Wiring a second subpanel

Previously I wired up a subpanel to supply power to the septic system. As long as we had the heavy equipment on site, I wanted to bring utilities to the yurt/RV site, too.

The plan was similar: 2" conduit from the main panel to a subpanel on a 6" x 6" pressure treated post by the yurt. A receptacle on the post.

Last time I used 2-2-2 aluminum feeder wire, which was rejected because it lacked a ground wire. This time I knew better, so I went for 2-2-2-4 aluminum. I went to Home Depot on Father's Day. I wanted to buy the wire in the morning, and bring my family out to install the subpanel in the afternoon. I figured it'd be fast since we'd done this before. At Home Depot it took a long time to find someone to help me with wire, and then he said I'd have to wait 2 hours while they got it down from the high shelf, measured, cut, etc. I didn't get home until 6pm. We decided to postpone Father's Day until Monday.

The wire was on a fresh 500' spool. I bought 240' (11 sticks of 20' conduit in the ground + 5' riser at each end + 10' extra, just in case). They measured 260' off the spool and gave me the rest. I think they should sell me the entire spool, and refund me what I don't use. It would save them the hassle of measuring & coiling 260' of wire, the spool is useful when running the wire, and I could avoid buying the extra.

As before, we used the Shop Vac to suck a mason's line through the conduit. We used that to pull a 1/4" nylon rope. My rope was only 230' long, and so it wasn't quite long enough. That's OK, we'll just start the pull with the mason's line (when it's easy) and then do the rest with the larger rope. Just when we were about to pull the wire, I lost the little bit of mason's line. We had to pull out the yellow rope, untangle the mason's line, and vacuum it through again, and pull in the yellow rope again.

We discovered we could communicate by talking through the conduit. That was pretty fun. Worked better than yelling through the woods, too.

240' of 2-2-2-4 Al wire on a big spool is pretty heavy. To unwind it, we put a stick of conduit through the middle and propped it up on a step ladder. The wire is so stiff that it's a job just to pull it off the spool. It's another job to push the wire bundle in to the conduit at one and, and 3rd job to pull the rope at the other end.

When I wired the first subpanel, I tapped the main panel with a 60A breaker. (Remember that my plan was 30A, but #2 wire will only fit in a 60A breaker. Fine). Well, the main panel has a restriction that the largest breaker allowed on the left side, with aluminum wire, is 50A. So the breaker goes on the right.

The panel only has 4 full-sized slots, two on each side, so that limited my options for tapping for the second subpanel:

• Splice the feeder down (in the panel) to smaller gauge copper. Since voltage drop and conductor cost are unimportant over this short distance, you can use minimum-sized copper (#8 for 50A, for example, much easier to bend) and it will fit in a smaller breaker.

• Crimp on a reducing pin adapter. These require a special crimping tool, which isn't useful for much else.

• Tap the feed-through lugs. You don't get a dedicated breaker, you just attach the feeders directly to the bottom of the main panel.
  
  
  
  There's a special rule that a subpanel's feeder wires can be protected by a breaker at either end - at the main panel or at the subpanel. (Or both, which can be convenient). The nice thing about protecting at the subpanel is that you don't have to walk to the main panel to shut off the sub. 

I selected the last option.

Some panels can take a main breaker, but the only outdoor-rated main breaker panel at Home Depot was enormous - 20 spaces - and I knew I didn't need that much. I went with the same 8-space panel I used for the septic subpanel, and added a backfed main breaker. This means a regular breaker in a regular slot, but the power is going through it backwards - from the wires *into* the panel, not the other way.

The main annoyance with a backfed breaker is that you have to attach a special retainer clip to the breaker, so a future electrician doesn't pull the breaker and assume that it's dead. I bought a backfed breaker retainer clip when I was at Home Depot, but apparently I bought the MBR2 and this panel needed an MBR1. Doh.

It's just a little bit of plastic, nothing complicated or expensive. But neither local hardware store had one. Double D Electric, an electrician with a retail operation, had a box full of MBR2, and an empty box labeled MBR1. Damn.

I had them special order the MBR1 and finished the rest of the wiring while I waited. There are receptacles in a weatherproof box on the post - this time I used a double-gang box so I could have 4 total outlets.

Ground rods in the ditch - the ground was very hard so they barely moved under the force of the rotohammer. They just made it in the first foot, and then I bent them over.

Neutral 3 lug kits - one for each end of the ground wire + one for the neutral wire at the main panel.

Because the wire is long and expensive, I wanted to cut it long. Suppose I screw up & need to cut the end off? Or I want to move the panel a short distance? At the main panel end, I put in a loop.

At the subpanel end there's not enough room for a loop, so I sent the wire on a long journey in the panel. It comes in at the bottom, turns right, then up the right side, across the top, down the left 1/2-way, and in to the breaker.

Finally the hold-down clip arrived at 2pm. The cutoff for requesting an electrical inspection is 4pm. I wanted to get the job 100% done before calling, in case something needed more work. Picked it up from the shop, headed out to the site, and spent 15 minutes trying to figure out which end was up. I snaps in to the bottom of the breaker in a specific way. Then you install the breaker in the panel and the clip snaps it a special slot. Turns out this slot is on the *right* side of the panel, and I had installed the breaker on the left. Time to re-route the feeder wire. This #2 stuff is hard to bend, and I had too much of it (on purpose). I wrestled it in to a new shape, going up the right, then down the right, then back up the right in to the breaker. It's a bit crowded in there, but it works. It was still before 4pm, so I called in the inspection.

The only work left was to label the panel's front plate and remove the knockouts for the breakers. I had waited to do this until the retainer clip was installed because I knew there was a chance I'd need to move the breakers around, and I wanted to avoid popping out the wrong knockouts. Good thing, since I had to move the breaker just as I'd feared.

I carefully oriented the front panel correctly, picked the right knockouts, and removed them. Then I put the panel on the breaker box and discovered that I had it backwards. Wrong knockouts. This is why I keep filler plates on hand.

I never saw the inspector, but the next time I looked at the panel, there was a sticker and the permit had notes of approval on it. Yes! I'm done wiring for a while.