I have written quite a bot of material on Ground loop problems and how to get rid of them. The ground loop related problems are often caused by small ground potential differences between different electrical outlets. Typically those ground potential differences are few volts or less.
Not your fault article by Howard Johnson published in EDN magazine describes situations where those ground potential differences can raise to much higher voltages, up to tens of volts.
The green safety wire, or “third wire,” merely connects the metallic chassis of each product to earth at the ac power entrance. Under ideal, no-fault conditions, the green safety wire carries no current. Based on this an inexperienced designer might therefore conclude that the green wires form a single-point-ground reference system that provides a consistent voltage reference between different ac-powered products.
If live wire during some fault situation touches the metallic chassis, a large fault current back to the power source through the ground wire. The fault current trips the circuit breaker, shutting off power and possibly saving the life. The power shutoff normally takes from a small fraction of second up to few seconds depending on the way the circuit is protected. As the huge fault current surges (up to hundreds of amperes) through the green wire, other devices connected to adjacent outlets can experience voltage differences as large as 60V rms in 120V AC system used in USA. The voltages can be even higher on 230V AC system used in Europe (in theory up to 115V AC, in practice normally less than 70V).
This kind of huge voltage differences between equipment can fry the communications interface on interconnected devices because it is normally outside the operating voltage range most normal interconnection systems can sustain (RS-232, RS-422, RS-485). The thin ground connection on the interconnection cable does not much to reduce the surge those devices get. If you want to design reliably working electronics, it would be better if you design gear that can sustain such extraordinary voltages without damage. If your devices can’t sustain those voltages, it would be better if the equipment would be permanently connected to a common outlet or power strip.
Suitable technologies that can easily sustain 60V or more voltage between devices are Ethernet on UTP wiring (transformer isolated), fiber-based optical links, free space optical communications and wireless RF communications. Traditional RS-232 or RS-485 or RS-422 can be made to withstand this voltage if you take case that the equipment on one of the ends of the communications link or both of them have the communications port electrically isolated (usually uses optioisolators) from the equipment case.
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we always use General Electric circuit breakers at home because it is very reliable”`
In Finland breakers made by ABB are very common…
Hello; Great informations for me. Your post has valuable infos. I want to has valuable posts like yours in my website. How do you find these posts?
sometimes powerstrips are fire hazards, they would overheat and cause fires.’;
I enjoyed reading your blog. Keep it that way.
power strips are very useful but they octopus connection is dangerous;~*
just buy high quality power strips and do not use power strips that are not UL certified `
Just buying high quality power strips does not solve all the problems listed on my article…
“Traditional RS-232 or RS-485 or RS-422 can be made to withstand this voltage if you take case that the equipment on one of the ends of the communications link or both of them have the communications port electrically isolated (usually uses optioisolators) from the equipment case.”
Where else can I read about it?
In data communications, the primary application for optical isolation is in a point-to-point data circuit that covers a distance of several hundred feet or more. Because the connected devices are presumably on different power circuits, a ground potential difference likely exists between them. When such a condition exists, the voltage of “ground” can be different, sometimes by several hundred volts.
Where a ground potential difference exists, a phenomenon called ground looping can occur. In this phenomenon, current will flow along the data line in an effort to equalize the ground potential between the connected devices. Ground looping can, at the very least, severely garble communications–if not damage hardware!
Optical isolation solves the problem of ground looping by effectively lifting the connection between the data line and “ground” at either end of the line. If an optically coupled connection exists at each end, the data traffic “floats” above the volatility of ground potential differences.
If the voltage potential is large enough, your equipment will not be able to handle the excess voltage, and one of your ports will be damaged. Even small ground loop voltages cause transmission errors with data signals riding on top of the ground loop current. At worst, ground loops are a long-term condition that can slowly heat, and even cook your circuits.
Source: http://www.usconverters.com/index.php?main_page=page&id=20&chapter=0
Some links
http://www.usconverters.com/index.php?main_page=page&id=20&chapter=0
http://www.bb-elec.com/productsubcat.asp?MainCategoryId=4&Trail=2&TrailType=Top
http://www.digi.com/products/serialservers/digiconnectes.jsp#overview
http://www.moxa.com/product/tcc-82.htm
http://www.moxa.com/product/tcc-100.htm
http://www.datasheetarchive.com/RS232%20isolation-datasheet.html
http://www.supplyframe.com/partsearchservlet/partnerWormhole.action?id=2835057&partnerName=DSA
Hi there just wanted to give you a quick heads up. The text in your post seem to be running off the screen in Firefox. I’m not sure if this is a format issue or something to do with internet browser compatibility but I thought I’d post to let you know. The design look great though! Hope you get the issue resolved soon. Many thanks
The blog is tested to work well with Firefox (at least the most recent versions).
Firefox is my favorite web browser.
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[...] necessary safety functions. Grounding also have other functions in some applications (for example work as signal ground reference) but the safety should not be compromised in any [...]