Septic wiring - 4 - grounding

Previously: wiring

It used to be that subpanels would run a ground wire back to the main panel, and that was good enough. That's 4 conductors: hot/hot/neutral/ground. The neutral and the ground are bonded in the main panel, meaning they connect to the same bus bar. In a subpanel, though, neutral and ground are kept separate, to stop the ground conductor from carrying the neutral current.

Today subpanels get their own ground rods. These are 8' long, 5/8" diameter galvanized steel rods. You drive them in to the ground 6' apart, and then attach a ground wire to them with special ground rod clamps.

Grounding has two important jobs. First, if lightening strikes the electrical system, the ground wires will carry the current away safely. Second, the metal housing on many machines & appliances is connected to the ground. Normally the ground conductor carries no current, but if a hot wire ever touches that metal housing, it will short & trip the breaker. If it's not grounded, then the housing gets energized, and can shock you if you touch it.

Around here, ground rods are trouble. The subsoil gets extremely hard around 4' below grade. When they put the water main in the street, they had to use a big jackhammer to break it up. They said it was harder than breaking up concrete.

There's no reasonable way to put ground rods in to an 8' depth. Luckily I already knew this from watching the pro install the main panel. You drive the rods in as far as they'll go, then bend them over in the trench. I rented a rotary hammer to put in the ground rods. I planned ahead so they'd still be 6' apart when bent over. When I was done, I discovered they were too close by about 2". I don't know if an inspector would get out a tape measure, or whether they'd reject the work for 2". It was easy to fix, though - I just turned one of them around, to face the other way in the trench. Unfortunately the ground wire ended up much longer, to be able to go from subpanel to one ground rod and then the other. That wire alone cost $25.

(In some places they require the ground wire to have both ends in the subpanel, so it makes a big loop. Guess we're lucky.)

Next: torque.

Septic wiring - 3 - wiring

Previously: shopping

Back at the ranch, I put the subpanel on the post, and glued up the conduit. I plugged in my shop vac and taped it to one end of the conduit. 

At the other end of the conduit we had a spool of mason's twine tied to a plastic bag. The shop vac easily sucked the bag through, pulling the twine behind. This goes really fast. In fact it's so fast that the twine quickly cuts a groove in the edge of the conduit. Watch out for that.

Realize that I was sticking my hands in to a hot electrical panel at this point. No good way to avoid that, though.

We used the twine to pull a 1/4" nylon rope, which we then used to pull the aluminum feeder wire through. Hard work even with wire lube. Arms tired.

I bought a 30A double pole breaker for the main panel, but found the #2 wire wouldn't fit the breaker lugs - too big! You can buy special reducers that crimp on, but then you need a special crimper, too. I decided to upsize the breaker to one that could take #2 wire. I ended up with a 60A breaker. Sheesh. My project to power a 15A pump had turned in to a 60A project.

I did try to push a length of 12/3 + ground UG cable through the 3/4" conduit to the pump. With 3 elbows, it was very difficult. We even used wire lube, but that wasn't enough. We eventually gave up. When we pulled the wire out, the lube picked up grit from the ground. Yecchh. It turned out that 12/3+G was unnecessary, as the pump is 240V only, not 240V/120V, and so doesn't need a neutral conductor. 

I wired up the subpanel feeder and the receptacle on the subpanel post. Then I plugged in the shopvac there, and used it to suck pull strings in to the 3/4" conduits to the septic pump chamber. Electricity is so useful. This may be a violation of electrical regulations, as I was using circuits that hadn't been inspected yet. But maybe none of this is historical fact, but merely my opinion.

With the pull string, it was easy to get the wiring through. I left a pull string behind in each conduit, just in case I needed to pull something else in the future.

While wiring the septic alarm/control panel, I realized I needed another circuit. It wants its own 120V circuit, separate from the pump. It's not uncommon for pump circuits to trip. If they shared a breaker, the alarm wouldn't sound. Another reason the subpanel approach was a good choice!

To wire the control panel, you first have to drill holes in the bottom for the conduit. One for incoming power, one for outgoing pump power, one for the transducer.

I had 3/4" conduit, so I drilled a 3/4" hole with a spade bit. Those are meant for wood, and this was plastic. Spade bits were what I had already. They cut really slowly and made a big mess of plastic shavings on the ground. Sorry, ground.

Wrong size, though. 3/4" conduit needs a larger hole for its fittings. OK, try a 1" spade bit. Closer, but still not big enough. Some internet research, and I found that 3/4" conduit connects to 1 1/8" holes. I bought a 1 1/8" hole saw. The holes turned out nicely, but controlling it was hard - it was easy to pop through the plastic and hit the delicate internals. Maybe I should have removed them first? I also used a small grinder to enlarge the first hole to the proper size.

I sure wish they drilled the holes at the factory, or even provided knockouts.

It took me a couple iterations to get the wiring to the control panel right. There are 5 conductors coming in:

• hot to alarm
• neutral to alarm
• hot 1 to pump
• hot 2 to pump
• ground

I had 12/3+G cable (black, white, red, bare). I also knew I could pull conductors out of a cable as needed. White is usually neutral, but you can can use it for hot if you mark it with colored tape or paint. I wasn't sure what combination of options I liked, so I went to DIY Stackexchange. I ended up with separate conductors, arrange liked this:

• blue hot to alarm
• white neutral to alarm
• black hot 1 to pump
• red hot 2 to pump
• bare ground

I like this because everything gets it's own color. It's obvious what is what.

Here's the 6x6 post with the alarm/control panel on the left, and the subpanel on the right. You can see the flex conduit with the conductors in it, ready to go.

To get the conductors, I stripped the outer sheath off the 12/3+G cable. That was kinda hard, so for the run from the control panel to the pump, I just used 12/2+G, and put red electrical tape on both ends of the white conductor.

I bought the blue separately. It was the only stranded wire, and it was much easier to work with in this confined space. I wish I had used all stranded wire. A professional electrician can keep 500' spools of stranded #12 wire in the truck in a variety of colors, and pull off what they need. I have to measure ahead of time, add 10% just in case, and go on a shopping trip.

Here's the result. 

From left to right: alarm speaker, power in, power out to pump, transducer cable.

I worry so much about cutting wires too short, or about needing to put a new end on a wire in the future, or about wanting to rearrange things and needing a little slack. I try to cut everything as long as I can. Perhaps I should just cut to length, as it would make the wiring much neater. Thanks to conduit, replacing wire in the future is not very hard. *shrug*

Next: grounding

Septic wiring - 2 - shopping

Previously: design

I didn't realize this before, but electrical work is primarily about taking trips to the store. There are so many specialized bits and pieces, you can't possibly have everything you need on hand. Apparently this is true for professional electricians, not just folks like me.

In order of distance:

There's the local hardware store. Friendly folk, limited selection, a bit pricey.

There's a lumberyard where I bought the 6" x 6" treated post, just outside of town.

There's a lumberyard / building supply close to the next town. They cater to pros, so you kinda have to know what you want ahead of time.

There's a bigger hardware store in the small town to the south, with friendly folk and a slightly larger selection, and better prices.

There's an electrician in that same small town, with a retail operation. Huge selection of electrical parts. Only open M-F, 8-5. 

There's a Home Depot in Sequim, which is 45 minutes away. I usually avoid big box stores.

Every time I needed something, I had to guess which place would have it. Closer = better, but stopping at each store in turn takes forever. I did learn to buy things I thought I *might* need, not just things I *knew* I'd need, with the plan to return unused items at the end of the project.

I had a particularly hard time finding the right feeder wire to the subpanel. I knew I wanted 8 gauge copper. #10 is required for 30A, so #8 is upsizing for voltage drop. No one had 8 gauge cable, but Home Depot did have separate conductors. I thought cable would be easier. Their price was $0.72 / ft for each conductor. 3 conductors required (hot, hot, neutral), so $2.16 / ft. 

They asked if I would take aluminum, as it's much cheaper. You have to use one size higher aluminum than copper (so 6 gauge in my case) but it's still cheaper. They didn't have any #6 Al, nor any #4, but they did have #2, as 3 strands twisted loosely together (called 2-2-2). Wow, that's huge. But it was still $1.00 / ft -- less than half the price of the #8 copper. I decided to go for it.

They didn't have 170' left on the spool. There was some 2-2-2-4 available, but I didn't need that extra conductor. The computer showed another full spool in stock somewhere. They found it on a high shelf (very high!). They brought in the forklift, closed off the aisle, pulled the spool down, took it off the pallet, and set it on a spinner to pull wire off. They measured out 170' and coiled it up for me. I thought about buying the whole spool of 500', since I have plans for a second subpanel with an even longer run, but I didn't know for sure this was the right thing. Also, I didn't know if the van could carry that much weight. I had arrived at 8:30pm, and closing time was 9:00pm. I left at 9:30pm with wire, a subpanel, and other bits and pieces.

Next: wiring things up.

Septic wiring - 1 - design

A few weeks ago they started building our septic system. Because of poor soil, we have a pretty large drain field, which requires a large effluent pump, at 1.5hp.

I decided to do the electrical work to power the pump. Previously I hired an electrician to wire the main panel, because I thought I was in a hurry and I didn't think I knew enough to do it right. I watched & learned, and this time I was ready to do it myself. 

You might think I wanted to save money, but that doesn't make much sense. I'm much slower than a pro, and only a small part of the price is the labor. Mostly, I like doing electrical work, so it was an opportunity for play.

Here's the setup:

- The main panel w/ power meter is at the edge of the property.

- A 150' long, 3' deep trench leads from the main panel to a convenient spot near the pump.

- The 240V 15A pump sits in a large, underground concrete tank. 

- A "transducer" also lives in the tank, to measure the water level.

- A small computer watches the inputs from the transducer, and turns the pump on as appropriate. 

The plan was to run 2" conduit from the main panel to a 6" x 6" pressure treated post near the pump. The post would also hold the septic control/alarm panel. Then there are two 3/4" conduit runs from the control panel to the pump chamber - one for the pump, and one for the transducer. I don't really know why they get two separate conduits. Maybe to avoid electromagnetic interference. 

I started with the idea that the pump needed a 240V 15A circuit, which normally requires 14 gauge copper wire. Long conductors should be a little thicker, because voltage drops over distance. So I was thinking 12 gauge wire. 12 gauge is very common, so that's good news. 

A 240V circuit has two hot conductors, and possibly a ground. There's no neutral wire. If you have two hots and a neutral, it's a 240V/120V circuit. Ovens and dryers are usually 240V/120V. Ovens often have a 120V clock and a 120V receptacle for your coffee maker or whatever. Dryers have a 120V motor, so the gas-heated model can use the same motor and not require special wiring. By comparison, electric hot water heaters are usually 240V only.

I wanted to include a convenience receptacle on the post as well, so I was going to pull a second set of conductors (hot + neutral) for that purpose.

I was considering the option of putting a subpanel on the post, and taking short-run circuits off that for the pump & receptacle. It seemed more useful in the long term to have a subpanel, but also more complicated and expensive. I wasn't sure which to choose, so I asked on the DIY Stackexchange site. Their answers were helpful but inconclusive. They did suggest oversizing the pump circuit even more, to 10ga, to further protect the pump motor.

Thinking about that problem, I realized a great benefit of the subpanel approach: it leaves plenty of headroom for one large load. Consider:

Option A: two 15A circuits, 100' long, on 12 gauge conductors. One circuit carries a 10A load. According to my 2011 NEC handbook (215.2(A)(4) and Chapter 9, Table 8), the voltage drop would be 2 x 100' x 1.21 ohm/kft x 10A / 1000 = 2.4V. 

Option B: one 30A subpanel, 100' long feeders, on 8 gauge conductors. One branch circuit carries a 10A load. Voltage drop is 2 x 100' x 0.764 ohm/kft x 10A / 1000 = 1.5V. That's because the 10A load gets to take advantage of larger conductor that it shares with the rest of the subpanel. When the subpanel's other circuits are idle, which is most of the time, there's a lot of headroom available. 

Using a subpanel would be good for the pump motor, so I decided to go that way.

So the plan is 8 gauge feeder conductors through 150' of 20" conduit from the main panel to the subpanel. A 240V 15A breaker to the pump circuit with 12 gauge wire. A 120V 20A circuit with 12 gauge wire to a convenience receptacle on the same post.

Next: shopping!

Slow!

The dirt road by our land was merely a public trail in the eyes of some of our neighbors. Between my family & another new house going up, we've brought in a lot more car traffic to this quiet area. My neighbors asked for our help in keeping the path comfortable for non-motorized users. So we put up this sign:

Mailbox

The mailbox has been up for a month or more, but I only just labeled it.

It's about 500' from the mailbox to our property, so I wanted to make sure I got a mailbox big enough for most USPS-delivered packages. This one looks large enough to fit a small child in. I haven't checked ... yet.

How to build a yurt platform - part 8

With the posts in place, it was time to install joists.

My carpenter was feeling better, but I decided to continue on our own. I was annoyed about some decisions he made that made a lot of trouble for me. I think that putting the pier blocks on the ground would have been fine. Perhaps with a little digging & filling in the soft spots, but I ended up with 5 yards of gravel packed in to holes. Also, the 12 marking strings parallel to the centerline (and their 24 batter boards) were unecessary; I could see that but he couldn't. He's probably a great carpenter, but his plan for a yurt deck weren't ideal. I'm not a great carpenter, but I figured I could handle it, and I was looking forward to the experience.

So, joists. Here's the manufacturer's suggested design:

They suggest 8', 10', and 14' lumber for the joists. When the yurt was in its previous site, several of the joists were much longer. This is a good thing, as it's stronger: load on one span partially transfers to the next span.

6 of the beams from the previous site were untreated lumber. I think they just found some 4" x 6" beams cheap, maybe from some other project, and put them to use. We decided to replace them with treated wood, so they wouldn't be the weak spot in the new deck. I bought a few 20' x 4" x 6" beams from the lumberyard and hauled them home on the lumber rack on my F-250. (And I used to be a computer programmer!)

I wonder how important the treating really is. Houses are built with untreated joists over a dirt crawlspace, and they last plenty long. Sill plates are typically treated, but that's because they rest directly on the concrete foundation. None of my wood rests on the ground or on concrete. It's all protected from direct rainfall. Maybe a little rain water can splash up off the ground, but you could just make the posts treated, or add a plywood skirting around the perimeter to keep out rain. Treated wood is expensive; you need special fasteners; its a health hazard to work with; the sawdust pollutes; its splinters hurt more; it's less straight.

My strategy was to install the middle joists first, then measure off them as we worked our way out. (Working from one side to the other would magnify error.) We plumbed 3 posts with material under the pier blocks and aligned them as best we could. We put the joist in place and leveled it out with a 4' level by adding/removing material under the pier blocks. We slid the pier blocks side to side to get the alignment right.

At the previous site they nailed the framework together. Taking that apart was such a pain, so I insisted on screws. Simpson Strong-Tie sells structural screws to go with their metal bracing, hot-dipped galvenized for use in ACQ pressure-treated wood. 1.5" screws are $15 per box of 100. They are nice to work with. Heads are 1/4" hex. Framing took about 4 boxes.

We did it repeated the process with the adjacent joist, and then leveled them relative to each other and set them 48" apart on center. Once everything looked good, we the joists against the posts (making many triangles) and against each other (more triangles).

We continued the process over all 30 pier blocks, for a total of 180' of joists.

This was a very tedious process. The pier blocks can move along the joist (not very important, except at the end of the joist). They can move across the joist (important). To plumb the posts, I would move the pier block, adjust the ground underneath, and restore the block. The tops of the posts have to be level in two directions, which I did by adding & removing material under the pier block. Each adjustment can affect all the others. So we would measure everything (4' level, tape measure, and post level), then adjust the one that was worst, then repeat.

I learned a few tricks along the way:

• If the pad under the block is pretty level, you can slide the block around without changing height of the joist.
• You can bend the metal bracket on the pier block to get the post close to plumb without moving the block.
• You can screw the post on to the joist with just 1 screw, brace the joist at 48" O.C. from the previous joist, then slide the block around until its plumb.

Once the joists were all in place and braced together, we filled in holes around the pier blocks with soil. Our soil is normally very hard. When you dig it up and mix it with water it's a very slippery mud, but when it dries out it's very hard again. The idea is to stabilize the pier blocks, to stop them from slipping sideways. I started with the spoils of our previous digging, but then I switched to fresh, loose soil from the septic install.

Next: bracing / flooring / insulation / perimeter blocking