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Discussion Starter · #1 ·
Hi everyone!

First of all, let me start out by saying that I am new to the community ("newbie") and I am learning a lot from the experienced electricians who are posting in these forums. As I am preparing to build a detached garage at my Virginia home (currently under NEC 2014 --> migrating to NEC 2017) in the Spring, I have consulted with numerous electricians and have received different opinions regarding my project, including opinions & recommendations from licensed electricians that do not comply with NEC. As a result, I thought I would try posting my project here in an effort to gather opinions and recommendations from the community in the hope that it would provide some clarity and perspective.

To summarize, I want to complete an electrical run from my current panel (I have 2x Square D QO 200A panels) to the opposite side of my unfinished basement in preparation for building the detached garage in the Spring (see attached drawing). My interior run is ~100 feet (through the basement) followed by an exit out the side of the house and an additional 15 foot run to where I plan on installing a Square D 100A sub panel for the detached garage. Just to be clear, I AM NOT doing this work myself and will be hiring a licensed electrician to complete the work. However, since I have received conflicting recommendations from licensed electricians, I am hoping to receive some input and feedback so that I can ask the right questions and better address my issues and concerns.

The first two electricians I spoke with recommended using either 3-3-3-5 SER Copper wire (2 hot, 1 neutral, 1 ground) or 1-1-1 Aluminum SER wire with 3 AWG ground from the main panel all the way to the sub panel. After doing my own research, however, I discovered that SER wire is not rated for in-ground (burial) use because the ground wire is base and not insulated. Needless to say, I chose not to hire either one of them.

After eliminating these "licensed" electricians, I did my own research and found that one common approach for my situation is to run four (4) individual 3 AWG Copper THWN-2 wires (2 hot, 1 neutral, 1 ground) in Schedule 40 conduit directly from the main panel to the sub panel. After contacting my County Inspector's office and speaking with one of the electrical inspectors, they indicated that this approach would be valid and consistent with current (NEC 2014) code. However, after discovering that the new NEC 2020 code requires an outside disconnect, I am starting to wonder whether I would potentially create an issue for myself in the future if I connect directly from the main panel to the sub panel using this approach.

As I researched NEC 2020 in further detail, I wonder whether I would be better off separating the runs into an "indoor" component (basement run from panel to exit), "outdoor" component (exterior run from house to detached garage), and add a junction box that could also serve as an outside disconnect. In this scenario, I could run SER wire through the basement to the junction box and then use either THWN-2 or USE-2 from the junction box to the sub panel in the detached garage. Alternatively, I have also heard about using "Mobile Home Feeder" (MHF) wire (2-2-2-4 Aluminum) but am hesitant about using Aluminum wire rather than Copper wire.

In closing, I would appreciate any input regarding the following:

1) Would you go with the "traditional" THWN-2 individual conductors in Schedule 40 PVC conduit that is compliant with current code but could be troublesome in the future with NEC 2020 outside disconnect requirement?

2) Would you go with a hybrid option using SER cable indoors to a junction box (disconnect) and then use THWN-2 or USE-2 from the junction box to the sub panel in the detached garage?

3) Would you consider using aluminum rather than copper given the poor history of using aluminum wire in residential housing? Or, it is worth it to pay the premium and use copper instead?

4) Is there another better option (e.g. Mobile Home Feeder, RHW-2, etc.) out there that I should consider?

Any information, opinions, and most importantly, perspective, would be greatly appreciated. Thank you!

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