Mysterious Voltage Potential

[HYDL]

We have a project at Yellowstone National Park and the contactor is experiencing a voltage potential issue. It started with a 5 volt potential between metal steps, in contact with the ground and the various job trailers. They turned the power off at the meter pedestal, which disconnected all the temporary power to the job site, but still measured a 5 volt potential between the steps and the trailers. They measured as high as 28 volts between the steps and the trailer. He was able to take care of the step / trailer issue by bonding the step to the trailer.
This issue is now appearing in the Visitors Center even though the building steel is bonded to the UFER ground, which is bonded to the ground rods in the mechanical yard. The shocks in the building have occurred in instances where someone will touch a metal choker and the building steel or standing on the wet floor and touch a metal saw table.

The Serviceman for Power Company was there. To check the potential they drove an independent ground rod and were able to measure 5 volts from the transformer to the ground rod. They then called some engineer for the Park Service who told them, because of glass content in the soil; there was always that 5 volt potential.

In talking with the contactor, it appears that the voltage is more of a static electricity that does not continue to shock.

Do you have any insight as to why they are seeing the voltage potential and what can be done about it?

 

[Skogsgurra]

You do sort of jump into the subject. Not much background information. Also sounds like some of the observations are less relevant. And - what the heck does a contactor have to do with it? Please!

Gunnar Englund

http://www.gke.org

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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

 

[HYDL]

Sorry if the info seems irrelevant....I tried to post what the contractor in the field reported to me. We did the lighting and power system engineering design for the building. The contractor is now installing what we designed....ie lighting, power, special systems. This voltage issue came up and I'm trying to help them figure out what might be going on. So, I was just looking for some insight into the topic of soils, content of soils and how that might be causing the issues they are having.

 

[Skogsgurra]

OK. Understand the "contactor" part now. I suspected something like that.

If someone tells you that you have a constant 5 V voltage because of glass in the soil - you either haven't understood what he is telling you, or he is telling fairy-tales.

Static electricity is not what you have in situations like this. I think it is all about bad grounding, missing bonding or such simple basic things. But, judging from the wording some of your colleagues are using, even basic mistakes can easily turn into something "mysterious". Get an educated electrical engineer there to do a check. Leaving as is can lead to injury or detah. Especially that saw table incident sounds very bad.

In most countries, it is your responsability to report things like these to your superiors if you cannot make your colleagues handle it properly.

Gunnar Englund

http://www.gke.org

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100 % recycled posting: Electrons, ideas, finger-tips have been used over and over again...

 

[HYDL]

I think what they may have going on is a high soil resistivity problem. Do you have any experience with a high soil resistivity and what occurs. I have the lightning protection folks checking that the bonding of the electrodes is complete.

 

[jghrist]

The following links may help:

http://www.strayvoltage.org/

http://www.mikeholt.com/technical.php?id=strayvoltage/technicalstrayvoltagenewslettersmenu

 

[magoo2]

Is it a three-phase service or single-phase (120/240 V)?

Is it supplied from an overhead system or an underground system?

I'm guessing because its a national park it's probably overhead single-phase service.

Did the power company take a reading with the load shut off?

From what to told us, you really don't know where to look. If they had dropped the load and still had 5 V, I'd say to look on the source side of the transformer. Maybe a bad connector somewhere on the neutral conductor. That would be something the power company could check if they drop the load first to see what they get at the transformer.

Looks like more work is needed to see which direction to search.

You might also want to review my recent post on procedures for handling stray voltage associated with residential installations.