100A above ground feeder

[sky jumper]

I'm planning to run 100A partially above ground to a detached garage. the main house is 200A with a main panel and sub panel. My plan is to connect to the subpanel via a 100A breaker, then run 1/0 1/0 1/0 2 AL to the garage 80ft away.

My plan is to punch it out the back of the house under the deck that spans the entire length of the house, and run it above ground under the deck 50ft, then burry it the last 30ft to the detached garage. the goal is to avoid trenching around the deck and mucking up future landscape plans in that area.

my question is --- what is the best way to do this? PVC above grade and then RMC under ground or do you have to stay with RMC the whole way? Is there any special specs for the wire? or will any 1/0 4 wire SER work for this?

I have more questions around the connections to the subpanel, and panel requirements in the garage, but I'd like to get my run figured out first.

 

[pattenp]

You need #1 not #1/0 for 100A. SER is not to go underground. Use PVC whole run, panel to panel if possible and use three #1 xhhw-2 and a #6 for ground.

 

[wyliesdiesels]

What he said ^^^

1/0 al is overkill for this.

Subpanel needs to have isolated neutral, which may require a separate ground bar kit, as well as 2 grounding rods.

 

[sky jumper]

ok. a few stupid questions...

1) this would be 4 separate wires, not a single 4 wire cable? I guess I thought feeders needed to be cabled together if run under ground?
2) in my area in Illinois conduit is required for residential wiring. for the 15' run inside the house to where it punches out under the deck... are you saying use the same PVC for this? or do RMC inside the house and switch to PVC outside?
3) does the PVC pipe under the deck need to be elevated/attached to anything? like hung from the underside of the deck? or can it just lay on the ground?
4) I'm not sure how to connect PCV or RMC of sufficient diameter to the house subpanel. Unless I can't use a branch circuit bay for this? do I need a 3rd panel?
5) the isolated neutral ... that is for the subpanel in the garage, correct?

sorry for the newb questions... never done this before, although I've done plenty of "normal" wiring, conduit runs, etc.

 

[Falcon67]

Consider MHF with a 90A rating, may well be cheaper and can also run through your conduit run. Sold as a complete 4 wire twisted cable. $1.80/ft around here.

 

[wyliesdiesels]

ok. a few stupid questions...

1) this would be 4 separate wires, not a single 4 wire cable? I guess I thought feeders needed to be cabled together if run under ground?
2) in my area in Illinois conduit is required for residential wiring. for the 15' run inside the house to where it punches out under the deck... are you saying use the same PVC for this? or do RMC inside the house and switch to PVC outside?
3) does the PVC pipe under the deck need to be elevated/attached to anything? like hung from the underside of the deck? or can it just lay on the ground?
4) I'm not sure how to connect PCV or RMC of sufficient diameter to the house subpanel. Unless I can't use a branch circuit bay for this? do I need a 3rd panel?
5) the isolated neutral ... that is for the subpanel in the garage, correct?

sorry for the newb questions... never done this before, although I've done plenty of "normal" wiring, conduit runs, etc.

1) yes 4 wires. All the wires of a circuit need to be grouped together. That could be individual conductors in the same conduit.
2) I would do PVC from panel to panel and forget about transitioning to metal
3) I would attach to desk
4) im not sure what youre asking here. You would use a terminal adapter that has threads on it. Put that through a knockout and then use a lock ring to secure it.
5) yes. Check to see if you need a ground bar kit for whatever panel you buy. Make sure its listed for the make and model of panel you have.

theres quite a few threads on here that cover most of this.

Check the Electrical FAQs sticky for a wiring diagram.

Consider MHF with a 90A rating, may well be cheaper and can also run through your conduit run. Sold as a complete 4 wire twisted cable. $1.80/ft around here.

#2 al MHF would be perfect for this.

Its $1.17 on https://www.wireandcableyourway.com/2-2-2-4-aluminum-mobile-home-feeder-cable.html

 

[pattenp]

Your local code may require metal conduit inside. There are connectors to change from metal to PVC.

 

[alfredeneuman]

ok. a few stupid questions...
2) in my area in Illinois conduit is required for residential wiring. for the 15' run inside the house to where it punches out under the deck... are you saying use the same PVC for this? or do RMC inside the house and switch to PVC outside?

Chicago and it's "sphere of influence" require conduit in residential, but not necessarily RMC, EMT is fine.
(they never forgot the cow that kicked over a lantern that caused the fire in 1871, and it reflects in their building codes)
I'm not sure of this, but PVC is probably prohibited inside wooden framed buildings too because when burning, it emits chlorine gas

 

[Norcal]

Your local code may require metal conduit inside. There are connectors to change from metal to PVC.

The IL areas that require conduit also can prohibit any PVC above ground and frown on any flexible wiring methods, check with them before proceeding.

 

[sky jumper]

thanks all.

the #2 MHF is a good tip.

our code is NEC 2008 with the following exceptions:

(B) Exceptions: In lieu of article 334, nonmetallic sheathed cable: types nm, nmc and nms all lighting and receptacle circuits must be enclosed in electrical metallic tubing, except for flexible metallic drops not to exceed four feet (4') in length.


so thinwall EMT is required inside. It's the above ground exterior run that's got me guessing.

I've spent some more time studying NEC 2008. from table 300.5 it looks like PVC (column 3) needs to be 18in deep where burried, but can be 0in or essentially on the ground "under a building" --- if I'm reading that right. 6in/0in for RMC.

So --- does a deck qualify as a "building"? I can find nothing in the code to specifically address running feeders under decks.

 

[wyliesdiesels]

I would ask your inspector but code is permissive so if there is no code prohibiting the specific method then youre good to go.

Is this a permitted and inspected job?

 

[sky jumper]

Yes it will be permitted & insepcted. The garage is new construction so the whole thing will be under a microscope. I just hope they don't snoop around on any existing stuff I've done over the years....

 

[wyliesdiesels]

There are probably local written amendments so you need to aks your inspector.

 

[sky jumper]

so here's my dilemma with the connection to the main panel in the house. see pics.

the house has a 200A main panel, and 100A subpanel. both are full. the sub panel is powering 3 separate 240V AC units, so I'm now thinking I can't just consolidate cirucits in the sub panel (using tandem breakers) to free up 2 slots to add a 100A feeder to the Garage.

I think I need a third panel in the house... fed from a 100A breaker in the main panel. which will require me to relocate a few circuits on the main panel to the new 3rd panel.

or is there someway to just run another SE off the meter to supply the garage and bypass the house panels altogether? that would also eliminate the need to run 2" EMT from the main panel out the house, which I'm not looking forward to.