How do I wire up a shed for 60A service today with the ability to grow later?

Question

I've been doing my research, reading tons of messages here and on other sites, and I think I know what I need to run power to my shed, but wanted to put it all together and have the collective mind check my work.

Physical: Detached Garage 75' from the panel box on the side of the house where I'm tying in the power. 90' wire distance.

SubPanel: - 60A Main Breaker Panel - I bought a CH22B100V panel for in the shed, but will swap the 100A main with a 60A Main Breaker. - From what I see the 60A Main can handle wire up to #2 as this panel is fed through the main not through lugs in the panel. - Need 2 Ground rods on the shed end tied to the panel ground. - Ground and Neutral bus not bonded at the shed

Wire: - Planning to run 2-2-2-4 Al wire as it's the largest I can tie into the 60A in the shed. MHF (Mobile Home Feeder seems to be suggested in multiple places) - That should get me the ability to upgrade to 90A later if needed as the breakers and panels are rated 75deg for Al. - Plan on running 1-1/2 or 2" conduit 24" underground to the shed.

Questions: - Is the wire choice right? I think I just need to make sure I am using THWN cable. Are there other types that would work. It will be in conduit all the way from the main panel to the subpanel. The MHF I see is RHH/RHW/USE rated, which I believe would work. No issues with running that cable in conduit the whole way?

• 4 wires (2hot) (1 Neutral) (#4 Ground). Do the colors matter at this size, or can you wrap them with tape if needed?

• Anything else I am forgetting?

Answer 1

This sounds good overall, with some exceptions. (Also, I basically just set up something similar very recently).

Physical: Sounds good. 90' isn't too bad, and not something where you should have to worry about more than a couple percentage points voltage drop.

Subpanel: If you are using a 100A subpanel, why swap the breaker for a 60A breaker? I am guessing this panel is fed by a breaker in your main panel so that breaker would be rated to protect whatever wire is run. For example, if you run 2AWG Al, it can be protected by a 100A breaker. You also don't need a main breaker in your shed's panel, but it might be nice for convenience.

Wire: I'm not sure what's available to you or what anything costs where you are, but 2AWG is very large, and a 4 wire cable of 2-2-2-4 would be pretty ridiculously stiff. Why not run 4AWG Cu THHN/THWN, which will be easier to work with, and potentially cost less? I'm also not quite sure what you mean about upgrading to 90A based on a 75°C rating... Even running 2-2-2-4 you can get a full 100A without needing to do anything. See below for more about grounding.

Answers:

• Your wire choice seems fine, but I'm still confused about your breaker choice
• THWN is the insulation that allows wet rating. The NEC also specifies several other cables that are suitable for wet locations, including MTW, RHW, RHW-2, TW, THW, THW-2, THHW, THWN, THWN-2, XHHW, XHHW-2, ZW
• Running cable through conduit can be difficult when it's large cable. It really depends on the number of bends, wire gauge, and what equipment you have available
• Colors matter but you can wrap the ends with the appropriate colors to ensure you know which is which
• Check out this question if you haven't already seen it. It has a great answer for what wires you should pull (including an EGC).

Answer 2

Subpanel

I'm glad you got a decently large panel because you don't want to know what a CH duplex breaker costs. CH products are great and sturdy, and I would use them everywhere, but the deal-killer is exotic breakers are wildly overpriced. Other people make great panels too.

You're making a classic blunder by worrying about the size of the main breaker in the subpanel. It doesn't matter; it's nothing but an on-off switch. Whatever practical reason you might imagine, isn't going to work the way you want. Particularly, you can't get the local breaker to trip first, doesn't work.

So just go ahead and do what's cheapest, e.g. keep the 100 it's supplied with. Its only purpose is a shut-off switch (and GFCI or AFCI if it does that, but you can't backfeed those.)

Gory details? OK. The breaker in the main service panel protects the wiring to the subpanel. The main breaker in the subpanel protects the subpanel itself, but that is almost never an issue and won't be here.

Conduit and wire

You upsized the panel, good plan. You're going conduit, good plan. Upsizing the conduit above minimums, also good plan: it makes pulling easier and lends future expansion. Easy pulling is vital for DIY, so you can avoid hiring an electrician simply for his truck full of pulling tools. Electricians won't like doing just the pull and will want a bigger bite of the whole job.

Try to keep bends to a bare minimum, as they make pulling much more difficult. I aim for a maximum of one 90 degree bend between access points (boxes, conduit bodies etc.) but that is not possible in an outdoor run.

"Cable" describes a bundle which contains more than one wire. You don't need to use cable in conduit; it's redundant and a waste of money (unless it's not, best to price it all ways). You can use individual wires such as THWN-2. You can use all-black if you want; wires 4 AWG or larger can be taped to indicate neutral and ground. Wires are easier to pull than cable.

Aluminum wire is perfect for this. You're absolutely welcome to oversize the wire (use a greater ampacity than you're breakered for). If it won't fit on the breaker or lug, pigtail it with a screwdown splice.

As of NEC 2017 you will need to use a torque wrench/driver to set torque on screwdown connections. So hurry :)