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Mon 29 Dec, 2003 12:44 am
I was wondering if somebody here might know this, noone I know in R/L seems to have a clue.
I am a reefer. No, not the kind you smoke, but as in "one who reefs"...
What I mean is - I study, maintain, and try to propigate captive coral reefs. To make a long story short, it is a VERY expensive hobby. (It's not uncommon to spend $8,000 or more setting up a decent sized system.) Now, I don't have that kind of money, so I have to be creative to cut costs. As such, I have been building my own tank stands and light fixtures my self. (A reef tank requires lighting similar to those used in hydroponics.)
So anyway, being a complete novice with electricity, I have made some mistakes. A few answers here would help me get things right, I hope.
#1 - If I want to put a switch (in-line?) in the power cord of one of my light fixtures, should it be wired into the positive line, or the negative line? I'm sure it wouldn't belong in the ground line... Pretty sure anyway.
#2 - How would I determine what type of switch (how many amps) I need in various applications? This looks to me like it could be hard to answer without more details, but I don't really have any. I have several different fixtures with different bulb/ballast combinations. I guess an equation is what I need, if there is one...
#3 - Same as above but dealing with the power cords themselves. How would I know what gauge would be appropriate from one project to the next?
Thanks!
If you are a novice with electricity, you should go to your local home improvement store. They should be able to point you in the right direction and answer all your questions. It's hard to determine what you need without first seeing the project.
Hey! Duh... I just remembered that I had documented most of these projects on my website.
Here's the one I want to put the in-line (just a toggle, on and off) switch into. It has 4, 40w normal output fluorescent bulbs, The cord I used for this is about 3/8" diameter, and it's about 8 feet long.
lights
Switches should ALWAYS go in the positive/active line.
As far the other questions you asked, the biggest issue with switches is fault levels. I would hope that most available can handle domestic fault levels.
Where abouts are you? What is the voltage level you use. In Australia, if you're just powering lighting, you would use cable 1.5 mm2. If you're powering something which uses more current, then you'd go for 2.5mm2. That's using 240v here. Generally lower voltages (such as the US) means higher current, but I don't know for certain.
The 3/8" diameter cable you refer to doesn't mean much. What are the size of the cores. As I said, here I'd use 1.5mm2 for the fluro's. Not sure about the current where you are.
The key figure in your calculations is the current draw (amps).
What you need to do is calculate the current draw of each item you'd be putting on the electrical circuit and then total it all up and see what you get.
Each of your electrical devices should have a label that lists the current it draws or the number of watts of power it uses. If you know the wattage you can calculate the current by dividing the number of watts by the applied voltage (i.e. 400 watts/120 volts = 3.33 amps). Note that the current calculations won't be exact because you don't have a power factor figure to work with here but they'll be close enough.
As far as wire size - ignore the diameter of the jacket. What you need to look at is the wire gauge and that is again determined by the current draw. You can determine what gauge wire is needed by referring to the National Electrical Code but a chart is also available here:
http://www.mc2-ice.com/popular_conversion/popular_conversion_files/electrical/insulated_conductors.html
If water is involved your really ought to use a double-throw switch that interruputs both the live and the neutral (See regulations regarding showers) and a 'residual current circuit breaker (These go under many names, but it is one of those emergency cut-outs that are recommended for workshops, garages, and such)
The rating for the cable is not difficult to find out. Everything you are using must be rated either in amps or in watts. Divide the watts by the voltage and you have the amps for those too. Add all of those amps up then, be smart, ask the cable suppliers for a cable to handle that current.
While you are about it, ask them about earth-bonding too and how to use it.
Once you have done that, get someone who knows to check it all out for you. If you have to pay them a few dollars - that is still cheaper than being dead, isn't it?
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