Detached Garage Power Planning

[draggindakota]

Construction just completed on my new 24 x 30 building, and I'm starting to think about the electrical. Due to budget constraints the electrical couldn't be completed at the same time, and will have to be added a few months down the road.

I've been doing A LOT of reading, on this forum and other sites, and I think I have a good start, but I'd like to get some input on my plans. I'm not un-familiar with electrical codes (permit drawings as part of my job), but the maximum extent of my electrical install knowledge is adding a circuit and wiring for my compressor in the main house garage.

The shop is in Florida, so 2017 NEC still applies. As I said, 24 x 30, 9' eave height metal building (Carolina Carports type), just a one man hobby shop. No electrical on the permit since it was originally going to be a while before I could afford it, but I will be pulling a permit when I do the work. One thing I screwed up on and DIDN'T do was add an UFER prior to the slab being poured. I planned to, spoke to the construction super about it, then the concrete day came & we all forgot about it until it was too late. So here is what I'm planning so far:

Loads:

• 240v compressor (Husky 60 gal, labeled as 3.2HP, but the nameplate just reads “spl”)
• 240v 200A welder
• 240v dust collection (2HP) eventually
• LED lighting (probably 4’ integrated T5 fixtures from Amazon)
• General receptacles
• Gable fan?
• Various wood working tools (table saw / router / bandsaw / planer / sanders)
• MAYBE a 24k mini-split some time down the line (wishful thinking)

Service:
The run is about 180 feet including drop/rise for the panels. The main house panel is 200A and there are plenty of spare spaces. I’m planning a 90A breaker in the main panel, feeding either 2-2-2-4 MHF (or separate USE-2 2ga conductors depending on cost) from the house to the shop and terminating in a 100A 24 space main breaker panel used as a subpanel. The subpanel will be grounded with 2 ~ 8ft driven rods. Separated neutral & ground bus in the subpanel.

Panel https://www.lowes.com/pd/Square-D-1...ug-On-Neutral-Load-Center-Value-Pack/50311147

Q1: Feeder to the subpanel be run in orange HDPE roll conduit? My B-I-L works in fiber and can provide the conduit he uses for next to nothing (he'll be trenching and pulling the wire regardless). 2" SDR11 I believe. I'll be running a parallel conduit with fiber as well for internet to the shop also. I know the NEC allows for HDPE conduit in direct burial applications, but I don’t see anything that requires a certain color. I know orange is typically used for telecom, but that’s just industry norms.


Q2: Can I / should I bond the ground to the metal building frame as well? I'm pretty sure I need to by code. If so, what is the proper way to do this? Separate #6 Cu down to one of the anchor bolts?

Branch Circuit Wiring

• 10/2 NM-B on 30A breaker for 3HP compressor. Compressor will be outside and covered so I'll be adding a 30A outdoor fusible disconnect.
• 12/2 on 30A breaker for dust collection
• 8/2 NM-B on 50A breaker for 200A multi-process welder. Maximum input amperage is 36A @ 240V @ 15% duty cycle. I'm counting on (2) 240V welder receptacles, 1 on either side of the shop (only 1 welder) and basing the wire size on the longest run.
• 12/3 NM-B for general 20A receptacle outlets (split wired)
• 14/2 NM-B for lighting circuits

Q3: Can this be done: I’m considering split wiring duplex receptacles for general power. I know I either need GFCI breakers or a GFCI outlet at the beginning of the circuit, and all of the receptacles will be tamper proof. Would something like the below diagram work for GFCI / split wiring? I’m planning 12 total receptacles, split wired to two separate circuits.

 

[nadogail]

I suggest you get a book on DIY wiring. I have seen them at my local Home Depot and Lowes Stores; we don't have an Orchard Supply or Menards. Your plan seems ambitious, but if you can find a local Electrician who will take on a "side job" you will save a lot of time and frustration. I would have the Electrician set your panel, wire your heavy loads and some of your lights. Once you get those done, and the Inspector satisfied, you can quietly finish the job with the knowledge you have gained.

I would avoid calling an Electrical Contractor, ask around; somebody will know someone. My cabinet maker turned me onto the Electrician who upgraded my service panels. Using the friend of my trusted Cabinet Maker saved me $1000 and the Cabinet Maker's referral earned him a favor from the Electrician.

 

[wyliesdiesels]

180' for #2AL is a bit long for 90a. I would go with #1 AL

Q1 you need to read NEC 353.12(2). The NEC does not permit HDPE for use inside a building. so how would you transition to PVC? Personally i would just run PVC for the entire length panel to panel and avoid the headache of the transitions on each end.

Q2 yes the metal frame of the building should be bonded.

Q3 That will not work. you cannot share a neutral between 2 point-of-use GFCIs. They will trip.

 

[Terry D]

To get your proposed way of your GFCI's to work, you would have to also split the neutral side of the receptacles and run separate neutrals. Keeping you load side white and black together. That wiring can get crazy, you would have (4) # 12 NM-b's at each duplex except the last one.

You could also install a 2-pole GCFI breaker that is rated for 120/240 volts in the panel and share the neutrals between the 2 separate 20 amp 120 volt circuits. But that breaker can get pricey.

To keep things simple and cost down, I would just do every other duplex on separate circuits.

 

[draggindakota]

Thanks for the replies. As for the conduit, he has couplers for HDPE to PVC that they use. He just said they could do it, but I wasn't sure if it was allowable by code. For the feederr, if I went with #1 AL, I could go with 3x #1 & a #2 ground correct? That's looking like a better deal at almost $100 less than the 2-2-2-4 MHF any way, especially since I'm not pulling it by hand.

My plan for the receptacles was to have one half dedicated to stationary tools like the table saw etc., then the other half for portable tools. But it looks like that's going to be too complicated.

My sister-in-law does have a friend that is an electrician, I might see if I can get her out to look at the shop as well.

 

[yatg]

That wiring can get crazy, you would have (4) # 12 NM-b's at each duplex except the last one.

Wire fill is going to push him into a 2 gang box. Might as well put two duplexes in it, one for each circuit.

 

[wyliesdiesels]

Thanks for the replies. As for the conduit, he has couplers for HDPE to PVC that they use. He just said they could do it, but I wasn't sure if it was allowable by code. For the feeder, if I went with #1 AL, I could go with 3x #1 & a #2 ground correct? That's looking like a better deal at almost $100 less than the 2-2-2-4 MHF any way, especially since I'm not pulling it by hand.

My plan for the receptacles was to have one half dedicated to stationary tools like the table saw etc., then the other half for portable tools. But it looks like that's going to be too complicated.

My sister-in-law does have a friend that is an electrician, I might see if I can get her out to look at the shop as well.

Technically you only need #6 AL for up to 100a breaker, for the EGC. Since you upsized (#2AL for 90a breaker to #1 AL), #4 AL should be fine...

 

[draggindakota]

So far I've bought the panel, ground rods, ground bus, disconnect for the compressor & all the interior lights. I'm getting ready to order all my wire.

For lighting I've got 12 of the Barrina 4ft "T8" LED lights and I'm going to put 3 lights on every other building frame. I want to have the lights switched on 2 separate banks. They will all be on the same 20A breaker. I say 20A because the panel came with 1 more 20A breaker than I actually need and it's looking like a cheaper option to run all the receptacles and lights in 12ga vs. buying 14ga just for the lights. I could obviously just run 2 sets of wires but I'm wondering if I could just run a 3-wire bundle and switch the black for one bank, and the red for the second like this:

To me this doesn't seem any different than wiring a ceiling fan with light to 2 separate switches, but sometimes common sense and code don't mix.

As for the wire, I'm leaning toward just buying and pulling separate conductors vs. NM-B. The walls won't be finished, so I'd need conduit for the drops regardless, so again this seems like it will be a cheaper option.