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Power line Backfeed Question…?

J

JRH

Solar Wizard
Joined
Mar 15, 2020
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2,068
Heard about it my whole life …seen it done during many hurricanes growing up …BUT …I always wondered …and I still wonder…

If the grid is on and the power lines ( high voltage ) on the road, is supplying power to the houses that is stepped down at the power poles transformer to be usable ( lower voltage ) by the house …

Let’s say it’s thousands of volts stepped down by the transformer to a couple of hundred volts ..

Ok , now a hurricane hits and knocks out the power..

So Mr home owner hooks the 240 outlet of his generator to the main inputs ( coming from the street) on the outside house disconnect feeding the house breaker panel…
He now has 240 coming in side an everyone is happy … but he also has no transfer switch or safty device to isolate his wiring from the street…

But … while he is powering his house , to my understanding he is also feeding the power back to the power line…back to where the linemen may be working ….

The power coming in to the house through the transformer was STEPPED DOWN when coming in before the hurricane…

When it is back feeding from the gen set , does it STEP UP the voltage back up OR send it back down the street at the 240 v being generated by the genset…?

Does the transformer work both directions…?

So does the lineman worker see a high voltage back feed…? or the 240v the gen set is producing…?

Probably a dumb question ,…but it pops up in my mind now and then.

Thanks J.



.
 
JRH said:
But … while he is powering his house , to my understanding he is also feeding the power back to the power line…back to where the linemen may be working ….
Click to expand...
Correct
JRH said:
When it is back feeding from the gen set , does it STEP UP the voltage back up
Click to expand...
Yes
JRH said:
So does the lineman worker see a high voltage back feed…?
Click to expand...
Yes

Doing this is very dangerous and illegal.
(As in possible incarceration)
 
This is indeed a problem. UL1741 means your inverter (not your generator) will shut down on loss of grid.

Two other solutions: Now your generator is trying to power every house in the neighborhood and it can’t so it trips it’s breakers.

Also linemen are wise to your foolishness and short out any lines that they are working on, which trips your generator breakers.
 
timselectric said:
Correct

Yes

Yes

Doing this is very dangerous and illegal.
(As in possible incarceration)
Click to expand...
Thx… I have a somewhat opposite opinion about doing this than many of the rural people that live near me.. they don’t believe me .
I didn’t know enough to explain it years ago , but now I do…I have just never asked some one that was in that line of work….

No don’t worry…that’s not in the cards for me under any condition unless I bought a big transfer switch and had an electrician come install it..

They are not cheap at all …

👍….J.
 
JRH said:
Thx… I have a somewhat opposite opinion about doing this than many of the rural people that live near me.. they don’t believe me .
I didn’t know enough to explain it years ago , but now I do…I have just never asked some one that was in that line of work….

No don’t worry…that’s not in the cards for me under any condition unless I bought a big transfer switch and had an electrician come install it..

They are not cheap at all …

👍….J.
Click to expand...
A simple breaker interlock is much cheaper. And performs the same function.
(If your service panel has a main breaker)
 
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Well, I can speak to this from experience.

30ish years ago in Guam typhon Omar came through and took out power to the island for weeks.

My roommates and I managed to borrow a generator the aircrew brought back from Japan. The power it put out was 110vac at 50hz. We goosed governor on it to get the voltage up to 120v and close to 60hz.

Anyways, my brainchild roommate took the romex from the outside dryer outlet and just jamed it into the 240 outlet on the generator and started it. It ran for about 10 seconds and our lights flickered as did the neighbors lights. Then fortunatly it died. I flipped the main breaker off and we had power until our string was turned back on. There were 13 strings in the power grid on the island at the time. And we were on the one with the hospital.
 
timselectric said:
A simple breaker interlock is much cheaper. And performs the same function.
(If your service panel has a main breaker)
Click to expand...
I am aware of that feature .. but I have no need to mess with it at all , plus it’s an old breaker panel and a mess… I use the solar set up powering the RV where I live …
I don’t live in the other place …I just store stuff there…
I’m fine if the power goes out ….I have been totally offgrid power for weeks now…

The 20 new panels showed up last week and when I get them hooked up I will have wayyyy more power than I need March thru November

I will probably not turn some on till late fall after testing then.
im over paneling for next winter…with anticipation to meet my needs with a 10% PV production .

Like I said to you last winter, I was seriously under paneled for winter…

Not again ….not again….

J.
 
Unless your transformer was isolated by the lines break, the generator would immediately trip as it would try to power all your neighbors. It might as well be a dead short.

And, linemen either ground out the wires before working on them or they work on them as though they're working on live wires. They don't just trust people not to backfeed.

Not saying anyone should be nonchalant about back feeding. But that's why it's very rare that this kind of accident happens.
 
robbob2112 said:
Well, I can speak to this from experience.

30ish years ago in Guam typhon Omar came through and took out power to the island for weeks.

My roommates and I managed to borrow a generator the aircrew brought back from Japan. The power it put out was 110vac at 50hz. We goosed governor on it to get the voltage up to 120v and close to 60hz.

Anyways, my brainchild roommate took the romex from the outside dryer outlet and just jamed it into the 240 outlet on the generator and started it. It ran for about 10 seconds and our lights flickered as did the neighbors lights. Then fortunatly it died. I flipped the main breaker off and we had power until our string was turned back on. There were 13 strings in the power grid on the island at the time. And we were on the one with the hospital.
Click to expand...
Cool … we lost all power for 4 to 6 weeks in 89 during Hugo …in Charleston SC …it was an eye opening experience that most have never witnessed…

wanna know how to make a prepper out of someone very quick..?

Let them go through several weeks of power outage ( phone , gas , water and food) in a major city…

J.
 
JRH said:
Cool … we lost all power for 4 to 6 weeks in 89 during Hugo …in Charleston SC …it was an eye opening experience that most have never witnessed…

wanna know how to make a prepper out of someone very quick..?

Let them go through several weeks of power outage ( phone , gas , water and food) in a major city…

J.
Click to expand...
I was there for that one.
My company traveled there to help with the repairs for customers, ahead of the utility companies turning sections back on.
 
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timselectric said:
I was there for that one.
My company traveled there to help with the repairs for customers, ahead of the utility companies turning sections back on.
Click to expand...
I was in there sitting on my boat tying up lines …untill at the last second i chickened out and
I hauled ass to shore…

Some that tried to fight the storm drowned when the whole marina washed away into a giant pile of a zillion dollars of messed up Fiberglass and wood and wires…
I got a away lucky that night.
The news said we lost 40,000 telephone poles in 2 hours… and pretty much alllll the trees.
I remember looking at the dark sky and seeing hundred of blue green explosions everywhere…
Them transforme make quite a racket it seems…
Simply amazing event ….

It totally changed my whole life ..I sold everything and moved to the top of beech mtn 2 years later..
To hell with hurricanes ….I have been through 11…Hugo was the last.

Im done them…

J.
 
OK so if the person does the wrong thing and back feeds the house I would think he has just powered up all the homes on his local transformer. Would not the generator overload? Ok maybe 100 led lights would work but then people start turning stuff on when a light comes on.
 
time2roll said:
OK so if the person does the wrong thing and back feeds the house I would think he has just powered up all the homes on his local transformer. Would not the generator overload? Ok maybe 100 led lights would work but then people start turning stuff on when a light comes on.
Click to expand...

Makes sence to me but I don’t know… I have never done it or tried…I would think the power co has some way of thwarting those that do… or attempt it……but I don’t know…
 
JRH said:
Heard about it my whole life …seen it done during many hurricanes growing up …BUT …I always wondered …and I still wonder…

If the grid is on and the power lines ( high voltage ) on the road, is supplying power to the houses that is stepped down at the power poles transformer to be usable ( lower voltage ) by the house …

Let’s say it’s thousands of volts stepped down by the transformer to a couple of hundred volts ..

Ok , now a hurricane hits and knocks out the power..

So Mr home owner hooks the 240 outlet of his generator to the main inputs ( coming from the street) on the outside house disconnect feeding the house breaker panel…
He now has 240 coming in side an everyone is happy … but he also has no transfer switch or safty device to isolate his wiring from the street…

But … while he is powering his house , to my understanding he is also feeding the power back to the power line…back to where the linemen may be working ….

The power coming in to the house through the transformer was STEPPED DOWN when coming in before the hurricane…

When it is back feeding from the gen set , does it STEP UP the voltage back up OR send it back down the street at the 240 v being generated by the genset…?

Does the transformer work both directions…?

So does the lineman worker see a high voltage back feed…? or the 240v the gen set is producing…?

Probably a dumb question ,…but it pops up in my mind now and then.

Thanks J.



.
Click to expand...
Linemen likely are wise enough to work around wires safely but your neighbor or his children may not be. Plus with damage that took out the utility you do not really know the extent of what you might power up. Fires can be caused or people shocked. Though the most common thing would be that you over load your generator and it trips off/explodes.

Yes transformers will step up the voltage if you back feed. This is what happens to those grid tie folks that have interconnect agreements with the utility to net meter.
 
Mattb4 said:
Linemen likely are wise enough to work around wires safely but your neighbor or his children may not be. Plus with damage that took out the utility you do not really know the extent of what you might power up. Fires can be caused or people shocked. Though the most common thing would be that you over load your generator and it trips off/explodes.

Yes transformers will step up the voltage if you back feed. This is what happens to those grid tie folks that have interconnect agreements with the utility to net meter.
Click to expand...
Thanks , I have always suspected it did…but have never really perused the conversation. finally a group who knew the answer ….
 
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