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Changing Breaker Box - Looking for Different Perspective

Discussion in 'Electronic Basics' started by emilio_estevez, May 5, 2008.

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  1. My question came up when a friend of mine asked if I could change out
    his Federal Pacific breaker box to a newer, safer one. My background
    is in industrial controls and I don't normally deal with power at the
    service level. I only have about two years experience so as I am now
    trying to learn more on my own, I'm finding a lot of things that don't
    add up.

    I started by doing some research to see what it would take to change
    out a breaker panel in a house without turning off the service power.
    It seems to me that it would not be any different getting shocked by
    one of the mains than it would be to get shocked by the 120V at an
    outlet. Each incoming line is 120V to ground (the same as the power
    at a receptacle) and my body's resistance to ground would be roughly
    the same. And according to Ohm's Law, the current that would go
    through my body would be the same. I don't understand the difference.

    Now obviously I don't plan on attempting this if the risk is actually
    as serious as i've read, and I do realize that even very low voltages
    can kill you if the current is high enough (would normally have to
    break through the skin and into the blood stream where resistance is
    very low), but the question still remains. Am I missing something?
    I've read that if you touch either incoming service line that you will
    most certainly die. Is that just to scare people that don't know
    enough about what they're doing into hiring someone?

    Lastly, I would like to point out that I work on a regular basis
    around 480V / 240V and am quite frankly, scared of being shocked, and
    I take every precaution available (which normally entails shutting off
    the power at its source) before working around any live circuits. I
    also understand that even 120V can definately be deadly, even at a
    receptacle. I only used that as an example because I know people will
    often change them without killing power.

    I'd like to leave this topic as purely hypothetical. Simply an
    example to learn from.

  2. bud--

    bud-- Guest

    The hazard is not just shock. If you short the hot wire to hot, neutral,
    or ground you will get a current of maybe 2,000A up to 10,000A. That
    makes things like screwdrivers evaporate. Worse, they evaporate onto
    your face. Added to the fun is that the transformer protection may allow
    the fault current for an extended time. You -really- don't want to
    change the panel with the wires 'hot'. If you work around 480 you should
    have some familiarity with 'arc flash'.

    An electrician might pull the meter. If you do, you have to be able to
    be sure that kills the power. The utility company may take a real dim
    view of cutting their seal on the meter. You better plan on telling
    them, in advance.

    And service panels have some unique features, like N-G bonding and
    grounding electrodes. Also maybe aluminum wire.

    Another problem is what you do if the wires are too short for the new
    panel as Tim wrote.

    I have read (but do not know) that Cuttler Hammer has replacement 'guts'
    for FPE panels.
  3. Dave

    Dave Guest

    Dude, don't go there. Have you ever heard of anyone changing out their own
    breaker panel, much less doing it live? No? Huh, wonder why that is?

    The power that'll slam into you through 0 or 2 ga wire is HUGE and
    UNFUSED... thousands of amps. The transformer on the pole has overload
    protection, but it won't kick in until WAY after you're dead.

    What you are considering is RIDICULOUSLY DANGEROUS. Trained professionals
    don't do it.
  4. You are right about that. The transformer is only fused at the primary to
    protect it from overloads and malfunction, and many of these "pole pigs"
    are 50 kVA or more. This means that a 120 VAC line to neutral or earth
    current of 500 amperes would just start to make the fuse notice, and the
    instantaneous current could be as high as 5000 amps (half a MegaWatt) for a
    few cycles. Certainly enough to create a huge fireball and hurl globs of
    molten copper and steel at the unfortunate amateur electrician who just
    happened to let a scredriver slip across the mains.

    A friend was working with another experienced test technician, doing
    routine breaker testing in a large facility. Most of the switchgear was
    disconnected, but the other test technician had to do some work in the main
    fuse box, which I think was a 480 VAC feeder with heavy bus bar, probably
    rated at 2000 amps or more. I think he had to tighten a bolt, and normally
    he would have used a wrench that was mostly insulated with rubber tape, but
    he was probably tired and in a hurry, and somehow the wrench slipped and
    landed across the live bus. My friend saw it happen, and turned to the side
    just as the fireball erupted, and it burned much of his face and body. The
    technician who was responsible was badly burned, and soon died from his

    Here is a website with some images and movies of actual electrical arc
    blasts so you can see the "potential" for danger: Note that one of them is "only"
    480 VAC.

    Actually, I changed out the old breaker box in the house where I now live,
    but I was completely remodeling it, and I had the utility company come out
    and pull the meter. I had a separate feeder from my other house next door,
    so I could provide temporary power. I actually located the new box on the
    other side of the wall, next to the meter, inside an enclosed porch, and I
    routed the 100 amp service cable into the new box while it was totally
    dead. Even so, I treated it with respect, and I taped the exposed
    conductors while I relocated them, and removed the tape only when I could
    safely connect them to the main 100 amp breaker. It was several years later
    that I was able to finish the bulk of the work, and I was able to have BGE
    come out and replace the meter. I had tested the installation beforehand by
    patching the other supply onto the mains, and I checked carefully for any
    loose strands of the incoming service cable. Even so, I was a bit nervous
    when the meter was reinstalled, but at least I had a main breaker directly
    on the incoming line. The old breaker box did not have a main breaker.

    More information and videos:

  5. Dave

    Dave Guest

    There was no way I was going to
    Would your wife and kids agree that $1,500 is WAY more than your life is
    worth? Or not...

    Life is full of unavoidable risks, why tempt fate when the odds are against
    you? I doubt the OP was even cognizant of the risk factor prior to his
    post, he is the WRONG person to attempt this... it would be beyond
    "dangerous", it would be reckless and stupid.
  6. Well, I've already gotten a hold of the Electic Company to come out
    and pull the meter. And there have been several things brought up
    that could go wrong that I didn't think of. But... the answer to my
    main question hasn't been answered. I have decided that it is not
    worth doing it live because of several of the possible accidents
    mentioned above. I realize that, because there is basically no
    circuit protection, an accidental short could create thousands of amps
    resulting in an enormous arc flash.

    But, what I still don't understand is when Dave said that, "The power
    that'll slam into you through 0 or 2 ga wire is HUGE". I know that
    size of wire is capable of delivering extremely high currents -- but
    that's what it's capable of doing. Not what it would actually do. If
    someone gets shocked by the 120V at an outlet or switch in their home,
    that wire is capable of delivering 20 amps before the breaker trips.
    But if you get shocked by it, the breaker doesn't trip because the
    resistance of your body keeps the current low. If you're body doesn't
    even trip out a 15A breaker, I don't see how the fact that because you
    use bigger wire, the current that flows with 120V potential, through
    your body (high resistance), to ground is any different.

    Sure there's plenty of reasons not to change a breaker box hot, but i
    still don't see how any of them have to do with the fact that getting
    shocked by the incoming feed is any deadlier than the 120V anywhere
    else. I really believe that it's just a misconception, and that the
    only true danger is the possibility of an arc flash because of an
    accidental short.
  7. bud--

    bud-- Guest

    An additional hazard is in most panels there is a lot of exposed metal
    that is hot. It is real easy to make accidental contact. And easy to
    make contact with larger skin area which means lower resistance. You can
    also get across 240V.
  8. Rich Grise

    Rich Grise Guest

    It's not about getting electrocuted - it's about the explosion of
    copper vapor that happens when you feel the tickle, react, and
    short one of the hots to ground. =:-O

    Be Safe! :)
  9. sparky

    sparky Guest

    About 30 years ago I was employed by a mining company for maintaining
    electric hoisting motors. One of the motors was an 8000 Hp DC motor
    operating from an SCR bank at 1000 VDC. The armature breaker was
    installed in a room about 10 feet square. The door was interlocked so
    the motor could not be energised if the door was open. One day the
    failed. The entire room looked like it had been painted with
    copper. The
    breaker contacts had vaporized and the copper condensed on the walls
    of the room.
    Thank God for interlocks!
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