Adding Second 100 Amp Panel for Detached Shop

Many apologies if this scenario has already been covered elsewhere and I have overlooked it. I read through numerous threads that were similar, but still didn't clarify things for my situation. Hoping someone on here can give me a definitive answer so I can finally wire my shop properly.

No laughing at the naive post or perceived ignorance... I am not an electrician.

As things are currently:
-House built in 1988.
-Underground 200 amp service to house.
-House has 100 amp main load center with a single 15 amp breaker currently running my pole barn (as purchased in 1998).
-Roughly 120 feet total wire run length from house load center to pole barn termination.

Ever since moving here in '98, I have wanted to install 100 amp service to the pole barn so I could run heat, air conditioning, welder, TV, etc., etc. I thought I hit paydirt when a salesperson at a Home Depot about two years ago said he used to be an electrician and knew exactly what I needed to do. I was instructed I would need a two circuit, 200+ amp main breaker that would come off the meter socket then feed the main house 100 amp load center as well as a new 100 amp load center out in the pole barn. He said there were other ways to do it, but this way would be the most cost effective. The wire he sold me on (that is already in conduit three feet underground) is AL Type SE Style U, 600V 2 CDRS 2 AWG 1 CDR 2 AWG (2/2/2). This wire has two main separately insulated conductors and the third conductor is essentially strands of wire surrounding the two main insulated ones.

Here's the question / issue: I have had three people now tell me the guy lied to me and I have to have at least 2/2/2/4, all insulated conductors, but I have had two other folks tell me that while unconventional in approach, I can technically use the existing wire (that, remember, is already buried) by using the two insulated wires as my hots, the strands grouped together as my neutral, and then create a separate ground that would go to a grounding rod just outside the shop wall (5/8" grounding rod buried at least 6 feet below grade). Will this work?

Thanks,
Neal.

kansei said:

Underground 200 amp service to house.
-House has 100 amp main load center

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These two don't quite add up.. we need a better understanding of what your existing incoming service is like. Presumably underground feeding up to a meter, then what? Is there any disconnect or breaker outside by the meter, or does it feed directly indoors? If your house has a 100A main pannel, what makes you think you have an incoming 200A service?

Is the existing 15A service to your pole barn currently running on the burried 2/2/2 AL feeder? #2 AL is good for 90A to a detached structure.

Up through 2005 NEC, 3 wires would be allowable as long as there are no other metalic pathways between buildings. You would bond together the neutral and ground (including a pair of ground rods 6' apart) at the detached structure.

However, starting with the 2008 NEC, 4 conductors are required to feed a detached structure.

If you could time travel back before your area adopted the 2008 NEC, you could legally use your 3 #2 AL conductors to provide 90A to your pole barn off a 90A two-pole breaker in your main panel (as long as you don't have any phone lines or metal water pipe between buildings.)

Sorry, I did leave a bit of detail out there...

- Current 15 amp service to pole barn is on it's own buried line (how things were when I bought the house). I think it is 12/3.

- Buried three conductor AL wire I mentioned is just that- buried only (in conduit), but currently not hooked up to anything on either end. I buried it roughly two years ago, but then started having friends who have done electrical work tell me the wire was not correct (maybe they were referring to NEC 2008 you mentioned).

- Confirmed with power company yesterday that the underground service wire to my house and the meter are OK for 200 amps. The only service panel in use right now is the main house one (100 amp) in the garage.

- No metal structures or metal pipes running between the house and pole barn in the path of the existing wire or newer buried wire in the conduit- except unless the rebar in the septic tank walls could pose a problem, as the wiring passes within about five feet of the side of the septic tank.

If it should technically work with the existing 2/2/2 AL wire I have buried, but adding the two grounding rods 6' apart as you mentioned, I may run with that for now just to get things up and running.

kansei said:

-Underground 200 amp service to house.

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More info needed ... if you have 200a underground service to the meter, what is the cable capacity between the meter and the existing 100a main panel?

kansei said:

AL Type SE Style U, 600V 2 CDRS 2 AWG 1 CDR 2 AWG (2/2/2).

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I'm not an electrician, but if I recall correctly, Type SE Style U cable is not suitable for underground service.

kansei said:

while unconventional in approach, I can technically use the existing wire (that, remember, is already buried) by using the two insulated wires as my hots, the strands grouped together as my neutral, and then create a separate ground that would go to a grounding rod just outside the shop wall (5/8" grounding rod buried at least 6 feet below grade). Will this work?

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This (using the bare strands) is not "legal" per the code. SE is not "underground" rated for starters, and what you need are two hots, an insulated neutral, and a ground wire. You can use 2-2-2-4 quadplex otherwise known as "mobile home feeder" and in most cases it can be used for up to 90 amps.

Charles

As Charles has said you got the wrong cable.

If this is the cable you got then you need to remove it and put in the right cable.


This is the right type of cable. Quadruplex.

pattenp said:

As Charles has said you got the wrong cable.

If this is the cable you got then you need to remove it and put in the right cable.

This is the right type of cable. Quadruplex.

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The bare AL conductor will turn into a toothpaste like substance underground on the SE cable pictured, "advice" from HD or others should be used at ones own risk.

Thanks for all the input- beginning to sound like I was (un)lucky enough to get ahold of one of those wannabe experts at the store that actually didn't know anything. I had been informed that the wire could be used above ground, or underground, so long as it was buried in conduit. Wonderful.

Obviously, the idea I had been told about using the strands grouped together to form the neutral was no good either. Wish I was just in the position to hire an electricing to do it all, but with 101 projects needing done, and only so much cash to do them all...

Thanks much for the assistance. Looks like I'll be digging all this up and starting over. Look for pics of my garage finished sometime around 2020.

Neal.

Again, I am not an electrician, but it appears to me that you have two options available ....

1) Assure that you have 200a cable from the meter to the main box. Replace the main box with a 200a box. Install a 100a breaker in the new panel to feed the pole barn. Replace the incorrect 2/2/2 Type SE cable with proper 4 conductor underground cable rated for 100a (this is the "mobile home feeder" described by Charles). Install a new 100a breaker box with a 100a main breaker in your pole barn. No new ground rods required, but do NOT bond the neutral and ground busses of the new box together.

Or ....

2) Most jurisdictions (but not all) accept a double-tap off the meter. Leave your existing 100a box alone and connect the new feed cable to the pole barn to a second set of lugs on the load side of your meter (you'll have to work with the power company to do this). Depending on your jurisdictional requirements you may need to install a new 100a disconnect in this pole barn feeder adjacent to your meter. Run correct 3 conductor 100a underground cable (a 3 conductor "mobile home feeder") to the new 100a breaker box with a 100a main breaker. (NOTE -- you cannot feed a 100a breaker box with 90a, No. 2 cable!) You must bond the neutral and ground busses together in the new box and install a pair of 5/8in diameter, 8 ft. long ground rods at the pole barn. Essentially, you are duplicating your house service at your pole barn (except for the possible additional disconnect at the meter that your local jurisdiction may or may not require).

In theory, you might think that the existing 3 conductor Type SE cable should be satisfactory for this double-tap method, but Norcal is correct ... even if installed in conduit, the unprotected aluminum wire wrapped around the two main conductors is subject to corrosion and long-term failure in underground applications .... and that would not be a good thing.
Bite the bullet and replace the Type SE cable with the proper underground cable and chalk the cost up to a learning experience.

kansei said:

The wire he sold me on (that is already in conduit three feet underground) is AL Type SE Style U, 600V 2 CDRS 2 AWG 1 CDR 2 AWG (2/2/2).

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kansei said:

Looks like I'll be digging all this up and starting over.

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If the existing SE-U is in conduit, can't you pull it out and pull in the correct wire, thus avoiding any digging?

This remined me of a conversation I had with my Uncle about my service out to my garage. I am mutual friends with the electrical inspector in my city. I need to find a new electrical expert as the three I know now are up in age and "retired".