OK, when I first started reading this thread, it was all way over my head so I just skimmed it and said “huh?”. Anyway now I’ve had an experience that has caused me to reread it to try to figure out what you guys are talking about.
I have 3 phase in my shop, and I assumed that I knew how it worked. Three phase has three power leads with the frequency of each lead 120 degrees from the other. While this is true, it is not all the story. In my particular case the power is also going to a residence. The only thing in the residence that is running three phase is the A/C compressor. So there is a separate fuse box for it and then the single phase main panel for the house. I tapped off the A/C line and brought it into my shop to a three phase panel. I then wired everything which included a 110 for outlets and a 220 for a band saw, both single phase. Everything worked and I thought I was golden. Then earlier this year something weird happened. The 110 outlets didn’t have enough power. When I would turn on a motor plugged into the outlet it would take forever to come up to speed. So I checked the voltage in the panel. Everything seemed to be OK except for one little oddity. Two of the lugs checked out at 120, but the third was 213. I had always thought that the voltage on all three legs were 120 just out of phase with each other. Anyway when I went to check the line to the A/C it was the same. Came back to my shop and everything was alright. Things worked normal again, and really that’s all I cared about. I didn’t need to know all about this electricity mumble jumble to do what I wanted to do. So I didn’t invest any time or energy trying to figure out what was going on.
This brings us to this past week. Now it was happening all the time. And every time I went to check the A/C line, it fixed it. I could see a pattern developing but didn’t know what it meant. Long story short (if that’s possible at this point) is I figured out that when I wired the three phase panel, I left something out. When I tapped into the A/C box, I pulled three wires into my three phase panel. But that’s not really how many wires there are in a three phase set up. There are four. Originally I didn’t trust the ground of the residence because it was built in an unincorporated area and there weren’t strict codes. So I drove my own ground rod and brought it into my three phase panel. Now I had my power and a ground, right? Not exactly. After doing some research on the web and googling “three phase electricity”, I’ve come to the conclusion that my three phase is what’s called a “high leg” or delta configuration. In this set up the two 120 legs are center-tapped at the transformer on the pole to make up the 213 leg. This 213 leg is also the return or neutral for the three phase. The problem in my case is that I didn’t have a neutral for my single phase circuits, and the safety ground was acting as the neutral. I guess everything worked until something happened to that ground rod, at which point there was nowhere for the electrons to go. The reason that checking the lines at the A/C box fixed it was because my ground wire came from the rod through this box and into the conduit leading to my three phase panel. When I checked it I would touch the ground wire and it would make contact with the A/C fuse box which was grounded with the neutral and would complete the circuit.
Now I know that I have to bring the neutral from the pole into my three phase panel and fix my safety ground. This will give me a proper return for my single phase. And it also explains why when things would go out of whack that my three phase equipment would still work (it had a proper return through the 213). It was just dumb luck that when I put the 110 circuit in my panel it happened to draw from one of the 110 legs. However, my 220 circuit was drawing from a 110 leg and a 213 leg. Don’t know if my band saw was running hot with to much juice or not.
I think this is all correct. If anybody can tell me yea or nay I would appreciate it. And maybe they can answer another question. When things were wacky, I would put a meter across the 110 leg and the ground in the panel and turn on the drill press. The voltage would drop down to 40. On the other 110 leg the voltage would go up to around 200. To use Tom’s phrase “What’s up with that?”
Anyway what made me put this on this thread is Tom getting the 208 on the one leg and 104 on the other two. Maybe there is a delta vs. wye problem.
This is the link that mostly led me to my conclusions. http://www.elitesoft.com/sci.hvac/ithighlg.html
P.S. I know there are those that are shaking their heads saying “This dude is going to burn his shop down or electrocute himself.” I always flip the main breaker when I leave the shop, just in case. And electro shock is a recognized form of therapy.
P.S.S. Pete you may want to split this onto another thread.
Stephen
3 Phase electricity Question
Moderator: crzypete
You are on the right track.
In my shop I use a converter. I take care to wire all of my three phase outlets with the smallest opening going to the hottest leg. That way when i wire the machine i can make sure to use the 110 legs to feed the coil, reverse motor direction and the like. I know pete had an issue once that was traced to a lack of a neutral line so perhaps he will be able to add something.
three pahse electric on a residential AC unit? How many tons is it? Or is it an efficiency thing?
In my shop I use a converter. I take care to wire all of my three phase outlets with the smallest opening going to the hottest leg. That way when i wire the machine i can make sure to use the 110 legs to feed the coil, reverse motor direction and the like. I know pete had an issue once that was traced to a lack of a neutral line so perhaps he will be able to add something.
three pahse electric on a residential AC unit? How many tons is it? Or is it an efficiency thing?
OK, so this shows just how little I know. All my three phase tools work properly. But when I wired them originally I didn’t know there was any difference in the voltage. So did I just get lucky and wire them correctly or are they just wired kinda right and I’ve got too much juice going to something?
I think the A/C is an efficiency thing. It’s just a 5 ton unit (remember this is Texas and the summers are brutal). This house was one of the first built in a development in the late fifties and as far as I know it’s the only one in the neighborhood with three phase. Lucky for me.
I think the A/C is an efficiency thing. It’s just a 5 ton unit (remember this is Texas and the summers are brutal). This house was one of the first built in a development in the late fifties and as far as I know it’s the only one in the neighborhood with three phase. Lucky for me.
Steve, I will be here soon to try to read that first post of yours- I have not had my full focus on to get through it the two times I have tried.
I have a feeling the answer has to do with the difference between balanced three phase and one hot leg three phase (i am pretty sure this is delta vs wye).
I did split you in to your very own thread, hope you enjoy it!
Pete
I have a feeling the answer has to do with the difference between balanced three phase and one hot leg three phase (i am pretty sure this is delta vs wye).
I did split you in to your very own thread, hope you enjoy it!
Pete
This is a useful resource. Only problem is that it may not be useful for this specific issue.
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