Reminder: Never connect a generator to home wiring without transfer switch

Thu Aug 26 02:02:38 UTC 2021

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.

https://www.leafelectricalsafety.com/blog/electrical-safety/equipotential-grounding-versus-parallel-grounding

 -mel beckman

On Aug 25, 2021, at 5:31 PM, Amir Herzberg <amir.lists at gmail.com> wrote:

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 :)

--
Amir Herzberg

Comcast professor of Security Innovations, Computer Science and Engineering, University of Connecticut
Homepage: https://sites.google.com/site/amirherzberg/home
`Applied Introduction to Cryptography' textbook and lectures: https://sites.google.com/site/amirherzberg/applied-crypto-textbook<https://sites.google.com/site/amirherzberg/applied-crypto-textbook>

On Wed, Aug 25, 2021 at 1:55 PM Matt Erculiani <merculiani at gmail.com<mailto:merculiani at gmail.com>> wrote:
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.

Ensuring that a generator physically cannot backfeed is just one layer of protection against the already very high risk of the job of a lineman. Then there is, of course, checking for the presence of voltage before starting work, but it's possible for a generator to start AFTER this check.

Another layer of protection is grounding all conductors prior to beginning work, so that if power does come back (via the grid or a backfeed) A: The lineman and bucket is not the best path to ground and B: The source is tripped.

Reading through that forum post, it sounds like that particular contractor had a reputation for lacking proper safety precautions, so one or more safety layers may have been removed, making the risk/impact of any single mistake much greater than it should be.

-Matt

On Wed, Aug 25, 2021 at 11:25 AM Mel Beckman <mel at beckman.org<mailto:mel at beckman.org>> wrote:
Jay,

No, because transformers work in both directions :)

Plus, to the previous commenter that talked about “suicide cords”: they’’re more correctly termed “homicide  cords”:

“ The lineman killed yesterday was working for Pike Electric and picked up a line that was connected to someones house that hooked up a generator and did not disconnect from the distribution system. The linemans name was Ronnie Adams, age unknown. He had two children and a wife. As far as I know he was from Louisiana. They are trying to set up a fund for his family, but nothing I have heard of yet. I will let yall know more as I hear of it. I wish they would really teach folks the proper connection of generators, this was a really tragic and preventable accident. Stay Safe and think about it before you do it.”

https://powerlineman.com/lforum/showthread.php?711-Storm-Death

 -mel

On Aug 25, 2021, at 10:12 AM, Jay Hennigan <jay at west.net<mailto:jay at west.net>> wrote:

On 8/25/21 07:04, Mark Tinka wrote:
On 8/25/21 15:59, Ethan O'Toole wrote:

How would this not load the generator or inverter into oblivion?
Not sure I understand your question. Say again, please.

If you fail to isolate your generator from the incoming utility feed so that you're back-feeding the utility and the power is out for your neighborhood or the whole city, would not the load of trying to light up the whole town completely overwhelm your little generator to the point that it fails, stalls, or trips its own output breaker?

--
Jay Hennigan - jay at west.net<mailto:jay at west.net>
Network Engineering - CCIE #7880
503 897-8550 - WB6RDV

--
Matt Erculiani
ERCUL-ARIN
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