!7: Power Bright Inverter Clearance Sale: November 2011

Tuesday, November 29, 2011

Wiring Your House and a Three-Way Switch

!±8± Wiring Your House and a Three-Way Switch

Building a house takes a lot of planning and a lot of though put into the little details. Where you put your electric outlets and switches may not seem that important, but when you start placing furniture and plugging in lamps and other electronics, it will. Taking the time to plan the wiring of a house always pays off in the long run.

If you aren't sure where everything is going to go in the house the best thing to do is place an outlet on every wall. Wiring you house this way will allow for a lot of flexibility on where you place your furniture. Also placing all the outlets a foot off the floor will make them easy to access. Switches are best placed where you enter a room so that you can turn on a light as you come in and you won't be stumbling around in the dark.

You need to determine where fixed lighting will go next. Canned lighting is appropriate for areas such as the kitchen and family room. It is best to put canned lighting on a dimmer switch since they can sometimes seem too bright. Ceiling fans with a light fixture are another option to consider. There is a wide variety to choose from and a fan is nice for a light breeze on a warm night.

Once you have made all the decisions on outlets, switches and fixtures it is best to draw out a plan for each room to be wired. Then you can easily make a list of materials that you will need.

This is also the time to decide if you would like any three-way switches installed. They can be useful for rooms that have two entrances, so that you can turn on and off the lights from either side.

The only real difference in a regular switch and a three-way switch is that the two switches on the opposite sides of the room are hooked together with what is called a traveler wire. You will have one end of the traveler wire pulled through both boxes at each entrance of the room. Then it is just a matter of twisting the wires from the traveler with the regular wires, by matching up the colors and then wiring the switch normally. When you look at the switch the only difference is that it will have double wiring on one side.

Once your planning is done and all your materials bought you can get started wiring your house.

Please remember though to make sure the power is off before you start.

Wiring Your House and a Three-Way Switch

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Friday, November 18, 2011

Solar Power Math Problems - Part I, Calculating Solar Panel Circuits

!±8± Solar Power Math Problems - Part I, Calculating Solar Panel Circuits

Math problems are everywhere when solar power is concerned, not only for reducing power losses, but also for safety considerations. Article 690 of the National Electrical Code (NEC) requires derating and correction factors based on the type of wiring involved and the locations the wires are installed. There's also a default "just because it's solar" calculation with a lot of good reasons related to the NEC's goal of life safety. I installed my system using the 2003 edition, which was the current edition at the time.

The first math problem deals with solar panel output. When planning your solar panel installation, technical details for stuff Pmax, Vpm, Ipm, VOC, and Isc are needed for a safe design. Here are the specs for the solar panels I used:

Sanyo HIP-180: Pmax 180 watts, Vpm 54.0 volts, Ipm 3.33 amps, Voc 66.4 volts, Isc 3.65 amps BP Millenia MST-43MV:Pmax 43 watts, Vpm 72.0 volts, Ipm 0.6 amps, Voc 98 volts, Isc 0.8 amps

The NEC requires a 'weather correction factor' to determine the highest possible voltage. Solar panels produce less power the hotter they get; they produce more power the colder they get. The NEC has a table (Table 690.7, Voltage Correction Factors for Crystalline and Multicrystalline Silicon Modules) that gives the correction factor, based on the coldest possible operating temperatures expected.

From the 2008 version of the NEC: [NEC 690.7]

-11C to -15C (13F to 5): 1.16 -6C to -10C (22F to 14F): 1.14 -1C to -5C (31F to 23F): 1.12

My area's coldest daytime winter temperature is usually above 22F so my weather correction factor would be 1.14, but I've seen 30 mph winds on bright sunny winter days, so I'll use the higher number to allow for windchill.

Each group of panels is a 'PV Source Circuit'. My panels are wired in parallel (two per circuit); the math runs like this: [NEC 690.8(A)(1)]

the sum of all the Isc numbers in the circuit, multiplied by the weather correction factor equals the 'PV Source Circuit Current' 3.65A + 3.65A = 7.3A times 1.16 = 8.468A

The PV Source Circuit Current is then multiplied "because it's solar" by 1.25. 8.468A times 1.25 = 10.585A. This is the maximum possible current that each circuit could possibly produce. If I selected only a 10 amp fuse for this circuit, there is a strong possibility I'd have to replace fuses pretty often in the winter time, especially on bright sunny days with lots of snow reflecting even more light onto the solar panels. [NEC 690.8(B)(1)]

Now that I've determined how much current might be produced, I need to select the correct wire size. I'm using type USE-2 cable from the solar panels to the combiner box where the circuit breakers are located. USE-2 cable is UL listed for outdoor use in hot areas (90C) and is also sunlight resistant. The temperature derating of USE-2 in 141-158F is 0.58 [NEC 310.16]

Ampacity of USE-2 cable, 10AWG: 40 amps 40 amps times 0.58 = 23.2 amps Ampacity of USE-2 cable, 12AWG: 30 amps 30 amps times 0.58 = 17.4 amps Ampacity of USE-2 cable, 14AWG: 25 amps 25 amps times 0.58 = 14.5 amps

The wire size has to be able to handle 125% of the derated PV Source Circuit Current (10.585A), so 10.585A times 1.25 = 13.23A. Our wire has to be thick enough to handle 13.3 amps, so either of these sizes would meet the electrical code.

Temperature derating for multiple cables. There is an additional factor to be aware of if these wires are running through conduit. Based on the number of current carrying conductors (positive conductors), the wire is derated according to the following: [NEC 310.15(B)(2)(A)]

4-6 conductors: 80% 7-9 conductors: 70% 10-20 conductors: 50%

If these 10 these circuits are running through conduit, then the rating for 10AWG (40A > 23.2A) is reduced yet again. 23.2 times 0.5 = 11.6 amps. I can either run 9 circuits in conduit and run 1 circuit free (allowed with USE-2 cable) and derate the circuits in conduit to 70% (16.24A), or divide the runs, with 5 circuits per conduit and derated to 80% (18.56A).

Solar Power Math Problems - Part I, Calculating Solar Panel Circuits

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Thursday, November 10, 2011

Flatbed Scanner Lamp into an Emergency Lamp

!±8± Flatbed Scanner Lamp into an Emergency Lamp

EDIT PLEASE READ!! This has been updated. I have added an old switch in line with the 12VDC power and this rig is hanging on my wall as an emergency light and runs off a digital photo frame external battery that I bought at walmart for 15 bucks. the battery is plugged in all the time so if the power does go out I still have bright light. I may post an update vid to this. Inspired by Kipkay's flatbed scanner hack video where he made a desk lamp from the guts of an old flatbed scanner. As seen on instructables. www.instructables.com Kipkay's Flatbed Scanner Hack Video www.youtube.com Found the correct voltage of my inverter here. 12VDC 500mA silenceisdefeat.com I plan to add a switch on mine, I kept the case that holds the light b/c it's very fragile and I didnt want it breaking. I insulated all the wires with good old electrical tape. Hope you like this one.