3 phase Delta High Leg Single Phase Load

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rattus

Senior Member
Senior moment:

Senior moment:

Why would the slash be acting like a vinculum (not to be confused with not)? Isn't that job filled by the parentheses?

You are right, but my aged mind recalls being taught differently, but then I also remember things that never happened!
 

rattus

Senior Member
Both right:

Both right:

You are right, but my aged mind recalls being taught differently, but then I also remember things that never happened!

Not quite senile yet!

(Monica of Glassboro, NJ. 2001-02-08)
What's the correct terminology for the line between
the numerator and denominator of a fraction?

When the numerator is written directly above the denominator, the horizontal line between them is called [either a bar or] a vinculum.
 

ohmhead

Senior Member
Location
ORLANDO FLA
Well this is some info one must think worst condition and not just install a breaker in a system because it works thats from GE . It may work now but will it work when the need for it to really work ?

What i was told is a bolted line to ground fault maybe much higher than a three phase fault since the zero sequence impedance can be less than the positive sequence impedance .

By example a wye connection fault is thur winding & phase conductor and limited by that . Meaning ground fault


A delta connection fault is thur winding A&B via c /ct in that all breakers do not trip at the same cycle in time lets say by example one cycle for one type or 2 cycles for another type .

How long does a breaker take to trip in the AC cycle of a wave meaning the one you installed on b phase hi leg?

And two paths can be found in a delta in that short trip time frame which even a fully rated single phase breaker on hi leg can be a fine line as to trip time when fault occurs .

Meaning do we always have a fault at the perfect time in a cycle the air gap between contacts can spark the gap twice in single phase delta high leg b phase but not in a wye ? What do you think two positives dont make it right ?
 
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jim dungar

Moderator
Staff member
Location
Wisconsin
Occupation
PE (Retired) - Power Systems
What i was told is a bolted line to ground fault maybe much higher than a three phase fault since the zero sequence impedance can be less than the positive sequence impedance .

Yes this is possible but not very probable, for locations with about 100' of conductors between a WYE (not delta) connected transformer the Zero Sequence will be less than the Positive Sequence. The actual distance is dependent on the size of the transformer, small transformer = short distance.
 

ohmhead

Senior Member
Location
ORLANDO FLA
Well Jim let me ask another question when a breaker trips during a positive or negative cycle meaning in one AC completed cycle and during fault lets say breaker opens up in .017 seconds can a arc between contact in that breaker continue in time passed the open point and or re strike again during this short place in time ?

My thoughts are it will stop at current zero . BUT

Now back at the delta hi leg its out of phase at 90 deg and each other phases 120 deg can this phase angle out of place on B high leg effect time of trip in a breaker back to the split center tap on C winding going to A / B its just that a 60 hz cycle one completed cycle is .016667 seconds in time and these phases are out of phase with B HL so during that arc if it last longer meaning time to trip can it re strike that gap in that short time in less than 1/8 TH of a second or less as its open contact can hold the ionized arc for a length of time .

Meaning winding C has two paths A/B less or more impedance on hi leg not in phase to b ?

OK now go easy on me Jim .
 
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jim dungar

Moderator
Staff member
Location
Wisconsin
Occupation
PE (Retired) - Power Systems
The arc across a set of breaker contacts is not out of phase with itself, a set of single pole contacts does not care about the other phases. As long as the contacts have enough physical separation, and internal arcing byproducts (i.e. gasses) have been vented, the arc will extinguish when it crosses zero.
 

mivey

Senior Member
Not quite senile yet!

(Monica of Glassboro, NJ. 2001-02-08)
What's the correct terminology for the line between
the numerator and denominator of a fraction?

When the numerator is written directly above the denominator, the horizontal line between them is called [either a bar or] a vinculum.
Horizontal line: Jury says yes.
Slash: Jury says no.
Senile: Jury still out. :grin:
 

Smart $

Esteemed Member
Location
Ohio
Not quite senile yet!

(Monica of Glassboro, NJ. 2001-02-08)
What's the correct terminology for the line between
the numerator and denominator of a fraction?

When the numerator is written directly above the denominator, the horizontal line between them is called [either a bar or] a vinculum.
So are you saying Monica's error was the reason for your's...

Finding it in hindsight don't count :D
 

Smart $

Esteemed Member
Location
Ohio
So are you saying Monica's error was the reason for your's...

Finding it in hindsight don't count :D

FWIW: I've found several references (non-authoritative) which say some writers call the division or fraction bar a vinculum. Yet in the strictest sense of the word, it is incorrect usage.
 

ohmhead

Senior Member
Location
ORLANDO FLA
The arc across a set of breaker contacts is not out of phase with itself, a set of single pole contacts does not care about the other phases. As long as the contacts have enough physical separation, and internal arcing byproducts (i.e. gasses) have been vented, the arc will extinguish when it crosses zero.


Jim question Do you consider a arc on breaker contacts during a fault to be at a high impedance due to the air now conducting in a plasma and current is now flowing thur the gap ?

Now considering this the total impedance of winding C with the added B winding on this high leg would it be possible to say that using the high leg would be more damaging to the system under a fault then your standard C winding single phase center tapped 120 volts on a delta transformer ?

Meaning due to the extra windings used to get your 208 volts higher impedance plus the impedance of the arc of the breaker used .

Which could lengthen time of fault as it would control current at a time limit but still trip breaker but not as fast as the 120 volt breakers on C winding with less impedance in circuit .

This is what i was trying to say before but iam not good a writing it Jim .
 
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rattus

Senior Member
So are you saying Monica's error was the reason for your's...

Finding it in hindsight don't count :D

Nup! Monica asked the question; someone else answered it, and this proves that the word means different things. Strictly speaking, I think the word means horizontal line or something like that. They quit teaching Latin just before I started high school, so it's all Greek to me. Natheless,

1/2/2 = ?

(1/2)/2 = 0.25?

1/(2/2) = 1?
 
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rattus

Senior Member
By the way:

By the way:

BTW, here we have an excellent example of the voltage phasors, Van and Vcn, being 180 degrees out of phase. Then,

Van + Vba = Vcn + Vbc = Vbn

or,

120V@0 + 240V@120 = 120V@180 + 240V@60 = 208V@90

If one draws the phasor diagram it is immediately obvious that the equation above is correct.
 

TonyEEINC

Member
Location
Yukon, OK
High leg use

High leg use

I have seen the high leg (wild leg) range from 180 to 215 volts to ground.
This is just a cheap way for the utility company to build transformers.
This is the can you see used in Residental area's a lot around here.
They just drop that tap, and send the 240volt phases to the residence.
I always tell my men, If you are on a commercial job and measure 240 volt expect a high leg.
I have seen this use on lighting circuits, expecially now that electronic ballasts are in fixtures.
They have auto sensing and will work just fine on the wild leg as long as it is between 100-277volt. you just have to use 277 volt switches, and mark everything well.
This is becoming common place. due to panel space limitations with the high leg taking 1/3 of the spaces, and only being able to use with a 2 pole operation.
I would be concerned about using this to run a motor load, or some other equipment, because the voltage may not be stable.
Because the NEC is only concerned with clearance for rated voltage, and equipment rated to voltage, I don't think this would be addressed in the NEC.
 

Stopmoving

Member
Location
Orlando, Fl.
I have a question to ask. The type of load wasn't really specified. Wouldn't it have to be a load designed to be connected phase to neutral? Otherwise you would be using the neutral as an ungrounded conductor; then 240.22 would apply?
 

Smart $

Esteemed Member
Location
Ohio
I have a question to ask. The type of load wasn't really specified. Wouldn't it have to be a load designed to be connected phase to neutral? Otherwise you would be using the neutral as an ungrounded conductor; then 240.22 would apply?
208V 1? equipment is designed to connect across a 208V source. Typically line-to-line connected, but phase to neutral on the system under discussion is also 208V. AFAIK, this class of equipment has never had a requirement that both conductors be ungrounded or that one not be grounded.

240.22 would only apply if there was an OCP inline with the neutral conductor. For example, if the utilization equipment had a two-pole "one handle" breaker, you could still connect it, but if it had two handle-tied single-pole breakers you could not both connect and be compliant. Also, if the equipment has only one integral OCP, it cannot both be connected and compliant if the OCP is on the neutral side of the load(s).
 
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egoy

Member
Location
Indiana
Sounds like a legend to me as they will just charge for what you use. Like with any load, you should tell them your loading so they can size the transformer correctly.

Depending on the type of metering the POCO is using, they may not be charging for this use. If I remember metering correctly from my POCO days, a 2 stator meter will not see the usage on the high leg. A 3 stator meter would have to be used and, since it is more expensive, they are not typically installed. Where I worked, we used all 2 stator meters and prohibited connection of load to the high leg.
 

mivey

Senior Member
Depending on the type of metering the POCO is using, they may not be charging for this use. If I remember metering correctly from my POCO days, a 2 stator meter will not see the usage on the high leg. A 3 stator meter would have to be used and, since it is more expensive, they are not typically installed. Where I worked, we used all 2 stator meters and prohibited connection of load to the high leg.
I think you did not remember it quite right and must have prohibited the use because of other reasons (probably having to do with transformer sizing).

When you meter a 3-phase 4-wire delta service, Blondel's Theorem does indeed state using three stators is the way to make an accurate measurement. As a refresher, Blondel?s Theorem states that for correct measuring of N conductors, you can use N-1 measuring elements as long as the voltage coils have a common tie to the conductor without the current coil. In the 2-stator case, there is a compromise in accuracy that is similar to the compromise made with a single stator 1-phase meter (voltage unbalance in the 120 volt legs), but it has nothing to do with the high leg not being measured.

The high leg has it's own stator and the power is correctly metered. The 120 volt legs are the ones that share a stator, like in a single-phase meter. The voltage is taken line-line and one of the currents is reversed through the meter to make the current fluxes additive with respect to each other. Since the voltage flux is doubled, the current coils are reduced by 1/2 to produce 1/2 the current flux and results in a proper reading for the lighting legs.
 

vinform

New member
Assuming that the source is a GROUNDED system 3 phase DELTA:

In a "2 wire" circuit that is composed of one GROUNDED conductors, it is best (a code requirement no less) to install the circuit protection in the NON-GROUNDED conductor only.
In this case A 208V. 2 wire circuit is composed on one GROUNDED conductor same as a 120V 2 wire circuit. The circuit breaker or fuse should be installed only in the NON-GROUNDED conductor or "high-leg". :)
 

LarryFine

Master Electrician Electric Contractor Richmond VA
Location
Henrico County, VA
Occupation
Electrical Contractor
Vin, welcome to the forum! :)

The circuit breaker or fuse should be installed only in the NON-GROUNDED conductor or "high-leg". :)
As long as the protection in the grounded conductor cannot open independently (i.e., by use of a 2p breaker), it is permitted.
 
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