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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?

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    Sounds good. Why the need to limit the service now though? Why not just feed for 100A and not deal with it later? – TFK Mar 27 '17 at 18:02
  • Just a little more background, and reasoning behind my thoughts: My main house has 2 panels, each with 150amp mains. At the moment, I won't be doing anything more than small 110v power tools, and lights in the shop, so I figure I can add in the 60A breaker without touching the house service. If I go to 100A, then I'll need to upgrade the house main breaker now. I'd rather not do that at the moment as I can add on a breaker in the panel leading to the sub, but don't want to mess with the line from the meter today if I don't have to. – AlanMattson Mar 27 '17 at 20:07
  • You don't need to upgrade the main breaker to be greater-than-or-equal-to the sum of the circuit/feeder breaker ratings. – Hari Ganti Mar 27 '17 at 21:07
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    I'm worried 22 spaces might be kinda small for a shed. :) (inside joke... I like large panels and have been known to take it to extremes :) Seriouly though, much as I love my CH panels, very well built... the problem is exotic breakers like tandems, GFCI, AFCI and the like are extraordinarily expensive, so I would never buy another one. – Harper Mar 27 '17 at 21:30
  • It's hard to predict the future, and I've been known to overbuild myself. I don't know at this point if I've come out ahead or not with my "savings" by putting in more than I need today in hopes of saving money by not needing to redo it in the future. Thanks for all the help @HariGanti – AlanMattson Mar 27 '17 at 21:50
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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).
  • So, it seems there are lots of opinions on the wire size. From what I see in this question, the temp rating of the breakers come into play. From what I understand, my breaker is rated 60* for Cu and 75* for Al. From the chart in the other page, at 60*, #4 copper is only good for up to 70A. I can fit #2 copper, but that still only gets me to 95A. If I do aluminum, I can bump up to the 75* rating of 90A on a 2-2-2-4 line. vs 95A on #2 copper. – AlanMattson Mar 27 '17 at 20:18
  • The 60A breaker ? vs leaving the 100A one that came with the panel is just a preference. I need to either buy (2) 60A breakers - One for each end of the shed link, or a 100A for the main panel link to the shed, and need to replace the 150A main with a 200A. Either way I'm buying 2 breakers, and I'd rather just wire up the downstream piece than have to worry about replacing the main breaker. (more details in the top comments)I don't need anything more than 60A at the moment, that seems like a better option. If I can get the largest wire I can, then at least I have a little flexibility later. – AlanMattson Mar 27 '17 at 20:26
  • It's interesting that your main breakers are rated for only 60°C... I would have imagined a 75°C minimum (as mine are). Anyway, this may be a reason to use a main lug instead of a main breaker. The terminations are often 90°C, from the panels I've seen. – Hari Ganti Mar 27 '17 at 21:03
  • Also, I still have no idea what you're saying about the 60A vs 100A breakers... Why do you need to replace other breakers? You can have 150A worth of circuit/feeder breakers installed in a 100A panel. For example, if you only use 60A (100% NC + 125% C), you can put a 60A 2-pole in your main panel, run your 95A of 2AWG Cu, leave the 100A breaker, and go on with your life. To upgrade to 100A, you'd only need a 75°C breaker to replace the 100A one in the panel, plus another in the main. – Hari Ganti Mar 27 '17 at 21:06
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    Follow this question (diy.stackexchange.com/questions/111063/…) – Hari Ganti Mar 27 '17 at 22:55
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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 :)

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    I suppose it's good that torque wrenches/screwdrivers don't cost too much. It's also great knowing you set things to a value instead of just "guddentite." – Hari Ganti Mar 27 '17 at 23:06
  • "You can't get the local breaker to trip first, doesn't work". Is this always the case? I have always wondered why the fuse blows in the house instead of the pony panel breaker in my shop. – user48010 Mar 27 '17 at 23:53
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    @FighterJet For a slow thermal trip (150A on a 100/60 breakering) the smaller one will tend to trip first. Usually. But for a magnetic trip (800A), it's closer to 50/50. However it also works like Roger Rabbit's handcuffs... if it's raining and the clock is ticking on the epoxy and the near one is Right There, you know what'll happen! – Harper Mar 28 '17 at 0:41
  • @HariGanti Torque screwdrivers are crazy priced right now. I plan to go with an old-fashioned $25 beam torque wrench. They rely on simple laws of physics and don't need calibration ever. – Harper Mar 28 '17 at 0:44
  • @Harper They're like $60... As for the beam wrenches... Those only don't need calibration if they stay within the linear elastic range, they don't apply torque in only one direction, and they are always used at the same temperature. Also, they don't typically ratchet. – Hari Ganti Mar 28 '17 at 17:15

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