# Sub panel in detached structure



## kolyan2k (Apr 13, 2014)

Is there something specific you need to do per NEC for installation of 100amp sub panel? I want to run 
3-3-3-8 Cu (or 1-1-1-6 Al) THWN inside PVC underground and just install main lug panel.


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## macmikeman (Jan 23, 2007)

kolyan2k said:


> Is there something specific you need to do per NEC for installation of 100amp sub panel? I want to run
> 3-3-3-8 Cu (or 1-1-1-6 Al) THWN inside PVC underground and just install main lug panel.


Buy a panel with a main breaker, drive a ground rod, run a gec to the rod.


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## telsa (May 22, 2015)

One should favor 1,1,1,8 IMHO. I like Aluminum for my Hots, Copper for my bonding and grounding conductors.

The raceway :: 1 1/2" PVC schedule 40. I'd rather have a loose pull.

Distance -- might make me bump up the conductors -- but I assume that this is a nearby out-building.

It's still going to need a Ufer or other Grounding Electrode System as it is not an attached structure.

Ask This Old House showed just such an install a few years back. It's on Utube.


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## HackWork (Oct 2, 2009)

The 6 stroke rule applies here, so if you are going to have more than 6 circuits, use a main breaker.

If it's new you need to install a UFER (attach to the rebar). If it's existing you need to drive a ground rod, which would mean 2 of them. If there is metal pipe you need to bond it.

Never run copper conductors, that is just silly.


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## kolyan2k (Apr 13, 2014)

I see... It's a new structure 150ft away as I was told, but I think they already have the foundation done, so I am guessing UFER is not an option anymore and then I would just need to install 2 electrodes 

Ive recently done a small shed with 40amp subpanel (bathroom and sauna), ran 8/3 UF, inspector didn't mention anything about the need for grounding rods


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## CoolWill (Jan 5, 2019)

kolyan2k said:


> I see... It's a new structure 150ft away as I was told, but I think they already have the foundation done, so I am guessing UFER is not an option anymore and then I would just need to install 2 electrodes
> 
> Ive recently done a small shed with 40amp subpanel (bathroom and sauna), ran 8/3 UF, inspector didn't mention anything about the need for grounding rods


Why would you rely on the inspector to tell you the right way to do the job?


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## JoeSparky (Mar 25, 2010)

You need a main disconnect, not necessarily main ocpd though but it's allowed. That being said, a main breaker panel is usually your cheapest option. Run a separate ground from the house and wire it like a subpanel Ground and bond it like a main service, but tie them to the separate ground bus, not neutral.


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## macmikeman (Jan 23, 2007)

HackWork said:


> The 6 stroke rule applies here, so if you are going to have more than 6 circuits, use a main breaker.
> 
> If it's new you need to install a UFER (attach to the rebar). If it's existing you need to drive a ground rod, which would mean 2 of them. If there is metal pipe you need to bond it.
> 
> Never run copper conductors, that is just silly.




225.30 Number of supplies. The six rule is mandated to conform to circuits approved by 225.30 and 225.30 doesn't allow up to six disconnects for a separate building downstream of the service disconnecting means unless they meet the provisions of 225.30 (A) thru (E). (You might be able to wrangle (E) since it is kinda vague who decides what is proper documentation and operation).........


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## macmikeman (Jan 23, 2007)

kolyan2k said:


> I see... It's a new structure 150ft away as I was told, but I think they already have the foundation done, so I am guessing UFER is not an option anymore and then I would just need to install 2 electrodes
> 
> Ive recently done a small shed with 40amp subpanel (bathroom and sauna), ran 8/3 UF, inspector didn't mention anything about the need for grounding rods



250.32 lays it all out.


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## HackWork (Oct 2, 2009)

kolyan2k said:


> I see... It's a new structure 150ft away as I was told, but I think they already have the foundation done, so I am guessing UFER is not an option anymore and then I would just need to install 2 electrodes
> 
> Ive recently done a small shed with 40amp subpanel (bathroom and sauna), ran 8/3 UF, inspector didn't mention anything about the need for grounding rods


Nope, you need the UFER. The foundation being done doesn't exclude you from that. My state put out a memo to remind everyone that they will be jackhammering concrete if they think they can get out of installing a UFER ground by saying the foundation was already poured.

That may be so, but they are still required and the inspector might call you on it in this job.


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## macmikeman (Jan 23, 2007)

kolyan2k said:


> I see... It's a new structure 150ft away as I was told, but I think they already have the foundation done, so I am guessing UFER is not an option anymore and then I would just need to install 2 electrodes
> 
> Ive recently done a small shed with 40amp subpanel (bathroom and sauna), ran 8/3 UF, inspector didn't mention anything about the need for grounding rods


See 250.50. Operative word: if Present. Your building was new and the rebar was available at some point that you missed. (but your inspector may be a cool guy who lets it slide and you can drive rods instead.). If he is not a cool dude, be prepared to do a bit of concrete foundation chipping. 


So, you can see how studying the code in advance has it's advantages over finding out afterwards ---- whoops---- good luck in your endeavors and watch out and learn about the chapter two codes before problems pop up.


Edit to add: If they brought you in after they poured the foundation, tell them they have to do the concrete chipping to expose the footing rebar , not you. Tell them don't F'up next time. Stand your ground. explain to them how they are simians and you are an advanced species to them , known to science as **** sapiens , something they won't become for another two or three million years.


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## HackWork (Oct 2, 2009)

macmikeman said:


> 225.30 Number of supplies. The six rule is mandated to conform to circuits approved by 225.30 and 225.30 doesn't allow up to six disconnects for a separate building downstream of the service disconnecting means unless they meet the provisions of 225.30 (A) thru (E). (You might be able to wrangle (E) since it is kinda vague who decides what is proper documentation and operation).........


I don't know what you are saying here. I looked it up and can't figure it out. I have passed many inspections with 4 circuits panels and I also checked Mike Holt's and they all agree that the 6 throw rule is good for a detached structure.


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## macmikeman (Jan 23, 2007)

HackWork said:


> I don't know what you are saying here. I looked it up and can't figure it out. I have passed many inspections with 4 circuits panels and I also checked Mike Holt's and they all agree that the 6 throw rule is good for a detached structure.


Is this a duel? Make ready your Mike Holt weapon sir, I have provided my choice...... 

225.30. A building or other structure that is served by a *branch circuit or feeder *on the *load side of a service disconnecting means* shall be supplied by only *one feeder or branch circuit *unless *permitted by 225.30 (A) thru (E).*

The *One* feeder can feed a sub panel, no problem with that. But six different feeders or branch circuits (run between the two buildings) not allowed.


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## HackWork (Oct 2, 2009)

macmikeman said:


> Is this a duel? Make ready your Mike Holt weapon sir, I have provided my choice......
> 
> 225.30. A building or other structure that is served by a branch circuit or feeder on the load side of a service disconnecting means shall be supplied by only one feeder or branch circuit unless permitted by 225.30 (A) thru (E).
> 
> The *One* feeder can feed a sub panel, no problem with that. *But six different feeders or branch circuits (run between the two buildings) not allowed.*


Dude, no one said anything about running 6 separate circuits or feeders between the buildings.

I said that if the subpanel at the separate structure had 6 circuits or less he would not need a main breaker in the panel as a disconnecting means for the structure.


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## kolyan2k (Apr 13, 2014)

Maybe I haven't done many new construction homes  I've never done or heard of UFER before. It was always 2 electrodes. I'll note that


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## Dennis Alwon (May 9, 2009)

kolyan2k said:


> Maybe I haven't done many new construction homes  I've never done or heard of UFER before. It was always 2 electrodes. I'll note that


Ma may not require the ufer or concrete encased electrode . Nc still does not enforce the concrete encased electrode- I wish they would.

You do need an electrode at the shed if you install a panel. You need 2- hots, neutral and a ground. I don't know why the inspector didn't make you put it in...


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## kolyan2k (Apr 13, 2014)

Well hopefully he doesn't request it at the final then. He did check the entire job careful, even measured direct burial distance


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## CTshockhazard (Aug 28, 2009)

kolyan2k said:


> He ..... even measured direct burial distance



Why?


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## HackWork (Oct 2, 2009)

CTshockhazard said:


> Why?


I wondered the same thing, but then I figured he meant the distance from the cable to the surface, the _depth_.


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## kolyan2k (Apr 13, 2014)

Yes, I that's what I meant


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## CTshockhazard (Aug 28, 2009)

HackWork said:


> I wondered the same thing, but then I figured he meant the distance from the cable to the surface, the _depth_.





kolyan2k said:


> Yes, I that's what I meant



Ahh, I was hoping for a voltage drop "code" or something. :biggrin:


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## kolyan2k (Apr 13, 2014)

Any recommendations which wire to run in PVC underground for 100amp sub? I mean is there anything else besides separate THHW x 3 + ground? I think maximum UF cable size is 6/3


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## Cow (Jan 16, 2008)

kolyan2k said:


> Any recommendations which wire to run in PVC underground for 100amp sub? I mean is there anything else besides separate THHW x 3 + ground? I think maximum UF cable size is 6/3



#2 AL mobile home feeder works great if you can live with a 90 amp sub.

The price per amp ratio can't be beat either.

https://www.mysouthwire.com/medias/...duct-specifications/hd1/h71/8854083567646.pdf


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## HackWork (Oct 2, 2009)

kolyan2k said:


> Any recommendations which wire to run in PVC underground for 100amp sub? I mean is there anything else besides separate THHW x 3 + ground? I think maximum UF cable size is 6/3


We spoke about this earlier, never run copper. Ever.

And don't run cable inside of underground pipe either.


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## kolyan2k (Apr 13, 2014)

Owner doesn't care if run Cu or Al. He actually priced all materials himself and included Cu. I usually run UF inside the pipe for protection, just wasn't sure if there is anything else with outer insulation that would work. It will be a pain to get PVC pipe all the way to the house panel. UF works great because you can run it inside PVC underground and when you enter the house no pipe is needed anymore


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## HackWork (Oct 2, 2009)

kolyan2k said:


> Owner doesn't care if run Cu or Al. He actually priced all materials himself and included Cu. I usually run UF inside the pipe for protection, just wasn't sure if there is anything else with outer insulation that would work. It will be a pain to get PVC pipe all the way to the house panel. UF works great because you can run it inside PVC underground and when you enter the house no pipe is needed anymore


You should charge for copper and use aluminum.

Getting cable into pipe is a giant pain in the ass.


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## kolyan2k (Apr 13, 2014)

Depends on the pipe size  I would rather have cable inside the pipe then do piping all the way to home panel and sub. So I am guessing there is nothing like SER with insulated ground.....


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## Cow (Jan 16, 2008)

Some folks will pull individual conductor, mhf, or similar into pipe. Then j-box it at the house with insulated taps or whathaveyou to change over to a cable wiring type like SER, etc for going through the house.


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## kolyan2k (Apr 13, 2014)

Alright thanks guys. Plan is to use #2 AL mobile home feeder for 90amp panel in 1 1/2 PVC, and for 40amp garage panel use 8/3 UF with same 1 1/2 PVC


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## kolyan2k (Apr 13, 2014)

On the other thought.... Why SER is not underground rated? Ground is not insulated but UFER ground is not insulated either


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## Jerome208 (May 10, 2013)

338.12 (A) (2) Uses Not Permitted. ... Underground with or without a raceway [regarding SER cable]


However the stuff I have seen has the individual conductors marked XHHW so it seems if the jacket was removed it would be OK.


I believe you should switch the bare aluminum ground to insulated or copper though because the water that always accumulates in the pipe would disintegrate bare aluminum after a while.


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## macmikeman (Jan 23, 2007)

Jerome208 said:


> 338.12 (A) (2) Uses Not Permitted. ... Underground with or without a raceway [regarding SER cable]
> 
> 
> However the stuff I have seen has the individual conductors marked XHHW so it seems if the jacket was removed it would be OK.
> ...



That happens to be the answer to the question he asked. The bare alum will go to powder in an underground ser wire pull if the teeniest hole in the sheath is present down there. And I don't think the insulation on SER is rated for fungus either. Sunlight and water- yes. Fungus amongus - no.


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## Jerome208 (May 10, 2013)

macmikeman said:


> And I don't think the insulation on SER is rated for fungus either. Sunlight and water- yes. Fungus amongus - no.



What do you mean by that? What is a fungus rating?


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## kolyan2k (Apr 13, 2014)

They do have SE/SER copper, but specs don't say it's underground rated but individual conductors are


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