[Worldtrippers home] [Mountaintop home]
In our Web letters about our mountain home construction, we have tended to gloss over much of the electrical wiring that our friend Dirk has been doing. This tends to short-change his hard work, but frankly we don't understand half of what he's doing.
In an attempt to give credit where it is due, we finally asked Dirk to write his own Web letter. After reading it, we still don't understand half of what he's doing. But here it is anyway…
“That sounds like it would be fun.” And with those words, I start on the biggest home electrical project I have ever taken on.
The goal is simple: design and install a wiring system for the Lee’s home that is functional (provides light and electricity where needed) and meets code (the rules specified at national, state and sometimes county/city levels). “Code” means the wiring system has to pass one of several inspections. Fortunately for me, the local inspector will answer any question I have ahead of time.
The challenge in joining the “build a house in Glencoe” project comes from a few factors:
The electrical supply comes into a residence over 3 wires – to “hot” legs represented as the black and red wires, and a “neutral” white wire as seen in the main electrical panel. This arrangement allows for two voltages to be available in the house: 120 volts for most lights, appliances and electronic devices; and 220 volts for heavy-duty usage such as the clothes dryer and floor heating. If you connect something between either hot wire and the neutral wire, you get 120 volts. For 220 volts, you connect the load (something that uses electrical power) between both hot wires.
There is also a fourth wire that you find extending throughout the house. This is the safety “ground” wire, which is either bare or insulated with a green coating. Under normal operation, the electricity flows through the hot and neutral wires, never the ground wire. The ground system is connected to a long, copper rod driven into the ground (hence the name for this wire) and is establishes the “zero” volt level in the system. As part of the electrical safety system in the home, the metal water pipes and gas pipes are also connected to the ground system.
A peek into the electrical panel shows the different wires coming into the house. The black and red wires are “hot” legs. The white wires are “neutral” legs. The green wires are “grounds”.
The National Electrical Code (NEC) specifies the amount of electricity (measured in amps) that a specific size of wire can carry. Wire sizes (or diameters) in the U.S. are measured in gauges. For the main electrical system, you work mostly with 14-gauge wire, which is limited to 15 amps; and 20-gauge wire, which can handle 20 amps. For a few bigger loads (such as the dryer and water heater), 10-gauge wire is used and can supply up to 30 amps.The wires in a home are run in cables that contain a ground wire, a white (neutral) wire and a black (hot) wire inside a protective insulating jacket. If this cable is made with 14-gauge wires, then it’s referred to as 14/2 (the ground wire isn’t counted) and the cable has a flat profile. If you add a red (second hot) wire to the cable, it becomes 14/3 and the cable takes on a round profile.
In recent years, to help everyone keep track of the wire size in cables, in California exterior jackets of 14-gauge cables are colored white, 12-gauge cables are colored yellow, and 10-gauge cables are colored orange.
In California, cables are color-coded by gauge
The wire to be used dictates the capacity of each circuit breaker you need to install in the electrical main panel to protect the system. Most hot wires are black and are connected to a breaker; in some case you will also see a red wire, usually in a 220-volt circuit. Neutral white wires all connect to a bar together, followed by all the ground wires that connect together on their own bus.
Dirk's configuration of the electrical main panel is a work of art. Each circuit breaker is labeled and color-coded.
Electrical panels are arranged so that the two hot legs alternate in the locations where breakers can be installed. This means that for any 220-volt circuit, you need two breakers installed side-by-side with the handles tied together. You can use a 14/3 cable for a “home run” from the panel to the first switch or outlet in a circuit, and split a second circuit off the red wire, sharing the white wire. However, to keep from running too much current over the white wire, these two circuits must be on opposite legs.
Beyond needing to put circuit breakers on the right legs, modern circuit breakers come in single and dual configurations. The latter are called tandem breakers. Tandem breakers can both have the same amperage, or they can have different amperages. If you are putting in 220-volt circuits, you still need to have the breakers side by side. In one case, we needed two 20-amp circuits for the kitchen and a breaker for the dryer. So a quad breaker was used, with the breakers arranged as 20, 30, 30, 20 amps and the second and third breaker handles tied together.
A close-up of the electrical panel, showing several of the breaker handles tied together
The panel in the Lee home has “spaces” for 20 single breakers or 40 tandem breakers. The house needs 32 circuits to keep everything running. It takes some planning to organize the circuit breakers in a panel. (If you start a home in 2009, there are new code requirements for the circuits in bedrooms that mandate arc fault circuit breakers, which don’t come as tandem breakers.)
So how does one decide what makes up any single circuit? There are no hard and fast rules for the overall house. However, the NEC has a whole bunch of requirements for the kitchen. The counter top outlets must be split evenly between two 20-amp circuits. Then the refrigerator, microwave oven, dishwasher and garbage disposal must all be on their own circuits.
Each bathroom needs its own 20-amp circuit as an outlet for hair dryers, curling irons, shavers and so on. A space heater in a bathroom to keep you warm after your bath also needs its own circuit.
After that you ground outlets and lights together, trying to keep the use of each circuit below 80 percent of its maximum at any one point in time. That’s 1440 watts for a 15-amp circuit. (The breaker trips if you use more than 1800 watts on a 120-volt circuit.)
As you run cable through the house, you don’t start every outlet and light circuit at the main panel. It would cost too much for wire, and you’d never get all the wires into the panel. So cable is run to the first outlet, then the second, then the third, and so on. Sometimes it makes sense to branch out to two outlets (or switches) from one outlet.
Dirk pulls wires to create a “home run” circuit from the load to the electrical panel
The NEC has rules for how many wires you can put in an electrical box. The math is funny, as all the ground wires don’t count after the first. The gauge of the wire has an impact; you can’t put as many 12-gauge wires as 14-gauge wires in a standard single outlet box (called a 1-gang box). And the presence of a switch or outlet impacts the calculation. It’s all based on the interior volume of a box. Fortunately, 1-gang boxes come in several depths, and once you get to 2-gang boxes (and there some 3- and 4-gang boxes in the house), the wire limit problem goes away.
Here is a 1-gang box on the right and a 3-gang box on the left
This specific project has also had a few non-code challenges.
Gail and Dirk spent a lot of time reverse-engineering the previous wiring – trying to figure out why certain cables went “hither” instead of “yon”
By the time this is all done, the Lee’s home will have lights and outlets where they need them, a sign-off inspection report, and a friend who has an expanded electrical knowledge base.
Dirk in his element – in this case, the tiny crawlspace closet between the master bathroom and the laundry room
[Worldtrippers home] [Mountaintop home]