Electrical Wiring - Part 1

Disclaimer: Electricity is dangerous, so I am never going to write a blog post about How to Wire a Tiny House as if I'm now an expert or something. There are books about wiring; read those if you really want to know the nitty gritty. All I'll write about are my impressions of the process and my personal experiences with wiring a tiny house made of SIPs.

So, how was it? Well, for at least the first 90% of the process, it was... torturously slow and rife with hand-wringing impasses and ignorance anxiety. One of the first receptacles I wired, I re-wired twice before I was satisfied. I scratched my hands all up, I cussed a lot, I even accidentally stabbed myself in the face with needle-nosed pliers.

This stuff is harder than it looks!

But do I think I did a good job? Yeah, I do. I'm pretty confident that my house won't burn down and that everything will work as intended. Why? (Because plenty of homeowners who are much dumber than me do it all the time without major catastrophes... But also--) Because I took it slow, because I wrung my hands, and because I constantly stopped what I was doing to look up references, draw out diagrams, and re-do even my hardest-fought work just to make sure it was right. There was zero "Eh, I'm sure it'll be fine." 

A lot of my anxiety stemmed from the conceptual aspects of wiring. How does electricity flow, how do these devices work, that sort of thing. Even after I basically understood it, I still had to make sure, make sure, make sure every step of the way.

My biggest surprise was how physically difficult wiring is, as well. It took a strong grip on the wire stripper to pull off the insulation. It took finesse to bend the wire into just the right shape to hook around the screw on the switch or receptacle. Pulling the cable into the box, twisting the wires together for pigtails, pushing and screwing the receptacle into the box--there was always resistance and frustration, and more of them than I expected (just keep reading, I'll tell you about it!). 

Now I know.

And actually, once I started to learn the physical tricks of the trade, wiring actually became almost--yes, almost--fun! But again, that was about the last 10% of what I've done so far. There is still a little bit of work to go--the ceiling fixtures, one outdoors outlet, the main bank of light switches, and the main hookup and circuit breaker box--so maybe that work will go smoothly, now that I'm not quite as big a rookie.

One big rookie hurdle is vocabulary. Like the rest of the construction trades, electrical wiring seems to have a language of its own--with a fair number of dialects, slang terms, and ambiguities in the mix. To the best of my ability, some key terminology (with my own definitions) follows:


TERMINOLOGY:

Device: a receptacle/outlet, switch, or hardwired light fixture.

By the way, Hardwired: permanently connected to the electrical circuit, i.e., doesn't have a plug and is often operable via a wall-mounted switch.

Receptacle: the thing you plug a plug into; the thing you install in an electrical box to create an electrical outlet; usually has two female plugs (i.e. a duplex receptacle).

Electrical box: the plastic, metal, or fiberglass box that contains a device and all the stripped wires and whatnot.

New work electrical box: is installed by nailing it to a stud in an open stud wall; assumes you're installing the box before any insulation or inner wall surface is installed.

Two-gang new work electrical box with two duplex receptacles and pigtails covered by wire nuts.

Old work electrical box: is installed via a hole cut through the inner wall surface (in a typical house, drywall) and attached via screws from the front of the box into the inner wall surface.

One-gang, two-gang, three-gang: of an electrical box; refers to how many receptacles or switches (or a combination thereof) will fit in the box.

Pigtails: a way to connect wires together by twisting their stripped ends together, so that electricity has a continuous path to flow in and out of an electrical box and to the device in that box. Each pigtail is tightened, covered, and insulated by a screw-on wire nut.

Circuit (or branch circuit): a set of devices and the electrical wires that connect them that originate from a common circuit breaker.

Circuit breaker: a small box-shaped device through which electricity flows before it goes into the wires in the wall and out to the outlets, light fixtures, and whatnot on a circuit. It automatically turns off the electricity to the circuit if something tries to pull more electricity through the circuit than the circuit is designed for; it can also be turned off manually to cut power to the circuit for safety, repairs, etc.; or, in the case of AFCI- and GFCI-protected circuit breakers, it will shut down if an arc or ground fault is detected in the circuit, to prevent fire and electrocution (respectively).

Main breaker: a big circuit breaker that mediates the flow of electricity from outside the house to the branch circuit breakers.

Circuit breaker box: a giant electrical box that contains all the breakers.

ELECTRICAL DESIGN:

Red, black: hot. White: neutral. Bare: ground.

The electrical supply to my house is a 50 ampere, 120/240 volt RV power inlet that will be connected to the main breaker via 6-gauge cable. It has two poles, that is, instead of one hot wire in the cable carrying 50 amps at 240 volts into the house, it has two hot wires each carrying 50 amps at 120 volts. (It also has a neutral and a ground wire.) These wires can operate independently of each other. This is great, because all of my devices and appliances will run on 120 volts of power; very few household appliances, like electric ovens and water heaters, require the full 240 volts in the United States. The fact that my power supply has two poles at 50 amps means that all together, I have 100 amps of 120-volt electricity at my disposal. Volts x amps = watts, so theoretically, I could run 12,000 watts' worth of lights, cooking appliances, heaters, computers, vacuum cleaners, fans, and everything else, simultaneously. When an LED lightbulb only takes 6 watts and (what is for me) a big-ticket appliance like a microwave uses 1,000 or less, that's a lot of power!

50 amp RV power inlet from the inside

Those theoretical 12,000 watts don't really add up in real life, however. Circuits actually have a maximum sustained capacity of 80% of the stated capacity; if you try to use more than 1,440 or 1,920 watts for a continuous period of time on a 15- or 20-amp circuit (respectively), it'll trip the circuit breaker. Of course, the same goes for if you ever, even for a moment, try to pull more than 1,800 or 2,400 watts through, since that's the absolute maximum. That means I could actually sustain 9,600 watts of electricity usage across all my circuits simultaneously. That's still a lot!

My 100-which-is-actually-80 amps of electricity are divided among six circuits: kitchen 1, kitchen 2, kitchen 3, bathroom, bedroom/living room, and exterior. The kitchen circuits are 20 amps each, and the other three are 15 amps each, which is pretty normal. The kitchen is where the majority of my electricity usage will occur, since my cooking appliances will all be electric (induction burners, convection/microwave combo oven, electric multipot). The main electricity user for the rest of the house will be heating in the bathroom and bedroom/living room, and at most that will only account for about 800 watts. Lighting, computer and phone charging, and ventilation fans will account for most of the rest of the daily loads.

You might notice that those six circuits add up to more than 100 total amps. That is okay. Did I say 9,600 watts is a lot? That was an understatement! It would take an extraordinary, intentional effort to max out all of the circuits at once--I just won't have room in my house, or counterspace in my kitchen, or quite frankly outlets to plug in all the appliances it would take to consume all that electricity! So, no, I'm not worried about overloading my system. I've got a nice, healthy cushion built in, not to mention self-enforced energy conservation.

My other safety net is that all my circuits are AFCI- or GFCI-protected. (AFCI stands for arc fault circuit interrupter, and GFCI stands for ground fault circuit interrupter. I noticed the guys in the local electrical supply store shortened it to AFI and GFI. Dialects, what did I tell you?) The bathroom and exterior circuits are GFCI-protected at the circuit breaker, while the kitchen circuits are GFCI-protected at the first outlet, which--as long as I installed them correctly, which I believe I did--confers protection to the rest of the outlets down the run. Protection at the circuit breaker is great for ease and versatility, but protection at the first outlet is cheaper, especially for higher-amperage circuits. The bedroom/living room circuit won't be in danger of getting wet--a major, if not sole, cause of ground faults--so instead I gave it AFCI protection at the circuit breaker.


THINGS I LEARNED (or, BITCH, BITCH, BITCH, SOLUTION):

Electricians hate SIPs, and I totally get it now. The SIP manufacturers' websites led me to believe it would be a piece of cake to install my electrical boxes and such, but those curmudgeonly-sounding guys on the online electrician/contractor forums were absolutely right: it's a huge pain in the butt.

As I mentioned before, you need to use old-work boxes in SIPs, since the interior wall surface is pre-installed. In most houses, you'd cut through drywall, maybe push aside some fiberglass insulation batts, pop the box in, and fasten it in place. However, OSB is much harder to cut than drywall, and then there's a solid core of polystyrene foam that you also need to excavate to make room for the box. It's messy, and that's not even the worst of it...

Cutting holes in SIPs is especially tricky when you've already pulled the wires through and have to avoid cutting them. I tried a jigsaw first, and it was slow and tended to wander off the lines. I also tried a keyhole saw, which is what you'd normally use to cut precise holes in drywall, but it was no match for OSB. A reciprocating saw (AKA Sawzall) did the best job--fast and straight--but you have to drill holes big enough to fit the blade to start, so you won't ever get perfectly straight lines all around. And in all cases, it's hard to hold the saw in just the right position where it's shallow enough to cut the wires, but deep enough for the blade to stay in the hole and not kick itself out.

Once the hole is cut and the foam excavated, you might want to know whether the box will fit. And that's too bad, because you have to pull the wires into the box to test-fit it, and it's next to impossible (by design) to pull the wires back out if the box doesn't fit... so good luck adjusting the hole size with the wires and the box in the way!

So, why not err on the side of too big? Mainly because the flanges on the front of the box through which you're supposed to fasten the box in place are tiny, so a hole that's just a little too big will cause that flange to miss the wall surface.

Finally, the solid core of polystyrene foam--while fantastic from an R-vale point of view--really gets in the way of fine-scale adjustments and, well, fitting everything into the hole in general. You want a little extra cable in the wall cavity in case you ever need to rewire the outlet, but that means excavating even more foam to create space for it.

I thought I could use extra-shallow boxes so that there would be more room in the wall cavity for everything. I quickly found that shallow boxes don't work except for end-of-run devices, that is, devices where wires run in from a previous box but not out to another box farther down the line. Otherwise, there's just too much that needs to go on inside the electrical box; pigtails take up a lot of space!

A solution to these woes, however, exists. It's simple, if unconventional: I plan to trim out the holes and install the boxes to the solid wood of the trim, rather than the OSB. The trim will hide the irregularities of the holes I cut; will make the outlets and switches project out from the wall, so they don't have to fit entirely inside the wall cavity; and will fit flush against the box, so those fastening flanges will definitely line up with a fastening surface. It might look funny, but more on the order of "quirky aesthetic" rather than "unskilled work," which I can live with!

I'm still not done with the electrical work, but I am done with installing boxes in SIPs, thank goodness. I'll post Part 2 once I finish the rest of the electrical work and hook up the main breaker box!