Generator in a outside building and powering the panel...

[GPintheMitten]

electrical - Can I connect ground to neutral in a 3 wire outlet? - Home Improvement Stack Exchange

If you don't have an EARTH wire DO NOT BRIDGE NEUTRAL + EARTH! This is potentially lethal as AC NEUTRAL is -115VOLTS! Earth is used in conjunction with LIGHTNING ARRESTORS and SHORT CIRCUITS prevention mechanisms! If you want earth- you need to UPGRADE your entire electrical system. neutral to ground should be 0 volts. If it's not, then it's not a neutral. For 220v circuits in the US, you have two out of phase hot connections at 110v each in addition to a neutral. That said, any issue anywhere in the wiring could result in an energized ground

The Definition of Alternating Current illustrates a Sine wave of t(time) in + then the same span in - (50/60hz) . Direct Current is always equal to or greater than 0! The very reason Negative AC is lethal if connected in the incorrect manner! eg. Never use AC negative as a radio antenna! Besides, Neutral in AC is only for distinguishing reasons as in theory there is never a + or - pole in AC

"Neutral Wire Facts and Mythology". There is a difference between neutral and hot even in AC circuits. One of the differences is that the neutral is grounded, therefore you shouldn't receive a shock if you touch neutral. Also notice that some plugs are asymmetrical so that you can't reverse the neutral with hot(the reason for this is explained in the document at the beginning).


I don't believe this is up to code, but it will pass the test from a standard outlet tester. The problem I see is if any device plugged into the outlet comes into contact with a ground (e.g. water) and that path is more efficient than going all the way back on the neutral wire through the house wiring, then hot current going through any appliance and onto the neutral would come out the ground and possibly electrocute anyone in that path.

That said, I've seen this implemented and have lived in a home where this was done without dying, or even getting shocked. But the fact that the electrician that used this trick was missing several fingers should give you pause.

Cat driver, he's not asking about a 3 wire sub. He's stated he has 4 wires going to the sub.

 

[aczlan]

Cat driver, he's not asking about a 3 wire sub. He's stated he has 4 wires going to the sub.

Correct. I have 4 wires going to the subpanel (which is currently bonded, but I will get that fixed this winter).
My question is if I can share the neutral and ground from the subpanel with the genset.

Aaron Z

 

[kenmac]

Sounds like you're just back feeding from 1 box to another ?? This will work. I do this from my swimming pool sub panel . Would it pass code. I doubt it. But, It works for me

 

[CobyRupert]

Correct. I have 4 wires going to the subpanel (which is currently bonded, but I will get that fixed this winter).
My question is if I can share the neutral and ground from the subpanel with the genset.

Aaron Z

Yes. Just make sure the neutral of the gen set isn't bonded/jumpered to the genny's frame/ground lug. The ground to neutral bond should only be at 1 spot, which already exists at your main panel. (Unless you install a transfer switch that has a switched neutral, which would be rare, but they do exist.)

 

[CobyRupert]

My inlaws have a barn on the outside of a paved U shaped driveway and a house on the inside of the driveway.
There is a conduit running to the barn that brings power out from the house, it has 3 #6 stranded wires in it for power, neutral and 4th wire for ground.
We are thinking of setting it up to run a generator out there (to reduce sound in the house), would I be able to share the same neutral and ground to feed back to the panel and just pull new wires for the power wires (so that I can install an interlock in the main panel)?
Currently, the generator I would use puts out less than 30 amps, so a 10/3 would be enough (and would fit in the conduit), but I would like to size the wires to run up to a 50 amp generator in the future and while there is space to put in either a 10/3 or 2 #6 wires, I don't think I could fit 3 #6 wires and a ground.

Aaron Z

What type of interlock are you referring to? The danger with generators is not being isolated from the utility line (i.e. running generator with your main panel main circuit breaker feeding into the utility line). This presents a danger to utility linemen who may be working on the line. The problem you have is wanting the sub-panel's breaker on when you have both utility power and when you are using it to back-feed the main panel (if that is what you are suggesting?).

 

[GPintheMitten]

If you read his post carefully you would see that he wants to run 2 hot leads from the main braker panel that would be bavkfed with the genny and he wants to install a interlock for the main disconnect and the genny backfed breaker in the same main panel. Its just that the wires from the gen are going to share the conduit between the house and barn.

 

[aczlan]

What type of interlock are you referring to? The danger with generators is not being isolated from the utility line (i.e. running generator with your main panel main circuit breaker feeding into the utility line). This presents a danger to utility linemen who may be working on the line. The problem you have is wanting the sub-panel's breaker on when you have both utility power and when you are using it to back-feed the main panel (if that is what you are suggesting?).

A physical interlock that will keep the genset breaker and the main breaker from being on at the same time.
My plan is to run new power wires (red/black) from the subpanel to the main panel, share the neutral and ground wires and just use the subpanel as a junction box, the generator will not connect to any breakers in the sub panel.

Aaron Z

 

[aczlan]

If you read his post carefully you would see that he wants to run 2 hot leads from the main braker panel that would be bavkfed with the genny and he wants to install a interlock for the main disconnect and the genny backfed breaker in the same main panel. Its just that the wires from the gen are going to share the conduit between the house and barn.

Exactly in the case of the power wires. My purpose in starting this thread was to see if the neutral and ground can be shared.

Aaron Z

 

[buickanddeere]

if there was male prongs on both ends of the cord then it's dead wrong.

 

[boggen]

have you called around, to see how much it would cost... to get one of them machines, that puts cables under roads, and like? no actual digging at surface it is all jetted through with water / drilling under the surface.

i am a tad iffy on 30 amp generator. they are not that strong, more length of wire ya put on them, the quicker they go down hill.

i can understand putting a cable from main panel in house, to a generator plug on opposite wall of house. so you could just wheel a small generator over and plug it in. but seems a bit extreme placing it over by barn.
placing it in the shed, has some concerns of exhaust fumes / carbon monoxide gas.

when ya get into 50 amp plus, ok i will bite, placing generator out away from house, and by shed (on the outside) in its own little enclosure if need be, i will bite on that.

but for a 30 amp unit, i would say save your cash on wiring, and get a honda unit, they are the quitest units i have found, granted ya pay for brand name with them, but for small generators. they really can not be beat. and i seen same like comments over and over again over the years on the internet and word of mouth from other folks. heck 30amp unit is set outside main door of a 20x24 cabin, and powers cabin, ((completely off grid)) granted only a couple lights, can be on, and needing to turn stuff off to run a small microwave, or run a small a/c window unit, but shrugs. 30amps not that much, and fairly easy to over use them to point ya get brown out condition (not enough power coming out of them) and overload switch gets thrown.

larger diameter wire able to hold a little bit more amps/watts on a generator can go a long ways. been there done that. from regular 12/3 to 12/3 wiring, to extension cords. a small little 30 amp generator just does not have the power to handle long lines of wire when undersized, or barely meet specs for regular 110v stuff.

 

[aczlan]

have you called around, to see how much it would cost... to get one of them machines, that puts cables under roads, and like? no actual digging at surface it is all jetted through with water / drilling under the surface.

I dont need a new conduit, I have a 1 1/4 conduit out the the barn which currently has 3 insulated #6 copper wires and a ground wire in it. The fill table I found says that I should be fine with up to 11 #6 wires in a 1 1/4" conduit. If I have to pull 4 wires instead of 2 wires I will, but if I can run 2 new #6 wires instead of 3 #6 wires and a ground it will be easier to pull and cheaper.

i am a tad iffy on 30 amp generator. they are not that strong, more length of wire ya put on them, the quicker they go down hill.

Hence the reason I am oversizing the wire to make room for a larger one down the road.

i can understand putting a cable from main panel in house, to a generator plug on opposite wall of house. so you could just wheel a small generator over and plug it in. but seems a bit extreme placing it over by barn.
placing it in the shed, has some concerns of exhaust fumes / carbon monoxide gas.
when ya get into 50 amp plus, ok i will bite, placing generator out away from house, and by shed (on the outside) in its own little enclosure if need be, i will bite on that.

The thought down the road is to get something like a MEP-003 which will need to be away from the house. There is a corner of the barn where a generator could be mounted out of the way with a CO2 meter next to it and run the exhaust right outside and have the sound blocked from the house.

Aaron Z

 

[buickanddeere]

I dont need a new conduit, I have a 1 1/4 conduit out the the barn which currently has 3 insulated #6 copper wires and a ground wire in it. The fill table I found says that I should be fine with up to 11 #6 wires in a 1 1/4" conduit. If I have to pull 4 wires instead of 2 wires I will, but if I can run 2 new #6 wires instead of 3 #6 wires and a ground it will be easier to pull and cheaper.

I would be surprised if the electrical authority would allow either the shared neutral or running all conductors in the same conduit. It's what maybe 50-60ft? It's like paying for a 200ft run of 200amp wiring.



The thought down the road is to get something like a MEP-003 which will need to be away from the house. There is a corner of the barn where a generator could be mounted out of the way with a CO2 meter next to it and run the exhaust right outside and have the sound blocked from the house.

The building code requirements to operate a generator inside a building a quit strict and $$$. A generator shack on the side of the building with a roof, two walls and a floor would be better.
I have run Draiger gas tests around running equipment and you would be amazed how much CO there is in and around the area.

Aaron Z

..............

 

[CobyRupert]

If you read his post carefully you would see that he wants to run 2 hot leads from the main braker panel that would be bavkfed with the genny and he wants to install a interlock for the main disconnect and the genny backfed breaker in the same main panel. Its just that the wires from the gen are going to share the conduit between the house and barn.

Ah-ha! Interesting question.
From a practical point:
I don't see any danger with sharing the neutral and the ground as long as the capacity of the generator is equal or smaller than the feed to the subpanel. Presently the #6 neutral wire is (indirectly) "protected" by the (50 amp?) breaker in the main panel that feeds the sub-panel. When used for the generator it will be protected by the 30 or 50 amp breaker of the generator. It's interesting, because when you're running the generator you're using the neutral conductor to return (a smaller possible) neutral current in the other direction, it's not like you're doubling up or adding current on the neutral. There's no danger of it being overloaded. Without looking it up, I believe the ground can be shared.

From a Code compliance point: Wow. The code isn't really set-up for a question like that. There are codes (NEC 200.4 & 210.4, etc..) that say you can't use a neutral for more than one branch circuit without provisions, but your not using it for more than one circuit at a time. It's just that "what that circuit is" changes. It would be interesting to install it and if the inspector has a problem make him cite exactly which code section it violates.

With that being said, there is a code requirement (NEC 310.15(B)(3)(c)) that when you install more than 3 current carrying conductors in the same conduit the allowed ampacity for a given cable size is reduced. 5 conductors means current carrying conductors are rated at 80% of their ampacity. (The "trick" around this is if you based #6 awg ampacity on a 60C insulation rating (55 amps) (because of the terminations (NEC 110.14)) but it's really 75C insulated cable (65amps), you can calculate 80% of the 65amps=52 amps and still be good for a 50 amp breaker.

 

[CobyRupert]

I suppose one could make the argument that when the generator is running this shared neutral violates NEC 300.3(B): "All conductors of the same circuit and, where used, the grounded (neutral) conductor... shall be contained within the same raceway.." in that, although there's only 1 conduit per se, one could argue the neutral of the subpanel feeder is no longer in that raceway, neutral current is now taking the short-cut directly to the generator.
But that's sort of a insignificant mind-exercise/technicality. And also wouldn't apply for nonmetallic conduit. If the inspector has the ability to think-up that logical contortion give him a gold star!

 

[boggen]

pouring a small concrete slab a couple feet wide couple feet long say 4 inches thick, (some 2x4's) and a few bags of pre mixxed concrete. pretty easy job, even if manually mixing it in a wheel barrow.

a couple sheets of plywood and some paint, or a sheet or 2 of metal siding for a metal barn or like. and some 2x4's or 2x2's and you have a mini enclosure / shed / doll house if you will. for generator to set outside. if ya toss in some eye bolt's in while concrete is being poured, you can run a chain through eye bolts and around generator with a paddlock to keep it from being stolen.

working on small engines, (weed eaters, push lawn mowers, etc...) to just driving in vehicles tractors into sheds. exhaust fumes get ugly quickly. and the fumes may not collect in area right were fumes are being created, but be concentrated much more in certain parts of the shed, and move about some with just a smallish fan or little blowing wind / opening a door togo in/out a couple times.

below not best diagram in world. but... *shrugs* maybe some more encourgment in placing genertor outside the shed. if not finding / buying / or building something to enclose generator.

 

[s219]

No one has answered his question if he can use the neutral and ground in the conduit from the main and the sub from his genset.

I can't see why he cant. As he states the are separate at his sub in the barn and bonded at the main.

I am making the assumption that there will be another neutral wire added between the generator and the sub panel as part of this connection. And that neutral is sized the same as the main (or whatever is sufficient to handle the maximum current of the phases and loads of everything). If that's the case, the neutral will only ever see the right flow, and should be fine. The main concern is that the phases/directions are combined OK, and that seems like it will always happen.

But if it was me, I'd put in the proper interlocks and re-use all the wires instead of running two new hots. As long as the barn sub panel isn't needed when running off generator, it seems pretty convenient to use the existing wires....

 

[aczlan]

I am making the assumption that there will be another neutral wire added between the generator and the sub panel as part of this connection. And that neutral is sized the same as the main (or whatever is sufficient to handle the maximum current of the phases and loads of everything). If that's the case, the neutral will only ever see the right flow, and should be fine. The main concern is that the phases/directions are combined OK, and that seems like it will always happen.

Neutral and ground for the run to the genset will match the power output of the genset.

But if it was me, I'd put in the proper interlocks and re-use all the wires instead of running two new hots. As long as the barn sub panel isn't needed when running off generator, it seems pretty convenient to use the existing wires....

The barn subpanel is needed as it feeds the shop, the animal barn (and its water heaters, lights, etc) which could be needed depending on the time of year.

Aaron Z

 

[CobyRupert]

The barn subpanel is needed as it feeds the shop, the animal barn (and its water heaters, lights, etc) which could be needed depending on the time of year.

Aaron Z

....and it still could. Generator plugs into sub panel circuit, sub panel back-feeds main panel when required. Main panel feeds sub-panel when under utility power. A "kirk-key" type interlock at main and sub panel prevents generator feeding utility line. No new wires between subpanel and main panel required.

 

[buickanddeere]

But if it was me, I'd put in the proper interlocks and re-use all the wires instead of running two new hots. As long as the barn sub panel isn't needed when running off generator, it seems pretty convenient to use the existing wires....

So tell me how do you manage interlocks and not have a condition where the generator can be connected direct to the utility ?
The transfer switch has to either be at the utility pole and a pair of conduits run to and from the shed. Or the transfer switch mounted at the shed. With all the utility power being routed to the shed, through the transfer switch and back out a 2nd conduit to the utility pole.

 

[buickanddeere]

....and it still could. Generator plugs into sub panel circuit, sub panel back-feeds main panel when required. Main panel feeds sub-panel when under utility power. A "kirk-key" type interlock at main and sub panel prevents generator feeding utility line. No new wires between subpanel and main panel required.

The Kirk-Key can and does have it's applications but this isn't one of them.