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

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1

Currently a problem in the north-east USA, but applicable after every storm.

People in the south have more experience with hurricanes, and are used to this advice. But apparently, some folks up north aren't in practice.

Never connect an electric generator to home electrical wiring without installing a transfer switch to disconnect power from the electric grid. Back feeding electric power into the utility lines is dangerous for the repair crews working on utility lines.

Also, never run a generator indoors or in the garage. Only outdoors 20-feet away from doors and windows.

FCC has activated DIRS reporting for tropical storm Henri. So we should see some communication system disaster reporting this afternoon.

2

Standard advice when you do any kind of distributed or embedded generation outside of the grid.

Mistakes like these are more likely to come from DIY'ers who put in 2hrs of Youtube and think they are suddenly qualified electricians.

Same advice applies to solar or stationery storage inverters. Typically, these are automated enough to disconnect from the grid after an outage, if you don't have a local battery; or the battery inverter will isolate away from the grid in case of grid failure, but still form its own micro-grid for the building. So back-feeding into the grid is not a concern.

But for combustion generators, yeah, have a qualified electrician do the install. Just saves time, money and lives.

Mark.

3

Back feeding electric power into the utility lines is dangerous for the
repair crews working on utility lines.

Same advice applies to solar or stationery storage inverters. Typically,
these are automated enough to disconnect from the grid after an outage,

if

you don't have a local battery; or the battery inverter will isolate

away

How would this not load the generator or inverter into oblivion?

(Just curious, I know people who use a suicide cord usually turn off the main breaker.)

     - Ethan

4

How would this not load the generator or inverter into oblivion?

Not sure I understand your question. Say again, please.

(Just curious, I know people who use a suicide cord usually turn off the main breaker.)

At the home, you typically have someone that is responsible for knowing what to do in case of an outage, and switching over to self-generation. If that person is not there, or has passed out from too many bottles of wine that evening, someone else might think it's just a matter of starting the generator, unwinding a suicide cord and plugging it into the wall - totally forgetting about the main breaker.

You need to make these things fool-proof. We haven't traveled in over a year but the day we do, it's a recipe for disaster if the person that deals with this stuff is on the road when the power goes out back at home.

Mark.

5

How would this not load the generator or inverter into oblivion?

Not sure I understand your question. Say again, please.

If you hook 100KW of neighbors up to your 5KW/20% THD garden generator it would probably trip the breaker, or stall.

I suppose it could be an issue if it was a single house on a branch where the break being serviced was just that branch (rural customers.)

Was just curious why it wouldn't overload the generator trying to power all the neighbors houses if connected to the grid.

       - Ethan

6

If you hook 100KW of neighbors up to your 5KW/20% THD garden generator it would probably trip the breaker, or stall.

Assuming that you don't want to deliberately simulate a utility grid on the same transformer as your neighbors, the bad news is that line workers could be injured by your back-feeding. Not so likely for your neighbors because they wouldn't be touching the lines, but yeah, not great for line workers actually working on them.

At any rate, you will trip any generator once you overload it. Worst case, you'll burn out its electrical components.

I suppose it could be an issue if it was a single house on a branch where the break being serviced was just that branch (rural customers.)

Typical assumption, regardless of it's urban or rural, as each house would have its own main breaker anyway - both at the customer panel, as well as at the utility source point (last one may vary by country).

Was just curious why it wouldn't overload the generator trying to power all the neighbors houses if connected to the grid.

If you did not isolate your self-generation equipment from the grid, then you may very well become a provider for your neighbors all hooked on to the same distribution wiring, or even on the same transformer.

It would likely never work in any meaningful way, and you increase your chances of starting a fire or breaking things irreparably.

AC-coupled grid-tied solar inverters automatically stop making PV power once the grid disappears, to avoid this very problem, if you do not have a local battery to substitute. This is defined under UL 1741 that all major PV inverter OEM's follow. There have been some changes defined under "California Rule 21 Tariff" that ease UL 1741 somewhat, to avoid PV inverters from disconnecting from the grid during an outage in order maintain grid stability, i.e., when a grid provider is accepting significant amounts of feed-in from private or commercial self-generation customers, a sudden disconnect of all that capacity during a main grid outage could make for a very unstable grid due to massive and sudden variations in voltage and frequency.

I'm not yet sure of any other places besides California that implemented this requirement against PV inverter OEM's. I haven't tracked it since 2017. I know that here in South Africa, UL 1741 is still the main and only requirement.

A grid-tied battery inverter will automatically disconnect from the grid when it disappears, so it has no chance of transferring PV or battery energy on to the grid network.

Generators are not usually that intelligent. Some manual switching required to avoid grid back-feed, which was Sean's initial point. If done well, the generator would have an ATS (automatic transfer switch, either integrated or an add-on) to take care of all of this. In the absence of that (due to cost management or a lack of a thorough job), a manual changeover is highly recommended.

Mark.

7

This is why I personally spent the $$ on a proper standby generator with multiple ATS for the multiple panels.

- Jared

8

Same here.

Massively painful, which led to some boring moments testing, testing and more testing. But after 5 months with electricians, electrical certifiers, battery vendors and inverter vendors (and a little voltage/amp sensor to capture slow voltage grid brownouts that kept tripping my battery), it's been solid for nearly a year. And looking good.

I can now travel and not worry about the Mrs. waking me up from my sleep, on the far side of the world :-).

Mark.

9

Back feed is a significant problem but bringing a generator that is not synchronized to the grid can have dramatic results, typically only once

Dave

10

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?

11

Hello Mark,

At the home, you typically have someone that is responsible for knowing
what to do in case of an outage, and switching over to self-generation.
If that person is not there, or has passed out from too many bottles of
wine that evening, someone else might think it's just a matter of
starting the generator, unwinding a suicide cord and plugging it into
the wall - totally forgetting about the main breaker.

At my home, I use this: https://www.amazon.com/gp/product/B00CONE4MG

The interlock kit is installed in such a way that either the main or
the generator circuit breaker is closed. If the main is on, you can't
switch to generator power, and vice versa (see the pictures on the
listing, mine is installed the exact same way).

Thanks,

Sabri

12

Jay,

No, because transformers work in both directions :slight_smile:

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

13

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

14

I think you mean, "Yes, because transformers work in both directions." First of all, I absolutely agree that no one should attempt to energize their home wiring with a standby generator unless there is a proper transfer switch in place. I very much understand the safety concerns.

The question that Ethan raised makes sense, however. If power to several blocks is out and I connect my little 2KW Honda to my house wiring without a transfer switch, because transformers work in both directions my generator will see the load of the whole neighborhood. This will immediately and severely overload the generator and at best cause it to stall out or trip its output breaker, at worst to fail catastrophically.

In the very rare case that the outage is at the fuse on the pole pig feeding just my house or that of me and one or two neighbors, then indeed the generator may continue to run and that transformer will have distribution voltage of 4KV or so on the utility side, a very dangerous condition. That's a pretty unusual situation, however. Typical power outages are substantially more widespread. My little generator would be looking at the load of the entire outage area reflected through the (bidirectional as you note) transformers. The load of half the town will, as Ethan speculated, completely overwhelm any practical residential standby generator to the point that it stops producing power either by failure or by tripping its breaker.

Even if the generator were massive and survived, its branch circuit breaker or the house main would trip long before sufficient power to feed a large area was able to flow back into the utility's wiring.

Yes, connecting a generator without a transfer switch is a horrible idea and likely to get someone killed, agreed.* However, as the vast majority of power failures involve more than a single residence, the generator will fail to produce power immediately anyway due to looking at essentially a dead short.

* Every time I've seen utility workers working on lines that are assumed to be dead, the first thing they do is clamp them to ground to be certain. When the lines are assumed to be live, massive insulation sleeves, heavy gloves, insulated booms and the like are used.

15

So the issue here is even a small 120vac current becomes a very fatal event at 7.2 or 11 or 14.4kV. It’s a safety issue for linepersons doing emergency restoration work.

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16

I know that a nearby house burned down and was blamed on back feeding the grid. I assume that it failed catastrophically. Bad idea all around.

Mike

17

Ok, I'll be the curmudgeon...

Is this really a problem in practice?

Most people I've known who worked around electrical mains etc assumed
the worst at all times and it isn't all that difficult to protect
against as one works.

I realize one can infinitely invoke "better safe than sorry!", "an
ounce of prevention...!"

<OBLIGATORY FUNNY STORY>

Except maybe that one guy at Harvard who came to replace what turned
out to be a 100+ year old, home made, "breaker" which fed our machine
room which was hidden in a narrow dark hallway winding around our
machine room behind an unmarked metal, locked doorway. I had no idea
it existed but we had no power so I called for help.

It was just a single copper bar about the size of a small candy bar
tensioned into hot clips. Probably 400A but who remembers.

He removed the old one confidently enough, grabbed the new one with
rubber-handled pliers and gloves and...

  Him: Have you ever played football?

  Me: Actually, yes, I have, why?

  Him: If something doesn't look right when I put this thing in just
  tackle me clear of it as hard and as fast as you can.

  Me: Um, ok.

It all worked out fine and I wrote a memo that maybe Harvard could
spring for a proper $500 breaker box?

</OBLIGATORY FUNNY STORY>

18

You need to make these things fool-proof. We haven’t traveled in over a year but the day we do, it’s a recipe for disaster if the person that deals with this stuff is on the road when the power goes out back at home.

This is why I personally spent the $$ on a proper standby generator with multiple ATS for the multiple panels.

Yah. I suspect that a fair bit of this depends on where you live. I have a fairly rural house, and the power comes across the (Shenandoah) river, and then down an overhead feed which branches off to 6 or 8 neighbors, before running up the hill to a transformer on a pole near my house. We would lose power around once every 2 or 3 months (trees, wind, snow, etc). We installed a whole house generator (with transfer switch), and … well, actually, just after we did this the local power company did a bunch of maintenance and now the supply is more stable, but still…

This all reminds me that I need to go and do an oil change/maintenance on the generator – it sent me an alert the week before last that it has reached its maintenance interval, but it’s been a bit too hot to do this yet…

W

19

Barry,

It’s really a problem. Several lineman are maimed or killed every year because of DIY ignorance. I’ve already provided one incident. You can easily find more.

It’s virtually impossible for lineman to protect against this risk while working. These guys aren’t idiots, they are highly trained professionals. They make sure power lines are de-energized from the grid before they touch them, but there comes a point where they have to put hands on in order to affect repairs.

It’s while they are doing this hands-on work that some thoughtles homeowner decides to fire up his DIY wrongheaded generator, feeding 120 V backwards through a cascade of transformers to produce 12,000 or more volts. It takes only a few milliamps through the heart to kill someone. But often these accidents result in horrific third-degree burns.

We all know people, and we might even be people, who have home generators. I suspect many of these use direct attach rather than transfer switches. You could help teach them the right thing to do.

-mel

20

Ok, I’ll be the curmudgeon…

Is this really a problem in practice?

Most people I’ve known who worked around electrical mains etc assumed
the worst at all times and it isn’t all that difficult to protect
against as one works.

I realize one can infinitely invoke “better safe than sorry!”, “an
ounce of prevention…!”

Except maybe that one guy at Harvard who came to replace what turned
out to be a 100+ year old, home made, “breaker” which fed our machine
room which was hidden in a narrow dark hallway winding around our
machine room behind an unmarked metal, locked doorway. I had no idea
it existed but we had no power so I called for help.

It was just a single copper bar about the size of a small candy bar
tensioned into hot clips. Probably 400A but who remembers.

He removed the old one confidently enough, grabbed the new one with
rubber-handled pliers and gloves and…

Him: Have you ever played football?

Me: Actually, yes, I have, why?

Him: If something doesn’t look right when I put this thing in just
tackle me clear of it as hard and as fast as you can.

Me: Um, ok.

It all worked out fine and I wrote a memo that maybe Harvard could
spring for a proper $500 breaker box?

</OBLIGATORY FUNNY STORY>

… and my “funny” story.

We used to live in San Jose. There was a large heat-wave, and much of SJC lost power because of A/C load, etc. Anyway, my wife and I go and camp in one of the office conference rooms for a few days because the office still has power and A/C.
Eventually PG&E claims that power is back on our street, so we drive back to San Jose and… no power. I flag down a passing PG&E truck and ask if they know when it will really be back. Lineman says that it is. I say it isn’t. He says it is. I say it isn’t.
He gets annoyed, opens up the pedestal box and sticks a meter in it, and agrees that I have no power. He then sticks the meter across the 800A fuse, and discovers that the fuse blew.
“Ah. I can fix that fer you…” he says, and goes to the back of the truck… “Doh. I’m out of 800A fuses. Um… er… well, here is a 6,000A fuse, that’ll do…”

I briefly question the logic of this (presumably the lines in the ground are sized somewhere around 800-1,200A), but he says that this’ll do, and he’ll come back in the next few days to replace it. I lived there for another 8 or so months, and it was never replaced, but, well,… not my wires, so, um ¯_(ツ)_/¯ I guess…

W