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Old 04-13-2010, 07:10 PM   #1
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Default 208/220/240

Had a guy ask me what differences are between the 3 208/220/240. As I started to answer him, I realized I could not answer him with an answer that was understandable for a green guy. Anyone have an easy answer for this, or maybe a good read explaining it?

Thanks

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Old 04-13-2010, 07:15 PM   #2
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I've had it explained to me in threads here and books. When I read it I understood it but I guess it never sunk in.I know what each system needs to work and how to tell which system I have but I couldn't explain it either. Seems like it has to do with phase relation and transformer type.

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Old 04-13-2010, 07:20 PM   #3
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Had a guy ask me what differences are between the 3 208/220/240. Anyone have an easy answer for this,
Thanks
One has more voltage than the other one.

Or the difference is 120 degrees vs 180 degrees.
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Old 04-13-2010, 07:23 PM   #4
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"220" and "240" are the same thing. "220" is what the unqualified use to describe 240 volt circuits.

208 can only be obtained from a 3-phase wye system. 240 volts can be obtained from either a 120/240 residential system or a 240 volt 3-phase delta system. Delta systems are quite rare nowadays, at least in my area where the poco has long since phased them out (pun intended.)
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Old 04-13-2010, 07:25 PM   #5
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Quote:
Originally Posted by Voltech View Post
Had a guy ask me what differences are between the 3 208/220/240. As I started to answer him, I realized I could not answer him with an answer that was understandable for a green guy. Anyone have an easy answer for this, or maybe a good read explaining it?

Thanks
It depends the difference between 240 and 208 is 32volts
the difference between 240 and 220 is 20volts
and the difference between 220 and 208 is 12volts

Okay- what are you looking for on this.. 220 volts is generally not available-- not sure I have ever seen it. 208 is from a 3 phase system and 240 can be from a single phase or a 3 phase system. If you are looking for how the different voltages are gotten then I can't help you.
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Old 04-13-2010, 07:45 PM   #6
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First of all, a double pole circuit is actually a single phase circuit.

Secondly, 208 volts is derived from a 3-phase system where the transformers are connected in a Wye configuration.

Thirdly, 208 volts can be used in a double pole, single phase circuit where the voltage potential is 208 volt between phases, or in a 3 pole, 3-phase circuit with 208 volts between each phase. Each of these phases wether it be a single phase or three phase all have 120 volts each to ground.
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Old 04-13-2010, 08:08 PM   #7
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I tell the new guys:

110/115/120 = all the same, different terminology. Seems to me that in the 60's, 110 was the standard number. Todays standard is 120.


A) 120/240 single phase = two hot legs @ appx 120 to gnd, 240 between them. Standard residential and small commercial system

B) 120/240 3 phase = Usually referred to here as "3 phase Delta". Two hot legs @ appx 120 to gnd, one hot leg @ appx 200 to ground, 240 between any two. Old school commercial system predating the current 120/208 wye system. Around here you will find it in older resi neighborhoods also. They used it to power those new fangled air cundishers.

If it's truly 120Volts, the high leg is supposed to be @ 208 volts but to avoid confusing people I avoid using this number. Besides that, around here it seems to be in the high 190"'s)

C) 120/208 = three hot legs, all 120 to gnd and 208 between any two. It's the modern standard for 3 phase sustems.

If they ask how it works, I tell them, all I know is what comes out of the end of the wires.
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Old 04-13-2010, 08:35 PM   #8
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110/115/120/125 can be either single phase or three phase systems and with older areas like here in Philadelphia it can be a two phase system as well. These voltages are all with in the same system that's why the word "nominal" is used.

220/240/250 The same explanation as above.

The most common systems would be,

277/480Y 3 phase 4 wire 277 phase voltage and 480 line voltage.
120/208Y 3 phase 4 wire 120 phase voltage and 208 line voltage.

120/240 delta 3 phase 3 wire. 240 line voltage. ( no grounded conductor)
120/240 delta 3 phase 4 wire. (grounded delta) High leg=208v.
the grounded delta allows for 120v loads to be served.
This can also be accomplished by using an open delta.

single pole breaker = phase voltage.
two pole breaker = single phase line voltage.
three pole breaker = three phase line voltage.

I don't know. This is the best way I could explain it.
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Old 04-13-2010, 08:42 PM   #9
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If they ask how three phase works tell them each phase is 120 electrical degrees out of phase with one another. This three phase business didn't make sense to me either until I started learning about motors and how they worked then it made all the sense in the world.
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Old 04-13-2010, 10:43 PM   #10
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OK, just to be a smart-alec, lets throw the grounded B system in.

It's a 3 phase system, and has 3 wires, one of them grounded. In a 240 volt system, there's 240 between any two, and 240 from either hot to ground. No 120 at all.

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Old 04-14-2010, 12:49 AM   #11
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Quote:
Originally Posted by Romex Butcher View Post
208 can only be obtained from a 3-phase wye system. 240 volts can be obtained from either a 120/240 residential system or a 240 volt 3-phase delta system. Delta systems are quite rare nowadays, at least in my area where the poco has long since phased them out (pun intended.)
Be careful with using absolutes like "only", any voltage can be had with the right transformer if you wanted.

Delta is still common, pretty sure the poco side is a delta/wye supply to prevent the harmonics still. But a Delta service would really only be a maintenance item now. Although delta connections are still used a fair amount for load connections.

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110/115/120/125 can be either single phase or three phase systems and with older areas like here in Philadelphia it can be a two phase system as well. These voltages are all with in the same system that's why the word "nominal" is used.

220/240/250 The same explanation as above.

The most common systems would be,

277/480Y 3 phase 4 wire 277 phase voltage and 480 line voltage.
120/208Y 3 phase 4 wire 120 phase voltage and 208 line voltage.

120/240 delta 3 phase 3 wire. 240 line voltage. ( no grounded conductor)
120/240 delta 3 phase 4 wire. (grounded delta) High leg=208v.
the grounded delta allows for 120v loads to be served.
This can also be accomplished by using an open delta.

single pole breaker = phase voltage.
two pole breaker = single phase line voltage.
three pole breaker = three phase line voltage.

I don't know. This is the best way I could explain it.
Great explanation.
We use three phase 4 wire 347/600 wye instead of 277/480 here though.

The 120/277/347 is not an arbitrary number either, its the line voltage/root 3.

Really you will learn all that in school though. Or at least we do, but not till 3rd year.
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Old 04-14-2010, 01:08 AM   #12
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220 is an old common European system voltage. The 3 phase value on such systems is 380 Volts between phases.

Newer upgraded systems use 240 Volts to ground, with 415 Volts between phases.
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Old 04-14-2010, 12:33 PM   #13
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Be careful with using absolutes like "only", any voltage can be had with the right transformer if you wanted.

Delta is still common, pretty sure the poco side is a delta/wye supply to prevent the harmonics still. But a Delta service would really only be a maintenance item now. Although delta connections are still used a fair amount for load connections.



Great explanation.
We use three phase 4 wire 347/600 wye instead of 277/480 here though.

The 120/277/347 is not an arbitrary number either, its the line voltage/root 3.

Really you will learn all that in school though. Or at least we do, but not till 3rd year.

We get it in 2nd year. AC theory, AC circuits(resistive, inductive, capacitive), Transformers and Generators, and Power quality.
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Old 04-14-2010, 12:45 PM   #14
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Originally Posted by Romex Butcher View Post
"220" and "240" are the same thing. "220" is what the unqualified use to describe 240 volt circuits.

208 can only be obtained from a 3-phase wye system. 240 volts can be obtained from either a 120/240 residential system or a 240 volt 3-phase delta system. Delta systems are quite rare nowadays, at least in my area where the poco has long since phased them out (pun intended.)
Why do people think that a 3 phase Delta system is old and being phased out??? Delta systems are being installed all over the US, everyday. In a industrial setting, they are more efficent. Everytime a Delta system is discussed, people come on here and say stuff like this..........WTF
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Old 04-14-2010, 04:47 PM   #15
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Why do people think that a 3 phase Delta system is old and being phased out??? Delta systems are being installed all over the US, everyday. In a industrial setting, they are more efficent. Everytime a Delta system is discussed, people come on here and say stuff like this..........WTF
The open delta 4-wire "high-leg" systems are indeed being phased out.
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Old 04-14-2010, 05:02 PM   #16
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Please justify this statement in some form..... I must install 30-50 120/240 3 phase Delta services each year, in brand new industrial parks. We spec the transformers from several large power companies. I have researched this (asked a few POCO reps from different areas in the US) at Electric West in Vegas this year and they all told me that was a crazy notion. So, please let me know where this information comes from.

So all these 3 phase 240 volt motors are just useless..... or they are gonna need their own transformer???
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Old 04-14-2010, 05:09 PM   #17
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Why do people think that a 3 phase Delta system is old and being phased out???
I am just speaking about my area. I have no idea what the rest of the planet is doing.
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Old 04-14-2010, 06:51 PM   #18
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Why do people think that a 3 phase Delta system is old and being phased out??? Delta systems are being installed all over the US, everyday. In a industrial setting, they are more efficent. Everytime a Delta system is discussed, people come on here and say stuff like this..........WTF
Because many power companies will no longer install new delta services.

They are no more efficient than Wye systems and generally the customer will have to make there own Wyes anyway.
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Old 04-14-2010, 06:56 PM   #19
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So all these 3 phase 240 volt motors are just useless..... or they are gonna need their own transformer???
First thing is there is no such thing as a 240 volt 3 phase motor, they are 230 volt motors which is exactly what you want with a 240 volt service.

Second they are not worthless at all, they are great for existing systems.

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Old 04-15-2010, 09:52 PM   #20
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I thought that the power companies like the delta system because if 1 of the 3 transformers goes down they can in an emergency reconnect the 2 to an open delta configuration with the same voltages,mind you having only 58% of the va.

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