How to feed 100A both ways on same wire..safely

[hobo698]

Hi all

Great Forum!

I'll apologize in advance for the length of my post but I wanted to put as much info about my problem as I could.

I have a garage located about 60 ft from my house.
The wiring in the garage in almost complete other than wind and water power feeds.

There is a 200 amp panel in my house and another 200A in the garage.
The garage is currently fed from my panel with a 30A and a 20A overhead wires. (I was just using 20A but bought a compressor that needs 30 so ran another line)

I've buried a #2 alum. cable from the house to the garage as well as a cat 5, a co-ax, and an 8 pair phone wire.
I would like to feed the garage 100A from the house.

My problem is that I would also like to feed from the garage to the house during power outages from a generator or a battery bank connected to inverters.

I plan to put another panel in the house to isolate certain circuits that I will use during outages as well as a disconnect to make sure power doesn't go back out to the grid.

So, first off, do I need 2 transfer switches?
And if I do, how would I wire them so that it is idiot-proof?

As I said, I have other wires buried as well that I could use to send signals to make it automatic if I have to.

I guess basically I want it set up to be able to throw a switch (or two) so power can travel the opposite way on the same line without having a chance of someone else doing it and putting power both ways at the same time.

It's been a head scratcher for me so far and will accept any thoughts or ideas.

Thanks in advance for any input.

Cheers,
Hartley

 

[ishiboo]

Hi all

Great Forum!

I'll apologize in advance for the length of my post but I wanted to put as much info about my problem as I could.

I have a garage located about 60 ft from my house.
The wiring in the garage in almost complete other than wind and water power feeds.

There is a 200 amp panel in my house and another 200A in the garage.
The garage is currently fed from my panel with a 30A and a 20A overhead wires. (I was just using 20A but bought a compressor that needs 30 so ran another line)

That's in violation of the NEC - you can have only one feeder.

I've buried a #2 alum. cable from the house to the garage as well as a cat 5, a co-ax, and an 8 pair phone wire.
I would like to feed the garage 100A from the house.

My problem is that I would also like to feed from the garage to the house during power outages from a generator or a battery bank connected to inverters.

I plan to put another panel in the house to isolate certain circuits that I will use during outages as well as a disconnect to make sure power doesn't go back out to the grid.

So, first off, do I need 2 transfer switches?
And if I do, how would I wire them so that it is idiot-proof?

As I said, I have other wires buried as well that I could use to send signals to make it automatic if I have to.

I guess basically I want it set up to be able to throw a switch (or two) so power can travel the opposite way on the same line without having a chance of someone else doing it and putting power both ways at the same time.

It's been a head scratcher for me so far and will accept any thoughts or ideas.

Thanks in advance for any input.

Cheers,
Hartley

Feed one from the other, and not both ways. Automatic transfer switches usually feature a mechanical interlock, so that there is no possible way to screw things up if something were to fail. With two switches, relays or contactors in different areas, they could get out of sync.

Your solution if you want the generator at the garage is to run a new underground feeder to the house, and use the phone cable with 2-wire start on the generator/house transfer panel if you want automatic start.

 

[CC1221]

Hobo - I have a somewhat similar situation and here's how I'm setup and what I do. Sorry for the long post on this one as well and I hope this all makes sense!

I have a 200a overhead service to the house that hits a pole in the yard with a main disconnect (breaker) below the meter can. Since there were additional lugs at this disconnect, I ran another 200' of 200a overhead service to the shop from there. Basically I split the main service into two to feed each structure (all of this suggested and OK'd by the electric co-op).

During time of outages, I open the main and all breakers (turn them off) in the house, then I go to the pole in the yard, and open the main (turn it off) so nothing feeds to the grid then I go to the shop drag out my gen set plug it in to a 240v welding plug and fire it up.

I then go back to the house, turn on the main and any breakers that I have deemed essential. Once on gen power, I have about 30a at 240v available which I have through trial and error, figured out that I can run pretty much anything I NEED in the house plus the freezer and frig in the shop without issue.

I have this process listed out on a sheet of paper that hangs on the fridge in the house and have marked all of the "essential" breakers in the house, pole, and shop so that should we have an outage while I'm not home, the girls know what to do and how to do it SAFELY. We also run through this a few times a year and I make them do a "hands on" run through so they don't forget how it's done correctly. This also gives the gen set a good workout in times when it's not critical.

As far as I can tell, the biggest difference from my setup and yours is that if you feed your shop from a 100a breaker in the house panel the only thing you would do different is that you would NOT turn on the main in your house when on the gen set to isolate everything from the grid. If you are going to have a stand by gen set that starts and runs automatically, then of course there will be the need for additional transfer switch(s) and since I've not had any first hand experience with an automatic system, I won't comment on how or the best way to accomplish that!

 

[Aceman]

I go to the shop drag out my gen set plug it in to a 240v welding plug and fire it up.

Using a suicide cord with a 3 wire welder recep(not even a 4 wire!) and no proper transfer switch is the farthest thing from safe. I quit reading your post after I saw this.....

 

[CC1221]

OK - Aceman is correct and I misspoke, it should read gen plug (sorry, I type faster than I think sometimes). The gen plug is a dedicated plug in my shop for the gen set and it IS a 4 wire setup.

 

[ishiboo]

OK - Aceman is correct and I misspoke, it should read gen plug (sorry, I type faster than I think sometimes). The gen plug is a dedicated plug in my shop for the gen set and it IS a 4 wire setup.

Doesn't matter what you call it... still not correct nor safe!

 

[pattenp]

Aside from the gen question, #2 al is not suited for 100A when used for a branch feed per the NEC, 90A is max. And in some install methods it may only be used for 75A.

 

[nehog]

You cannot do what you want with the generator with a single feed. Period.

And aluminum #2 cannot be used for a 100 amp feed, it is too small.

You cannot dual feed the building.

 

[hobo698]

I agree, I can't have a dual feed.
That's why I want to get rid of it.

I'm in Canada and as far as I know a #2 aluminum (direct burial cable but I put it in PVC) is good from one panel to another (fixed) for 100A.
It was rated at 125A but I was told they only use it for 100A
The entire run is less than 100 Ft.

Ishiboo, as you said "With two switches, relays or contactors in different areas, they could get out of sync."

I've been told that and was just trying to find a way I might switch it on the one cable....cheap out I guess.
I know another cable would solve the problem but I live on a rock pile and another trench across the lawn and driveway isn't likely to happen for a while.

So, by the sounds of it, I am going to feed the garage on the cable that's there.
Then put a transfer switch and panel in the house to hook the generator into, on an above ground cable, when I need it once or twice a year.

I'll be a while before I am making more 'free' power than I can use in the garage anyway.

I don't want to rely on a piece of paper telling me or anyone else how to use it because I've seen that go bad before.
I work away some times and don't want anyone to have any chance to screw it up and feed both ways or out to the pole.

Thanks everyone.
Cheers

 

[theoldwizard1]

The entire run is less than 100 Ft.
.
.
.
Then put a transfer switch and panel in the house to hook the generator into, on an above ground cable, when I need it once or twice a year.

You did not mention what size generator you have (or are going to buy), but a typical generator is usually less than 7000 watts, continuous.

The simplest thing to do is buy 100' of 10/4 "cordage" install the appropriate plugs and use that.

 

[Herb67SS]

Direct burial cable in conduit is also a violation where I live. It's called double insulating and I was prevented from doing it by inspectors. Its like running romex inside coduit, aint kosher. I Ran two strands of 550 ft of standard single 0 in 2" conduit for a 100 amp sub panel to. A barn. Put 2 ground rods 8ft apart at the sub panel location. Can't do that any more either. NEC code now requires 3 strands for a ground return to the feed source.

 

[pattenp]

Direct burial cable in conduit is also a violation where I live. It's called double insulating and I was prevented from doing it by inspectors. Its like running romex inside coduit, aint kosher. I Ran two strands of 550 ft of standard single 0 in 2" conduit for a 100 amp sub panel to. A barn. Put 2 ground rods 8ft apart at the sub panel location. Can't do that any more either. NEC code now requires 3 strands for a ground return to the feed source.

The inspector is wrong about the direct bury in conduit. NM can also be put in conduit. They made up their own rules. Also NEC requires 4 conductors for a branch feed, was three. Plus you still need the ground rods at the outbuilding.

 

[ishiboo]

Direct burial cable in conduit is also a violation where I live. It's called double insulating and I was prevented from doing it by inspectors. Its like running romex inside coduit, aint kosher. I Ran two strands of 550 ft of standard single 0 in 2" conduit for a 100 amp sub panel to. A barn. Put 2 ground rods 8ft apart at the sub panel location. Can't do that any more either. NEC code now requires 3 strands for a ground return to the feed source.

Apparently you have an inbred mountainperson for an electrical inspector, that's definitely ********!

 

[rockwithjason]

the big problem i see is the interlock between your main from the utility and the generator feed. in all cases you will have to have some way of making sure that the main is never closed when the generator feed circuit is closed. here at the utility work in we use kirk key interlock for this purpose but it may not be practical for you because of the expense.

here is the bottom line, in order to use the generator you will have to isolate the main from the utility anytime the generator circuit is closed. that will be safe but it may or may not be code compliant. the most direct route would be to install a transfer switch at the main and then make a provision to connect the generator at the same location.

 

[VHF]

Being able to run power both directions on a single feeder without the possibility of energizing two sources at the same time turns out to be a wicked problem.

I think a Kirk Key solution would be really cool, but of course there are no pre-engineered UL-approved solutions so you would be on your own.

The Kirk Key would allow either your main breaker in the house for utility power to be on OR a breaker in the garage to enable backup power, but never both at the same time. To switch from utility power to backup, you would use the following procedure:

1. Turn off the main breaker.
2. Turn and then remove the Kirk Key at the main braker. This would extend a metal pin that would prevent the main breaker from being turned on while the key is removed.
3. Take the key with you to the garage.
4. Insert and then turn the Kirk Key. This will retract a metal pin allow the "backfeeding" breaker in the garage to be turned on, allowing you to put inverter/generator backup power onto your wiring, but not at the same time as utility power is enabled.
5. Turn on breaker when you are ready to supply backup power to your garage and house.

There is only one key, which is either in the house or garage, but not both. Just don't drop the key in the snow on the way to garage!

I have no idea how much a pair of Kirk Key locks cost. It might be more than the cost of running a second feeder back from your garage to the house, at least in AL.

The "generator at a detached garage" scenario is very common. Someone should engineer a pair of pre-made pannels with a Kirk Key and get it UL-approved just for this scenario.

 

[HunterWare]

I had the same desire/plan. What I've had done is two wire runs to the garage. One lineset powers the garage from the house (sub-panel off house panel), and the other lineset powers the house automatic transfer switch from the generator. You have to run twice the cable but otherwise it works fine... just make sure to size appropriately, keeping track of the fact that when on generator the wire length for the garage is effectively double distance.