Monday, July 27, 2009

Shocking experience at the dump station

As we left Westworld this morning, we stopped at the dump station on the northwest side of the park (I believe there is also one just south of the big tent, but it was hard to be certain, whereas the one we used was clearly labeled).

As with many things at Westworld, including all 400 RV pedestals, the dump station was surrounded with four bollards, consisting of 4" or so diameter galvanized pipe driven into the ground, then filled with concrete, about 3' in height. A sensible precaution, given RVers' propensity to run into things with their rigs.

As I was wrapping up the dumping procedure, I had my hand on the bus someplace, and my arm brushed up against one of the bollards. I was quite surprised to get a shock. Hmm. After looking at the bollard and noticing some rough patches where the paint was flaking off, I decided that I must have just gotten scraped a little, and it just felt like a shock. I went back to what I was doing.

A minute or two later, it happened again, this time much stronger. In fact, the shock was so strong that I was reluctant to touch both items at the same time again until I knew what was going on. I finished up with the dumping, and, despite it already being 108° in the shade, got out my cheap backup voltmeter to check it out. Even though I knew intellectually that the bus was insulated from the ground, and therefore nothing on the bus could be creating this problem, my gut instinct was to make certain we did not have an on-board electrical problem.

When I connected the meter between the bus chassis and a bare spot on a bollard, at first I read 20 volts AC, but I knew the shock was stronger than that. After poking the probe around to get through the patina of rust on the bollard, the reading jumped to 239 volts AC, then jumped so high my cheapo meter would not read it -- it just flashed "OL" (overload), which meant it was over 400 volts AC. Wow -- that's a lot of voltage, and no wonder I got a shock.

Nothing aboard the bus produces that kind of voltage (well, OK, the HID floodlights do, internally, but they were off), and I was just about to conclude that the bollards were somehow carrying a voltage, when I realized I was hearing a 60-hertz hum coming from someplace nearby, and it was rather loud. Just then, I noticed that we were right under some high-tension lines.

I had noticed the two sets of transmission lines running across the property several times, but it did not really register that the dump station was right underneath them. The bollards, being metal and driven well into the ground, which, at the dump station, was very wet (I was doing cleanup, and so had the water hose running, washing down the dump hose and the ground all around the dump area) were at ground potential.

The bus, on the other hand, being 13' tall and sitting on rubber tires, was at a much higher potential (more than 400 volts above ground, clearly) sitting there in the enormous electric field of the high-tension lines. It was an eye-opening experience, and I will pay much more attention in situations where we find ourselves parked under transmission lines in the future.

This was also a graphic demonstration for me of something that I've known academically for a long time, and also is drilled into us every year when we re-certify on the Red Cross Emergency Communications Response Vehicles, which have 50' aluminum antenna masts that must scrupulously be kept away from power lines. We're even trained on how to hop out of an energized vehicle, then hop away, feet together, until well clear of the hazard. A difference of only a couple of feet in these kinds of fields can represent hundreds of volts -- enough to stop a beating heart.

I survived the experience to blog another day. But I have to wonder how many other people have gotten a shock while dumping there, and wondered where it came from.

Images uploaded by bre pettis. Illustrations from the book Elektroschutz in 132 Bildern.


  1. did you notify people there of the problems?

    you don't want someone to come by tomorrow and get electrocuted. you wouldn't want that on your conscience.

  2. My goodness - what a close call! Glad you are safe and well.

  3. Whoa... A little too close for comfort, I'd say. Our old bus had grounding issues from time to time, giving our dog quite a yelp when she went up the metal step.

    Not something to play around with. Glad you're alright sean!



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