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

1. Originally Posted by flangatang7
EDIT: For those looking for more information see below.

Thank you!

COMPRESSOR WHILST RUNNING
these 3 don't tell you much except they are energized (hot)
Ground to #5 on Potential Relay = 120v
Ground to #1 on Potential Relay = 120v
Ground to # 2 on Potential Relay = 120v

Start Capacitor
Ground to either terminal = 120v
L1 (Common) to either terminal = 208v This tells you the terminals are powered through L2

Run Capacitor
Ground to either terminal = 208v
L1 (Common) to either terminal 250v yep..... 250v

L1 (Common) to Start winding = 250v

L1 (Common) to Run winding = 208v Shows common is powered by L1, run is powered by L2

L2 to Run winding = 0V
proof of above, R and L2 are the same potential

You should really take a class on electrical theory or read up on it, or get a senior tech to help you understand what you are looking at. It will also keep you safer!

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Both windings are both powered by L1 & L2.

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Originally Posted by BNME8EZ
proof of above, R and L2 are the same potential

You should really take a class on electrical theory or read up on it, or get a senior tech to help you understand what you are looking at. It will also keep you safer!

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.

Thanks for your response!

4. 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.

Thanks for your response!
Terminal 5 is one end of the relay coil, it is the same power leg as C terminal on the compressor.

5. If you took that relay apart , you would be like .... oh .... so thats how it works

Its just a magnetic coil , and a set of points

The magnetic coil kicks the points open , and that drops out the Start Cap

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Originally Posted by Snapperhead
If you took that relay apart , you would be like .... oh .... so thats how it works

Its just a magnetic coil , and a set of points

The magnetic coil kicks the points open , and that drops out the Start Cap
Yep!

Is it fair to say that the contact on terminal 1 opens once compressor reaches 75% running capacity?

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The voltage is generated in the start winding. If the pick up voltage of your relay is higher than what you measure it won't pick up. if you take 80% of it you are close to the proper pu voltage. I have used potential relays on farm motors to replace the switches in the end caps.

8. Would that be the centrifugal switches ?

9. Originally Posted by Snapperhead
I have gotten bad motors straight out the box ....

Maybe you finally got yours
I have got several over the last couple years.

Sent from the Okie state usin Tapatalk

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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.

Thanks for your response!
Is 208v in canada a twin phase circuit?

11. Originally Posted by MadeInAustralia
Is 208v in canada a twin phase circuit?
Here in the States we use the term single phase or 3 phase. 208 / 230 can be both. (I know gets confusing) 3 phase does not get start components.

12. A little reading material

Hope it helps

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So you call a circuit with active and neutral 1ph

and also call a circuit between two phases of a three phase supply 1ph as well?

14. YES

15. Originally Posted by MadeInAustralia
So you call a circuit with active and neutral 1ph

and also call a circuit between two phases of a three phase supply 1ph as well?
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?

16. .

17. Originally Posted by VTP99
.
Now I'm confused!

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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?
415v 3ph standard supply, 230 any phase to neutral.

19. Originally Posted by MadeInAustralia
415v 3ph standard supply, 230 any phase to neutral.
OK that's the difference.

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maneurope made a 415v phase to phase sump heater back in the day.

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