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Adventures in Wiring

Split-Phase 220VAC/240VAC wiring strategies

A NEMA 6 connector.

I can't believe what a headache it has been wiring up my detached garage for 220 so I can run my construction heater. I have a cheap, simple 220V heater that I brought with me from my old house, where I had it successfully wired up in my garage there. It's been sitting around the garage for the last couple of years because I wanted to try out one of those propane dish things instead - the dishes are good, but on really cold days in small spaces the fumes make you hallucinate a little, and even though table saws and hallucination go together like peanut butter and jam, I thgouht I'd better stop being lazy and wire up my garage for 220...

Now, I went through a bit of a conceptual struggle years ago when I wired up my old garage for 220. You see, my construction heater has what's called a a NEMA 6 connector. We are all familiar with simple 110V outlets with a hot side, a neutral side, and a ground. We all know that hot is hot, current flows from hot to neutral, and the ground is there to provide a path to the ground in case there is a problem - so that the current doesn't use you as a path to ground. (I simplifiy all of this because that's the only way I can get my head around it...)

Some of us may even be familiar with the kind of 220V wiring used in something like a washing machine. There you have everything that the 110V connection has, plus you have a second hot wire. The first hot flows to neutral, the second hot flows to neutral, and you have your ground too. The great thing about this is that the washer can now use both hots (220V) to power the motor, while still having availiable just one hot (110V) to power the timer...

Now contrast all that with my little construction heater. There are only three wires used to connect it up - a hot, another hot, and a ground (for safety.) There isn't a neutral "to accept" the current flow from the hots. The first time I was faced with wiring this up I didn't really understand what the instructions were telling me so I called an old friend who is a journeyman electrician for advice.

He said, "You wire it up hot, hot, ground..."

I said, "Where's the neutral?"

"There is no neutral" he said.

"Then where does the current flow?!"

"I don't know," he said "that's just the way it's done."

Later (after completing the wiring as instructed and being utterly amazed that it worked) I learned about phases. I'm not sure about other towns nearby, but in Peterborough, Ontario, Canada we use current that alternates at 60 cycles (times) per second. That means that the hot wire alternates between 110V and 0V sixty times per second. Like a pulse. I think I have actually felt the pulse on the few occasions I have inadvertently grabbed onto a hot wire; I swear I've felt the current pulsing up my arm towards my heart. (That statement more than any other I make in this post should underline to you that I am not responsible at all, let alone responsible for what you do with the information I give you here ...) And it's this pulsing that is the secret of how my simple little two wire 220V NEMA 6 connection to my construction heater works.

You see, it relies on the fact that the two hots supplying it must be 180 degrees out of phase. So sixty times per second, while the red wire is 110V and the black wire is 0V, then the red flows to black. And in the next cycle when the red is 0V and the black is 110V, then then the current flows the other way. It's like when I was in army cadets and they sent 15 guys into each end of a tight 30 foot culvert pipe at the same time and demanded we come out the other side. I'm pretty claustrophobic and I'm not proud of how much crying I did that day, but that has nothing to do with electricty.

Gomer Pyle

Get it? You've got two hots coming into your house from the street, a red and a black and they are 180 degrees out of phase. When you install the double pole breaker into your main panel to feed the garage sub-panel, you need to make sure that you straddle both bus bars in the panel with that breaker, so that you are supplying 2 times 110VAC with each leg being 180 degrees out of phase (split phase). If you wire it up so that you garage is fed twice by the same bus bar in your main panel, then you will be supplying 2 times 110VAC single phase...and that's exactly what the Gomer Pyles who lived in my house previously did when they wired up my garage's sub-panel to the main panel in the house. I made the mistake of thinking that the wiring in my home was workmanlike and to code, and so couldn't understand at first why my heater wouldn't power up even though I obediently straddled both bus bars in my sub-panel in the garage. (BTW, I didn't literally straddle them. That's frowned upon by electricity hobbyists like myself.)

Luckily the fix is simple. In my main panel, if I pop out the 15 amp breaker next to the 30 amp double-pole breaker going to my garage, then move the double-pole over by half into the now vacated space, and then re-plug in the 15 amp (master bedroom breaker) on the other side, then that new position straddles the bus bars and I will them be supplying split-phase power to the garage. And since the master bedroom breaker is only 15 amp, single-phase it doesn't matter where it goes. As I said, it's a simple fix. But man, that's a weird main panel...

Adventures in Wiring

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