# 3 phase?



## ralph (Apr 6, 2008)

Came across a 3 phase sevice on a service call . Burnt out ac equip.
My supply is 120 on A , 240 on B, and 120 on C. Ive never seen this. I am assuming that the 3 phase equipment is not liking the high b leg.
Has anyone ever seen this recently ?


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## 480sparky (Sep 20, 2007)

I assume your measurements are each phase to ground? Did you take any Line-to-Line voltage measurements?

My guess is you've got a Delta system.


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## micromind (Aug 11, 2007)

Take a few more voltage readings. I'd bet you'll find 240 volts from A-B, 240 from B-C, and 240 from C-A. I'd also bet that B to neutral is more like 208 volts. 

As stated above, this is almost certainly a 120/240 3 phase 4 wire delta. It's pretty common around here, most 3 phase motors actually like this system better than a 208 wye. 

One problem with a delta system is if the two 120 volt legs are loaded to the gills and the high leg (phase B in this case) has little load on it, there'll be a voltage imbalance between the 3 line-to-line voltages. On a 240 volt system, anything more than about 6 volts of imbalance will wreak havoc with 3 phase motors. 

Rob


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## ralph (Apr 6, 2008)

Thats it. Its the first time Ive ever come across it. I guess i probably read about in my schooling days , but that was forgotten. You are 100% correct on the a and c being totally maxed.
What is the primary purpose of this supply ? It doesnt seem to be helpfull to anyone in this workshop ( marine mechanics, fiberglass workers )
Thanks for the input


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## micromind (Aug 11, 2007)

A couple of reasons for this service come to mind;

1) If a single phase service already existed, and a 3 phase load was added, it was very easy to convert the existing service to a 240 delta. The POCO would hang another pot on the pole, and replace the existing triplex with a quadplex. The electrician would change the meterbase (often just the interior) from a 4 jaw to a 6 jaw, and run another wire up the mast. The existing single phase panel was left as-is, and another 3 phase panel was added, or sometimes the existing single phase panel was replaced with a 3 phase one. 

2) A lot of older electrical contractors had a hard time adapting to the new-fangled wye system. They just couldn't bring themselves to connect a 230 volt motor to a 208 volt supply. (In 18 years of working with a LOT of motors, I've yet to see a problem with any 230 volt motor running on 208 volts.)

3) If the POCO only had 2 primary phases available, two transformers will make a 240 delta. It takes all 3 primary phases to make a wye.


One problem I've encountered with this system is that a large number of electricians are scared to death of the high leg. Frequently I hear "It's only for 3 phase", or, "It's dangerous". When I hear these reasons for not using the high leg for a straight 240 volt single phase load, I know I'm dealing with a very inexperienced person. I always use the high leg for any 240 volt load that doesn't involve the neutral. It helps balance the voltage. 

Rob


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## electro916 (Jan 16, 2009)

micromind said:


> One problem I've encountered with this system is that a large number of electricians are scared to death of the high leg. Frequently I hear "It's only for 3 phase", or, "It's dangerous". When I hear these reasons for not using the high leg for a straight 240 volt single phase load, I know I'm dealing with a very inexperienced person. I always use the high leg for any 240 volt load that doesn't involve the neutral. It helps balance the voltage.
> 
> Rob



I cant tell you how many times I've seen this. 240v Delta Main panel filled up, with very few 3pole breakers, almost every space which if a breaker was there would be on the B phase bus, is empty. They then Installed a single phase sub panel to run all of their 120 single phase circuits out of, I laugh and laugh, usually because there was enough space in the main panel to accommodate all the 120v single phase circuits.


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## nap (Dec 26, 2007)

micromind said:


> 2) A lot of older electrical contractors had a hard time adapting to the new-fangled wye system. They just couldn't bring themselves to connect a 230 volt motor to a 208 volt supply. (In 18 years of working with a LOT of motors, I've yet to see a problem with any 230 volt motor running on 208 volts.)
> 
> 
> 
> Rob


I just want to emphasize you said a _230_ volt motor, not a _240_ volt motor. Obviously a 240 volt (rated) motor is not acceptable to run on 208. A 230 volt (rated) motor is although it is at the very bottom of allowed tolerances. A low voltage area or sags can cause it to be below the lower allowed tolerance of 207 volts though.


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## micromind (Aug 11, 2007)

Indeed true! Most motors are marked 115/230, or 230/460. One must be careful when connecting these to a 208 volt system.

A lot of NEMA motors these days have an alternate rating on the nameplate, usually something like 'usable on 208 volt systems at XX amps, and 1.XX service factor. Usually the amps are higher, the HP is the same, and the service factor is lower. 

Some are marked 115/208-230, or 208-230/460. The amps will be something like 10.6/5.5-5.3, or 15.2-14.6/7.3 Everything else is the same. 

Rob


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## Southeast Power (Jan 18, 2009)

micromind said:


> A couple of reasons for this service come to mind;
> 
> 1) If a single phase service already existed, and a 3 phase load was added, it was very easy to convert the existing service to a 240 delta. The POCO would hang another pot on the pole, and replace the existing triplex with a quadplex. The electrician would change the meterbase (often just the interior) from a 4 jaw to a 6 jaw, and run another wire up the mast. The existing single phase panel was left as-is, and another 3 phase panel was added, or sometimes the existing single phase panel was replaced with a 3 phase one.
> 
> ...


I know you are not suggesting using the high leg to neutral for a 208 connection. It could almost read that way.
Of course, you mean that the use of single 240 phase to phase regardless of it being A B or C is proper. 
Ralph, If you pull up to a job and see two transformers on a pole with one being a bit smaller than the other it is a dead give away that you are going into an installation that will have an open Delta. 
If you see three transformers it could be a closed delta or a WYE. Always check! Not all are high legs are marked with orange tape. Could be on B or C phase around here depending on how old the building is.


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## JohnJ0906 (Jan 22, 2007)

jrannis said:


> . Always check! Not all are high legs are marked with orange tape. Could be on B or C phase around here depending on how old the building is.


And not all legs labeled orange are high legs, either. 

I went to add a couple of circuits last week in a storefront office, and "B" leg was labeled orange. When I checked voltage I had 120v to ground on all 3 legs, and 208 between any 2. (208Y/120v) I haven't the slightest idea why orange was improperly used.


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## nap (Dec 26, 2007)

jrannis said:


> I know you are not suggesting using the high leg to neutral for a 208 connection. It could almost read that way.
> .


 
You're going to have to tell me why that would not be feasible?


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## RePhase277 (Feb 5, 2008)

JohnJ0906 said:


> And not all legs labeled orange are high legs, either.
> 
> I went to add a couple of circuits last week in a storefront office, and "B" leg was labeled orange. When I checked voltage I had 120v to ground on all 3 legs, and 208 between any 2. (208Y/120v) I haven't the slightest idea why orange was improperly used.


Why is it improper to use orange? The code does not specify that ONLY a high leg shall be orange. It only specifies that where a high leg is present with a grounded conductor that it shall be identified orange. Millions of 480 V installs out there have an orange B phase with no high leg whatsoever.

I myself stopped using orange as a conductor color for about 4 years. I believe that it should only be used to ID high legs. When I pull 480/277, it's brown, purple, yellow, and gray.


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## nap (Dec 26, 2007)

InPhase277 said:


> When I pull 480/277, it's brown, purple, yellow, and gray.


 
when an engineer/architect specs colors, they spec brown, orange, and yellow. Not neccessarily in that order.


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## RePhase277 (Feb 5, 2008)

nap said:


> when an engineer/architect specs colors, they spec brown, orange, and yellow. Not neccessarily in that order.


This is why I started it. Got a set of plans that spec'd brown, purple, yellow and gray. I liked it and stuck with it. Never had anyone call me out on that one wire color choice. I have never seen an architect open a panel and take a look anyway. Probably wouldn't know which way to turn the cover screws...


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## JohnJ0906 (Jan 22, 2007)

InPhase277 said:


> Why is it improper to use orange?


NEC amendment here. (Sorry, should have said that)

http://resources.baltimorecountymd.gov/Documents/Permits/ElectricalInspections/elec_color_code.pdf


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## JohnJ0906 (Jan 22, 2007)

InPhase277 said:


> Why is it improper to use orange? The code does not specify that ONLY a high leg shall be orange. It only specifies that where a high leg is present with a grounded conductor that it shall be identified orange. Millions of 480 V installs out there have an orange B phase with no high leg whatsoever.
> 
> I myself stopped using orange as a conductor color for about 4 years. I believe that it should only be used to ID high legs. When I pull 480/277, it's brown, purple, yellow, and gray.


And also, my point was - don't trust the markings, use a volt meter.


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## Southeast Power (Jan 18, 2009)

nap said:


> You're going to have to tell me why that would not be feasible?


OK had to go back to Mikes to get this post by e57. He has the best short explanation I have read to date.

_What makes this voltage unusable? I don't understand. Is it not practical, or not possible?_

You _could_ use it - it is possible, but _practical..._ NO! Thats a _yes _BUT no question? It's current path and impedances will vary with the load (AB/BC) and and make voltages unstable all around. (ABC. BCA, CAB) It is only measurable at 208 in a balanced system, and adding an unintentional load (and unintentionally reconnecting the transformer for a separate voltage) through the load(S), (Portions of BC, and AB, and various portions of AN, and CN) changes the voltage and the true VA (loads) of all the phases.

If you drew a *circle* of the current path of a high leg to neutral path - it would look like a figure 8......:thumbsup:


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## micromind (Aug 11, 2007)

I can think of two reasons why the high leg isn't used to neutral.

1) If the transformer connection is a closed delta (3 transformers), then the high leg to neutral voltage will be as stable as the phase to phase voltages are. If it is an open delta (2 transformers), then the voltage isn't as stable. Phase angle on the primary side will have a more pronounced effect on voltage stability. 

2) You'd need a single pole breaker that's rated for at least 208 volts. Not 120/240 volts, as the first rating is voltage across one pole, and the second is across two or more poles. The only breakers I've seen that would be legal here are 277 volt. None that I know of will fit in a 120 volt panel.

Rob


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## wwilson174 (Apr 25, 2008)

nap said:


> You're going to have to tell me why that would not be feasible?


In the three phase four wire system under discussion the Voltages are 240 phase to phase and 120 to neutral from A phase and C phase. the voltage between B phase and the neutral is the vectoral sum of the phase voltage on B and The Voltage between A Or C and the neutral.


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## nap (Dec 26, 2007)

wwilson174 said:


> In the three phase four wire system under discussion the Voltages are 240 phase to phase and 120 to neutral from A phase and C phase. the voltage between B phase and the neutral is the vectoral sum of the phase voltage on B and The Voltage between A Or C and the neutral.


and the point is? 

You still end up with 208 volts.

and technically it is only a neutral in relation to A and C phases and if grounded, a grounded conductor. It would not be a neutral when considering anything other than the one set of windings where it is the center tap of that winding.


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