# 208/220/240



## jwjrw

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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## 10492

Voltech said:


> 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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## Romex Butcher

"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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## Dennis Alwon

Voltech said:


> 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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## Magnettica

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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## 220/221

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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## slickvic277

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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## Magnettica

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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## micromind

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.

Rob


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## Jeff000

Romex Butcher said:


> 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. 



slickvic277 said:


> 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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## kbsparky

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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## slickvic277

Jeff000 said:


> 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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## Innovative

Romex Butcher said:


> "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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## Magnettica

Innovative said:


> 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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## Innovative

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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## 220/221

> 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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## Bob Badger

Innovative said:


> 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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## Bob Badger

Innovative said:


> 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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## crosport

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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## Loco vin

Will i damage a three phase motor 240 volt delta if hooked up to a 208 volt wye system


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## MTW

Romex Butcher said:


> "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.)


That Romex Butcher sure was smart, and probably extremely handsome too.


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## micromind

Loco vin said:


> Will i damage a three phase motor 240 volt delta if hooked up to a 208 volt wye system


Only if it is overloaded. 

There are millions of motors marked 230 volts that have been operating on 208 volt systems for a very long time.

The difference is that the locked-rotor, pull-up and breakdown torques will be less at 208 and it'll turn slightly slower for any given load. 

As long as the nameplate full-load amps is not exceeded, it'll be ok.


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## sbrn33

micromind said:


> Only if it is overloaded.
> 
> There are millions of motors marked 230 volts that have been operating on 208 volt systems for a very long time.
> 
> The difference is that the locked-rotor, pull-up and breakdown torques will be less at 208 and it'll turn slightly slower for any given load.
> 
> As long as the nameplate full-load amps is not exceeded, it'll be ok.


What about a RTU or AC unit? I am going to replace a single phase and delta service with a wye this summer and that is a major concern. I really don't want to buck/boost those RTU's.


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## JRaef

slickvic277 said:


> 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.
> 
> *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.


Good answer, but I fixed it for you. If there is no "grounded conductor"*, there is no 120V available. 

*Let's not get into corner grounded deltas, it's too much for the uninitiated.


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## JRaef

All good answers if you are willing to explain single and three phase theory to a non-electrical professional, but in my experience their eyes will glaze over before you get half way through it. 

So in direct response to the question in a way that can make sense to a Liberal Arts major:

"110/220" is an old standard voltage level that goes back to the days of Edison, but in most places no longer exists other than in the minds of people who don't really know. The new standard for single phase coming from utilities has been 120/240V for a generation of people now, but old habits die hard. You get 120V from Hot to Neutral and 240V from Hot to Hot.

"208" is actually 208/120V and is always coming from a three phase commercial distribution system, whether or not all three phases are used, stemming from the fact that 120V from Hot to Neutral is what most small equipment needs, then 208 is 120 times the square root of 3, for the three phase service, so Hot to Hot is 208V and can work fine on most small equipment that is designed for 240V.


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## paulengr

JRaef said:


> All good answers if you are willing to explain single and three phase theory to a non-electrical professional, but in my experience their eyes will glaze over before you get half way through it.
> 
> So in direct response to the question in a way that can make sense to a Liberal Arts major:
> 
> "110/220" is an old standard voltage level that goes back to the days of Edison, but in most places no longer exists other than in the minds of people who don't really know. The new standard for single phase coming from utilities has been 120/240V for a generation of people now, but old habits die hard. You get 120V from Hot to Neutral and 240V from Hot to Hot.
> 
> "208" is actually 208/120V and is always coming from a three phase commercial distribution system, whether or not all three phases are used, stemming from the fact that 120V from Hot to Neutral is what most small equipment needs, then 208 is 120 times the square root of 3, for the three phase service, so Hot to Hot is 208V and can work fine on most small equipment that is designed for 240V.


Almost right. The national standard for voltages is ANSI C84.1. There are two voltage ranges: the system voltage, and the utilization voltage. The transformer will be set to the system voltage which would be 240/120 single phase or 208/120 three phase wye. However we have losses in the power lines between the transformer and the utilization equipment so there is an associated set of utilization voltages which is 230/115 V single phase (most people incorrectly state 110 V) or 200/115 V. On top of that there are tolerance ranges. For example UL and NEMA standard conditions specify a tolerance of -15/+10% so the actual acceptable voltage for 115 V rated equipment is 98 to 126 V. This is all text book. Real systems are usually a little more tolerant, except APC UPSs that dont even meet UL.

Sent from my SM-T350 using Tapatalk


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## brian john

220/221 said:


> I tell the new guys:
> 
> 
> 
> *B)* 120/240 3 phase = Usually referred to here as "3 phase Delta". Two hot legs @ appx 120 to gnd, one hot leg @ appx *208* 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.
> .


FIFY sssssssss


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## paulengr

I've sort of done the reverse. An office building had 208/120. We were providing emergency power to an IT system and a separate HVAC system. Nobody caught it and there was essentially no documentation so what got installed was a single phase 240/120 generator and a 240 V HVAC system. So without ripping everything out and starting over we basically had to support both 208/120 and 240/120. It turns out that the HVAC system was fine...it was actually rated for something like 200-250 VAC and ran without a hitch on either system. The 120 VAC loads were also fine. It was only two pesky APC UPS's running on 208 or 240 that freaked out because the input voltage was too high. Since there were so few loads we had very little voltage drop in the first place so we tweaked the generator down to around 220 VAC output which just barely made what the UPS systems would tolerate and still kept the 115 VAC loads down around 108 V (actual measured voltage) which was low but everything "worked" without a problem.

Generally there is enough wiggle room between transformers, generators, and so forth that you can "fake it" between 240 and 208.


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## emtnut

Nawww ... It's still 440 and 110/220


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## flyboy

220 221 Whatever it takes...


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## HackWork

MTW said:


> That Romex Butcher sure was smart, and probably extremely handsome too.


Is that one of mine or your's?


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## MTW

HackWork said:


> Is that one of mine or your's?



I'm pretty sure it was me.


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## 220/221

brian john said:


> FIFY sssssssss


1) Well,...... 208 *is* appx 200

2) I know that it's _supposed_ to be 208, _according to what I've read_, but it generally measures 190 something around here.


And, damn this is an old thread. Damn rookies




> Will i damage a three phase motor 240 volt delta if hooked up to a 208 volt wye system


Generally, no.


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## drsparky

Zombie thread.


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## MTW

drsparky said:


> Zombie thread.


And not bumped by me for a change.


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## eddy current

220/221 said:


> 1) Well,...... 208 *is* appx 200
> 
> 2) I know that it's _supposed_ to be 208, _according to what I've read_, but it generally measures 190 something around here.
> 
> 
> And, damn this is an old thread. Damn rookies
> 
> 
> 
> 
> Generally, no.


Interesting. Around here 208 is actually 208.


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## brian john

Talking phase to phase I have seen everything between 187 and 256.


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## 220/221

eddy current said:


> Interesting. Around here 208 is actually 208.



Our 120/208 is generally right on the money but the high lag of our 120/240 delta systems always seem just shy of 200V to ground but right at 240 phase to phase.


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## lighterup

eddy current said:


> Interesting. Around here 208 is actually 208.


I ran into something curious once.

I was involved in a remodel of an Industrial job.
This place used to be a Lubrizol Plant that was bought
by a company that makes mattresses , so I was removing
a lot of explosion proof products , old unused pipe & wire
reusing what I could etc... for the various phases of the
new companies production phases...(they had divided 
the building up into a logical order , for efficiency etc..)

I came across a residential grade electric distribution panel
that was fed with 2 hot legs off of a 120/208 main...basically
a 240 volt rated panel , standard plug in breakers but fed with
208 volts , a neutral and an grounding/bonding conductor..

I showed it to the General contractor cause I thought
this was wrong...ended up running another leg and installing
a 3 phase panel...

Would anyone else have left it alone?


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## eddy current

lighterup said:


> I ran into something curious once.
> 
> I was involved in a remodel of an Industrial job.
> This place used to be a Lubrizol Plant that was bought
> by a company that makes mattresses , so I was removing
> a lot of explosion proof products , old unused pipe & wire
> reusing what I could etc... for the various phases of the
> new companies production phases...(they had divided
> the building up into a logical order , for efficiency etc..)
> 
> I came across a residential grade electric distribution panel
> that was fed with 2 hot legs off of a 120/208 main...basically
> a 240 volt rated panel , standard plug in breakers but fed with
> 208 volts , a neutral and an grounding/bonding conductor..
> 
> I showed it to the General contractor cause I thought
> this was wrong...ended up running another leg and installing
> a 3 phase panel...
> 
> Would anyone else have left it alone?


I would do the same.


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## micromind

lighterup said:


> I ran into something curious once.
> 
> I was involved in a remodel of an Industrial job.
> This place used to be a Lubrizol Plant that was bought
> by a company that makes mattresses , so I was removing
> a lot of explosion proof products , old unused pipe & wire
> reusing what I could etc... for the various phases of the
> new companies production phases...(they had divided
> the building up into a logical order , for efficiency etc..)
> 
> I came across a residential grade electric distribution panel
> that was fed with 2 hot legs off of a 120/208 main...basically
> a 240 volt rated panel , standard plug in breakers but fed with
> 208 volts , a neutral and an grounding/bonding conductor..
> 
> I showed it to the General contractor cause I thought
> this was wrong...ended up running another leg and installing
> a 3 phase panel...
> 
> Would anyone else have left it alone?


The only way I would ever have a single phase panel using 2 legs of a Y is if it had less than 3 breaker spaces. I'd also use single phase panels on apartment units when the building service was 120/208Y, but I'd rather use 3Ø ones.


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## JRaef

lighterup said:


> I ran into something curious once.
> 
> I was involved in a remodel of an Industrial job.
> This place used to be a Lubrizol Plant that was bought
> by a company that makes mattresses , so I was removing
> a lot of explosion proof products , old unused pipe & wire
> reusing what I could etc... for the various phases of the
> new companies production phases...(they had divided
> the building up into a logical order , for efficiency etc..)
> 
> I came across a residential grade electric distribution panel
> that was fed with 2 hot legs off of a 120/208 main...basically
> a 240 volt rated panel , standard plug in breakers but fed with
> 208 volts , a neutral and an grounding/bonding conductor..
> 
> I showed it to the General contractor cause I thought
> this was wrong...ended up running another leg and installing
> a 3 phase panel...
> 
> Would anyone else have left it alone?


It’s done all the time, especially in large apartment complexes. If there is no need for 3 phase, running it is a waste. But balancing loads does get a little trickier. In residential settings that’s always the case anyway, but in an industrial setting that was likely such a tiny percentage of the total load that it wouldn’t have made much difference.


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## readydave8

Saw 220v 3-phase once in either Hayesville or Murphy NC

Metal Halide wall cubes (multi-tap) were failing in short time, maybe ballast replacement twice a year for example

Voltage was 220 (probably around 228 or so), not 208 or 240

POCO said it had to do with odd voltage on their lines that was chosen to match what local mills wanted (don't remember #'s)


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## lighterup

JRaef said:


> It’s done all the time, especially in large apartment complexes. If there is no need for 3 phase, running it is a waste. But balancing loads does get a little trickier. In residential settings that’s always the case anyway, but in an industrial setting that was likely such a tiny percentage of the total load that it wouldn’t have made much difference.


my concern was balancing of the neutral.

The reason you gave for not being concerned would
not hold up cause you have no idea what "others"
are going to add to this configuration once you 
(the contractor) are out of the picture.

Now maybe if you work for a place full time in their
maintenance dept and you would be around to monitor
it's use , i could see your point.


Me? I'm in contracting...not maintenance personnel.
I would still replace that if I seen it again.


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## Sheila Walker

Well I just spent a half hour explaining phase relationships, 120, 240, 208 and 277 volt outputs of transformers and spiffy diagrams of the sinusoidal phase relationships.
All neat and nifty and I clicked on Post.

_To be able to post links or images your post count must be *20* or greater. You currently have *0* posts.

Please remove links from your message, then you will be able to submit your post.
_
So you all get this post instead.


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## Wirenuting

Sheila Walker said:


> Well I just spent a half hour explaining phase relationships, 120, 240, 208 and 277 volt outputs of transformers and spiffy diagrams of the sinusoidal phase relationships.
> All neat and nifty and I clicked on Post.
> 
> _To be able to post links or images your post count must be *20* or greater. You currently have *0* posts.
> 
> Please remove links from your message, then you will be able to submit your post.
> _
> So you all get this post instead.


Welcome to ET Sheila,, please finish filling out your profile. 
Yes you need to post 20 times before you can upload or send/receive messages.


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## micromind

Sheila Walker said:


> Well I just spent a half hour explaining phase relationships, 120, 240, 208 and 277 volt outputs of transformers and spiffy diagrams of the sinusoidal phase relationships.
> All neat and nifty and I clicked on Post.
> 
> _To be able to post links or images your post count must be *20* or greater. You currently have *0* posts.
> 
> Please remove links from your message, then you will be able to submit your post.
> _
> So you all get this post instead.


Lol.....keep posting, you'll get to 20 soon enough.

But yes, it's pretty frustrating to put a bunch of time into a post only to have it rejected.


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## 3DDesign

This is an old school explantation;
110 or 120 = 115 +/- 5%
220 or 240 = 230 +/- 5%
120/208 = 3 phase Wye


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## Sheila Walker

*Why the juice we have today?*

Straight (and a bit twisted) from my electricals class, without going into the horrible details, some horrible details anyway.

Back a ways, iron core transformers sucked. Not all that efficient. They sucked in more on the primary than the zomp that came out of the secondary. They needed quite a bit of push to go any length down the wires of the day. 

So the forebearer of modern electrics in the US was 240 volt secondary transformers with a center tap. Center tap to either outside leg gave half the zaps. But efficiency was crap. 
The original 120 volts was actually around 117, half of 240 minus core loss in the magnetics. The standard the powers that be decided was no more than +/- 10%. So the real voltage was 106 to 130 volts. 110 volts was around the best the transformers could usually do on average so it became the common term for quite some time.

The commercial zap was 240 volts. Considered too much for household appliances, 240 was handed the everything light duty in industrial application.

But the single and split phase transformers weren't very efficient and the wave form crossing zero made things worse. Also, there was a huge demand for self starting electric motors without special start windings. So three phase became the zap of choice for local power distribution. 

3 phase. Each zoomph of the juice 120 degrees apart. While one chunk of the transformer was crossing zero volts, two other chuncks were always charging. Much more efficient. 

But the snivellers got in on things. They wanted juice light to keep Aunt Esmerelda from glowing too brightly when she got to digging around in the toaster with a kitchen knife. The leg 1 to leg 2 to leg 3 back to leg 1 of the 240 volt Delta transformer didn't cut it.

So someone said lets reference each leg to zero, neutral. Enter the wye. Any two legs produced commercial duty juice, all three together started motors, forwards or backward, and they got their juice light. Enter 208 that wasn't looking directly across the zero at the other side of the sinusoidal wave. Instead, the other side was either 120 degrees behind or in front.

All about the phases pumping the iron, 120 degrees apart.

Make sense?


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