Editor’s note: This is one in a series of blogs detailing the construction of a net-zero energy house in Point Roberts, Washington, by an owner-builder with relatively little building experience. A list of Matt Bath’s GBA articles can be found at the bottom of this page. You’ll find Matt Bath’s full blog, Saving Sustainably, here. If you want to follow project costs, you can keep an eye on a budget worksheet here.
My net-zero home will be all-electric, in hopes that someday I can move from net-zero to completely self-sustaining and off-grid as technology improves. Battery prices are dropping rapidly and in my opinion it is only a matter of time before the electrical grid becomes a thing of the past. (If you aren’t a believer, check out this presentation by Tony Seba, a Stanford professor who has spent his life researching the advancement of technology.)
Fully electric houses require larger service entrance panels that contain space for more circuits than those of the average fossil-fuel house. This is absolutely not to be confused with a higher power rated service entrance panel. If you build your net-zero home properly and buy the right appliances, you won’t use any more power than the average home that uses electricity and fossil fuels.
I started with a list of all the circuits I would have, as well as the breaker and wire gauge sizes, all of which I will explain shortly. [Editor’s note: Wiring is potentially hazardous. Check with your local building office on whether a licensed electrician is required to do the work. Know your local codes, and never proceed when you are in doubt.]
The modern electrical service uses two nominal 120-volt “phases” of electricity that cancel each other out (nominal meaning they won’t actually be exactly 120 and will vary). This allows you to power circuits with either 120 or 240 nominal voltage.
Some circuits that use a lot of power take up two spaces in the main panel. These are 240-volt circuits. The first step in installing the electrical work is the same as with almost every step in the building process. You’ve got to have a detailed plan. That means deciding where all your receptacles, lighting fixtures, smoke alarms, and appliances will go, and what types of appliances you will have.
Locating receptacles and light fixtures
Receptacles must be located on every wall that is greater than 2 feet long and be placed no greater than 12 feet away from another receptacle along the same wall or an adjoining wall. On kitchen countertops, this distance is reduced to 4 feet. Additional outlets may be desired for areas with computer equipment or television screens. For example, I will be using Japanese-style toilets so I needed to install receptacles behind the toilet locations. The toilets will help me save sustainably by eliminating toilet paper waste, which in turn will help my septic system remain in good condition.
Receptacles can be placed at any height below 66 inches. I used an 18-inch mark on a piece of scrap wood to ensure that all of my receptacles were the same height. I used another scrap piece of wood to ensure that the boxes were spaced 1/2 inch out from the stud so that they will be flush with the drywall.
Every room must have an operable light fixture. Three-way light switches must be installed in stairways so the light fixture can be operated from either the top to the bottom of the staircase. More than one light fixture per room probably will be desired. Recessed lighting is attractive but not advisable when placed under an unconditioned space due to the difficulty in air sealing them. Surface-mounted LED lights are a newer technology that is hardly distinguishable from recessed lighting but much easier to air seal.
Every bedroom must have a smoke alarm, and an additional smoke alarm must be installed near the sleeping areas on each floor of the house. Smoke alarms must be wired in series together so that if one of them detects smoke they will all go off.
Be sure to check with your local electric utility to see if rebates are offered and save sustainably by balancing the cost of the appliance with the yearly operating cost. Check the specifications for each appliance and note the breaker size (also known as overcurrent protection) and voltage required. Appliances that say 120/240 need both 120 volts and 240 volts.
Additional wiring may be desired for doorbell, internet, speakers, and security. You may also want to provide additional circuits for the future. For example, I don’t currently own an electric car but I am fairly certain I will in the future so I included wiring for a charger.
Running cable for receptacles and appliances
With all of the gang boxes nailed into place, it was time to run the cables from the main panel to each outlet. Bear in mind that what we refer to in English as an electrical outlet is known as a “receptacle” in the electrical code.
When I refer to an outlet as an electrician, I am talking about the location where electricity will be utilized. This could be a receptacle, but it also could be a light or an appliance. The wires will carry the electrical current from the panel to the outlets. Most electricians use use NM-B type wire, commonly known by its trademark name, Romex. Standard Romex contains two (one white and one black) or three (white, red, and black) insulated conductors, and a paper-wrapped copper ground wire, all bundled together and wrapped in its own paper and insulation.
The paper might seem dangerous, but it is treated and it allows the wires inside to shift and slide without as much friction, making installation much easier. For any appliance you wish to power, you first need to decide whether to use Romex with two conductors or three. Appliances that require 120 or 240 volts only need two conductors. Appliances that say 120/240 require both voltages and you must run a three conductor cable to power them. You also use three-conductor wire for smoke alarms and for lights that are controlled by multiple switches.
The next thing you need to decide is what size conductors you need to use. The more current a given appliance needs, the bigger the wire should be to ensure the voltage doesn’t drop significantly by the time it reaches the appliance, and the wire doesn’t heat up so much to melt the insulation and cause a fire.
Properly sizing conductors can be quite involved, but doesn’t need to be when dealing with residential construction under normal circumstances. It can usually be simplified to just using the table above found in the NEC (National Electrical Code), unless the appliance is going to be running continuously.
As you can see, from the chart below, I listed all of the wire sizes for each circuit. In this way, I was able to plan which route each wire would take from the main panel to the outlet it is powering. When several wires take the same route, that is referred to as a raceway. It helps to plan out raceways in advance so you can drill one big hole that is just the right size for the wires instead of a bunch of smaller holes for each individual wire.
It is easier to start by running the larger wires first, and then run the smaller wires around them. For example, the first wire I ran was one of the bigger ones, for my induction range. The manufacturer states it requires a 40-amp circuit, with access to both 120 and 240 volts, so using the table above, the circuit requires 8-3 cable.
Circuits for appliances like the range are very simple, and usually consist of just a single cable. Once I had wired all of the appliances, I started on the circuits for the receptacles. Each of these circuits contains multiple receptacles, so you run a wire to the first gang box, and then another wire from the first box to the second box, and so on.
Building codes require some receptacle circuits to be on their own, such as those in bathrooms and the garages. Kitchens must have two separate receptacle circuits, although one can be combined with the dining room as I did. This is to ensure that several high powered items like blenders, hair dryers, power tools, etc. can be used at the same time without using up all the available current in the circuit.
Don’t overstuff the boxes
Bedrooms, on the other hand, can be wired on the same circuit since those receptacles are usually only used for low-power items like phone chargers, lamps, and computers. In these cases, thorough planning is required so you don’t run too many wires into a gang boxes.
Boxes allow only a certain volume of wires and devices to fill them. Box- fill calculations sound difficult at first, but it’s pretty easy once you get the hang of it. Each box is labeled to show its volume, and using a table in the NEC you can quickly see how many conductors of a certain wire size are allowed.
The gang boxes that I used were labeled so I knew exactly how many conductors they could accommodate. Most gang boxes have a light or a switch or a receptacle in them, so that counts for an additional two conductors. You have to count an extra conductor to account for all the ground wires bundled together.
This all adds up. For example, in the gang box pictured below, there are three 14-gauge cables that each contain two conductors, one cable that contains three conductors, and two switches. So you have to add nine for the conductors, four for the switches, and one for the ground wires, for a total of 14. This box must be sized for at least fourteen 14-gauge conductors.
Wiring the lighting circuits
Lighting circuits are by far the hardest ones to wire. LEDs use very little power, so I only used two lighting circuits for the entire house. One powers the first-story lighting, and the other takes care of the second story.
There are multiple ways to wire lights, and I will go over several of them, but the important thing to keep in mind is that every light needs power from the panel, and every light needs to be wired to a switch. Sometimes it is easier to bring power to the switch, and then run a wire from the switch to the light. In this instance, the black wires go through the switch and the white, neutral wires are joined together in the box.
Alternatively, the power can be brought first to the light, and then to the switch. This gets just a little bit more complicated due to the wire coloring.
What about the ground wires? You must be wondering, if electricity doesn’t pass through those wires, why are they even there? This is a great question. Ground wires are only used in emergencies, and are part of the grounding system of the house to protect people from being shocked. Let’s say that somehow the “hot” wire comes loose or becomes corroded over time and comes into contact with part of the light fixture. That fixture is now electrically charged so if you touch it, you could get electrocuted.
Fortunately, the ground wire also is connected to the light fixture, and connected to the ground, so the current will flow through the ground wire to the ground. Building codes require the path of the grounding wires to encounter very little resistance; this low resistance will cause the current to spike and trip the breaker, cutting power off to the circuit.
You will need to use three-conductor cable when you connect a light to multiple switches. Three-way lights are required by building code over a stairway so you can operate the same light from either the top or the bottom of the stair. The third conductor is wired between the two switches so that the light can be powered through one conductor if both switches are up, or through the other conductor if both switches are down. If one switch is up and the other is down the circuit is disconnected and the light will not be lit.
In the master bedroom, the main light can be operated via a switch at the door, or via switches at either side of the bed. In effect, three different switches are capable of operating the same light! This is called a 4-way switch.
For light fixtures, you can use wall boxes for sconces or octagonal junction boxes for hanging fixtures. There are reinforced boxes you can use that are capable of handling heavy chandeliers as well. Just as with the gang boxes, it is important to do box-fill calculations to ensure that the box you are using has enough room for the number of conductors you wish to pass through it.
Securing wire and making up boxes
After all of the cables have been run between the main panel and the outlets, all the cables must be secured to the framing. The cable must be attached within 6 inches of an outlet and at least every 54 inches until they reach the main panel.
There are many products you can buy to secure the cable properly, but I went with the cheapest one and just used electrical staples. These allow you to staple two 2-conductor cables wires or one 3-conductor cable, and are very easily driven into the framing with a hammer. You must take care not to hammer them in so hard that they break the insulation on the wire.
On long raceways, it is important to separate the wires when possible to prevent them from overheating. In addition, wires can’t be stapled closer than 1 1/4 inch from the face of the framing. If cable goes through a hole that is closer than that, a metal plate must be attached to the framing to protect the cable from a nail or screw.
Once the wires are secured, it is time to make up the boxes. I used a sharp utility knife to cut a long slit in the sheathing on the Romex, exposing the conductors. If you cut the side that has the writing on it, the paper wrapping will be a lot easier to remove. It is important to cut the sheathing off at the very back of the box. Sometimes when there are multiple wires it helps to write which one is which on the nearest stud.
The easiest box to make up is a receptacle at the end of a circuit. You just strip the sheathing and paper away and leave the conductors and ground wire neatly folded near the front of the box, as the photo below shows.
The next simplest is a switch at the end of the line. This is done just like the receptacle except you need to wrap black electrical tape over the white conductor to show that it is “hot.” I like to use some leftover Romex sheathing to mark that the outlet is a switch.
The remainder of the boxes will have more than one wire. It is easiest to start with the ground wires. If there are only two ground wires I twist them together six or seven times. Then I slide a crimp ring over them and use a pair of crimpers to pinch them tightly together, as the photo below shows. Next, I trim off any unnecessary ground wires (leave one remaining for each switch/receptacle in the box).
White conductors come next. If you are wiring a switch, make sure that none of them need to be taped to mark them as “hot.” This is usually due to power going to a light before the switch that controls it. If you mark a white conductor at one end, you must also mark it at the other end, at the box where the wire terminates. If you find yourself trying to connect a black conductor to a white conductor without an electrical device in between you will know right away you are doing something wrong.
The black and red conductors are the most difficult, and this is where it becomes very important to have written down which wires are which. Receptacles require one black conductor, while switches require two. Just as with the white conductors, if you have only two black conductors, you can attach both of them to a single receptacle.
For switches, one of the black conductors will need to be incoming power, and the other one will need to be going to the load. When there are multiple switches, you will need to use a pigtail. This time, instead of using a pigtail to turn multiple conductors into a single conductor, you will use the pigtail to turn a single wire coming from power into multiple wires that can each power a different switch. You may have power entering the box pigtailed to multiple switches, but you will also need to add to the pigtail other black conductors that will bring the power out of the box and into the next one.
It is really important that you pay attention to the packaging for the wire nuts you are using for your pigtails to ensure that it is the right size for the number of wires in the pigtail. Tan ones, for instance, can be used for between two and five 14-gauge conductors.
Wiring the panel
For some reason, I take immense pleasure in stripping wires and making them look good, so making up the main panel was a very enjoyable task. I spent a great deal of time making it look as clean as I could make it. At the end of the day, it really doesn’t matter as the number of people that will ever remove the “dead front” and look inside the panel is very limited. But building a house is much more rewarding if you take pride in the small things.
As I explained earlier, it is important to know the proper size circuit breaker for each individual circuit. Each circuit is built to power a “load,”whether it be a water heater or a refrigerator or a light. The proper size circuit breaker will know when the current increases above the planned maximum current for the load you have planned on the circuit and cut power.
The NEC requires that receptacles in garages, kitchens, bathrooms, outdoors, and laundry areas are protected by a special type of device called a ground fault circuit interrupter, or GFCI. This type of breaker will not only trip when the current rises above the maximum for the load, but also measures the current as it returns to the main panel to make sure that no current has “leaked” out of the system.
For example, let’s say someone is in the kitchen and doesn’t notice that the “hot” wire on the toaster cord has a puncture in it and is lying in a small puddle of water. When someone touches the water, they will be electrocuted. The current in the circuit won’t change significantly enough to trip the regular circuit breaker — it’s still powering a load. Unfortunately, that load would be a human being. The GFCI will trip in this case, however, because it senses that the power it is sending to the hot conductor is not returning to the main panel on the white neutral conductor.
Alternatively, instead of using a GFCI breaker, you can use a regular circuit breaker with a GFCI receptacle. This is what I will be doing as it is much more cost-effective, yet just as safe. You can connect multiple regular outlets downstream of a GFCI outlet and they will all have GFCI protection — provided it is wired correctly.
The last type of breaker is an arc fault circuit interrupter, or AFCI. These are required on almost all circuits that power multiple devices inside the house, other than bathrooms. If you have ever seen a spark plug work, you have seen an arc. Sometimes wires are just a little loose, so electricity can arc between them.
In this case, the load is still powered, so a regular breaker doesn’t detect anything amiss. The loss of power is so low that the GFCI breaker doesn’t detect it, and yet the spark is powerful enough to start a fire in the same way that the spark plugs in your car ignite the gasoline in your engine.
The AFCI has the ability to detect these arcs and will trip, alerting the homeowner to a potential problem in the wiring. I used a special AFCI breaker that is designed to connect not only to the main hot bus but also the neutral bus bar in the main panel. Again, the breakers work by monitoring the power as it returns to the panel and comparing it to the power that is leaving the panel.
Once the proper breakers are installed into the panel, it is just a simple process of stripping the wires and connecting them. The ground wires always go in any location on the neutral bar unless you are wiring a subpanel, in which case there must be a separate bar for the grounds that connects to a single ground wire that is wired directly to the main panel neutral bus bar.
White conductors also are connected to the neutral bar, unless they will be connected to a GFCI or AFCI breaker. The exception is when you have a 240-volt only circuit, in which case both the black and white conductors are hot and must be connected to the breaker. In this case, the white wire must be taped black to alert anyone operating on the panel that it is being used as a hot wire. The black and red conductors are always connected to the breakers.
Other blogs by Matt Bath:
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