New construction. Home is being built within 75ft of a TVA high voltage line (161kv)...construction workers were being shocked by the metal roof. Voltage measurement to ground is around 500v. Would bonding the roof to ground rods eliviate the problem ??
"Hot" roof
- Thread starter augie47
- Start date
Elect117
Senior Member
- Location
- California
- Occupation
- Engineer E.E. P.E.
I would say insulate the roof. Or figure out a way to eat at the electric field prior to the charge being on the roof.
If the electric field being generated by the wire is enough to induce voltage than making the building a better reference to ground might not help. It could keep the roof at a closer voltage to zero and mitigate the issue but so would putting in random steel beams closer to the line to eat at the electric field.
Do you know what direction the line is in? Like the vector. So would the building's roof be 75' east of the closest conductor and then 100ft up or does that 75' include verticality?
I look at it like a faraday cage but your walking on the cage.
If the electric field being generated by the wire is enough to induce voltage than making the building a better reference to ground might not help. It could keep the roof at a closer voltage to zero and mitigate the issue but so would putting in random steel beams closer to the line to eat at the electric field.
Do you know what direction the line is in? Like the vector. So would the building's roof be 75' east of the closest conductor and then 100ft up or does that 75' include verticality?
I look at it like a faraday cage but your walking on the cage.
Elect117
Senior Member
- Location
- California
- Occupation
- Engineer E.E. P.E.
You know what. Maybe try reducing your ground impedance. Thought I would probably try to utilize some type of rod to capture or eat away at the field.
I found this from a old online document.
"An electric field is stopped by ground and can be shielded by enclosing it within a grounded metallic object. Trees, bushes, houses, etc., will also significantly attenuate electric fields.3Two electric fields may tend to add together or cancel each other depending upon whether they are in the same or opposite directions.4Electric fields will induce a charge on ungrounded metallic objects within the field. Thus, electric utilities take precautions to ground fences and metal buildings that are very close to transmission lines"
I found this from a old online document.
"An electric field is stopped by ground and can be shielded by enclosing it within a grounded metallic object. Trees, bushes, houses, etc., will also significantly attenuate electric fields.3Two electric fields may tend to add together or cancel each other depending upon whether they are in the same or opposite directions.4Electric fields will induce a charge on ungrounded metallic objects within the field. Thus, electric utilities take precautions to ground fences and metal buildings that are very close to transmission lines"
synchro
Senior Member
- Location
- Chicago, IL
- Occupation
- EE
I would try bonding the metal roof to a single standard length ground rod.
Then bring a wire from a shallow ground rod on the side of the house opposite to the high voltage line just for reference purposes. Measure the voltage between this wire and the ground rod that was bonded to the roof. That way you can see what you are up against to determine if more extensive measures are needed. Measuring the current on the wire bonding the roof would be helpful to understand the situation. Start with a standard clamp meter on the most sensitive scale, and then use a leakage type clamp meter if a higher sensitivity is necessary to observe the level of current flowing.
Then bring a wire from a shallow ground rod on the side of the house opposite to the high voltage line just for reference purposes. Measure the voltage between this wire and the ground rod that was bonded to the roof. That way you can see what you are up against to determine if more extensive measures are needed. Measuring the current on the wire bonding the roof would be helpful to understand the situation. Start with a standard clamp meter on the most sensitive scale, and then use a leakage type clamp meter if a higher sensitivity is necessary to observe the level of current flowing.
- Location
- Illinois
- Occupation
- retired electrician
Is the structure outside of the power line easement?
Then when your done power your landsacpe lights off it.
synchro
Senior Member
- Location
- Chicago, IL
- Occupation
- EE
Then when your done power your landsacpe lights off it.
I've heard of cases where people were taking power from metal structures near transmission lines. I think something would be needed to limit the voltage though. Maybe a small transformer or reactor that goes into saturation at a low enough voltage, assuming that there's enough current to energize it. Possibly something solid state but it would have to be rugged enough. Of course, I don't approve of this.
Joe.B
Senior Member
- Location
- Myrtletown Ca
- Occupation
- Building Inspector
hbiss
EC, New York NEC: 2017
- Location
- Little Falls, New York NEC: 2017
- Occupation
- EC
Who the heck would want to live in a house like that? I can't imagine what would happen to electronics and induced voltage on the NM. Interested to see how the AFCI and GFCI breakers will behave.
I suggest tin foil hats with ground leads, perhaps ankle bracelets also.
-Hal
I suggest tin foil hats with ground leads, perhaps ankle bracelets also.
-Hal