# wiring a detached shed for AC power *and* generator backhaul



## joed (Mar 13, 2005)

No sub panel required for the single circuit you are running. I would run an extra hot and have a multi wire circuit. This would give you 2 20 amp circuits for the shed. Still no sub panel needed. 1" conduit is way more than required for this. 

Plan for generator sounds good .You could run all the wires(power to shed and genreator power) in the same conduit. You could fit them all in a 1" conduit.

Low voltage needs a separate conduit.


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## jbfan (Jul 1, 2004)

I would not protect the feed with a gfci, only the receptacles at the barn.
Everything else looks good.
If you do use a small subpanel and feed it with 240, you need 2 ground rods at the barn.


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## secutanudu (Mar 15, 2009)

Joed and jbfan are certainly more well versed than I, but it sounds good to me too. Excellent planning and well thought out.


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## vsheetz (Sep 28, 2008)

While I was expending money and effort I would consider to put 240 volts to the shed and have a small subpanel there, rather than 120 volts. While you are buying #6 you may find it economical to quantity buy enough to do the 240 volt power to the shed and the genny back to the house.

If no desire for 240 volts, I would add a wire to make it a multi-wire and have two 120 volts circuits as joed suggested.


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## Scuba_Dave (Jan 16, 2009)

My understanding is that you can't have more then 1 feed to a detached structure unless it is a MWBC
Best bet is to put the transfer switch out in the shed
Then run a sub-panel in the shed & feed that with the Gen & thus the house

I think I will probably do this with my Gen since I already have a sub-panel in the shed


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## wrooster (Apr 16, 2010)

Guys,
Thanks for the replies and info above.

Question -- given that I can run everything in one conduit (of course, the AC stuff only, separate conduit for the low voltage) -- what size Schedule 80 PVC conduit do I need for the following:

qty 4 of #12 THHN/THWN (branch circuit, L1/L2/N/GND)
AND
qty 3 of #6 THHN/THWN (generator backhaul, L1/L2/N)
qty 1 of #10 THHN/THWN (generator backhaul, GND)

Thanks!


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## wrooster (Apr 16, 2010)

Scuba_Dave said:


> Best bet is to put the transfer switch out in the shed
> Then run a sub-anel in the shed & feed that with the Gen & thus the house ... I think I will probably do this with my Gen since I already have a sub-panel in the shed


I don't see how I could put the transfer switch out in the shed, unless this is just a terminology thing.

The type of transfer switch I am talking about sits adjacent to your main breaker panel, and selected circuits from the panel (up to the ampacity or positions of the transfer switch) are brought out to the transfer switch. The position of the transfer switch determines whether these circuits are energized by either the utility power or generator power. 

That said, in order to put this type of transfer switch out at the shed, LOTS of branch circuit wires would have to be extended out to the shed. I don't think this is a good idea at all, and I would never take this approach.

Regards


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## Scuba_Dave (Jan 16, 2009)

The problem is that you can only have one circuit to a detached stucture OR a MWBC

You aren't allowed to run multiple circuits between the house & shed
Actually the Interlock switch & transfer switch won't work either

I'm not sure if an emergency feed from shed to the house is considered a 2nd feed


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## secutanudu (Mar 15, 2009)

wrooster said:


> Guys,
> Thanks for the replies and info above.
> 
> Question -- given that I can run everything in one conduit (of course, the AC stuff only, separate conduit for the low voltage) -- what size Schedule 80 PVC conduit do I need for the following:
> ...


According to this conduit fill calculator, the minimum size is 1" for sch. 80.

I do think dave is right, though, about only being able to run one circuit (or one MWBC) to the shed.


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## Scuba_Dave (Jan 16, 2009)

It might be OK since it can be considered an emergency backup system
NEC section 700 (702) covers this
Reading thru it now.....


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## wrooster (Apr 16, 2010)

Scuba_Dave said:


> It might be OK since it can be considered an emergency backup system
> NEC section 700 (702) covers this
> Reading thru it now.....


Article 702.9 ?

Thanks.


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## wrooster (Apr 16, 2010)

Anyone help me with closure on this?

Thanks.


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## Scuba_Dave (Jan 16, 2009)

One issue I see is you now have (6) current carrying conductors in the conduit
But 90c column is used to derate so you may be OK
80% derating required for 6 conductors
So #6 can still carry 60a, #12 wire is OK too


1" is the Min conduit size, I would up that to 1.5" for an easier pull
I pulled (3) #6 & 1 #8 in a 1" & that was a pain

I would run the Gen connection by your Inspector
He might ask for a 2nd conduit...better safe then sorry


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## AndrewF (Dec 29, 2008)

I dont believe making a wirenut connection in a LB is acceptable. I was under the impression by my inspector that it was not to NEC.

I also would upsize the conduit to at least 1.5" and run the low voltage in separate SH 40 conduit separated by at least 6" of dirt in the trench.

Slightly different scenario.

I ran 100 amp service to my barn about 180' from the house. 
I ran 3 #2 and 1 #6 wire for the main service.
I ran 4 or 5 - #12 in the same conduit for 2 - three way switches so that I could control some exterior lights on the barn from the house.
IIRC, I ran this all in 1.5" conduit.

The county inspector said this was fine and approved it. So technically, I have 3 circuits out there. (100 amp, and 2 - 15 amps)


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## micromind (Mar 9, 2008)

The more than one feeder or branch circuit limitation is found in 225.30

Basically, it states that only one feeder is allowed except for certain conditions. One of these conditions is an emergency system. 

Therefore, you certainly can run wire from the house to the shed for lights, receptacles, or even a sub-panel plus another feeder from the generator back to the house. 

Since this is an optional standby system, there's no requirement for a separate conduit. In fact, 702.9 specifically allows the generator wiring to be in the same conduit as normal wiring. 

If it were me, I would run a separate conduit for the gen. I'd also run a big enough conduit for the lights, etc. to allow for a 60 amp sub-panel to be installed in the future. A 1" would be OK. 

If the gen is auto-start, and it's more than about 20' from the transfer switch, I'd run a separate conduit for the controls. 

Consider a bug-eye type of emergency light somewhere near the gen. That way, if it fails to start (or needs to be started by hand), you'll have light to work with.

Rob


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## homerb (May 7, 2010)

This is a really interesting topic. I'm actually considering the exact same thing. 

I've written up a crude diagram about how the setup should look.









I have a detached shed about 50 feet from the back of the house, and I'm thinking of running 3 types of wiring to the shed.
1) A generator inlet box going to the sub panel in the garage with an interlock breaker. The sub panel runs everything except for the stove, A/C and furnace, which are powered from the main panel outside. I have a Generac 7500w, 13,500w surge portable generator with a NEMA 14-50 240V 50A plug on it. I'll use a short 10/4 connector cable with a 14-50 plug on the generator side and a 50a female plug on the inlet box side. In the shed, the generator will sit right next to a 16" "shutter type" exhaust fan facing away from the house that will run directly off of the generator instead of being hard wired into the house-supply.









2) Regular 120v power to a 40a sub panel in the shed for lights, outlets, etc. I don't see the need to run 240v TO the shed. 

3) Low voltage wiring, such as a coax cable for TV, and I'll probably run 4 CAT-5e or maybe CAT-6 cables as well. While I don't plan on having 4 computers out there, I can use "Baluns" to run pretty much any type of signal out there over CAT-5/6 cables including HDMI video, USB, etc. 

The question I have is: Is there a maximum length you should use when running the generator to the sub panel? The extension cord will probably be 3-5 feet, and the buried cable in conduit will be at least 50 feet. 

What do you think of the exhaust fan setup? Would this be a good idea? Or should I just sit the generator on the "covered porch" portion of the detached shed? The main reason why I want to put the generator inside the detached shed is for noise reasons. The Generac 7500 is LOUD. I don't want anyone knowing that I'm running a generator or where it's located. 

Homer


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## wrooster (Apr 16, 2010)

homerb said:


> I've written up a crude diagram about how the setup should look.


14/3 out to the shed 50 feet away?


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## homerb (May 7, 2010)

wrooster said:


> 14/3 out to the shed 50 feet away?


I only plan on having a few power outlets and a couple compact fluorescent lights for the 120v powered side. 15 amps MAX. That's not for the generator circuit. 

What would you recommend? 12 AWG? 10 AWG? 

Since the generator circuit and power circuit would share a ground and neutral, I guess you wouldn't need to run two grounds and two neutrals bac to the house, all you'd need to run would be two 10 AWG hots, a 10 AWG neutral, perhaps a 10 AWG ground, and then a 10 or 12 AWG single hot for the 120 V power outlet circuit that'll be on regardless of whether or not the generator is running? Correct? 

Or do you think it'd be good practice to run 10/4 with its own separate neutral and ground for the generator (240V) , and maybe 12/3 with it's own neutral and ground for the power outlets (120V)? 

Or, depending on how many power outlets and devices you'll have out in the shed, you can run two separate hots for two sets of 120v circuits? 

Homer


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## wrooster (Apr 16, 2010)

homerb said:


> What would you recommend?


12AWG.



homerb said:


> Since the generator circuit and power circuit would share a ground and neutral


Don't do this.



homerb said:


> Or do you think it'd be good practice to run 10/4 with its own separate neutral and ground for the generator (240V) , and maybe 12/3 with it's own neutral and ground for the power outlets (120V)?


Do that.



homerb said:


> Or, depending on how many power outlets and devices you'll have out in the shed, you can run two separate hots for two sets of 120v circuits?


Yes you could do that -- google "MWBC".


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