high leg value
- Thread starter j rae
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I always am suspicions when a question like this is asked. Yes, you have 208v from the "high leg" to the neutral of delta transformer with a 240/120, 3ph4w secondary that has a lighting. BUT the more important thing is why are you asking the question? Is this a loaded question?
- Location
- New Jersey
- Occupation
- Journeyman Electrician
As Augie stated 240 volts phase to phase, 208 volts {120 * √3} high leg to ground or to the neutral.
- Location
- Wisconsin
- Occupation
- PE (Retired) - Power Systems
It is basic trigonometry.
Right triangle: short leg = 120 and hypotenuse = 240, there are several ways to determine the value of the long leg.
What confuses(?) many people is the answer is 208V, which they often only associate with wye systems and the √3.
Right triangle: short leg = 120 and hypotenuse = 240, there are several ways to determine the value of the long leg.
What confuses(?) many people is the answer is 208V, which they often only associate with wye systems and the √3.
Yes, I agree. My point was how useful is 208v L-N?
kwired
Electron manager
- Location
- NE Nebraska
About as useful as single phase when connected L-L. Problem is you will not find a single pole circuit breaker rated for more than 120 volts unless you get into the 277/480 series breakers.
- Location
- Wisconsin
- Occupation
- PE (Retired) - Power Systems
But you can use a 2-pole 240V L-G rated breaker (which are not that hard to order) and get the valid L-N voltage of 208V.
The problem isn't getting the voltage, it is what happens when you use it. Most 2-transformer, open-delta, banks were not sized with this loading in mind.
ptonsparky
Tom
- Occupation
- EC - retired
In my past expereince, it generally means some one gets a new drill.
kwired
Electron manager
- Location
- NE Nebraska
Before doing that, one would complain about all the unused and unusable spaces left in the panel because they are all wild leg spaces, now you want to burn some of the 120 to ground spaces so we can use the wild leg
hmy:I do see your point though. I can't recall ever wanting to use just the wild leg to power a 208 volt load. I have used it a few times with double pole breaker to supply single phase 240 volt loads though.
Not all systems are two transformer open delta systems. 3 transformer full delta systems are pretty common around here on the farms that do use three phase, wye systems are pretty scarce for these applications, the three phase is generally needed for power applications like motors for fans, augers, conveyors, etc. and not necessarily for lighting and receptacles like it maybe would have higher demand for in a light commercial building.
Exactly, too my point. As in my first response to the OP what is the point of his inquiry, to fun with the answer that he wants to hear and misapply the answer?
- Occupation
- Licensed Electrician
Or a new vacuum cleaner, or a new vending machine, or a new alarm system.
It is interesting that those who discover that they have a secret 208v from the high leg L-N and wonder how they can use it when there isn't any point to it at all. It only spells trouble.
As far as I'm concerned, this is one configuration I wish was never offered.
I know it may be more efficient for serving Motor Loads or the like, but I would offer 208/120v or 480v.
Theres still (1) Service in our small town on a Community Hall that is 240v Delta, all the rest have been
done away with, and I can't wait until this one bites the dust also.
I know it may be more efficient for serving Motor Loads or the like, but I would offer 208/120v or 480v.
Theres still (1) Service in our small town on a Community Hall that is 240v Delta, all the rest have been
done away with, and I can't wait until this one bites the dust also.
It's not that common as you've said.
And also I have had more then one establishment where the power company has changed over the existing
services from 240/120 3ph 4w system to 208/120v 3ph Y on a Service Upgrade,and the number of single
pole spaces that now become usable that were once a "Space Only" is quite nice.
The biggest kicker is if someone does'nt go in and relabel the voltage on all of the panelboards to
read, 208/120 3ph 4w, it gives the appearance of still being 240/120 3ph 4w at first glance.
And also I have had more then one establishment where the power company has changed over the existing
services from 240/120 3ph 4w system to 208/120v 3ph Y on a Service Upgrade,and the number of single
pole spaces that now become usable that were once a "Space Only" is quite nice.
The biggest kicker is if someone does'nt go in and relabel the voltage on all of the panelboards to
read, 208/120 3ph 4w, it gives the appearance of still being 240/120 3ph 4w at first glance.
delectric123
Senior Member
- Location
- South Dakota
I kind of like 240/120 delta for hog finisher barns. i did an installation for 3 - 2400 head barns. the lights have multi-voltage ballasts, and nearly all the other loads are motors. there are only a few times i had to skip the wild-leg space. lots of ventilation equipment comes from overseas and is really designed for 240. and there are long runs of wires to fans where i would have had to increase the wire size TWO sizes due to voltage drop.
kwired
Electron manager
- Location
- NE Nebraska
Come to rural areas, and farms, there is a lot of delta systems around. There are advantages and disadvantages of both wye and delta systems, especially in the 120-208/240 voltage range. 480 volts is always 277/480 Y unless there is not all three phases or is a limited load and it is supplied by open delta configuration to save on costs on the primary side of things. If running to a remote area it costs extra $$ to run the extra conductor to get a wye when an open delta will get the job done. And it definitely is better than having a single phase service and a phase converter in most cases.
There's no arguement from me that there are several places where it is used a lot,and needed. I've worked on my fair share of them.
It still doesnt change my opinion of a strictly Delta Service. I just don't like em.
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