ECOURSE DAY 5:
TINY HOUSE ELECTRICAL WIRING
TINY HOUSE ELECTRICAL WIRING OVERVIEW
When wiring your tiny house, I strongly recommend that if you are not comfortable and somewhat experienced with electrical work that you hire out the job to someone who is. Electrical work can be very dangerous and the potential for mistakes high. If you are a detail oriented person who is eager to learn how to wire your own tiny house though, you will find a nearly limitless pool of step by step instruction on how to safely wire a house. With enough research and instruction, you can most likely wire your own tiny house. We always recommend that you hire a professional to come and inspect your electrical work before it gets buried into the walls, even if you have a fair amount of previous experience.
There are many wiring options available out there including single wire, stranded wire, armored cable, and others. The most common wiring used in residential construction, and the one I recommend you use in your tiny home, is known as Romex or NM-B. The NM stands for Non Metallic sheathed cable. The B refers to the rating of the wire which allows for both exposed and concealed work in locations that are typically dry and that have temperatures that will not exceed 90°C (140°F). The voltage rating for NM-B cable is a maximum of 600 volts. There are different wires gauges within the NM-B rating. The two most commonly used in residential construction are 14g and 12g, with 12g being the slightly larger gauge wire of the two. For most outlet and light locations, 14g wire is adequate; however, I always tend to build to the highest standards possible and as such, I recommend 12g wire for your tiny house circuits.
Assuming you use 12g wire, most circuits will require NM-B 12-2 wire. The “2” means there are two conductors plus a ground wire within the non metallic sheathing. The black wire is used as the “hot” and the white wire is the neutral or “return.” Keep in mind that electricity runs in closed circuits, i.e. loops, so even though a white wire may be referred to as “neutral,” it can just as easily kill you if the circuit is moving electricity. The ground wire is the only wire inside the sheathing that does not have a secondary coating on it. In other words, it is a bare copper wire.
Even though your home is tiny, you may want to include what is called a three way switch for one or more of your lights. A three way switch allows you to turn off and on a light from two different switch locations, like the top and bottom of your stairs. This is really helpful with a sleeping loft as it is nice to turn the light on before you go up to the loft to sleep, and equally nice to not have to go back downstairs to turn the light off when you are ready for bed. A three way switch requires one extra wire, typically red, so would require 12-3 NM-B wire. Again, this would mean 3 coated wires: white, red, and black, and one bare ground wire.
There are a lot of details about how NM-B wire needs to be run and attached to the frame in order to meet code. You will need to review your local code book to ensure that you are within the requirements. Some simple things to keep in mind is that any wire needs to be attached to the frame within the first 6” of exiting a box. If you are running the wire up and down a framing member, the wire will need to be attached periodically to ensure it is secure (check for specific spacing in your code book). Wires running perpendicular to framing members should run through holes drilled in the middle of the framing (where possible) to minimize the risk of being hit by a nail. No stapling is required when the wires run perpendicular to the frame.
Be sure to label all of your wires with a permanent marker as you run them so that you don’t get confused later when you complete the circuits. For example, when coming into a switch location, mark the end of the wire which brings power in as “hot” and the end of the wire that runs to the switch as “switch”. Once the walls are closed in, all you will see is the ends of the wires in each box and knowing exactly what goes where is a must. For this reason, I strongly recommend that you take a lot of photos of the walls while they are still open so that you can reference them should there be confusion later on. This, by the way is true for the entire building process. Take as many photos as you can. There can never be too many!
If you are using NM-B, then you can use plastic boxes for your switch and outlet locations. These are lightweight and easy to install. Fiberglass boxes are also an option as are metal; however, metal boxes must be grounded and that is an additional step that you can avoid by using fiberglas or plastic. Locating boxes at the right height is important, especially in the kitchen and bathroom. There are common heights for outlets and switches that should be used in your tiny home as much as possible. It will make everything easier moving forward and will place the boxes where your body expects them to be.
• Light switches, refrigerator and kitchen counter outlets should all be placed at 48” to the top of the box from the floor.
• Standard outlets should be installed 16” to the top of the box from the floor.
• Bathroom outlets and light switches (if installed over the sink counter) should be installed 44” to the top of the box from the floor.
• Washer/Dryer outlets should be placed 36” to the top of the box from the floor.
Be sure to space your boxes well around the room. Code requires that there be an outlet every 12’ measured along the wall, including going around corners. Chances are, you will want more outlets than that in your tiny house, but be sure you don’t have less than this requirement. Additionally, don’t install two outlets next to each other, on either side of a stud. This leaves only 1 1/2” of material in between the two boxes, making it very difficult to finish with your wall board material. Instead, use a double gang box (a box designed for two receptacles) attached to one side of the stud. You can also increase the box size to triple gang or more (typically for light switches); however, I find that anything more than three switches starts to get confusing. I prefer to move a switch to a different location and max out at triple gang boxes.
Be sure to read the specs inside of the box. It will state the cubic inches of the box and will tell you how many conductors (wires) you can insert into the box. Do not exceed this number as it will render the box illegal. You will also notice that the space designed for wire entry into the box may be a permanent plastic tab or it may be a plastic tab that swivels and even breaks off. Be sure not to break the tab off unless you are installing a new anchor for the wire. These plastic tabs are part of the anchoring system for the wire, and without them, the box may be considered illegal. I like to seal the penetrations of my electrical boxes with expansion foam to help minimize air infiltration into the house. I do this after the wires are installed and the walls are closed in.
It is really important to make sure your electrical system is properly grounded. If you plan on leaving your tiny home in one location, I recommend that you drive a ground rod into the ground and run a grounding wire from it to your electrical panel. If however, you plan on moving your trailer a lot, be sure to ground your electrical panel to your frame so that when you drop the stabilizer jacks, your home will be grounded. Each box location needs to be grounded as well. This typically means attaching the ground wire to either a green screw on the receptacle (outlets and switches) and to a ground wire provided with the light fixture. Grounding is your safety net, so make sure you do it right. In addition, check with your local codes about grounding other aspects of your home like propane and water lines. This is often missed by first time homeowner/electricians.
How you power your home will depend on your specific needs. If you plan to move it around a lot, you may want to install solar panels on the home and use DC fixtures or an onboard inverter to change the solar power to AC power.. If you plan to stay put, you may want to connect with a hard line to your power source (either solar or grid power). If you plan to do both, move around and stay put for a while, then I recommend you create a power dock that allows you to plug in and unplug as you please. There is a very important detail to consider here, and one that I have heard even seasoned tiny home owners get wrong. You cannot simply plug your tiny house into a standard plug. Your home will draw too much electricity to run through a standard extension cord and outlet. Most outlets are run on a maximum 20 AMP breaker. Your home will likely pull at least 30 AMPS worth of draw. So you will need to provide a dedicated, 30 AMP circuit for your power dock and you will need at least a 10g power cord to make the attachment. Anything less, in either the breaker or the cord, could result in a fire.
Stay tuned to tomorrow’s lesson: Plumbing and mechanical systems!