# Thread: Help explaining 208v system with compressor & capacitors

1. Originally Posted by pecmsg
Our 115 Volt can use any of the 3 phases with a Neutral. Phase to Phase is 208 / 230 Single phase

I believe you use 230 volt for standard power supply. Each leg to ground shows 110 volts?
Just to be clear depending on the transformer you can sometimes have a wild leg that will read substantially higher to ground. You do not want to use that for a 120V circuit because it is not 110-120V. As I understand they have been trying to eliminate those transformers but you still find one on occasion.

Maybe this just muddied the water more

2. Originally Posted by pecmsg
Now I'm confused!
Yeah I should have clarified that the single phase could be coming from a 3 phase system and a transformer is used to get the single phase in residential.

3. Originally Posted by BNME8EZ
Just to be clear depending on the transformer you can sometimes have a wild leg that will read substantially higher to ground. You do not want to use that for a 120V circuit because it is not 110-120V. As I understand they have been trying to eliminate those transformers but you still find one on occasion.

Maybe this just muddied the water more
That's a whole other discussion!

4. Originally Posted by pecmsg
That's a whole other discussion!
I totally agree. The only reason I posted it was so if someone that didn't understand read your post that they wouldn't unknowingly tie into a wild leg for a 120V circuit.

5. Originally Posted by BNME8EZ
I totally agree. The only reason I posted it was so if someone that didn't understand read your post that they wouldn't unknowingly tie into a wild leg for a 120V circuit.
sought of like how we learned!

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So, on a typical 3 phase system( no high leg). So, I can use L1 & L2 to power up a typical Single phase residential AC cond unit. So, why is that not called two phase? So, there is no single phase center tap xformer to produce a typical single phase power source for the typical single phase 208/230 vac res AC Cond Unit..???
Last edited by TechmanTerry; 05-10-2021 at 09:13 AM.

7. Originally Posted by BNME8EZ
I totally agree. The only reason I posted it was so if someone that didn't understand read your post that they wouldn't unknowingly tie into a wild leg for a 120V circuit.
Yep

8. Originally Posted by flangatang7
100% electrical has never been my strong point coming from Australia where we don't use 208v it's a little harder. I am trying and taking time out to learn though. Will see if I can find some classes.
Can you explain to me what #5 does on the potential relay? All I can say for certain is it has 120v coming in from L1.

Here is a cleaner schematic. This is what the #5 terminal does.

9. Of course it would turn out sideways!

10. Originally Posted by BBeerme
Of course it would turn out sideways!
Electrons know no direction

11. Well, I guess if they go in L1, gravity will take them to L2, LOL.

Originally Posted by pecmsg
Electrons know no direction

12. Originally Posted by TechmanTerry
So, on a typical 3 phase system( no high leg). So, I can use L1 & L2 to power up a typical Single phase residential AC cond unit. So, why is that not called two phase? So, there is no single phase center tap xformer to produce a typical single phase power source for the typical single phase 208/230 vac res AC Cond Unit..???
Terry that's a interesting question.
If I'm understanding correctly your question is this.
How does a residential 208/230 volt residential condensing unit work off of opposite phases on three phase as well as a residential single phase ( split phase ) service ?
I gotta think about that and get back with you 🤔

If you look at your home transformer you'll see only one line feeding the transformer. The primary side then has two wires coming off the secondary side. This transformer splits that single phase into two with a center tap for the neutral.

13. Not sure if I'm following you guys, but if you draw it out, single phase has one sine wave, and three phase has three sine waves.

14. Maybe this will help

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Originally Posted by VTP99
Terry that's a interesting question.
If I'm understanding correctly your question is this.
How does a residential 208/230 volt residential condensing unit work off of opposite phases on three phase as well as a residential single phase ( split phase ) service ?
I gotta think about that and get back with you ��

If you look at your home transformer you'll see only one line feeding the transformer. The primary side then has two wires coming off the secondary side. This transformer splits that single phase into two with a center tap for the neutral.
I am more interested in "why" a regular 1 phase (2 hot legs w/ center tap,180* out of phase AC cond unit) is still called "single phase" when it is hooked up to a 3 phase power source and using 2 hot legs L1-L2/L1-L3/L2-L3.

16. Because the phases are out of phase from one another. Be it two opposite phases from 3 phases or 1 phase split from single phase .

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Originally Posted by VTP99
Because the phases are out of phase from one another. Be it two opposite phases from 3 phases or 1 phase split from single phase .
The 2 phases of a 3 phase power source are 120* out of phase w/ each other. 1 phase is 180* out of phase w/ each other

18. Now

I need a drink!

19. Originally Posted by TechmanTerry
The 2 phases of a 3 phase power source are 120* out of phase w/ each other. 1 phase is 180* out of phase w/ each other
That is correct but we still don't have a answer to your original question.
Why do we call a single phase condensing unit connected to two opposite phases of a three phase system single phase ?

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Originally Posted by pecmsg
Now

I need a drink!
You are late,lol.

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