# 120/208/240/480?



## dietdrkelp (Sep 22, 2013)

What does it mean when a device has this on it? Does that mean it will accept either of the two voltages? 

I understand that hot to hot is the higher of the two and neutral to hot is the lower? 

Also can one clarify if 120/208 means commercial writing and 120/240 means resi? 

My jm decides to skip out on theory when "teaching".


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## BBQ (Nov 16, 2010)

You are asking some great questions and we could fill pages about it.

Lets start with this.










Notice that a motor for a supply voltage of 120 will have a name plate of 115, a 480 supply gets a 460 tagged motor.


Next thing I will mention is pay attention to detail.

In general something marked 208-230 will operate on any voltage in between. On the other hand if its was marked 208/240 it could run on either of those voltages but there will likely be different connections to make in order to select which voltage.

Others will add to your questions.


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## HARRY304E (Sep 15, 2010)

dietdrkelp said:


> What does it mean when a device has this on it? Does that mean it will accept either of the two voltages?
> 
> I understand that hot to hot is the higher of the two and neutral to hot is the lower?
> 
> ...


120/208 is usually 3 phase.in commercial buildings.

120/240 is usually single phase in residential .

480/277 is also 3 phase in a commercial building.


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## dietdrkelp (Sep 22, 2013)

BBQ said:


> You are asking some great questions and we could fill pages about it.
> 
> Lets start with this.
> 
> ...


I have to say i wish your attitude on explanations were where i worked. thanks bbq for the encouragement on asking questions.


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## MTW (Aug 28, 2013)

dietdrkelp said:


> I have to say i wish your attitude on explanations were where i worked. thanks bbq for the encouragement on asking questions.


He's pretty disappointing in real life. :whistling2:


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## BBQ (Nov 16, 2010)

MTW said:


> He's pretty disappointing in real life. :whistling2:


:clap::clap::lol:


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## JRaef (Mar 23, 2009)

Just FYI, OFFICIALLY there is a convention on the order in which the numbers are presented that technically helps, although unfortunately most people don't realize this and trow them around willy nilly.

If the larger voltage is listed first, it is a 3 phase Wye service. So it would be 208Y120 or 208/120; 480Y277 or 480/277.

If the smaller voltage is listed first, it is a split-phase service, meaning a transformer winding is center tapped and grounded to derive 1/2 of the phase to phase voltage. So for residential service, it is called 120/240. 

So _technically_, we should not call 3 phase 208 Wye "120/208V", it is supposed to be called "208Y120V" to help avoid confusion. But like I said, hardly anyone knows this and we generally know what we are talking about anyway.

The only time that becomes more important is when talking about 240V 3 phase services. There is a 3 phase 240V _delta _service that is occasionally offered, where one winding is center tapped as well, like a single phase service transformer. So it is called 120/240 3 phase 4 wire. Phase-to Phase it is always 240V, Phase to Neutral on the tapped winding is 120V, usually the A-C winding. So A-B, B-C and C-A are all 240V, A-N = 120V, C-N = 120V, B-N is not a valid voltage reference (it's floating) but typically measures out as 208V, so it is called "High Leg" delta.


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## dietdrkelp (Sep 22, 2013)

Now what would be the purpose in wiring a light at 208 instead of 120? I know the amps drawn would chance as explained by my understanding of ohms law, but performance wise what difference would it make if any? I would imagine it could provide faster (motor) or brighter (lighting) capabilities?


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## CanadianSparky (May 10, 2011)

JRaef said:


> Just FYI, OFFICIALLY there is a convention on the order in which the numbers are presented that technically helps, although unfortunately most people don't realize this and trow them around willy nilly.
> 
> If the larger voltage is listed first, it is a 3 phase Wye service. So it would be 208Y120 or 208/120; 480Y277 or 480/277.
> 
> ...


I didn't know about that thanks!


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## guest (Feb 21, 2009)

HARRY304E said:


> *120/208 is usually 3 phase.in commercial buildings.*
> 
> 120/240 is usually single phase in residential .
> 
> 480/277 is also 3 phase in a commercial building.


And as usual, the Left Coast has to be an exception to the rule, 120/208 (or as JRaef said, 208Y/120) is very commonly used in apartment complexes of 10 or more units here. The main service is three phase with each apartment unit being tapped off of two of the phases (and the neutral of course) with the panels connected to balance the use of the phases as much as possible. 

Most residential clothes dryers are rated for 120/240 volt and work on 208Y/120 but they do take longer to dry the clothes.


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## hardworkingstiff (Jan 22, 2007)

JRaef said:


> Just FYI, OFFICIALLY there is a convention on the order in which the numbers are presented that technically helps, although unfortunately most people don't realize this and trow them around willy nilly.
> 
> If the larger voltage is listed first, it is a 3 phase Wye service. So it would be 208Y120 or 208/120; 480Y277 or 480/277.
> 
> ...


In the case where a 208Y120 transformer feeds two ungrounded and one grounded conductor to multiple services, how would you correctly write the voltage that feeds the single-phase panel?


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## CanadianSparky (May 10, 2011)

mxslick said:


> And as usual, the Left Coast has to be an exception to the rule, 120/208 (or as JRaef said, 208Y/120) is very commonly used in apartment complexes of 10 or more units here. The main service is three phase with each apartment unit being tapped off of two of the phases (and the neutral of course) with the panels connected to balance the use of the phases as much as possible.
> 
> Most residential clothes dryers are rated for 120/240 volt and work on 208Y/120 but they do take longer to dry the clothes.


I have worked in many apartment building like that. They seem to bring it in for 3ph motor loads.


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## 220/221 (Sep 25, 2007)

dietdrkelp said:


> Also can one clarify if 120/208 means commercial writing and 120/240 means resi? .


Simple explanation:

_120/208_ *3 phase* is a more modern system called _*Wye*_. It has 120V to ground on all 3 legs and 208 volts between any of them.


_120/240_ *3 phase *is an older system called _*Delta*_. It has 2 legs @ 120V to ground and one leg @ 208 V to ground with 240 between any of the hot legs.

Ask someone else how this works :laughing: I'm just a mechanic.

And, *120/240 single phase* is 120V to ground on both legs and 240 between them.


_Generally speaking_, most resi has a single phase system and most commercial has a 3 phase system.

Large commercial buildings will have 277/480 3 phase systems coming in. That has 277V to ground and 480 between legs. AC and mechanical loads will be 480V. It allows smaller wires to operate larger loads. Lighting will be 277Volts, one hot, one neutral. Same principal here, more lights on a circuit.

In the equipment rooms there will be transformers to take the 480 down to 120/208 to feed separate panels for the receptacle and incandescent lighting loads.


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## BBQ (Nov 16, 2010)

mxslick said:


> And as usual, the Left Coast has to be an exception to the rule, 120/208 (or as JRaef said, 208Y/120) is very commonly used in apartment complexes of 10 or more units here. .


It is here too, Harry just did not mention it.

We also have entire residental neighborhoods with 208 volt services.


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## MTW (Aug 28, 2013)

mxslick said:


> And as usual, the Left Coast has to be an exception to the rule, 120/208 (or as JRaef said, 208Y/120) is very commonly used in apartment complexes of 10 or more units here. The main service is three phase with each apartment unit being tapped off of two of the phases (and the neutral of course) with the panels connected to balance the use of the phases as much as possible.
> 
> Most residential clothes dryers are rated for 120/240 volt and work on 208Y/120 but they do take longer to dry the clothes.


I can't believe you left out your dissertation about SCE's distribution system.


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## Rochsolid (Aug 9, 2012)

mxslick said:


> And as usual, the Left Coast has to be an exception to the rule, 120/208 (or as JRaef said, 208Y/120) is very commonly used in apartment complexes of 10 or more units here. The main service is three phase with each apartment unit being tapped off of two of the phases (and the neutral of course) with the panels connected to balance the use of the phases as much as possible.
> 
> Most residential clothes dryers are rated for 120/240 volt and work on 208Y/120 but they do take longer to dry the clothes.


We do a lot of assisted living complexes and senior residences, we had one older gentlemen complain to us (not knowing that he had a 120/208 service) that he was only getting 208 volts at his range, an then told us it was due to "poor craftsmanship" Man that was good for a laugh haha


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## MWayne (Nov 8, 2010)

Commercial light fixtures and ballast kits may be called 5 tap or multitap and have leads for 120/208/240/277/480 volt sources.


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## HARRY304E (Sep 15, 2010)

BBQ said:


> It is here too, Harry just did not mention it.
> 
> We also have entire residental neighborhoods with 208 volt services.


True I was too lazy to type it all out.:laughing:

However it's good practice to do so , so next time I should.


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## Meadow (Jan 14, 2011)

JRaef said:


> Just FYI, OFFICIALLY there is a convention on the order in which the numbers are presented that technically helps, although unfortunately most people don't realize this and trow them around willy nilly.
> 
> If the larger voltage is listed first, it is a 3 phase Wye service. So it would be 208Y120 or 208/120; 480Y277 or 480/277.
> 
> ...


Regarding the order of the numbering Ive always listed the smaller voltage first, it makes more sense for me.


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## bsdiceman (Nov 23, 2021)

Thanks for this info folks!


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## micromind (Aug 11, 2007)

bsdiceman said:


> Thanks for this info folks!


There's a TON of info on this site.


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## HertzHound (Jan 22, 2019)

One thing not mentioned, that I always go by, is that a slash rating will require a neutral. So looking at equipment cuts, if it calls for 120/208 or 120/240, you better pull a neutral. If the equipment cuts say 208 or 240, then it doesn’t need a neutral. It should also specify single phase or three phase. So 120/208 single phase would need two hots and a neutral. If it says 208 single phase, then it just needs two hots. Same with any other voltage and phase setup. / = neutral in my book.


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## micromind (Aug 11, 2007)

HertzHound said:


> One thing not mentioned, that I always go by, is that a slash rating will require a neutral. So looking at equipment cuts, if it calls for 120/208 or 120/240, you better pull a neutral. If the equipment cuts say 208 or 240, then it doesn’t need a neutral. It should also specify single phase or three phase. So 120/208 single phase would need two hots and a neutral. If it says 208 single phase, then it just needs two hots. Same with any other voltage and phase setup. / = neutral in my book.


True for most stuff but something like a motor that's rated 230/460 doesn't need a neutral but something like a dryer does. 

Also, a lot of stuff that has a slash rating will need to be reconnected for the different voltages where something that has a - (like 208-230) doesn't, it indicated a range of voltages. This is especially true on electronic stuff, if it's 120/240, you'll need to flip a switch or change wiring but if it's 120-240, it'll accept either voltage.


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## paulengr (Oct 8, 2017)

The one people are dancing around is 120/240 high leg delta.

So with the “200ish” 3 phase systems there are 4 choices.

There is 208/120 eye which is a 5 wire system with a true neutral. Once in a while a few loads struggle with the low 208 voltage but balancing the neutral is usually easy.

There is 240 delta ungrounded. Popular in the 1950s. Please just don’t do it.

There is 240 corner grounded dekta, easiest way to fix 250 ungrounded. It’s grounded but one phase only and 120 is not available. Not a bad system, just not popular.

The other one is 120/240 high leg delta. There are two versions depending on if it’s an open or closed delta. With either one two of the phases are center tapped so you get 120/240 single phase center tapped. The third leg can be created with two more transformer coils in a true delta or with only one coil which is often just another single phase transformer. It’s a cheap method with say just one pump or HVAC unit but one phase has lousy impedance.

The same thing can exist at 480 plus resistance and reactance grounding but the split voltages aren’t that useful. I do occasionally run into 277 lighting.


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## bsdiceman (Nov 23, 2021)

paulengr said:


> The one people are dancing around is 120/240 high leg delta.
> 
> So with the “200ish” 3 phase systems there are 4 choices.
> 
> ...


I was learning about high leg delta from my ugly's reference book yesterday. Very interesting. It can do two legs of 120. One leg of 208. And three legs of 240. Is that correct. Most of your explanation of high leg delta went over my head, could you simplify and explain it once more please?


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## paulengr (Oct 8, 2017)

bsdiceman said:


> I was learning about high leg delta from my ugly's reference book yesterday. Very interesting. It can do two legs of 120. One leg of 208. And three legs of 240. Is that correct. Most of your explanation of high leg delta went over my head, could you simplify and explain it once more please?


You can get 208ish but I’ve never seen it used that way.

So just draw a triangle on a piece of paper. Do it in pencil. Draw as close to an equilateral triangle as you can (3 equal sides). Mark the two upper sides 240. Now at the bottom draw a ground symbol in the middle of the side. That’s your ground/neutral. Mark the two half lines on either side as 120 and the whole side is 240 again. You can make these voltages with three single phase transformers where each one powers one “side”. The bottom transformer needs to be a center tapped 120/240 transformers. The sides do not have to be. They often are though and we just don’t hook up the center tap because we don’t need it.

The only tricky thing here is the “high leg” (top corner). At the bottom corners we get 120 V to neutral and 240 phase to phase just like a single phase system. But if you drew the triangle accurately it’s obvious that the voltage from the third corner at the top to neutral is a lot more than just 120 V. In fact it’s nearly double that. It’s 208. So you cannot just hook up 120 V loads anywhere. Only three phase loads should be hooked up to the high leg. Current NEC Code says it MUST be orange instead of the usual black red blue or brown orange yellow which is convention, not mandatory. Even then, ALWAYS test voltages to neutral if you are working with three phase/single phase mixed systems because it’s easy to mix them up or assume you are working with 208/120 when it may be 120/240 high leg or 240 corner ground.

Finally while the drawing is out just erase the line on one of the 240 legs. The VOLTAGE and phase angles (120 degrees) stay the same but you need one less transformer. Obviously since the third side draws power through two series transformers the impedance is doubled so it won’t quite act right but unless you have heavy motor loads most if the time this is a cheap way to get three phase. The remaining high leg transformer can be smaller and is just sort of a “helper” for the three phase load where often most of the load in an office is on the single phase 120/240 side.

This system may seem strange if you are used to everything is all symmetrical because it’s anything but.


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## bsdiceman (Nov 23, 2021)

I've attached my drawing as you instructed. Did I represent the three single phase transformers with the bottom one center tapped correctly? What is the purpose of using these transformers in this kind of circuit? Does the impedance double because the transformers are connected in series? Would a wye connection avoid this impedance? What Is impedance?


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## bsdiceman (Nov 23, 2021)

I find it interesting that these drawing are attempting to represent voltage to scale. Both linear distances and angular representations of phase. I'm trying to understand how these drawing relate to real life systems which I assume are seldom shaped as a triangle or delta symbol. What I want to understand is: how does the inputs look, through what type of connections, wires, gaps and coils do they go through before becoming a usable output? Why must I hook up a three phase load to 208 as opposed to a single phase load to 120?


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## gpop (May 14, 2018)

bsdiceman said:


> I find it interesting that these drawing are attempting to represent voltage to scale. Both linear distances and angular representations of phase. I'm trying to understand how these drawing relate to real life systems which I assume are seldom shaped as a triangle or delta symbol. What I want to understand is: how does the inputs look, through what type of connections, wires, gaps and coils do they go through before becoming a usable output? Why must I hook up a three phase load to 208 as opposed to a single phase load to 120?


You need to understand what a ac sine wave is before some of this will make sense. 

on a simple split phase 120/240 home circuit 180 degrees out of sync you will see that when one wave peaks in the positive while the other wave is also peaking into the negative. The peak of either wave is 120 from the center line. As we ground the center line we can now say that we have 2 legs of 120v to the grounded conductor (neutral) and leg to leg we have 240v. (remember voltage is pressure so your meter is not reading 2 waves it reading the pressure difference between the 2 waves. E.g its reading the pressure differential which will look like a 3rd sine wave).

A common misconception that was taught in school was that voltage flow was pushed which makes sense if your teaching basic DC to kids but that makes no sense that on AC. You have to think that the power generator is actually pushing and pulling. If one line pushes 120 and one pulls 120 then it makes sense that you have 240 between them.

Now if you look at 3 phase you will see the sine waves are 120 degrees out of sync. Pick a spot on one phase then compare it to sign wave of the other 2 phases and you will see why its 208 rather than 240v.

High leg delta we start with a standard split phase home transformer which gives us phase A , N and phase C. Now we add a extra transformer and connect one end to phase A which gives us pressure between phase A to phase B. As the waves are 120 degrees out of sync we end up with pressure between phase C and B with out having to add the third transformer. 
The 208 ish was never really designed to be used on a high leg delta but that does not mean you can not use it. If you google the sine waves for each system you will see how the waves interact with each other.


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