Novice places hand in open panel

homeboundAugust 19, 2010

First off, I leave the major electical to other folks, but let me share what happened tonight. I was at a party to celebrate the completion of a basement project by another young contractor (and was curious to see the work, of course). As I walked into the unfinished area of th basement the homeowner (young guy) was showing off the rewiring of his panel to some other guys and I almost had a heart attack. The cover was off and he was randomly putting his hand on the wiring as he talked - oblivious to the risk. I calmly said as soon as I could "you can't do that, etc...." but he confidently cut me off saying "nah, it's all grounded...." The guy practically was groping the main leads while wearing flip-flops (which may have saved his life somehow)! Maybe he didn't touch both simultaneously, or another combo), but I don't know how he dodged the bullet. It's still all slow-motion to me. I wasn't fast enough, just lucky to not witness something awful.

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If he did not touch anything live AND bare he would not have gotten a shock at all.

You have to consider, there is the chance that he actually knew what he was doing. Then again, he may also be stupid and lucky at the same time.

    Bookmark   August 20, 2010 at 6:51AM
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Not quite sure how equipment grounding is supposed to help a person poking around in a panel...
My money is on stupid and lucky.

    Bookmark   August 20, 2010 at 7:28AM
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He's a guy that knows nothing about home improvement or electrical, for that matter. But help me understand something. For the sake of discussion, if one were to randomly place their hand and fingers into a live panel with cover off, espcially in the upper center where he did, how easily can one get shocked? I thought the main terminals where the service connects to the panel would be live to the touch, not to mention that those main wires are bare at those terminal connections. Isn't that so?

Anyway, I've seen pro's work on live panels before and can't say I've ever seen a guy put there hand in there such as that.

    Bookmark   August 20, 2010 at 7:38AM
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Just to be clear, I'm talking about what the homeowner did, not the contractor, who was in the other room. When the contractor came in after, I told him about it and he replied "maybe I should put the cover back on". Yup.

    Bookmark   August 20, 2010 at 7:58AM
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50's house with 100 amp panel and the main breaker is factory wired. This is an upgrade from original. There are no bare main lugs showing until you pull a breaker.

Previous house had main lugs in the open, no main shutoff on the main panel or under the meter. That was fun to work on.

    Bookmark   August 20, 2010 at 8:25AM
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It is stil only 120 volts, or 240 volts if he manages to touch both legs of the feed (keep one hnd in your pocket).

The larger current availble in the panel has no real effect, since dry skin resistance is pretty high (at least a few 10s of kilo-ohms).

    Bookmark   August 20, 2010 at 6:06PM
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The hazard of electrical shock at 120v really depends on the individual. That voltage (or even less at times) can be seriously dangerous or fatal for someone with heart disease or who is otherwise infirm. Children and the elderly are vulnerable. Anything which reduces the skin resistance, such as moisture, also contributes to the hazard.

I suspect that one reason many pros don't hesitate to work on live circuits is they've been shocked enough times that they know what to expect and how to react. Like martial arts training maybe?

But if you haven't much experience with electrical shock, you don't know how your body will react (no, I'm not suggesting that you experiment).

If you're a healthy adult, your body is dry, you're wearing insulated shoes, and you're not bridging the voltage source with both hands (so that the current path crosses the heart), the risk is minimized, but not small.

If you're on a ladder there's significant danger of falling when you get a surprise shock. This is obviously not good. Other injuries are possible from the reaction to an unexpected shock, even without a ladder.

All that said, sticking your hands into a live panel is something that most of us do with caution, and not when there's the distraction of casual conversation and socializing going on.

Of course, there's the possibility that this guy actually DID know what he was doing. "It's all grounded" might mean that he knew he was touching only neutral and ground connections. (Remember that one of the main lugs is a neutral.)

Hendricus, being a non-pro I've never seen a panel with covered main lugs, but I really like the idea.

    Bookmark   August 22, 2010 at 7:22PM
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The current density required to disturb the pace node of the heart is around 10 mA/cm^2.

That requires a path resistance of well below 12 kOhm including the heart tissue.

While it is possible under the wrong circumstances for this to happen, it is not all that common.

You have a valid point about falling.

Even the mildest shock can surprise someone not expecting it, and cause a fall from a ladder.

Working on hot wiring can be performed safely (the POCO does it all the time) but is not for the inexperienced.

Years ago I had a subcontractor send his apprentice to pull some wire.
He decided to pull it all the way into a hot panel.
He failed to carefully control the separate conductors inside the panel and one found its way to a 3-phase 440 V main lug.
A few feet of the wire disappeared in the flash, luckily he was the only one nearby and received only minor burns.

He learned why you only work in hot panels when absolutely required and that you need to keep track of everything going on (like those wires you are shoving through a clamp into the panel).

    Bookmark   August 23, 2010 at 1:52PM
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Ron Natalie

Hey brick, I had a similar issue. I was feeding liquidtite under a computer room floor. Because of the location, I couldn't pull it, but it's fairly stiff (like 1" stuff) so I was pushing it. What I didn't realize is that it was riding on top of some other ones and went up into the PDU and hit the 480V primary. I wasn't hurt (thanks for the plastic on the outside of the thing) but the nut on the end of the conduit was fused in place. My coworkers put up a sign on the site the next day proclaiming "Ron's welding service -- arc welding a specialty".

    Bookmark   August 24, 2010 at 9:01AM
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I just hate working blind.

I want to see anything that can bite.

I had a building standing engineer once that could not understand why I would not push a new piece of 27 kV primary feed into a hot transformer vault that we could not enter or see into.

    Bookmark   August 24, 2010 at 9:50AM
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