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

[aczlan]

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

 

[MossRoad]

Is there a subpanel in the garage?

 

[s219]

With two interlocks you could just use the existing wiring.

I wouldn't pull new wire in the existing conduit unless you were sure it was large enough to satisfy code. There are rules about the number, size, and current load of wires for a giving conduit size. So you often can't add more wires even though there appears to be space.

Also, be sure to factor in voltage drop if there is a distance from barn to house, so that you don't lose a lot of voltage when running off generator. I had about 100' from generator shed to house, and had to upsize wire by two sizes in order to keep voltage drop low. So consider what is needed for the amperage and then figure voltage drop considerations will drive the size larger.

 

[aczlan]

Yes there is a subpanel in the barn. The conduit is 1 1/4" (I think, haven't measured it, but it looks to be 1 1/4").
It is not more than 100' from the barn subpanel to the main panel in the house.
Looking at the fill table at: http://sparkyjohn.com/pipefill/pipefill.pdf it appears that I could put 11 #6 wires in a 1 1/4" conduit, so conduit capacity shouldnt be a problem as long as I can pull them through (I would prefer to avoid removing the existing wires from the conduit if possible).

Aaron Z

 

[aczlan]

With two interlocks you could just use the existing wiring.

How would 2 interlocks 100" apart work?

I wouldn't pull new wire in the existing conduit unless you were sure it was large enough to satisfy code. There are rules about the number, size, and current load of wires for a giving conduit size. So you often can't add more wires even though there appears to be space.

There should be enough space per the table linked in my last post.

Also, be sure to factor in voltage drop if there is a distance from barn to house, so that you don't lose a lot of voltage when running off generator. I had about 100' from generator shed to house, and had to upsize wire by two sizes in order to keep voltage drop low. So consider what is needed for the amperage and then figure voltage drop considerations will drive the size larger.

Per Voltage Drop Calculator at 150' #6 copper in conduit should be good for up to 50 amps of 240VAC with a 3% voltage drop.

Aaron Z

 

[JBourquin]

I can see putting an interlock in the sub panel but wouldn't one in the main panel prevent you from feeding the sub panel when on grid power? Of coarse with only one in the sub panel it's going to prevent you from feeding back to the main panel in the first place.

 

[GPintheMitten]

Here's a thought but I don't know if it violates code or not. Maybe a pro can weigh in on it.

The idea is to bring your subpanel feeder wires to a 4 wire receptical. Then have a short plug to connect your subpanel to the receptical. Then when needing the generator you unplug the barn panel and plug in the generator. Then you wouldn't need to pull any more wires thru the conduit.

I see two problems with this, but with exercising care one could switch over. One is there would be no proper interlock and two the generator input would be a male plug.

As to using the neutral and ground feeding the panel, I can't think of why that wouldn't be appropriate.

 

[CobyRupert]

How would 2 interlocks 100" apart work?

A Kirk-Key set up, one at the main panel utility main breaker, one at sub-panel branch circuit breaker to the genny. The common key to enable the genny breaker is only released from the main panel's main breaker lock when the main is in the off position & vise versa.

 

[jaotguy]

I see two problems with this, but with exercising care one could switch over. One is there would be no proper interlock and two the generator input would be a male plug.

one could also wire a receptacle to the gen set and make a male to male connection cord ( so no male end is "live" by accident)...

 

[buickanddeere]

Here's a thought but I don't know if it violates code or not. Maybe a pro can weigh in on it.

The idea is to bring your subpanel feeder wires to a 4 wire receptical. Then have a short plug to connect your subpanel to the receptical. Then when needing the generator you unplug the barn panel and plug in the generator. Then you wouldn't need to pull any more wires thru the conduit.

I see two problems with this, but with exercising care one could switch over. One is there would be no proper interlock and two the generator input would be a male plug.

As to using the neutral and ground feeding the panel, I can't think of why that wouldn't be appropriate.

Don't even mention such a code violating and dangerous scheme . Somebody looking for the quickest, easiest and cheapest generator connection is going to look for somebody to "approve" such a hazard.
The transfer switch with the interlocked breakers or the double pole/double throw break before make switch has to be together and at the utility common supply to all buildings.