• Skip to primary navigation
  • Skip to main content
  • Skip to primary sidebar
  • Skip to footer
  • Subscribe
  • Advertise

Power Electronic Tips

Power Electronic News, Editorial, Video and Resources

  • Products
    • Power Supplies
    • AC-DC
    • DC-DC
    • Battery Management
    • Capacitors
    • Magnetics
    • MOSFETS
    • Power Management
    • RF Power
    • Resistors
    • Transformers
    • Transistors
  • Applications
    • 5G
    • AI
    • Automotive
    • EV Engineering
    • LED Lighting
    • Industrial
    • IoT
    • Wireless
  • Learn
    • eBooks / Tech Tips
    • EE Training Days
    • FAQ
    • Learning Center
    • Tech Toolboxes
    • Webinars & Digital Events
  • Resources
    • Design Guide Library
    • Digital Issues
    • Engineering Diversity & Inclusion
    • LEAP Awards
    • Podcasts
    • White Papers
    • Design Fast
  • Video
    • EE Videos & Interviews
    • Teardown Videos
  • EE Forums
    • EDABoard.com
    • Electro-Tech-Online.com
  • Engineeering Training Days
  • Newsetter Subscription

Halt and catch fire: The perils of cheap PoE

April 24, 2018 By Lee Teschler

Dave Jeskey tells an interesting story about what happened when an LED lighting company operated a few of its products in a test chamber. The RJ45 plugs, used for making a connection to a Power over Ethernet cable, melted. The RJ45 plugs came from Sentinel Connector Systems where Jeskey is director of sales and marketing. When Sentinel tore down and examined the damaged units, the problem became obvious: Cheaply built RJ45 jacks into which Sentinel’s plugs fit.

“There were transformers built into the jacks that had been badly hand-wound rather than machine-wound. They had also Lee-Teschlersubstituted a cheaper ferrite core that was slightly conductive,” says Jeskey. The melting of the RJ45 plug (which had been designed to melt at 250⁰C, more than melting point of tin) had probably prevented the poorly made jack from causing a fire, he says. It let the conductors pull away and disconnect before the heat from bad connections caused more damage.

The near catastrophic failure of that RJ45 jack is a microcosm of the problems that will soon plague PoE installations. New specifications let PoE lines deliver up to 100 W using plugs, jacks and cabling that are similar to those for ordinary Ethernet. But small imperfections and corner-cutting on costs can make for big problems when that much power passes through the relatively small conductors of Ethernet connections.

Corner-cutting on PoE gear is particularly wide-spread among foreign suppliers Jeskey adds. One of the easiest places to cut corners is with gold plating. “The plating on a contact is supposed to be 50 µin. of 24-carrot gold over a minimum of 50 µin. of pure nickel. We’ve studied over 70,000 part numbers and 94% of them failed to meet those minimum standards. I’ve seen parts using as little as 1.5 µin. of gold and even parts with a statement in the specification saying, ‘gold color only.’”

It isn’t just scrimping on gold that is problematic. “RJ45 conductors have a surface smoothness specification. The proper way to realize it is to first electropolish the contacts, coat them with nickel, and then add the gold. Some foreign suppliers will just wire-brush the surface to make it smooth. The brushing creates ridges and valleys which make the connection less reliable,” says Jeskey.

Other problems arise because PoE connections are hot pluggable. Small sparks form when the plug disconnects from the jack. The sparks may cause problems even in well designed connections, he says. Cheap connections are even worse. “Jack contacts are supposed to be phosphor-bronze but some suppliers cheat with brass and other cheaper metals,” he adds. “When you create a spark, it alters the crystalline structure of the contact and eventually makes it brittle. Some equipment makers claim that spark isn’t a problem because it happens away from the data transmission lines. But a spark alters the whole contact, not just the area where it occurs.”

And it isn’t just PoE connections that are problematic. Ethernet cables can contain different wire sizes. “Some companies use 22 gauge wire, which is good if you have plugs and jacks able to handle it,” Jeskey says. “The best-selling cable contains 28-gauge wire. But some foreign suppliers are selling Ethernet cable with much thinner 30 and 32-gauge wire. That is dangerous.”

You may also like:


  • Gallery: Technical highlights of the Electric & Hybrid Vehicle Technology…

  • Gallery: Scenes from Texas Instruments’ power supply design seminar

  • Helpful Tips About Minimum Load & Cross Regulation Specs

Filed Under: Editor's Blog, Featured, IoT Tagged With: sentinelconnectorsystems

Reader Interactions

Comments

  1. Adrian A. says

    May 24, 2018 at 11:22 pm

    oho, and many cables today are found to be aluminium copper-clad, which are about two times more rezistive than copper, and I found even IRON CORE cables, copper platted, which are useless being six-seven times more resistive

Trackbacks

  1. ACRS e-Connect - WINTER 2018 - Australian Cabler Registration Service says:
    July 4, 2018 at 2:39 am

    […] Source: https://www.powerelectronictips.com/halt-and-catch-fire-the-perils-of-cheap-poe/ […]

Primary Sidebar

Featured Contributions

Meeting demand for hidden wearables via Schottky rectifiers

The case for vehicle 48 V power systems

GaN reliability milestones break through the silicon ceiling

Developing power architecture to support autonomous transportation

What makes SiC tick?

More Featured Contributions

EE LEARNING CENTER

EE Learning Center

EE TECH TOOLBOX

“ee
Tech Toolbox: Internet of Things
Explore practical strategies for minimizing attack surfaces, managing memory efficiently, and securing firmware. Download now to ensure your IoT implementations remain secure, efficient, and future-ready.

EE ENGINEERING TRAINING DAYS

engineering
“power
EXPAND YOUR KNOWLEDGE AND STAY CONNECTED
Get the latest info on technologies, tools and strategies for EE professionals.
“bills

RSS Current EDABoard.com discussions

  • 12VAC to 12VDC 5A on 250ft 12AWG
  • Lightbox circuit help
  • Engineer's own PCB layout software guide?
  • LVS Mismatch Error in Simple Layout
  • Does mobility carrier ratio changes with Wn? (0.18um) inverter design

RSS Current Electro-Tech-Online.com Discussions

  • Actin group needed for effective PCB software tutorials
  • How to repair this plug in connector where wires came loose
  • Lightbox circuit
  • Fuel Auto Shutoff
  • Kawai KDP 80 Electronic Piano Dead

DesignFast

Component Selection Made Simple.

Try it Today
design fast globle

Footer

EE World Online Network

  • 5G Technology World
  • EE World Online
  • Engineers Garage
  • Analog IC Tips
  • Battery Power Tips
  • Connector Tips
  • DesignFast
  • EDA Board Forums
  • Electro Tech Online Forums
  • EV Engineering
  • Microcontroller Tips
  • Sensor Tips
  • Test and Measurement Tips

Power Electronic Tips

  • Subscribe to our newsletter
  • Advertise with us
  • Contact us
  • About us

Copyright © 2025 · WTWH Media LLC and its licensors. All rights reserved.
The material on this site may not be reproduced, distributed, transmitted, cached or otherwise used, except with the prior written permission of WTWH Media.

Privacy Policy