load, not with physical movement of the cable. Memory tip: think “Power under load, link unload”—if the network drops only when the system works hard, suspect the PSU before the patch cable.
⚠ Common exam trap
The trap here is that candidates focus on the cable or switch port because of the 'Network cable unplugged' message, but the key clue is the correlation with PSU load, which points to a power delivery issue rather than a physical cable or Layer 2 problem.
Answer choices
Why each option matters
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
The power supply unit (PSU) is failing and cannot provide stable voltage to the motherboard under load, causing the integrated NIC to drop link.
The intermittent loss of connectivity under heavy PSU load, combined with the 'Network cable unplugged' message despite a known-good cable and switch port, points to voltage instability from a failing PSU. When the PSU cannot maintain stable voltage to the motherboard, the integrated Gigabit Ethernet NIC may drop its link because the PHY (physical layer transceiver) requires a clean power rail to maintain the 1000BASE-T signal. This is a classic symptom of a failing PSU causing link drops under load, not a cable or driver issue.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Electromagnetic interference (EMI) from power cables running near the Ethernet cable is disrupting the signal.
Why it's wrong here
EMI can cause intermittent connectivity but would manifest as packet loss or speed drops, not a complete 'cable unplugged' state. The error indicates the NIC is not detecting any electrical link, which is more likely a power or hardware issue.
- ✗
The workstation has a duplicate IP address on the network, causing intermittent disconnections.
Why it's wrong here
A duplicate IP address produces address-conflict errors and intermittent loss of connectivity, but the adapter would still report a link, not 'Network cable unplugged'. That status reflects physical-layer link loss, consistent with the NIC losing power under heavy PSU load. Duplicate IP diagnosis applies when two hosts share an address on the same subnet.
- ✗
The switch port is experiencing a broadcast storm, flooding the network interface.
Why it's wrong here
A broadcast storm saturates the segment but does not produce a 'network cable unplugged' status, which reports physical link loss. It is tempting because broadcast storms cause intermittent connectivity, and would be correct if the adapter still showed a link and only throughput collapsed.
- ✓
The power supply unit (PSU) is failing and cannot provide stable voltage to the motherboard under load, causing the integrated NIC to drop link.
Why this is correct
Under heavy load, a failing PSU may output fluctuating voltages. If the motherboard's chipset or NIC controller does not receive stable power, it can cause the NIC to reset or lose link, resulting in a 'network cable unplugged' error. The correlation with heavy load points to the PSU.
Quick reference
OSI Model Reference
| Layer | Name | PDU | Key Protocols / Devices |
|---|---|---|---|
| 7 | Application | Data | HTTP, HTTPS, DNS, SMTP, FTP, SSH |
| 6 | Presentation | Data | TLS / SSL, JPEG, ASCII encoding |
| 5 | Session | Data | NetBIOS, RPC, SIP |
| 4 | Transport | Segment / Datagram | TCP, UDP |
| 3 | Network | Packet | IP, ICMP, OSPF — Routers |
| 2 | Data Link | Frame | Ethernet, Wi-Fi, PPP — Switches, Bridges |
| 1 | Physical | Bits | Cables, NICs, Hubs, Repeaters |
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Same concept, more angles
1 more way this is tested on 220-1101
These questions test the same concept from different angles. Work through them to make sure you can recognise it however the exam phrases it.
Variation 1. A technician is troubleshooting a workstation that loses network connectivity intermittently, specifically when the user runs CPU-intensive applications like video rendering. The link light on the network interface card (NIC) turns off during these episodes. The technician has already replaced the Ethernet cable with a known-good cable and switched the workstation to a different port on the same switch, but the problem persists. The same port and cable work fine when tested with a laptop. The workstation has a recently installed high-end graphics card and a 400W power supply that came with the case. Which of the following is the MOST likely cause?
hard- A.Faulty network card
- ✓ B.Insufficient power supply wattage
- C.Outdated network driver
- D.Electromagnetic interference from the GPU
Why B: The intermittent loss of network connectivity specifically during CPU-intensive tasks like video rendering points to a power supply issue. The 400W power supply is likely insufficient to handle the combined load of the high-end graphics card and the rest of the system, causing voltage drops that starve the NIC of power, making its link light turn off. Replacing the cable and switch port with no effect, while the same port works with a laptop, isolates the problem to the workstation's internal power delivery.
JA
Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This 220-1101 practice question is part of Courseiva's free CompTIA certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the 220-1101 exam.