Single phase vs 3 phase systems

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Kevin.hndz

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When opening up a panel I sometimes see black red blue phases and sometimes see blue red black. Any measurements between phases show 208v and 120v between phase and neutral. Is this single or 3 phase system? Also why wouldn’t I see 240v ? Or 277v ? All these voltages are confusing and youtube videos explain the THEORY of 3 phase vs single phase systems ... windings in the transformer all 120° of each other blah blah all useful information BUT I'm yet to see a in field explanation of these situations. With that being said I also understand we live in the age of being able to obtain whatever voltage we need via buck boosters or transformer inverters or converters. Simply put what voltages can single phase supply or not supply and same for 3 phase systems?
 
Black, Red, Blue, and White would typically be a 3 phase, 208Y/120 volt system. In NYC you might see Blue, Red, Black as A, B, and C phase.

Welcome to the Forum. :)
 
Kevin.hndz said:
Simply put what voltages can single phase supply or not supply and same for 3 phase systems?
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Voltage Ratings: 110/115/120, 220/230/240 or 440/460/480

This subject comes up a LOT in this and other forums, so I thought it would be a good idea to make it a "Sticky" that can be found and referred to easily when it comes up. There are two "standards" for voltage in North America depending on which END of the wire you are looking at; "Distribution...
forums.mikeholt.com

-Hal
 
Kevin.hndz said:
? All these voltages are confusing and youtube videos explain the THEORY of 3 phase vs single phase systems ... windings in the transformer all 120° of each other blah blah all useful information BUT I'm yet to see a in field explanation of these situations.
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I'm not sure there is any "in the field" way to explain it. I think looking at a picture of the delta and wye connections showing the angles and the voltage as the lengths pretty much explains it clearly (assuming you remember some basic high school algebra and trig).
 
infinity said:
Black, Red, Blue, and White would typically be a 3 phase, 208Y/120 volt system. In NYC you might see Blue, Red, Black as A, B, and C phase.

Welcome to the Forum. :)
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I was working on a town house in Manhattan and it was the first time I have ever seen Blue red black does it matter ? We updated the electrical in the house and just matched the phase orientation in the sub panels but it definitely caught me off guard as I had never seen it before
 
YouTube is not an acceptable alternative to formal training. You should get your mitts on some official textbooks.

Delmars Standard Textbook Of Electricity is a good start.

Also, be aware that someone at sometime may have switched phases, based on phase rotation.
 
Kevin.hndz said:
When opening up a panel I sometimes see black red blue phases and sometimes see blue red black. Any measurements between phases show 208v and 120v between phase and neutral. Is this single or 3 phase system? Also why wouldn’t I see 240v ? Or 277v ? All these voltages are confusing and youtube videos explain the THEORY of 3 phase vs single phase systems ... windings in the transformer all 120° of each other blah blah all useful information BUT I'm yet to see a in field explanation of these situations. With that being said I also understand we live in the age of being able to obtain whatever voltage we need via buck boosters or transformer inverters or converters. Simply put what voltages can single phase supply or not supply and same for 3 phase systems?
Click to expand...

Any voltage can supply either system. What you need to understand as you continue your reading and education is the relationship between voltages in a system.

If the line-to-line voltage is approximately 1.73 times the line-to-neutral voltage, you are dealing with a 3-phase wye system. The most common examples in the US are 208/120 and 480/277, in commercial. But do the math and note the relationship. You don't get 120 and 277 in the same system because they don't follow such a relationship.

If the line-to-line voltage is approximately twice the line-to-neutral voltage, then you are dealing with single phase with a center-tap. Usually 120/240 in residential.

High leg delta is the weird one, a three-phase system where one line-to-neutral will be approximately 1.73 times the others, with the lower voltage being half the line-to-line voltage. Most often L-L is 240V, with two lines being 120V to neutral and the 'high leg' is 208V to neutral.

These three will most likely cover everything you see in your career although there is other weird stuff out there.

The coloring and order of coloring doesn't positively tell you anything, except whether the previous electrician cared about following a convention. Black,red,blue is typically 208/120 wye. Black,red is typical in single phase 120/240. But this isn't actually code required and can't in any way be counted upon. (Only orange for high-leg, or purple in at least one place, is required.) You need to count conductors and measure voltages to understand what you're working with.
 
as noted, there are a few areas where the Code addresses color; white, green,orange etc. but depending on that would be an easy way to get ones-self in trouble. Often, the color used is dependent on the color that was handy.
 
Kevin.hndz said:
I was working on a town house in Manhattan and it was the first time I have ever seen Blue red black does it matter ? We updated the electrical in the house and just matched the phase orientation in the sub panels but it definitely caught me off guard as I had never seen it before
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Yes Blue, Red, Black, was a standard for 3 phase 208Y/120 volt systems in NYC for many decades.
 
It is also helpful to make all of the voltage measurements, like Line-Line, Line-Neutral, Line - Ground, and Neutral - Ground, when you are trying to identify your voltage system.
 
jaggedben said:
Any voltage can supply either system. What you need to understand as you continue your reading and education is the relationship between voltages in a system.

If the line-to-line voltage is approximately 1.73 times the line-to-neutral voltage, you are dealing with a 3-phase wye system. The most common examples in the US are 208/120 and 480/277, in commercial. But do the math and note the relationship. You don't get 120 and 277 in the same system because they don't follow such a relationship.

If the line-to-line voltage is approximately twice the line-to-neutral voltage, then you are dealing with single phase with a center-tap. Usually 120/240 in residential.

High leg delta is the weird one, a three-phase system where one line-to-neutral will be approximately 1.73 times the others, with the lower voltage being half the line-to-line voltage. Most often L-L is 240V, with two lines being 120V to neutral and the 'high leg' is 208V to neutral.

These three will most likely cover everything you see in your career although there is other weird stuff out there.

The coloring and order of coloring doesn't positively tell you anything, except whether the previous electrician cared about following a convention. Black,red,blue is typically 208/120 wye. Black,red is typical in single phase 120/240. But this isn't actually code required and can't in any way be counted upon. (Only orange for high-leg, or purple in at least one place, is required.) You need to count conductors and measure voltages to understand what you're working with.
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So far has been the best answer I think I'm beginning to understand this topic a bit better. I've definitely been reading a lot and not relying on YouTube as one comment said , I just used YouTube as a example for the fact that they aren't any good at explaining these situations. Now I'd like to have a follow up question. What determines what voltage the residence is dealing with ? Is it the size of the wire at the meter ? Or does it just depend on whatever the area is already dealing with. When you upgrade a service are you increasing the size of the wire to deal with more loads or increasing the voltages supplied at the panel ?
 
Kevin.hndz said:
So it's just standard? No particular reason ? Was it just matched at the pole or .... ?
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It may have originated with ConEd but I've seen it going back to buildings that are 100 years old. I'll look at my old NYC codebook to see if there is anything written in stone.
 
Kevin.hndz said:
What determines what voltage the residence is dealing with ?
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The utility transformer, essentially.

Note that a voltage like 120/240 is a *nominal* voltage. The utility is supposed to keep the actual voltage within 5%, typically. So for example if you measure 124/248 on a residential service with two hots and a neutral, that is still a single phase 120/240V service. The grid voltage is just a bit high at the moment.

Is it the size of the wire at the meter ? Or does it just depend on whatever the area is already dealing with.
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Wire size is essentially proportional to amps, not voltage.

When you upgrade a service are you increasing the size of the wire to deal with more loads or increasing the voltages supplied at the panel ?
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If you are just upgrading, say, a single family home from 100 to 200 amps, that's just wire size and equipment rating. (The utility may not even upgrade their part of it.) For larger buildings and commercial, it may involve a higher voltage, and/or switching from single phase to three phase. With a lot more coordination with the utility.
 
jaggedben said:
The utility transformer, essentially.

Note that a voltage like 120/240 is a *nominal* voltage. The utility is supposed to keep the actual voltage within 5%, typically. So for example if you measure 124/248 on a residential service with two hots and a neutral, that is still a single phase 120/240V service. The grid voltage is just a bit high at the moment.



Wire size is essentially proportional to amps, not voltage.



If you are just upgrading, say, a single family home from 100 to 200 amps, that's just wire size and equipment rating. (The utility may not even upgrade their part of it.) For larger buildings and commercial, it may involve a higher voltage, and/or switching from single phase to three phase. With a lot more coordination with the utility.
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So you would coordinate with the utility for higher voltages for a bigger building ? And wire size is relative to amps NOT voltage. Thank you all of you have been extremely helpful I'm glad we didn't the old timer on here saying if u don't know what single and 3 phase are you shouldn't be doing electric !! Hahaha we all start somewhere.
 
Kevin.hndz said:
So it's just standard? No particular reason ? Was it just matched at the pole or .... ?
Click to expand...
Electrons are color blind, they couldn't care less if it was Purple Yellow and Red. An electrician who follows should know to measure voltage and determine what the system is. Phase rotation? Only important for replacing a motor, usually. Jog and correct if needed to change direction. There are phase meters, I've only found them handy when moving equipment around, check phase rotation when the equipment is removed, make sure same rotation hooked up at new location.
 
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