Electrical Back Feed Question

[SimS]

I have read several recent posts about panel disconects and auto transfer switches,etc. My question is if there was a backfeed from an improperly installed stand by generator during a power failure; how far would the POCO lines be energized? Would it travel beyond the POCO transformer? I don't know if the transformer works in "reverse". BTW I don't have a stand by generator; I was just wondering about electrical operation with the transformer. TIA

SimS

 

[Stuart in MN]

240vac coming out of your generator will backfeed through the transformer. On the utility side it will get stepped up to something in the range of thousands of volts. The actual value will depend on how your local utility operates things, in my area it's typically 7200 volts. As you can imagine, that's something their linemen don't want to come inadvertently into contact with.

 

[wyliesdiesels]

I have read several recent posts about panel disconects and auto transfer switches,etc. My question is if there was a backfeed from an improperly installed stand by generator during a power failure; how far would the POCO lines be energized? Would it travel beyond the POCO transformer? I don't know if the transformer works in "reverse". BTW I don't have a stand by generator; I was just wondering about electrical operation with the transformer. TIA

SimS

No one can answer that because every grid is different.

Could go a few feet to an open cutout or disconnect.

Or several thousand feet to a substation...

But yes, if 240v is applied to the transformer secondary, it will output voltage in reverse, on the primary side. Whatever the primary coil turns ratio is, Could be 4160, 12Kv, etc....

Heres a video for you:

 

[malibu101]

Just wondering......
IF one was to backfeed the utility feed wouldn't that try to power everything connected to the utility lines and cause the generator breaker to trip?

Granted ever backfeeding the utility is very bad for any period of time and could cause injury/death to line workers.

 

[matt_i]

Imo besides protecting line workers from ** kV spikes, the bigger danger is having your generator connected when they turn on the utility power. Its like a lightsaber vs a flyswatter. You will be out of phase with the utility and will be destroyed by its overwhelming EMF.

 

[Stuart in MN]

Just wondering......
IF one was to backfeed the utility feed wouldn't that try to power everything connected to the utility lines and cause the generator breaker to trip?

It depends on what's connected at that particular time. If the power is out, that means some lines are down somewhere, so you could be trying to power the entire neighborhood or you could be trying to power nothing.

 

[alfredeneuman]

There's a good chance the generator would trip it's circuit breaker or stall the generator
because of the transformer's inrush magnetizing current (like a motor's), even with no load on the transformer.

 

[toplessHO]

one of the reasons its not a good idea to power the house thru a dryer cord plugged in to the dryer outlet
IF YOU ABSOLUTELY HAVE TO DO THIS PULL AND SAFETY OFF THE METER FIRST AND TAKE IT INSIDE.ALSO TURN OFF MAIN AT PANEL. there Im done shouting

 

[Bretny]

If you back feed your pannel wrong most likely your generator will be trying to run the whole neighborhood. It cant do that so will just pop the breakers.

 

[Bretny]

You dont need to pull the power meter. The main breaker does the same thing.

 

[mike93lx]

one of the reasons its not a good idea to power the house thru a dryer cord plugged in to the dryer outlet
IF YOU ABSOLUTELY HAVE TO DO THIS PULL AND SAFETY OFF THE METER FIRST AND TAKE IT INSIDE.ALSO TURN OFF MAIN AT PANEL. there Im done shouting

No one that will backfeed is going to pull a meter. That is crazy. Best case, the main will get flipped

 

[pjmariner]

You can back feed legally and easily with an interlock kit and breaker dedicated for backfeeding via your genrerator, and a male NEMA outlet

 

[sberry]

This is a big benefit of being on 200A service vs 400.

 

[rlitman]

...and a male NEMA outlet

Its called an inlet.

 

[pjmariner]

Its called an inlet.

Now I know. And knowing is half the battle

 

[Jack_Toepfer]

You can back feed legally and easily with an interlock kit and breaker dedicated for backfeeding via your genrerator, and a male NEMA outlet

Just did this, and cost roughly $400 with 100' of 10/3. 50-60' in the house through the garage and 30' extension cord to go outside to generator. Once it is installed, you'll never worry about it again (and hopefully never need to use it )

 

[pjmariner]

That 10/3 gets pricey.
My fuse box is in garage right next to garage door so I went out house just above the box.

The interlock was most expensive piece. I think with the 30 foot generator cord I spent about 180. Hopefully I never need it again either but after back to back nor’easters this year it was a must.