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Banana Skins – October 2022 (#397-403)

397. Experiences of testing aircraft with high intensity radiated fields (HIRF)

During the testing of one aircraft we suffered a very marked and complete electrical failure of the aircraft (much to the alarm of both the test engineers and the cockpit crew) which turned out to be due to the EUT we were testing being next to the ground power supply controller which didn’t like the field we were generating. Since this controller would not be in operation in flight its upset was not critical and it had to be shielded using a sheet of RAM (radio absorber material – Editor) when testing continued.

It’s not just the aircraft that can be upset. One trial kept setting off the hangar fire-alarms to the point where the fire brigade eventually disabled the system and left one fireman, with a hand-held extinguisher and radio, to act as the building fire-alarm system fort the duration of our testing.

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Expect the unexpected – one can often start testing believing nothing is going to happen to the aircraft and be very surprised when it does. When testing a reasonably large (50 seat) turboprop the whole team was caught slightly unawares when it tried to crawl up and over the chocks as our transmissions upset the propeller pitch controller.

(Taken from: “Whole Aircraft HIRF Test Experiences: A Practical Viewpoint”, by Roger Marson, EMC-UK 2006 conference, Newbury, October 17-18 2006.)


398. Checkout terminal display interferes with radio service, FCC close down the store 

A new grocery store had been opened in St Louis, MO. This new “high-tech” (now normal) store included the installation of 15 scanning checkout stands with customer enunciator panels. A week before the big grand opening, store management turned on the new checkout stands to verify their functionality. The function tests carried on the rest of that day and into the next. However, the next morning, a group of men walked in carrying radios and red tags. The checkout stands were red-tagged and turned off. The men left.

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The late Chris Kendall (CKC Laboratories) was called in as an EMC Consultant to find out what was happening and to fix the problem. Chris went to work and found the problem right away. The enunciator panels had a display driver at the bottom of the display and there were 5MHz data lines running around one side of the panel and then returned on the other side of the panel. The men who arrived were, of course, from the FCC. They were upset because a local repeater was being jammed (at around 110MHz). The fix introduced by Chris was to tie a wire to the ground path and lay the wire on top of the clock traces as an image return. Once this was done, the interference problem went away, the red tags were removed, and the store opened. The lesson? Remember Mary and her little lamb… everywhere the signal goes, its ground is sure to follow.

(Taken from “Who are you guys, and why can’t I open my store?” in “Chapter Chatter” by Todd Robinson, IEEE EMC Society Newsletter, Issue 210, Summer 2006. Todd in turn had extracted this item from a compilation of EMC stories presented several years previously by Patrick André of André Consulting, Inc., at a meeting of the IEEE EMC Society’s Seattle Chapter.)


399. HVAC system interferes with TV

In April of 2004 I installed a new HVAC system to include a Honeywell EAC F300 Electronic Air Cleaner. Immediately, I noticed on channel  9 off-air TV lines of ‘snow’. I subsequently found out that the air cleaner was causing this problem. I checked the air-cleaner’s electrical power supply outlet, and it is properly wired and grounded. I have both anew ground to the electrical supply panel and the old one to the cold water pipe. I found a reference to a CORCOM EMI filter Honeywell recommends and installed it. I wired up a metal box, wired it in, tested it with my outlet tester, and it worked for about a day. Now, the snow is back. My wife is broadly hinting if I don’t fix it she will want either cable or a dish. Anyone have any ideas?

(From Interference Technology e-news, October 5th 2006.) 


400. If electromagnetic waves can penetrate walls, think what they can do to your skin

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(We always try to use an amusing or off-beat item for every 100th Banana Skin. Robert Higginson adds (April 6th 2007): Reading what looks like new-age trickery, I put “Thermus Thermophillus” into Google. Some hits include the following. (Quackometer!!!) Post for Tuesday, March 20, 2007 (Very entertaining comments.)

We don’t think that EM shielding manufacturers need worry about losing customers to Clarins, but if people are really that concerned maybe there’s a new market opening up for total-body-covering metallised clothing!)


401. Interference problems with lifts (elevators)

I suppose my two worst ‘banana skins’ were a shopping centre in Leeds and a big manufacturing company in Germany. The shopping centre was a four car VF (variable frequency motor-drive) group of elevators that had been working fine for 3 years and then blew £3,000 worth of central traffic dispatching computer. I was asked to take a look, spent 3 days on site and found 180 earth faults – which was a shock as this installation had been checked for earth loop impedance at my request and passed with flying colours (this was done by a reputable engineering company we all know).

After another £3,000 worth of kit failed again I went back and to my absolute horror I found the 5” mains riser was terminated to a brand new distribution panel being installed while I was on site. The riser went into a gland plate which sat on a cork gasket, nylon insulation washers and powder coated metalwork – no earth conductor at all.

The problem with this is two-fold: firstly, if we suffered a secondary fault such as a door lock short to earth then the elevator could run with the doors open; secondly, the DC bus rises to 600V on each VF drive and could have proved fatal to the users pushing buttons etc. outside the lift. I can recall running into the electrical contractors office and gripping the chief engineer’s lapels – and that’s about all I can recall. 

The second ‘interesting’ site was one for a big manufacturing company in Germany. A whole factory the size of a car plant with automated trains and conveyors would ‘dump’ it’s Allen Bradley PLC software, roughly every week. The company spent a fortune sending engineers out to re-program these huge machines for six months. 

The problem was that the main control system was fed from a supply the other end of the factory and they didn’t want the expense of installing an earth conductor, as one was located next to the control panel. Unfortunately this earth conductor turned out to be the roof lightning conductor connecting to hundreds of square metres of roof lead. 

I recall this day very well as it was the Saturday of the Hillsborough disaster, and I spent most of it sitting down watching German electrical contractors dig floors up. Thank goodness it worked. I did receive a few funny comments about the disaster, and I thought if this modification doesn’t work I’ll be in big trouble. Cross bonding? – none…a long and stressful, but successful trip.

(Sent in by Gary Morgan of Liftstore Ltd, February 2007.)


402. Some more interference problems with lifts

I’ve been doing some EMC training for our customers and one very interesting story came out about a circa 1990’s control system with a VF controller. There’s a notice on the outside of the controller to say no mobile phones because entering the cubicle with a 3G phone causes both IGBT’s to fire at the same time causing a huge bang as two phases join together momentarily before the HRC fuses blow.

All these training days bring out the same stories, you can almost create a tick list for items to check (e.g. a tacho fault will be poor bonding of the trunking runs and pigtails on the screen for the tacho…). From what I can see the two biggest problems are pigtails on the hoist motor terminals combined with poor bonding of the trunking runs.

(Another one from Gary Morgan of Liftstore Ltd, February 2007. Pigtailing cable screens has been deplored by EMC experts and IEC 61000-5-2 for many years – but nevertheless electrical contractors still do it. How long will it take to retrain them all so that fixed installations in Europe stand any chance of complying with 2004/108/EC, as they should from 20th July this year?)


403. Mobile phone masts can interfere with lifts in the same building

Mobile phone masts are something that most people do not want erected close to where they live. As a result of this, phone companies will on occasion approach building owners to see if they would lease space within a building to enable a transmission mast to be erected. If its location is out of sight so much the better as residents will be unlikely to know of its existence and will therefore be unlikely to object. 

An obvious out of the way place in a lot of buildings is a lift machine room. One LEIA member has recently come across a NHS hospital where a mast had been erected on the roof and the cables and associated equipment have been located in what was the lift machine room. The hospital trust erected a partition wall in the machine room so the equipment was in a separate area. Although when in the machine room the mast and equipment were out of sight, the cables for the mast ran along ducts through the machine room with the lift supply cables. The problem came to light when the lift was found to be developing serious faults in its drive and safety systems. On investigation, it was found that interference was being introduced into the lift equipment though the earth cable route of the transmission device. 

There are guidelines for installers of masts for mobile phones base stations but these had not been followed. The most crucial requirements to avoid interference is the separation distances between cables and the separation of earth cables from other common earth points. 

There should not be any equipment related to base stations visible in lift machine rooms. The mobile phone base station aerials should be isolated from earth, but the tower structures they are mounted on had to be at zero potential to earth. This has to be achieved by a large cross-sectional conductor, directly connected to the building earth at the main intake. Any part of the base station that has to be earthed is then connected to this common point. However, the common earth point for the base station must not be connected to the building earth at any other point, such as the machine room lighting conduit. It is then that interference is likely to occur. 

Problems with base station installation should be referred back to the building owner who should instruct the base station owner to get the issue resolved. It is also important that access routes to machine rooms do not necessitate walking close to transmission equipment.

(Copied from “Are You Aware (25)”, March 2006, a publication of the Lift & Escalator Industry Association (LEIA), We are not sure how the above instructions fit with lightning protection requirements. We understand that these days the lifts and escalator industry now does reasonable EMC testing of control systems, including testing with the controller cubicle doors open – to simulate what a site engineer would do. The problem is that older equipment has never been EMC tested to any standard and can cause some very strange and even dangerous behaviour. In the case that gave rise to the LEIA advice above, we understand that the circa-1985 drive system for the lift decided to travel in any direction and at any speed, and did indeed trap a number of people on many occasions.) 

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, 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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