100 amp subpanel in detached garage -HELP PLEASE!

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  #1  
Old 06-14-19, 10:29 AM
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100 amp subpanel in detached garage -HELP PLEASE!

Hi everyone!

I am installing a 100amp subpanel in my detached garage for a woodworking shop thatíll be about 120-130 feet from the main 100amp panel in my basement (will upgrade to 200 eventually). about 80 feet will be outdoors and the rest in the basement.

Hereís my plan:

install a 60 amp breaker in Jen main panel and run three #1 aluminum THWN wires in 1.5Ē pvc conduit from the main panel all the way to the subpanel. Outside the conduit will be buried at 18Ē depth. I am planning on installing two copper grounding rods by the workshop as well.

Questions:

- what size ground wire do I need?
- will this be sufficient enough to carry 100amps to the shop (or close to it, eventually, once I upgrade the main panel)
- is there anything I should do differently?
- is there anything I should do in addition?

All and any help is MUCH appreciated! The maze of google hits is way too confusing and unhelpful. Thank you!
 
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  #2  
Old 06-14-19, 10:36 AM
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The equipment ground (in the conduit) should be #8 copper or #6 aluminum. The grounding electrode conductor (from the subpanel to the ground rods) should be #6 copper.

Your plan is good for up to 100A.

Aluminum conductors are often more available in XHHW insulation instead of THWN, but either is OK based on whatever your supplier stocks.

Make sure to keep less than 360 degrees of bends between pull points in the conduit (panels, j-boxes, LB fittings). A rope can be pulled through while you assemble the conduit, but the wires can't be pulled in until the conduit is fully assembled and glue dry.

The subpanel at the shop needs to have separate ground & neutral bars which usually requires you to remove a bonding screw and to buy and add-on ground bar kit.

See Ray's diagram:
 
  #3  
Old 06-14-19, 10:59 AM
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This is extremely helpful, thank you so much!

so, inside the conduit- should I stick to aluminum ground wire or copper? Is it okay to mix the aluminum ones with copper or not a big deal?

Can i tape the three (or four, with the ground wire) individual wires (2 hot and the neutral) together inside the conduit to make pulling through easier or is that a big no-no?

Why stay under the 360 degree rule? Just out of curiosity.

Also, Iíve read somewhere that itís a good idea to run a FIFTH wire back through the conduit to ground it to the main panel. That seems like overkill if Iím putting in 2 grounding rods already, no? Not to mention, it seems like 1.5Ē pvc conduit would be maxed out at 4 wires in there already. Am I thinking this correctly?

Last question- and this might sound dumb- a #1 wire is NOT the same as a 1/0 wire correct? I am yet to find a site online where all this is clearly written down and marked.

Thanks again! Your help is MUCH appreciated!
 
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Old 06-14-19, 11:21 AM
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> copper or aluminum ground
Unless you plan on installing a pool or spa in that building, code is silent on the issue. You can use whichever suits your budget / supplier.

> tape
Don't tape the wires in the conduit, other than at the pull-head. If you're not pulling directly off a spool, lay them out straight and pull them through as a group. Do apply plenty of wire lube.

> 360 rule
1. it's a code requirement; 2. bends add a lot of friction to the pull, and you risk damaging the wires or conduit if you have to pull too hard.

> extra ground?
There's no reason to do that.

> Wire gauge.
#1 and #1/0 are different -- they're actually #1 and #0. For whatever reason, wire suppliers say 1/0, 2/0, 3/0, 4/0 rather than 0, 00, 000, 0000 when talking about gauges. Larger than 4/0, they switch over to kcmils - 250, 400, 500, etc, which is a unit of cross-sectional area related to the diameter of the wire.
 
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Old 06-14-19, 12:54 PM
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Got it- thank you!

One last question (I think):

would I be able to use either EMT or flexible conduit under ground or even in the basement? The trench I dig has some curve to it at the end and rather than digging a new one there, I was hoping to get around it if I can.
 
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Old 06-14-19, 01:17 PM
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EMT can only be used above ground. Some flex can be buried, but most is above ground only. The underground portion should be PVC, which you can flex a little bit, or make a custom bend if you heat it up.
 
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Old 06-14-19, 01:22 PM
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Got it! So just heat it with a torch and then bend it?
Also, the 360 rule you mentioned thatís on the whole line, right? As Iím thinking about it, Iíll be really close, if not over the 360...could I get around that with putting a JB in the middle?
 
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Old 06-14-19, 06:48 PM
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You need a total of 4 wires to the panel from the house. HHNG.
 
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Old 06-15-19, 03:30 PM
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the ground rod at the garage is a WRONG. You are making a ground loop which can produce dangerous conditions.
Just use the ground wire in the conduit and your good to go.

Mod Note: The NEC requires a ground rod at detached structures provided with more than a single circuit. The above information is incorrect.
 

Last edited by pcboss; 06-15-19 at 04:31 PM. Reason: Added Mod Note
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Old 06-15-19, 03:38 PM
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Drangd

the ground rod at the garage is a WRONG. You are making a ground loop which can produce dangerous conditions.
Just use the ground wire in the conduit and your good to go.

You are wrong. NEC 250.32 requires an electrode grounding system at detached structures. The equipment ground between structures is for clearing fault current, not diverting lighting strikes.
 
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Old 06-15-19, 04:30 PM
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The 360 limit is between access points, not necessarily the whole run. A pull point or box restarts the degree count.
 
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Old 06-15-19, 05:16 PM
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Iíll be really close, if not over the 360

As the degrees in the bends and elbows add up, so does the difficulty pulling the wire past those bends. Even when just close to 360, the pull can be nearly impossible to make. As pcboss has pointed out, the 360 limit is between access points. An access can be a junction box, an LB condulet (or LL or LR) or even a C condulet.
 
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Old 06-16-19, 08:06 PM
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Thank you all! Very helpful and appreciated!

I also received this response an different platform. Now Iím kinda torn between my plan above (which I believe would leave room for getting the full 100amps once I upgrade the main panel) and this one - any thoughts?

URD cannot be inside the building unless it has an RHH/RHW-2 rating, and even then it must be in conduit inside the building. Outside it can be direct buried or run in conduit the entire length, which I would recommend. Typically you will find MHF (mobile home feeder, black/black/green/white) wire in 2-2-2-4 which has the RHW-2 rating. URD that is typically stocked in home improvement centers (black conductors, one with yellow stripe) is not RHW-2 rated and cannot be used indoors. If you already have the URD wire you could use that outdoors and transition to SER (2-2-2-4 AL) inside the building, which can be stapled to the joists and does not need to be in conduit. 18" is an acceptable depth if PVC conduit is used underground. Though 2awg aluminum is acceptable for a 100 amp main service, for a sub-feed you can only use it up to 90 amps. Unless you plan on having multiple people out there working and using lots of power-heavy tools, even 90A would be overkill. I would feed it with a 60A or whatever the highest you can find locally and not worry about it unless you trip that. Yes the 2awg will fit the 60A breaker, but you'll need a lug for the ground bar in the subpanel. Nothing wrong with feeding a 100 amp subpanel from a 100 amp main panel. All that of course is what should be done to meet code. If you don't care about meeting code you can do whatever you want.
 
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Old 06-17-19, 05:16 AM
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Everything in the linked reddit post appears to be correct.

My usual preference is to not have splices in panel feeders when possible which would mean pulling conductors through conduit. This preference just comes from the additional cost & labor to install the splices, and introduction of an additional point of failure.

There is little practical difference between 90A and 100A. In a home shop you would never notice the difference.
 
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Old 06-17-19, 01:35 PM
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A point to clarify the 18" depth for PVC conduit in the linked info. The NEC specifies 18" of cover for PVC, so technically the depth of the trench needs to be deeper than 18".
 
  #16  
Old 06-17-19, 04:52 PM
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Thank you all so much for the help!

I ended up going with the 2-2-2-4 URD for outside and 2-2-2-4 SER for inside.

Any suggestions on how to connect them together? The supply store suggested a heat shrink sleeve with some nuts or whatever inside but for one wire (out of the 4) itís $20...any suggestions?

Also- the ground rods I got are 8ft long (shortest they had)- am I supposed to burry the whole thing? Anyone has input on this?
 
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Old 06-17-19, 07:26 PM
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I use splice/reducers or split bolts taped very well. Rods need to be driven straight down just below ground surface. To add.. junction box needs to be at least 6 times the size of the entering conduit. Example 2" conduit = 12"x12" box, 1.5 conduit = 10"x10" box.
 
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Old 06-18-19, 05:29 AM
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Originally Posted by TBEGR
Any suggestions on how to connect them together? The supply store suggested a heat shrink sleeve with some nuts or whatever inside but for one wire (out of the 4) it’s $20...any suggestions?
Originally Posted by ibpooks
This preference just comes from the additional cost & labor to install the splices
You've got to buy connectors of some type. On the easier, but more expensive end are insulated splice blocks (Polaris, Ilsco, etc) with rubber insulation and set screws. On the cheaper, but more labor end are split bolts wrapped with a layer of friction tape then a few layers of quality vinyl tape. In either case since you're using aluminum, apply noalox paste to the splice to reduce corrosion.

Most of the time ground rods drive just fine with a sledge hammer. If you hit a big rock you might have to back it out and try a different spot.
 
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Old 06-18-19, 06:35 AM
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MAKes sense, thank you very much!
 
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