Wild leg and compressors

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Stiff,

Back to your question about loading:

If you are talking open-delta, wild-leg, loading either closed side would produce the same PFs in the transformers, but loading the wild leg or the open side would produce different PFs.
 
hardworkingstiff said:
Yup e57, that's what I was thinking about. I don't remember ever seeing a closed delta service. Most of the deltas I've seen have been in commercial buildings with a small 3-phase load, I guess that's why.

The code section for B phase being the high-leg is 408.3(E). I remember in the 70's, it was C phase.
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See also 110.15, 215.8, and 230.56, And there is an exception to 408.3E
Exception: Equipment within the same single section or multisection switchboard or panelboard as the meter on 3-phase, 4-wire, delta-connected systems shall be permitted to have the same phase configuration as the metering equipment.
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Around here the original POCO installs are High-C phased, and often if there is an existing transformer they will continue to use C rather than break out the rotation meter - LAZY!
 
e57,
Around here the original POCO installs are High-C phased, and often if there is an existing transformer they will continue to use C rather than break out the rotation meter
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Are you sure? Around here the high leg is landed on the C phase postition because of the metering requirement, however you will find that it really is B phase if you put a rotation meter on it.
Don
 
don_resqcapt19 said:
e57,
Are you sure? Around here the high leg is landed on the C phase postition because of the metering requirement, however you will find that it really is B phase if you put a rotation meter on it.
Don
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As most things that would depend on rotation would oringinally be set up clockwise or at least operate that way - if you move B to C, and still call it B, you need to move/swap the other two and rename them too. (Or suffer having to swap everything connected to it. (Huge hassle for an existing building if they change it. Especially dangerous with a high-leg.) Whats in a name though? Left to right, top to bottom - ABC, 123 or XYZ - It is rotation that really counts! Which brings up a great point, never thought of "rotation" being required, if it isn't it should be. The NEC is not specific on it.
 
e57,
if you move B to C, and still call it B, you need to move/swap the other two and rename them too.
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At the transformer they are connected A, B, C, at the metering equipment they are landed A, C, B and at the service disconect they are landed A, B, C. The only place the rotation is different is from the line side of the metering equipment to the line side of the service disconnect.
Which brings up a great point, never thought of "rotation" being required, if it isn't it should be. The NEC is not specific on it.
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Actually it is required by the code. See 408.3(E), 430.97(B) and 409.102(B)
408.3(E) Phase Arrangement The phase arrangement on 3-phase buses shall be A, B, C from front to back, top to bottom, or left to right, as viewed from the front of the switchboard or panelboard. The B phase shall be that phase having the higher voltage to ground on 3-phase, 4-wire, delta-connected systems. Other busbar arrangements shall be permitted for additions to existing installations and shall be marked.
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Don
 
don_resqcapt19 said:
e57,

At the transformer they are connected A, B, C, (Clock-wise) at the metering equipment they are landed A, C, B (Counter Clock-wise) and at the service disconect they are landed A, B, C. (Clock-wise) The only place the rotation is different is from the line side of the metering equipment to the line side of the service disconnect.

Actually it is required by the code. See 408.3(E), 430.97(B) and 409.102(B) (2005?)

Don
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Don the exception to 408.3E allows you to keep rotation the same thoughout the panels if connected originally as High-C, be it clock-wise, or clock-wise.
(2002 commentary) The high leg is common on a 240/120-volt, 3-phase, 4-wire delta system. It is typically designated as ?B phase.? Section 110.15 requires the high-leg marking to be the color orange or other similar effective means of identification. Electricians should always test each phase to ground with suitable equipment in order to know exactly where this high leg is located in the system.
The exception to 408.3(E) permits the phase leg having the higher voltage to ground to be located at the right-hand position (C phase), making it unnecessary to transpose the panelboard or switchboard busbar arrangement ahead of and beyond a metering compartment. The exception recognizes the fact that metering compartments have been standardized with the high leg at the right position (C phase) rather than in the center on B phase.
See also 110.15, 215.8, and 230.56 for further information on identifying conductors with the higher voltage to ground. Other busbar arrangements for making additions to existing installations are permitted by 408.3(E).
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Simularly if you had High-B, the code doesn't state specificaly that it needs to be clock-wise or counter clock-wise. Calling a phase A, B, or C is arbitrary until it lands in a panel, disco or secondary transformer in the building. If you are handed 4 unmarked conductors from the POCO, one being grounded, another a high-leg, and you make that your B phase - the code doesn't say what the other two should be. Only common sense says that you would make it clock-wise. Naming as >ABCABCABCABC> rather than <CBACBACBACBA< because 'BACk' is written in there rather than ABC....
 
e57,
Simularly if you had High-B, the code doesn't state specificaly that it needs to be clock-wise or counter clock-wise. Calling a phase A, B, or C is arbitrary until it lands in a panel, disco or secondary transformer in the building. If you are handed 4 unmarked conductors from the POCO, one being grounded, another a high-leg, and you make that your B phase - the code doesn't say what the other two should be.
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It is my opinion that the code requires that when you hook up the phase meter with the leads landed in order left to right, that the meter should indicate A B C rotation. Of course the exception would apply if the meter is part of the service equipment or if you are adding to an existing installation. The only high leg services that I have worked on have used self contained meters and in that case the code requires A B C rotation at the service equipment.
Don
 
The code only uses the word 'Rotation' once in 430.35(B) exception b1. It may imply it in phase arrangment - but only states where it wants the hig-leg should/could be - not the other two. Nor does it require you to test for rotation. Although I'm sure you and I would see that as common sense? I think it's something the code should, and could be more clear on.
 
e57,
(E) Phase Arrangement The phase arrangement on 3-phase buses shall be A, B, C from front to back, top to bottom, or left to right, as viewed from the front of the switchboard or panelboard. The B phase shall be that phase having the higher voltage to ground on 3-phase, 4-wire, delta-connected systems. Other busbar arrangements shall be permitted for additions to existing installations and shall be marked.
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If the A B C in the above is not phase rotation, what is it?
Don
 
don_resqcapt19 said:
e57,
If the A B C in the above is not phase rotation, what is it?
Don
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I infer that Va leads Vb by 120 degrees. Right? Then C B A would mean that Vc leads Vb by 120 degrees. Right? I hope so. Rattus
 
rattus,
I infer that Va leads Vb by 120 degrees. Right? Then C B A would mean that Vc leads Vb by 120 degrees. Right? I hope so.
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As there is no reasonable way to identify A phase, all ABC requires is that the left phase leads the center by 120 degrees and the center leads the right by 120 degrees. ABC=BCA=CAB and are all code compliant. CBA=ACB=BAC and would all be violations.
Now the utility needs to know that A phase is A phase and not just the rotation. If they would parallel an ABC system with a BCA system, the circuit breakers should open.
Don
 
don_resqcapt19 said:
e57,
If the A B C in the above is not phase rotation, what is it?
Don
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I think that is where it implies rotation, but fails to state "rotation". It wants >ABC, but fails to state it can not be <ABC. And goes further with the exception to say within the same premises essentially you could have the high leg on B or C if the meter and associated sections are set up as C. Or what to do with the placement or marking of the other two once they leave the meter cabinet or panel. It only mentions the placement of one leg if higher to ground. And says nothing with, or without a high leg about "rotation" specifically.
 
don_resqcapt19 said:
rattus,

As there is no reasonable way to identify A phase, all ABC requires is that the left phase leads the center by 120 degrees and the center leads the right by 120 degrees. ABC=BCA=CAB and are all code compliant. CBA=ACB=BAC and would all be violations.
Don
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Don, how would BCA and CAB not be violations (compliant) and of what code would CBA ACB and BAC be in violation of if that were said? And they would still be 120 difference no matter what position they were in. Nothing states that it lead or follow.
 
It seems that, for other than a specific motor's rotation direction, 3-phase rotation direction is really arbitrary. Relative rotation, I can see, but absolute phase identification? We know A follows C, but which is which?

If we have a single-phase service, how do we know what phase we're on? If we have an open Delta, how do we know which two phases we have? When the POCO lands a service drop, how do we know what is what?

Sure, we can identify the high-leg when there is one, and existing motors can help us re-connect a new service with rotation the same way the old one was, but in a new installation, doesn't each motor have to be tried?

How can we look at any set of conductors, primary or secondary, and say which wire is A phase? Compared to what? At the generating plant, there are three wires. Which one is A phase? Why isn't that one B or C?
 
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Me again. I couldn't sleep.

What I mean is, let's take an open Delta. We know the primary is two phases, but which two? Does it matter? We know the timing is 120, 240, 120, 240..., but do we know whether the main or high-leg secondary leads or follows? Again, does it matter?

When we bring the service to the premises, of course we need to know which is the high leg, but do we know which pair of lines straddle the missing secondary? Do we need to know? Do this and the rotation direction have any interaction? I think not, myself.

I've seen that the POCO strives to keep one phase in the center on the poles, but I've also seen them cross. When they branch off two for an open-Delta line, which two? How do they keep track of which is which throughout the line? Do my questions make sense?

"How do it know?" :-?
 
LarryFine said:
Me again. I couldn't sleep.

What I mean is, let's take an open Delta. We know the primary is two phases, but which two? Does it matter? We know the timing is 120, 240, 120, 240..., but do we know whether the main or high-leg secondary leads or follows? Again, does it matter?

When we bring the service to the premises, of course we need to know which is the high leg, but do we know which pair of lines straddle the missing secondary? Do we need to know? Do this and the rotation direction have any interaction? I think not, myself.

I've seen that the POCO strives to keep one phase in the center on the poles, but I've also seen them cross. When they branch off two for an open-Delta line, which two? How do they keep track of which is which throughout the line? Do my questions make sense?

"How do it know?" :-?
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I cant sleep either Larry - back pain.... :mad: First the primaries, be it wye (not to common, but I have one in my back yard) open or closed delta on the distribution will be roughly the same KV. (no high-legs there.) FYI an open delta has 57.7 of available power than a closed would.

And for load balacing purposes they will use different phases at different points to maintain that balance. For instance a 100kva on A, then on B, and C etc. Just to load them equally as possible then down the line have a wye or delta of any flavor, and only according to the load on the phases and the load of the transformer served determine what 3 gets what 3 on the trany. It still get 3 phases open or closed delta. It really doesnt matter which 3, but they shoot for clock-wise. (Or should...)

fig1-8.gif


And you NEED 3 primaries for an open or closed delta. 3 for wye, and grounding the center but not totaly nessesary. Everyone DUCK!:D But if you want a nuetral thats where it goes...

fig1-2.gif


And you wont really notice the missing transformer on an open delta, it will still read ~240 or ~480 phase to phase, and if you swap two it will still read the same way, but you have changed the rotation. That swapping seen on poles is called "transposition" and done to reduce capacitive and inductive coupling in the lines. Done clock-wise toward the load end. which is also clock-wise toward the line side... :wink: Neat huh? (Simularly you see this in multi-conductor cable and UPT data wiring, and done for the same reasons.)

Does it matter which leads or follows? Oh yes! Fire up 3 phase motors and equipment counter clock-wise and they dont work right. (unless they are self correcting - but you wont see that often.) Do it on an elevator an you're in for a wild ride. Do it with the high leg and you changed voltage on the system and better just call the fire dept.
 
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Mark I think, and Larry feel more then free to correct me here, the question becomes which phase is really 'A'?

In my experience the power company does not identify any phase as A B or C.

I can certainly get clockwise rotation without knowing which phase is actually A B or C.
 
Could it be that the NEC is just trying to get us all to communicate better? Since the NEC has dictated where the phases are, when I say use A-phase on a circuit, we all know that we need to pick the phase that is on the left (or B in the middle and C on the right) of the panel bus. Does it really matter which is which? It may only be a means to provide better communciation.
 
Definition Please:

Definition Please:

Someone tell me what is meant by "rotation".

Is it a matter of motor direction?

Or does it pertain to the phase sequence?
 
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