Burned while working on low volt - Page 1
Forum section: electronics / general

author: jmctech
author_rank: Contributor
timestamp: October 12, 2015, 01:21:45 am
content: I work for the phone company, I was working on Wednesday at a customers home and received a burn to my hand when I disconnected their phone drop at the house, initially I had checked the line with our non contact voltage tester and it didn't show any power on the line. I checked it again and it still didn't show power on it. Thinking my tester was bad I hooked a volt meter up and it showed 0.7 ac volts and 0.3 dc. Had the power company come out and check and they replaced the customers power drop saying it was rotted. Went back Friday and checked and it will still burn skin. 2 power techs came with their manager along with myself and my manager. There is no detectable voltage on the line, but if you touch the copper it burns your skin, I even stood on a rubber insulating mat rated to 15kv. We are all at a loss as to what causes this to happen. There are radio towers across the residential road from the customer, but the are supposedly only outputting am radio, which according to the RF safety training I took last month won't cause burns. Anyone got any ideas?

author: IanB
author_rank: Super Contributor
timestamp: October 12, 2015, 01:30:44 am
content: What is meant by "burn"? Is this a tingle, a painful feeling, or actual skin discoloration?

author: LA7SJA
author_rank: Regular Contributor
timestamp: October 12, 2015, 01:34:59 am
content: It sounds like "RF Burns". How many KW and what frequency on the AM transmitter?http://www.hamradioschool.com/t0c07-rf-burn/Johan-Fredrik

author: jmctech
author_rank: Contributor
timestamp: October 12, 2015, 01:35:07 am
content: Actual burns to the skin, discolored and painful, the weird thing is I know what an electric shock feels like as I was an electrician prior to this job, but this just felt like the wire was extremely hot but not live with electricity. It's kind of hard to see with the freckles, but this was actual skin damage

author: gibbled
author_rank: Regular Contributor
timestamp: October 12, 2015, 01:35:25 am
content: RF burns.

author: jmctech
author_rank: Contributor
timestamp: October 12, 2015, 01:42:06 am
content: 1500 am, and according to Wikipedia they use a 50kw transmission during the day

author: NiHaoMike
author_rank: Super Contributor
timestamp: October 12, 2015, 01:45:26 am
content: Prime spot to install a "free energy" gadget?

author: AF6LJ
author_rank: Unknown
timestamp: October 12, 2015, 01:54:46 am
content: Sure enough RF burn...Look around and see which AM, TV, or FM transmitter is near by.

author: LA7SJA
author_rank: Regular Contributor
timestamp: October 12, 2015, 02:07:42 am
content: 1.5MHz 50.000W "across the residential road" = RFBurns. No wonder the customer has problems with the telephone.Johan-Fredrik

author: jmctech
author_rank: Contributor
timestamp: October 12, 2015, 02:10:44 am
content: What scares me the most is I just went through rf training and they told us no safety issue until you get up to microwave transmission, especially if you are not working on the tower itself or at the broadcast equipment with a transmission line open

author: retrolefty
author_rank: Super Contributor
timestamp: October 12, 2015, 02:39:18 am
content: Your not a real HAM radio operator until you have experienced RF burns on your lips from talking too close to the microphone.

author: vk6zgo
author_rank: Super Contributor
timestamp: October 12, 2015, 02:55:27 am
content: Quote from: jmctech on October 12, 2015, 02:10:44 amYour "RF Training" is all about the direct effect of radiated.RF upon your body.RF burns are something altogether different.Even if you don't touch something directly energised,anything metallic within close proximity of a radio transmitting antenna will act as an antenna to some extent,& pick up some RF energy.In most cases,this is not enough to even notice,but fairly close to a high powered Broadcast site,it can cause ,(usually quite minor) RF burnsIn your case,you had a long length of phone line as an "antenna"working against earth,so when you completed a circuit to earth,you got burned.I used to work at a Broadcast site with 55kW & 10kW MF Transmitters feeding a Dual Mast,plus 50kW & 10kW HF Transmitters feeding their own individual antennas.The aluminium trim on the table in the lunchroom of one building would give you minor "zaps",& the telephone in the main building always had 6WF's program at low level in the background(from RF pickup on the phone lines).It actually sounded better than some "music on hold" you hear these days!

author: vk6zgo
author_rank: Super Contributor
timestamp: October 12, 2015, 03:06:40 am
content: Quote from: NiHaoMike on October 12, 2015, 01:45:26 amIt may be an urban myth,but various "oldtimers" swore that it was true.One bloke living across the road from the Broadcast site I described in my last post,is alleged to have set up atuned circuit resonant at 6WF's frequency,in his normally unlighted outside "dunny".This operated a "dial light" bulb ,which enabled him to see what he was doing during nocturnal toilet visits.

author: AF6LJ
author_rank: Unknown
timestamp: October 12, 2015, 04:02:31 am
content: Quote from: LA7SJA on October 12, 2015, 02:07:42 amsurprised that would be all the customer's problems.

author: RickBrant
author_rank: Unknown
timestamp: October 12, 2015, 05:37:58 am
content: The reason you're not measuring it is that you're not using a meter with high enough frequency response on the AC range. Try a scope.

author: Halcyon
author_rank: Unknown
timestamp: October 12, 2015, 05:51:41 am
content: There were cases in the 1930's where people living close to the W8XO 500 kilowatt AM radio transmitter (later reduced to 50 kilowatts) have reported hearing radio transmissions at night through the metal coils in their mattresses and other metal objects.

author: Psi
author_rank: Super Contributor
timestamp: October 12, 2015, 05:52:11 am
content: It seems likely that, by pure coincidence, something is exactly the right length to act as an antenna for a frequency being transmitted by the tower.If you can find the conductor in question you can probably change its length and the problem will go away.You may also be able to solve the problem by adding a capacitor into the mix to detune it.

author: vk6zgo
author_rank: Super Contributor
timestamp: October 12, 2015, 06:58:16 am
content: Quote from: Psi on October 12, 2015, 05:52:11 amThat close,it probably doesn't have to be resonant.A capacitor to earth,or ferrite beads on the phone leadin might work---although such things may not be allowed by the Regulatory Authority.The phone companyshouldbe able to sort it out---I'm amazed that no one among the people the OP called in had enough knowledge to put two & two together!

author: GNU_Ninja
author_rank: Regular Contributor
timestamp: October 12, 2015, 07:26:02 am
content: Quote from: gibbled on October 12, 2015, 01:35:25 amYep, they're RF Burns. I used to work on Radyne 500KHz induction heaters and 27MHz plastic welding equipment. Had quite a few unintentional RF burns in my time

author: Zero999
author_rank: Super Contributor
timestamp: October 12, 2015, 07:47:29 am
content: Quote from: jmctech on October 12, 2015, 01:21:45 amThat would not provide any protection against high frequencies. The capacitance between your body any earth would provide a low impedance path for the RF current.

author: dmills
author_rank: Super Contributor
timestamp: October 12, 2015, 08:36:25 am
content: I used to work on a largish low frequency AM transmitter site, where you could sometimes hear ghostly voices just walking around the site, eventually traced to a rusty chainlink fence around the site (Which also turned out to be the source of a hard to find intermod product).And yea, at sufficient field strength (Or RF voltage) RF will reach out and touch you, I am very surprised that that customers phone worked at all, and was the only problem they had with electronics as from the sound of it they are in the near field.My worst RF burn was a 1KW VHF set, on the bench with yours truly mucking about with the output LPF, phone rang, so I stopped what I was doing, took the call, then turned back and decided I wanted a little more inductance in the filter, so I reached in and squeezed the inductor..... I had completely missed that I had powered up just before taking the call. The worst thing is that you usually don't feel it immediately, and it don't half hurt a few minutes later.Sounds like your RF training was aimed more at the guys working on microwave backhaul dishes and such on the cell towers, rather then being a general RF thing.73 Dan.

author: amyk
author_rank: Super Contributor
timestamp: October 12, 2015, 03:24:37 pm
content: Those crazy Ukranians demonstrate this effect:

author: SeanB
author_rank: Super Contributor
timestamp: October 12, 2015, 05:40:07 pm
content: If you are a phone company you should have some large ferrite rings around, to pop onto the service side of the phone line, winding around 10 turns of the twisted pair through it. That should reduce the music on hold on the line, which normally is charged for if you want the service.Try taking a simple bare neon lamp and hold it near the line, it will glow from the RF induced into the line. Hold a CFL lamp by the glass part and do the same and it will light, and might even have some faint sound of the radio station as well from the ballast area.If they are trying to do DSL on the line you will never get it working reliably until the whole length of line from the CPE to the central office, including the DSLAM, is a buried cable. If there is not DSL and the phone has issues, try adding a DSL line filter to the CPE side, and connect the phone to the phone port. If you have some DSLAM DSL injectors use one, and put it in the service box, where it will attenuate the RF. Connect the ground of this to the service ground, or drive in a ground stake. All costs ( aside from the DSL CPE side filter, will be to the TELCO cost, the radio station probably is grandfathered in.Good reason to listen to This wewek in radio tech, where the last episode ( 276), touched on this a little.http://thisweekinradiotech.com/twirt-home/2015/10/4/twirt-276-wsb-am-transmitter-party.html

author: RickBrant
author_rank: Unknown
timestamp: October 12, 2015, 07:03:28 pm
content: The first college I went to was just a couple of miles downrange from a full-time 50 kW AM station. Their antenna array was six towers - two stacked beams, firing at the city it served. We were between the station and the city. Nobody reported RF burns but their carrier frequency was on every piece of ungrounded metal on the campus... some of the grounded, too. Made the EE labs interesting!The station was allowed to run 50 kW 24 hours, even though it was not a "clear channel" station, because once the signal was past the city the next thing it hit was the Pacific Ocean. So there were no other "local markets" to interfere with. The directionality of that array was astounding; in the wrong direction they were all but inaudible just 30 miles away.

author: AF6LJ
author_rank: Unknown
timestamp: October 12, 2015, 08:38:34 pm
content: The real phone company the one they broke up in the 80s knew how to deal with RF interference problems.

author: Galenbo
author_rank: Super Contributor
timestamp: October 12, 2015, 09:14:26 pm
content: Quote from: vk6zgo on October 12, 2015, 03:06:40 amQuote from: Halcyon on October 12, 2015, 05:51:41 amI saw and heard it myself.In Wavre, Belgium, there are antennas of RTBF. A fluorescent lamp, without anything, is always on there, and the radio could be heard in a metal garage box.

author: vk6zgo
author_rank: Super Contributor
timestamp: October 13, 2015, 03:27:55 am
content: Quote from: AF6LJ on October 12, 2015, 08:38:34 pmSo would have our one,Sue----they actually operated the Transmitters, under contract.Now they are just a money-making machine!They are stuck with owning the copper-wire network,but hate fixing faults.The "Techs" they send out know very little---their training is pretty much "monkey see-monkey do" these days.

author: AF6LJ
author_rank: Unknown
timestamp: October 13, 2015, 03:36:54 am
content: Quote from: vk6zgo on October 13, 2015, 03:27:55 amThat really is a shame.

author: vk6zgo
author_rank: Super Contributor
timestamp: October 13, 2015, 05:06:19 am
content: Quote from: blueskull on October 13, 2015, 04:31:43 amNope!--the Radio Station is operating within its licenced conditions.It was probably there years before there were homes in the area,plus the Phone company should anticipate the possibility of RF on their lines in that close quarters.I think the FCC are still the Regulatory Authority for Phones,too,so any unapproved stuff hung across the linewillbe an FCC violation.The OP didn't say whether the line was under,or above ground.I haven't heard of actual RF burns on underground lines which are the usual practice in Western Australia.Some other Australian States do have above ground ones,so they might have such happenings.

author: Tomorokoshi
author_rank: Super Contributor
timestamp: October 13, 2015, 04:30:08 pm
content: Is it a recent problem?If it is, then how has the weather been over the summer? Has the ground dried out so much that it isn't "ground" anymore?

author: jmctech
author_rank: Contributor
timestamp: October 13, 2015, 06:36:26 pm
content: All the lines are overhead, I was doing some repair work when it happened, the lines should be underground but I don't see that happening, the lines have been there since 1968. I don't know when the station started there.

author: RickBrant
author_rank: Unknown
timestamp: October 13, 2015, 07:41:36 pm
content: Assuming this in the U.S., you can check the station's license info and history at fcc.gov . (Maybe they had a power increase recently?) In the following URL, change "xxxx" to the station's call sign:https://transition.fcc.gov/fcc-bin/amq?call=xxxxe.g.https://transition.fcc.gov/fcc-bin/amq?call=KFIFor FM stations change the "amq" to "fmq".

author: vk6zgo
author_rank: Super Contributor
timestamp: October 14, 2015, 01:28:47 am
content: Quote from: jmctech on October 13, 2015, 06:36:26 pmMost AM Broadcast Sites in Oz have been around since the 1930s,so that would suggest a similar age in the USA.This is going to happen wherever there are High Power Transmitters & overhead lines.It isn't something nasty that this particular Radio station is doing!Your Employer should either know the correct working procedure for such situations,or know where to find it.Unfortunately "Phone Companies" are no longer Engineering oriented,but are profit driven,so your Boss is probably a "suit",not an Engineer.

author: jmctech
author_rank: Contributor
timestamp: October 14, 2015, 03:05:41 am
content: Quote from: vk6zgo on October 14, 2015, 01:28:47 amThat is the exact problem.