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Thread: Arc flash damage ongoing in friend's house following the downing of a utility line

  1. #1
    Join Date
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    Arc flash damage ongoing in friend's house following the downing of a utility line

    Hello All:

    I am an electrical engineer and am new to this forum. My area of study is primary solid state low voltage hardware so I need some help from some power guys. My friend has a very odd problem that I am trying to help him to understand. Perhaps I can get some ideas from all of you. Simply, a couple years ago, someone drove their car into a utility pole a few blocks from my friend's home. I am not sure exactly what happened, but I was told that when the pole came down, the ground was "energized" for some period of time. I think this is a 7.2KV system.

    All of the homes on that side of the road experienced instantaneous high voltage damage to their appliances, etc. It was severe. Since the original event a couple years ago, my friend continues to experience damage consistent with a several thousand volt arc flash. I see this is receptacles, switches, appliances, circuit board, exposed branch circuit wires, etc. Products and switches have been replaced several times and the arc flash insult continues. His wiring passed megger testing to 1.1KV.

    Since I know that voltage of the magnitude that can generate such damage can only come from the utility, I am trying to figure out what had gone wrong since the initial faulting of the utility lines. For example, could his pad mount transformer now be intermittent and primary is somehow being shorted directly the the secondary, albeit randomly and intermittently? How about the neutral from the utility as connected to the primary side of his pad mount? Could that be overstressed, degraded and compromised?

    Can anyone help me with a scenario that would allow a multiple KV surge to randomly energize the branch circuits of this home? Also, he reports being shocked when turning on some switches. He also reports dimming of lights and multiple outages.

    Look forward to your responses!

  2. #2
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    Quote Originally Posted by LighningRod View Post
    Hello All:

    I am an electrical engineer and am new to this forum. My area of study is primary solid state low voltage hardware so I need some help from some power guys. My friend has a very odd problem that I am trying to help him to understand. Perhaps I can get some ideas from all of you. Simply, a couple years ago, someone drove their car into a utility pole a few blocks from my friend's home. I am not sure exactly what happened, but I was told that when the pole came down, the ground was "energized" for some period of time. I think this is a 7.2KV system.

    All of the homes on that side of the road experienced instantaneous high voltage damage to their appliances, etc. It was severe. Since the original event a couple years ago, my friend continues to experience damage consistent with a several thousand volt arc flash. I see this is receptacles, switches, appliances, circuit board, exposed branch circuit wires, etc. Products and switches have been replaced several times and the arc flash insult continues. His wiring passed megger testing to 1.1KV.

    Since I know that voltage of the magnitude that can generate such damage can only come from the utility, I am trying to figure out what had gone wrong since the initial faulting of the utility lines. For example, could his pad mount transformer now be intermittent and primary is somehow being shorted directly the the secondary, albeit randomly and intermittently? How about the neutral from the utility as connected to the primary side of his pad mount? Could that be overstressed, degraded and compromised?

    Can anyone help me with a scenario that would allow a multiple KV surge to randomly energize the branch circuits of this home? Also, he reports being shocked when turning on some switches. He also reports dimming of lights and multiple outages.

    Look forward to your responses!
    Sounds like the primary neutral is gone. How old is the cable? Is it concentric neutral or jacketed on the underground padmount? Also, is the primary neutral connected to the secondary some other way than the copper strap supplied? How about at the top of the riser pole? I think the easiest thing to do is to have a good electrician pinpoint the problem to the POCO. May have to give the POCO some ground potential (or step potential) readings to convince them. Being an engineer, you may be able to look up at the riser pole, trace the neutral and see the problem.

  3. #3
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    Jul 2012
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    Indiana
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    Thanks for the prompt response. Do you think that the surge/fault event from the line coming down up the street (and on the feeder for this house) stressed and compromised the neutral? Everything was fine until this event occurred. House is about 12 years old. Not sure what type of cable is on the primary...

  4. #4
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    Quote Originally Posted by LighningRod View Post
    Thanks for the prompt response. Do you think that the surge/fault event from the line coming down up the street (and on the feeder for this house) stressed and compromised the neutral? ...
    No. I think there is a bad connection somewhere, and the pole seems to be the logical place to start. Seems odd that someone would put up with the problem for a couple of years though...

  5. #5
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    Call the POCO utility first. They have special equipment & training to identify dangerous stray distribution voltages.

    Do a google search for "Tic tracer" and you'll see one tool used by POCO linemen. Checking for distribution voltages should only be performed by qualified persons trained in proper use of PPE and hot stick accessories, required to extend distance from tool and user.

    After the POCO's linemen verify service-equipment safety, and rule out open neutrals at the service or energized grounding electrodes from adjacent properties, an inside wireman can be called to rule out energized EGC's or open neutrals in the branch circuits.
    Roger Ramjet NoFixNoPay

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