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Banana Skins – March 2023 (#417-421)

417.  Mains harmonic distortion from electronic equipment upsets energy providers 

The increasing use of electronic equipment is causing ‘harmonic distortion’ on the UK supply network. This is caused by non-linear loads on the electricity supply system, such as PCs, lighting systems, switch mode power supplies and variable speed drives.

Regulation ER G5/4-1, published by the energy networks association (ENA) is the UK’s instrument to control this distortion and to assist compliance with the harmonised network standards such as EN 50160. ER G5/4-1, which was first published in 2001 and subsequently updated in November 2005, is the UK’s attempt to control harmonic distortion back onto the supply network and is the updated version of the earlier G5/3 which was published in 1976. Ironically, many of those affected by power quality issues remain unaware of the original regulation, let alone the updated version.

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I have personal experience of a number of installations where compliance issues have been tackled badly and the remedial measures have more costly than early preventative considerations. A £50k investment in preventative measures, for example, for example, could have saved a small food and beverage company in the North of England around £1m which they subsequently had to spend on mandatory remedial issues.

One example, in the food and beverage industry, concerns a soft drinks company which was inadvertently creating power quality issues onto the local 1kV supply network and causing domestic lighting in the area to flicker uncontrollably. The first the company knew of this problem was a visit from its electricity supplier threatening to cut them off!

(Extracted from “The Hidden Cost”, Steve Barker, IET Computing and Control Engineering, February/March 2007, pp10-11, https://www.theiet.org. Other very similar articles by Steve Barker on the same subject (compliance with G5/4-1) and containing the same examples include: “The Hidden Cost of Power Quality Problems”, Electrical Engineering, February 2007, pp 36-37, http://www.connectingindustry.com, and “Industry Vulnerable to Hidden Power Costs”, Electrical Review, Vol. 240 No. 3, pp 10-12, https://www.electricalreview.co.uk.)

418.  Crocs slippers can cause ESD interference to hospital equipment

A hospital in Sweden has banned workers from wearing ‘Crocs’ slippers after learning the popular footwear can build up static electricity. 

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After officials at the Blekinge Hospital in Karlkrona determined the comfortable shoes built up so much static electricity they interfered with medical equipment they decided to ban the offending footwear, The Local reported Wednesday. 

The fashion statement-turned-medical problem began in February when a two pieces of respiratory equipment for premature babies shut off for no discernable reason. 

Eventually the machines’ mysterious power outage was linked to the plastic slippers that many staff members wore on duty and the ban was suggested. 

“Everybody generates static electricity. But it usually loses its charge, either by disappearing through one’s shoes or elsewhere,” said Bjorn Lofqvist, a spokesman for the hospital. 

The Local said the slippers were found to be capable of becoming charged with a maximum electrical charge of 25,000 volts. 

(Copied entirely from “Insulating slippers have shocked hospital”, NewsTrack – Quirks, United Press International, UPI, April 19, 2007 12:28 AM http://www.upi.com, sent in by Paul Bertalan of Sensis Corporation on 19th April 2007.)

419.  Portable transmitters could interfere with control of nuclear power plants

Although the power output from handheld RF devices is generally limited to a maximum of 7 watts because of RADHAZ safety constraints, their portability makes them particularly troublesome. As illustrated in Table 2, the higher power hand held devices can easily create electric field levels over 20 V/m. Tests performed by Oak Ridge National Laboratories (ORNL) summarized in Figure 3 indicated that approximately 50% of electronic devices are susceptible to EF levels in the amplitude range from 20 to 50 V/m. Devices tested were predominantly non-RF solid state analogue control systems used in Nuclear Power Plants.

Although operational controls exist for these handheld type emitters, the number of people who carry these devices is great so relying completely on operational constraints in the handheld frequency range is a risk.

(Extracted from “Modern Spacecraft – Antique Specifications”, Ron Brewer, Launch Service Program, Analex Corporation, IEEE International Symposium on EMC, Portland, OR, USA, August 14-18 2006, ISBN: 1-4244-0294-8/06.)

420.  Powerful solar bursts interfered with GPS in December 2006

The National Oceanic and Atmospheric Administration (NOAA) reports that a solar eruption last December affected global positioning systems (GPS) and other technologies using radio waves. That conclusion, based on findings by researchers at Cornell University, were announced on April 4, 2007 at the first Space Weather Enterprise Forum in Washington, DC. This group of academic, governmental, and private sector scientists are examining Earth’s ever-increasing vulnerability to space weather impacts. 

Forecasters from the NOAA Space Environment Center in Boulder, CO observed two powerful solar flares on December 5 and 6, 2006. These violent eruptions originated from a large sunspot cluster. On December 6, a solar flare created an unprecedented intense solar radio burst causing large numbers of receivers to stop tracking the GPS signal. 

“The solar radio burst occurred during the solar minimum, yet produced as much as 10 times more radio noise than the previous record,” according to Dale Gary, Ph.D. of the physics department at the New Jersey Institute of Technology. “Measurements with NJIT’s solar radio telescope confirmed that, at its peak, the burst produced 20,000 times more radio emission than the rest of the sun. This was enough to swamp GPS receivers over the entire sunlit side of the Earth.” 

(Copied entire from: “Powerful Solar Bursts Affected GPS Systems in December”, Interference Technology News, April 20 2007. Also see Banana Skin No. 388, which predicted this problem. Why are so many organisations planning to rely on GPS for safety-critical systems? A quick search through ‘Banana Skins’ should show them what an unreliable system it is.)

421.  Spacecraft interference experiences from Mark Simpson

  • Programs that cut corners usually cut too many and run into serious trouble with interference
  • Checklists are very helpful in preventing missing following one or more good EMC design rules
  • Most interference problems that have occurred could have been caught by using highly skilled and experienced engineers
  • Many engineers have experience limited to a handful of programs, and most problems occur when an engineer works on a program with more stringent and complex requirements than they are familiar with
  • Most programs use requirements and units from last program: ‘Built to boilerplate’, hope it works, test and patch when it inevitably doesn’t work
  • Heritage (legacy) claims of ‘no problems’ are almost always wrong – only a small percentage of problems make it back to current program people (This approach is sometimes called ‘proven in use – Editor)
  • Some failures have been serious, e.g. transmitters jamming sensors; jammed command receivers; premature deployment; failure to deploy
  • Over the past 12 years, 7 programs have each taken more than a year to fix their interference problems
  • Most programs have operational problems caused by interference
  • ESD from spacecraft charging continues to plague programs – sometimes only discovered after several vehicles have been launched
  • One program had to be cancelled due to EMI
  • A payload had to be turned off because it caused massive interference
  • I have personally saved several programs from complete mission loss due to interference problems
  • Independent EMC oversight saves programs
  • Using my ‘lessons learned’ will help you save your program

(From “Speaking the Unspeakable: The Role of Independent Oversight”, Mark Simpson, presented at the Workshop session on “Aerospace EMC at the Centennial of Flight”, IEEE 2004 International EMC Symposium, Santa Clara, CA, August 2004,ISBN (CD-ROM) 0-7803-8444-X, IEEE reference: 04CH37559C .)  


The regular “Banana Skins” column was published in the EMC Journal, starting in January 1998. Alan E. Hutley, a prominent member of the electronics community, distinguished publisher of the EMC Journal, founder of the EMCIA EMC Industry Association and the EMCUK Exhibition & Conference, has graciously given his permission for In Compliance to republish this reader-favorite column. The Banana Skin columns were compiled by Keith Armstrong, of Cherry Clough Consultants Ltd, from items he found in various publications, and anecdotes and links sent in by the many fans of the column. All of the EMC Journal columns are available at: https://www.emcstandards.co.uk/emi-stories, indexed both by application and type of EM disturbance, and new ones have recently begun being added. Keith has also given his permission for these stories to be shared through In Compliance as a service to the worldwide EMC community. We are proud to carry on the tradition of sharing Banana Skins for the purpose of promoting education for EMI/EMC engineers.

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