As I puzzle through wiring this building I find myself humming along with Thomas Dolby.
Sandra and I have spent a lot of time over the last couple of weeks thinking about all things electrical.
I mentioned a few weeks ago that I was trying to come up with a sketch of our electrical layout, but what I discovered in the process was that I did not have enough information (more importantly knowledge) to even start a sketch.
Let me see if I can explain …
Standard Residential Wiring
A typical house in North America is wired for 120/220 volts AC (alternating current). Given the simple reality that virtually all residential wiring is done this way the process is well understood and very well documented. Some excellent references for residential wiring that deal specifically with the Canadian Electrical Code are Electrical Code Simplified: Residential Wiring and Electrical Code Simplified: Commercial & Industrial Wiring both by P.S. Knight.
Our project deviates from standard residential wiring.
The most fundamental difference for our wiring is that we plan to generate our own electricity via solar, wind, wood or a combination of all three. We would also like sell this power back to our power utility with the aim of being energy neutral, and possibly some storage capacity (batteries). In other words we hope to generate as much electricity as we consume on an annual basis.
This means that our electrical layout will include generation, storage, and transmission (back to the grid) of power. I am ignoring all of these issues for now and concentrating on what I thought was the simpler problem of lighting and appliance branch circuits.
We have evaluated a number of lighting options including incandescent, compact fluorescent, and LED.
Incandescent – There was no real evaluation here. Incandescent lighting is terribly inefficient, with the vast amount of electricity consumed being wasted as heat. Ironically, in older houses that are refitted with compact fluorescent lights as part of an efficiency upgrade there is some debate to the value of the upgrade. In some cases the heat lost from the incandescent lights in the winter has to be replaced by more expensive heating options!
Compact Fluorescent – This is the current efficiency choice and does have some merit. I dislike compact fluorescent bulbs due to the required ballast (it is environmentally bad), and the fact that all the ones we have ever installed have not lived up to their longevity claims.
LED – This is probably the newest efficiency option and is comparable to compact fluorescent technology in energy saved. It is a DC (direct current) technology and if it is used in an AC branch circuit a transformer must also be included to convert the power. Home generated power is stored in batteries (also DC technology) so there is a definite fit between LED lighting and home power. LED lighting does not need to be inverted (changed from DC to AC voltage) and consequently you avoid conversion power losses of approximately ten percent. LED lighting is not as effective at diffuse lighting, and right now is used more in task lighting.
We plan to use LED lighting for both our room and task lights.
We have not done significant research on efficient appliances but are fairly convinced that a DC fridge makes sense in our situation.
The problem lies in laying out the branch circuits for these DC appliances and lighting.
A branch circuit is simply electrical wiring that supplies power to some of the electrical loads in a building and terminates at the electrical service or panel with breaker or fused protection. In the case of 120/220 volt AC residential branch circuit wiring the rules for lighting and receptacles are well established and wiring is straight forward.
DC and AC appliances cannot share the same wiring so the DC branch circuits must be laid out separately. Further, the rules for AC branch circuit wiring do not apply as DC appliances operate at lower voltages and higher currents. In fact, low voltage DC wiring merits its own section in our electrical code and is referred to as a Class II circuit. Practically, this means that an equivalent DC circuit usually requires heavier gauge wire.
Class II branch circuits are not common in residential wiring and consequently there is more thinking (and learning) required to figure them out.
Some Questions that I have been thinking about, and the (hopefully correct) answers I have come up with are:
- Are there any issues with using standard NMD-90 wire for DC circuits? No. As with AC wiring the wire needs to be suitable for its intended location, and be sized correctly for the ampacity of the circuit in question.
- How effective is LED room lighting and how do we evaluate (style, wattage and quantity in a room)? I am assuming an LED room lighting solution equivalent to a 60 watt incandescent bulb will be 13 watts. I am using this assumption to lay out my branch circuits.
- What gauge wire should I use for my DC branch circuits? How many lights and receptacles can I hang off each branch? Do I simply need to design each one? (i.e. no established rules) Yes, I will be designing each one. The best reference I have found to help with this job is a book I tracked down in the library, Photovoltaics: Design and Installation Manual by Solar Energy International.
I think I have enough information to rough in the branch circuit wiring for our house. This means I can FINALLY get on with decking the roof. I was starting to believe we would never place the first board!
I leave you with …