- Michael J. Hammel - https://www.graphics-muse.org/wp -

Learning about power

What do you get when an old software geek [1] tries to learn about electricity?  The same thing you get when you teach a 5 year old not to put their hands on the red coils on the stove.  Experience through interactivity.  Today's lesson:  fat wires vs thin wires [2].

I've been using small gauge wire [3] to connect relays to outlets in my power controller project [4]. I did this because I thought I needed thick wire to handle potentially large loads through the outlets.  I expected to have multiple lights and possibly multiple water pumps attached to each outlet.  Fatter wires are used for larger loads (ever seen thin wires on power poles?).  So I chose fat wires to connect the relays and outlets.  Wire thickness is measured as a gauge.  Fat wires have a smaller gauge, which means thin wires have a higher gauge.  Why?  Beats me.  That's just the way it is.

20151222_140023 [5]

This looks safe, doesn't it?

The smaller gauge wires don't fit in the screw-down holes for the relays on the Sainsmart board [6]. I had to trim off some of the wire to make them fit cleanly.  But the relays only handle 10A max and the distance between the relays and the outlets is less than 6 inches.  I'm running standard 110V from the wall through the relays to the outlets. So how thick do these wires need to be?

After looking at an online wire capacity char [7]t I realized I didn't need the smaller gauge. I could use the larger 22 gauge wire (remember that larger gauge means thinner wire) for the very short runs between the relays and outlets. This is because if I take an average load per outlet of 6 lights averaging about 75 watts per bulb (remember this is lighting for my aquaponics at the moment) I find I'm only using 450 watts over the 110V power input. Using an online calculator [8] I can see I'm only pulling about 4.1 amps. That's far below the max for the relays and well within the safe limits listed in the Capacity Chart for 22 gauge wire. And this gets better if the lights are switched from high wattage incandescent bulbs to LEDs and CFLs, which most of them are now anyway.

So now I'll be able to use thinner wire inside the enclosure, leaving more room for the relays and my custom boards [9].  But more importantly, I won't have a bunch of frayed wires hanging out of the tie-downs to short out the whole thing.  And remember:  short-out is Latin for frying myself, because software guys are a danger themselves, their pets, their families and essentially entire neighborhoods when handling hardware.

And yet, I'm still doing it.  Go figure.