And it would have only taken that lineman a few seconds to attach a grounding bond to the supposedly dead feeder and transformer before grabbing it bare-handed while speculating as to why it sounds like there's an engine running at constant RPM coming from the house connected to the service drop.
Serious accidents are often caused not by a single failure but several.
It’s the specific combination of current and voltage that is hazardous.
Too much current, through/across the heart, is the main, potentially fatal, hazard. This is why 120v GFCIs trip near 5 milliamps (mA). (20-30 mA in the wrong place is too much.)
A voltage pushes a current through a resistance, be that insulation or skin or soil.
A 12 volt car battery can produce several hundred amps current, enough to weld, if the terminals are shorted together, but a 12 volt battery doesn’t have a high enough voltage to push that current through dry skin. It isn’t dangerous to touch a single battery with dry hands.
Static electricity can be thousands of volts, but at extremely low current. We feel it as the voltage is high enough, but it isn’t actually dangerous (to people; electronic equipment is another matter).
Holding the current constant at the danger threshold (20 mA), we can also look at the power levels for various voltages.
20mA at 120v = 2.4 watts. On the other side of the transformer, 20 mA at 7200v = 144 watts. Conclusion: a single small 150 watt inverter is powerful enough to be create a hazard for linemen working on an islanded section of 7200v powerline.
There are several categories of electrical hazards, as delineated by voltage. Under 50v is generally considered to not be a shock hazard. More details on voltage categories:
https://eecoonline.com/determining-safe-distances-from-electrical-hazards/
More details on GFCIs:
https://en.wikipedia.org/wiki/Residual-current_device
When I was working at the MCI training facility in 1994, I went into the power facility classroom where they had battery strings, rectifiers, transfer switches, etc for students to learn on. I noticed that every 8-10 feet there was an 8 foot long 3/4 inch PVC pipe with about 16 feet of rope threaded through it. When I asked what those were for, the instructor said “We will use those to pull people off the electricity in case anyone gets shocked.”
I never heard that they were used, so that’s good.
—Chris
In theory, Jay is correct, but assuming that theory will always work in practice is, in this case, how linemen end up dead. We’re all well aware of never assuming theory = practice, but admittedly the stakes tend to be a little lower in our world.
right. my grandpa was a high-voltage/wattage engineer. He always said, `an engineer can make an error, but only once’.
Luckily, we can make many errors 
Matt,
The practice you describe, called “parallel grounding”, was flawed and discontinued in the 1970s. It was replaced by equipotential grounding, which protects against accidental grid-delivered voltages, but still can’t protect against customer-delivered voltages.
-mel beckman
Long answered.
Mark.
Yes, I've seen these on some Youtube videos. Work great.
Mark.
Oh dear. This is sad.
There are some people that say UL 1741 is draconian because, in general, linesmen ALWAYS check wires before they start working on them. Even if they did before and there was no voltage, it could easily happen after the fact :-(...
Mark.
The issue is that "it can be".
Solar inverter OEM's have long argued that UL 1741 is too stringent because the assumption is that linesmen always check for voltage on the line before working on it.
Multiple layers of protection are the way to go here. Just as in our industry, just a route-map may not be enough. A route-map + prefix list is a better plan.
Mark.
Yep, because the home generator will be boosted up by the neighborhood transformer, in the back-feed direction.
Mark.
You annoyed him enough to give you a larger fuse, and be done with you :-). Obviously, a safety hazard all on its own. Mark.
Yes, this is a real and dangerous problem. Today. Even with grounding I’m afraid. Source: I’ve been working in an engineering capacity for 27 years and I have the license you’d need to build a nuclear power plant.
Things people underestimate in my opinion: Water. Wind. Transformers. Earthquakes.
—L.B.
Ms. Lady Benjamin PD Cannon of Glencoe, ASCE
6x7 Networks & 6x7 Telecom, LLC
CEO
lb@6by7.net
"The only fully end-to-end encrypted global telecommunications company in the world.”
FCC License KJ6FJJ
Would you care to educate me on this?
If you ground the phases on both sides of the work-site, how are you going to end up being a better path to ground?
-A
Aaron,
If you read back in this thread (using the NANOG mailing list archive), you’ll find this has been explained in great detail. In a nutshell, phase grounding won’t help if a generator is energized from the customer end, and this technique was discontinued in the 1970s due to the many deaths that resulted.
-mel
I’m not sure if it applies to work sites for linesmen, but my limited understanding is that you don’t generally want to ground at more than one point. Mark.
Even they conclude that multiple grounding points should all converge at the main single point.
Grounding is probably the most misunderstood element of electricity. In cases where earth and neutral may be bonded, grounding at more than one point is generally ill-advised.
Mark.
Yes, that...
Mark.
I’ve been following the thread.
If I’m dumb enough to back feed through the transformer into the downstream side of the downed line, how is it going to be a problem if linemen are grounding the phases on both sides of the work area.
That’s what Ben seemed to be implying.
-A
I’ve been following the thread.
If I’m dumb enough to back feed through the transformer into the downstream side of the downed line, how is it going to be a problem if linemen are grounding the phases on both sides of the work area.
I suspect that there is a non-zero amount of “in an ideal, perfect world, when all of the wires are simply lines on a piece of paper, and you can look at them from the comfort of your office chair, this is easy” - but, in the real world, linesmen are rushing about and trying to get the lights back on, cut through the big ash tree that is wedged between the oak and the pole, etc. Even the nice idea of “well, just take the conductos and tie 'em to ground” means that you need to go trudging through hedges and vegetation and tree limbs and lions and tigers and bears, often while it is pissing down with rain or baking hot.
I guess I’m missing how we’ve moved from the “some people are putting their lives on the line, let’s try to make their life less dangerous” into a “weeeeell… if they simply followed these set of steps perfectly at all times, and never made a mistake they’d be fine.”
This is NANOG – I’m sure that we’ve all followed a set of steps perfectly and still managed to redistribute BGP into the IGP, or apply an ACL and lock ourselves out of a box, or types “show run” and watched the router randomly reboot. Now consider this, but with the added drama of potentially ending up dead…
W