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# Thread: Electrical Engineers: Whats the difference between 208/240/277...

1. ## Electrical Engineers: Whats the difference between 208/240/277...

I know that 208 is related to 120v in that if you run it in 3 phase, 120V*1.73= 208V but how do you get 208V single phase?

Can anyone explain or link me a place I can read about line to line voltage, line to neutral voltage and how the hell I relate 208/240/277/120/460V ??

2. im not an electrical engineer, but i can tell you that i don't know.

3. Originally Posted by OfficerRodFarva
im not an electrical engineer, but i can tell you that i don't know.

ok anyone else that isn't a full retard?

4. Originally Posted by Spetsnazos
I know that 208 is related to 120v in that if you run it in 3 phase, 120V*1.73= 208V but how do you get 208V single phase?

Can anyone explain or link me a place I can read about line to line voltage, line to neutral voltage and how the hell I relate 208/240/277/120/460V ??
120/208 and 277/480 are wye voltages. The transformer secondaries are configured to look like a Y. Each branch of the Y is a phase and the lines (wires) are connected here. The neutral is connected to the midpoint of the Y.

To get 120 or 277 single phase, connect between one of the endpoints of the Y and the neutral at the midpoint. (line to neutral)

To get 208 or 480 single phase, connect between any two phase wires. (line to line)

Not gonna ever find this thread again. If you have more questions, either PM or Rep this post so I'll know. Not rep begging, mind you.

Wish I could draw a picture for you.

5. Originally Posted by Dave76
120/208 and 277/480 are wye voltages. The transformer secondaries are configured to look like a Y. Each branch of the Y is a phase and the lines (wires) are connected here. The neutral is connected to the midpoint of the Y.

To get 120 or 277 single phase, connect between one of the endpoints of the Y and the neutral at the midpoint. (line to neutral)

To get 208 or 480 single phase, connect between any two phase wires. (line to line)

Not gonna ever find this thread again. If you have more questions, either PM or Rep this post so I'll know. Not rep begging, mind you.

Wish I could draw a picture for you.
Correct, and rep'd from a journeymen wiremen

6. Originally Posted by Dave76
120/208 and 277/480 are wye voltages. The transformer secondaries are configured to look like a Y. Each branch of the Y is a phase and the lines (wires) are connected here. The neutral is connected to the midpoint of the Y.

To get 120 or 277 single phase, connect between one of the endpoints of the Y and the neutral at the midpoint. (line to neutral)

To get 208 or 480 single phase, connect between any two phase wires. (line to line)

Not gonna ever find this thread again. If you have more questions, either PM or Rep this post so I'll know. Not rep begging, mind you.

Wish I could draw a picture for you.
this.

7. there are 5 voltages in the system
480 delta
277/480 Y
120/240 Y
120/208 Y
240 delta

on a normal 120/240 transformer
you got 1 primary 2 secondary coils rated at 120V
3 bushings on the transformer
120 neutral 120
x1 to x2 is 120
x2 to x3 is 120
x1 to x3 is 240

120/208 i wish i could explain more on it
thats all 3 phase volatage (i didn't do my 3 phase class yet)
weird way of how you wire the transformer to get that voltage

8. Originally Posted by artm
there are 5 voltages in the system
120/240 Y
120/240 three phase is a delta connection.

Edit: Found a pic

9. so if I connect 120V line to line in a Y i get 240V right? and line to neutral I'll have 120V.

I think its starting to click Thanks guys.

10. Originally Posted by Dave76
120/240 three phase is a delta connection.

Edit: Found a pic

hmm i wish i had transformer drawings

11. Originally Posted by artm
hmm i wish i had transformer drawings
here you go

12. Originally Posted by Spetsnazos
so if I connect 120V line to line in a Y i get 240V right? and line to neutral I'll have 120V.

I think its starting to click Thanks guys.
No. In a wye connection, the three phase voltage is sqrt 3 *line voltage.

If you want 120 and 240 in a three phase configuration, you use the delta connection. The above pic doesn't show the neutral for the delta connection. You have to center tap one of the phases.

Like artm said, you have two 120 secondary coils in a single phase transformer. Connect them in parallel for 120 volts. Connect them in series for 240 volt.

Once you have three transformers connected for either 120 or 240, you connect the three transformers together. Connect transformers wired for 240 in delta for 120/240 three phase. Connect three transformers wired for 120 in wye for 120/208. If you want 277/480, we normally use pad mounted three phase transformers. If you want to use single phase transformers, you need 277 volt transformers.

13. so I just came across a piece of equipment that comes in 230V. What in the world...How do you achieve this voltage? 120V line to line is 240V, 120 *1.73 = 208V.

I'm guessing 230V = 240V?

14. Originally Posted by Spetsnazos
so I just came across a piece of equipment that comes in 230V. What in the world...How do you achieve this voltage? 120V line to line is 240V, 120 *1.73 = 208V.

I'm guessing 230V = 240V?
maybe so but some things are sensitive to very small voltage differences. like say a tanning bed. its made in europe where there 230v to use it here you would need a buck boost transformer or change the taps on the primary transformer to get the voltage as close as possible.

15. Originally Posted by .800king50
maybe so but some things are sensitive to very small voltage differences. like say a tanning bed. its made in europe where there 230v to use it here you would need a buck boost transformer or change the taps on the primary transformer to get the voltage as close as possible.
So if I have 120V, 240V, etc, I'd need a transformer to step down to 230V right?

16. Originally Posted by .800king50
maybe so but some things are sensitive to very small voltage differences. like say a tanning bed. its made in europe where there 230v to use it here you would need a buck boost transformer or change the taps on the primary transformer to get the voltage as close as possible.
I see thanks, wikipedia'd the buck boost transformer after you mentioned it and it helped out. So 115V/230 is basically what is provided in Europe right?

17. This thread makes me want to prepare my angus for sophomore and junior year. Im in for some hard stuff.

This thread makes me want to prepare my angus for sophomore and junior year. Im in for some hard stuff.
Sophomore year is hard, but Junior year is when it starts to get fun

I don't even remember half of this stuff though

This thread makes me want to prepare my angus for sophomore and junior year. Im in for some hard stuff.
my angus is peppered everytime I walked into any electrical engineering classes. The worst was mechatronics(got an A but had to study all the time). Unfortunately I never really learned all the power stuff because my major is mechanical engineering and we focused on small electronics with diodes, transistors, capacitors, resistors, etc.

20. here op i dug around and found one of my books that shows the wiring

21. Originally Posted by artm
here op i dug around and found one of my books that shows the wiring

sweet thanks man!

22. Originally Posted by Spetsnazos
I see thanks, wikipedia'd the buck boost transformer after you mentioned it and it helped out. So 115V/230 is basically what is provided in Europe right?
don't know for sure but in all the tanning salons(beds manufactured in europe) i have done. Ive needed the buck boost to get to 230v from either 240 or 208/ or ive had to get a sub panel that is dedicated to just the 230v loads (nothing else) and have a separate transformer that feeds that panel.

23. Originally Posted by Spetsnazos
So if I have 120V, 240V, etc, I'd need a transformer to step down to 230V right?
Nah, you're fine using 240 volts.

Equipment ratings (110, 220, 460, etc) are always lower than transformer ratings (120, 240, 480). The theory is that you'll have some voltage drop between the transformer and the equipment. Even if they are next to each other with little wiring in between (so no voltage drop), it's Ok anyway.

24. Originally Posted by Dave76
Nah, you're fine using 240 volts.

Equipment ratings (110, 220, 460, etc) are always lower than transformer ratings (120, 240, 480). The theory is that you'll have some voltage drop between the transformer and the equipment. Even if they are next to each other with little wiring in between (so no voltage drop), it's Ok anyway.
i think it is allowable to supply 6V below or above of what is needed

25. Originally Posted by Dave76
Nah, you're fine using 240 volts.

Equipment ratings (110, 220, 460, etc) are always lower than transformer ratings (120, 240, 480). The theory is that you'll have some voltage drop between the transformer and the equipment. Even if they are next to each other with little wiring in between (so no voltage drop), it's Ok anyway.
I see. The voltage drop thing definitely makes sense.

Thanks!

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