the delta high leg

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Old 12-27-06, 04:29 PM
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Wink the delta high leg

Have a friend who"s having some problems with some three phase main panel commercial hook-ups. (delta )Apparently he's burned out 6 light ballasts already and is unsure if he'l have problems with the exixting A/c units. The problem is related to the "high leg" of the Delta T/f. Any advise I can give him, would be highly appreciated. What are the issues, concerns related to the "high leg". (basic stuff ) This question may be beyond the purpose, scope of this site?? Long live Raycract/Speedey Petey
 
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Old 12-27-06, 05:56 PM
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Originally Posted by sidecutter View Post
Have a friend who"s having some problems with some three phase main panel commercial hook-ups. (delta )Apparently he's burned out 6 light ballasts already and is unsure if he'l have problems with the exixting A/c units. The problem is related to the "high leg" of the Delta T/f. Any advise I can give him, would be highly appreciated. What are the issues, concerns related to the "high leg". (basic stuff ) This question may be beyond the purpose, scope of this site?? Long live Raycract/Speedey Petey
If you buddy connected the light ballast between the "high leg" he may need to get some advice from a professional. The voltage between the high leg and neutral is 208 volts. I suspect the ballast is rated for 120 volts. This leg is used with the other two to feed 3 phase equipment.
 
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Old 12-27-06, 06:52 PM
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First off thatnks for the accolades.

I must say, unless he is an experienced electrician he really should not be messing with 3-phase, especially a delta system. There is WAY too much (else) that can go wrong!
This IS NOT diy territory.
 
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Old 12-27-06, 11:47 PM
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This is definitely not diy. The high leg of a 240/120 4 wire center tapped delta is 208 volts to neutral or ground..... 1/2 the phase to phase voltage times the square root of 3. Be careful this is not a common electrical supply these days. Do not confuse it with 208Y120 3 phase. NEC requires the high leg to be terminated on phase B which is the center bus in the panel, and should be color coded orange. A and C phases will be 120 volts to neutral or ground. There generally is little use for 208 volts single phase (some motors) and rare for lighting. Essentially you can supply 120 volt loads from phase A or C pulling the neutral and ground with the branch circuit. You can also supply 240 volts from any two phases. You can supply single phase 240/120 volts provided you do not pull the high leg as one of the phases in the branch circuit. It is not uncommon on older high legs from years ago that the ******* (high) leg is not terminated on phase b or identified.... it is therefore very prudent that you test each phase to ground or neutral to determine the high leg. If your lighting is three phase then it will be getting 240 volts. If your supplying 120 volt ballasts from the high leg your giving them 208 volts....not good. Supply them from phase A or C plus neutral and ground. First thing is to be sure you are dealing with high leg delta or some other configuration by proper testing if the panel is unreadable.

I would agree with Speedy, this aint no place for guess work if you are unfamiliar with the configuration and how it is utilized.

Roger
 

Last edited by Roger; 12-31-06 at 04:36 PM.
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Old 12-28-06, 12:48 AM
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Thank you Roger for the very usefull info concerning the delta high leg. It will come in handy for me also. I'm a HVAC tech and years ago almost burned up my vaccum pump. center leg, orange, but not necessarily so. got it . Thank you so much for your precious time.
 
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Old 12-28-06, 01:22 AM
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Help!!!

Sorry, but this reply has nothing to do with your question. I need help. I just registered w/diy and don't know how to post a question on the forum. Can you tell me how to do this? Thanks!
 
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Old 12-28-06, 04:30 AM
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Go to this page : http://forum.doityourself.com/forumdisplay.php?f=9
and use the "new thread" button.
 
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Old 12-28-06, 06:45 PM
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Originally Posted by Roger View Post
This is definitely not diy. The high leg of a 240/120 4 wire corner grounded center tapped delta is 208 volts to neutral or ground..... Roger
corner grounded center tapped??

Hmmm. Could you find a diagram of this?

High leg is center tap grounded of one winding of the transformer.
Corner grounded is a different animal.

jwhite; I thought you had been elevated to moderator status. What happened?
 
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Old 12-28-06, 08:20 PM
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Guys, interesting discussions but what keeps drawing my attention is the original post. The friend has blown six ballasts and it sounds like he did them one at a time not all at once. Logic would dictate a check with a volt meter after the first one or surely the second one but we are talking _six_. It sounds like the friend needs to call a real electrician before he does something worse like explode a panel.

(Nothing like seeing a cover travel 20 feet and dent a sheet metal wall to instill a healthy respect.)
 
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Old 12-28-06, 09:32 PM
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That is pretty much a given.

Not to be condescending but realizing there is a high leg and measuring to be sure you are not using it for an intended 120 volt circuit is pretty basic.


So, to the original poster; simply measure the voltage. If the appliance is intended to be on 120 volts and you are reading 208 or so, you have the high leg.

If you need to go further, because of the lack of understanding, I would strongly suggest an outside electrician to take care of things.
 
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Old 12-29-06, 09:17 AM
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This is a common problem.
I've seen this many times.
I remember one time a plant maint man wired his brand new little 120V welder to the high leg that was mismarked.
The only thing that new welder welded was its internal components.
You couldn't even move the adjustable lever after he plugged it in.
Always check the voltage BEFORE using the new outlets!
120V lights will leave you in the dark when you supply them 208V!!!
 
  #12  
Old 12-29-06, 10:51 AM
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Smile Oops

Hmmm. Could you find a diagram of this?

High leg is center tap grounded of one winding of the transformer.
Corner grounded is a different animal.

I'll try but it would take me awhile.... since you are correct.... center tap grounded. Thanks for catching my error in the configuration. I'm not exactly sure what I was thinking on that one. Maybe too much eggnog over the holidays.

The corner grounded delta would not be able to supply phase to neutral loads....and you could not have both center tapped and corner grounded...thanks for keeping things accurate.

Roger
 
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Old 12-29-06, 10:39 PM
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Originally Posted by Roger View Post
Hmmm. Could you find a diagram of this?

High leg is center tap grounded of one winding of the transformer.
Corner grounded is a different animal.

I'll try but it would take me awhile.... since you are correct.... center tap grounded. Thanks for catching my error in the configuration. I'm not exactly sure what I was thinking on that one. Maybe too much eggnog over the holidays.

The corner grounded delta would not be able to supply phase to neutral loads....and you could not have both center tapped and corner grounded...thanks for keeping things accurate.

Roger
Roger
I don't want this to feel like piling on but the first sentence of your last paragraph has me puzzled. At one pharmaceutical plant I worked on we had a corner grounded delta to supply the three phase 240 volt air conditioning equipment. For reasons that were never clear to me the transformer had been sized much larger then the air conditioner required. We ended up making the mechanical engineer very happy by offering to install a 240 volt three phase motor control center so that he could use a lot of single phase 240 volt motors instead of the 208 volt motors that had originally been planned. We took no special care of which legs the single phase motors were on. The only strange thing about the MCC was that one leg showed no voltage to ground because it was grounded. There isn't actually a neutral in corner grounded delta but the voltage across any two legs is the same. So for the sake of my education what am I missing?
 
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Old 12-30-06, 01:10 PM
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There isn't actually a neutral in corner grounded delta but the voltage across any two legs is the same. So for the sake of my education what am I missing?
__________________
==========================================================

True, there is not a neutral but there is a grounded conductor. Neutral is often a misnomer anyway. Realize that 240 single phase utilizes two legs of a system. The only difference between that and 3 phase delta 240 is the number of phases involved. The ground provides a reference point. Without that, any one of the legs could become grounded without it being known. There are systems specifically designed to detect a unintentional ground with ungrounded delta's because of the safety hazards they pose. They are also more difficult to troubleshoot because there is no ground reference. The grounded lega does not actually change what and how the system can be utilized. It still provides single and 3 phase 240 power, exactly as the ungrounded system does.

There are reasons to use the grounded over ungrounded and vice versa but that is another topic.

I found this website that has drawings of most of the typical transformer connections here. http://www.bmillerengineering.com/elecsys.htm

An ungrounded delta is not used anymore in my area and if/when they are discovered, the are converted to a grounded delta.(as a service anyway. some businesses may use an ungrounded delta internally for purposes not discussed here.)
 
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Old 12-31-06, 05:54 PM
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Tom... you can pile on.... not a problem. Sorry if I was confusing the sentence was just meant to point out that there is no neutral in corner grounded delta b phase. And to essentially imply that you cannot supply dual voltage service from a 240 corner grounded delta. We could spend a long time discussing the corner grounded delta. It is different though and frankly that configuration confuses even some seasoned industrial electricians that are unfamiliar with the use of it because of its rarity or lack thereof in modern transformer design. You have to be very careful how you treat the grounded conductor when installing circuit breakers and fuses.

I'm curious though if you paid no attention to the phases how did you treat the grounded conductor at the motor overloads (if fuses) and contollers? In my limited experience with this service my understanding is that you must use controllers that will not allow the opening of the grounded conductor without opening all other conductors of the circuit. In the overload you must fuse the grounded conductor where in contrast you would not at the disconnect for the power souce. So seems you would have to consider the phase you were utilizing at the controller and overload if it was the grounded (b) phase for those 240 volt motors. You would also be smart to identify the grounded phase throughout the circuit. Maybe you were just meaning that phase to phase is 240 volts regardless.

Ok go ahead and pile on but lets try not to make this a marathon of who is the smartest because I will problay lose to those more knowledgable. Understand I am a industrial apprentice not a seasoned pro as you. However I love learning and I dont mind being corrected when wrong. I strive for accuracy and do from time to time error, I apologize for any vague or ambigous statements that is not my intention.

This is kinda cool.....


http://www.bussmann.com/services/training/docs/240-85Pres.ppt#3

Roger
 

Last edited by Roger; 12-31-06 at 11:19 PM.
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Old 12-31-06, 06:17 PM
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Wink

Don't be paranoid Roger,
22 years and I'm reading and watching with great intensity. I've come across a few of these systems but don't really understand them. Here The High (Bast-rd)leg is taped purple, Thats a good indication to ASK!! and handle with care.

So party on boyz. It's great.
 
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Old 12-31-06, 07:20 PM
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a, lee........ you need to go everywhere they have done the purple and remark it with orange which is an NEC requirement section 110.15.

Now to corner grounded delta

when using fuses, the B phase (which is what it is supposed to be) would use a strap to replace the fuse since you are not allowed to allow the grounded conductor to be opened without opening the ungrounded conductors.

With a motor overload, all circuits are opened simultaneously by the overload since the overload controls either a magnetic or mechanical contactor that all the circuit conductors would pass through.

and yes Roger, I understand the point of not having dual voltages available. Sorry about throwing in my input. It did tend to muddy things regarding your intent.

and BTW, although I happen to be a journeyman wireman (IBEW trained and carry my JW card in Mi) I still learn a LOT from those here. The first guy to claim he knows everything is the first guy to prove he is wrong. As a matter of fact, I have been corrected here enough to know that

1.I don't know everything and
2. there are some great guys here with a plethora of knowledge they are willing to share.



Now you want something that really threw me one day.

Went to a service call. Never been there before. press not working. checked voltage. L1 500 volts to ground L2 0 volts to ground L3 500 volts to ground.

For soem reason I was having a stupid attack and the number (500) just hit me really weird. For the life of me I could not realize all this was was a 480 volt corner grounded delta. I kept thinking some odd foreign voltage since it was a European made press.Took me a few minutes to get my head back around that. 'Til that point I sure was confused though.

In one of the cities work in, it is not unusual for the POCO to supply 500 volts rather than 480. The fact it read exactly 500 volts just hit me very weird that day.

if we had the time, I have a hilarious story about a carpenter, a brand new side grinder (actually 3 eventually), an electrician and 120v high leg power.
 
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Old 01-01-07, 12:12 AM
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Marking colors

The District of Columbia electric code specifies the marking colors brown orange yellow as required for three phase wye connected 480/277 volts and gray for it's neutral. That's fine until you have high leg delta transformer in a building as a derived system. You then run up against the US NEC rule found in 210.4, Multiwire Branch Circuits, that requires the identification of ungrounded conductors by phase and system. Since the DC code is just the NEC with some added material you have a built in conflict. We have been using the color purple in place of orange for 480/277 wye connected B phase for a while now but I've never checked to see if the code was altered or the inspectors are just taking a more practical approach. It would seem to me that the since the NEC calls out orange as the high leg color it would be wise not to use it for anything else.

210.4, Multiwire Branch Circuits

D) Identification of Ungrounded Conductors. Where more than one nominal voltage system exists in a building, each ungrounded conductor of a multiwire branch circuit, where accessible, shall be identified by phase and system. This means of identification shall be permitted to be by separate color coding, marking tape, tagging, or other approved means and shall be permanently posted at each branch-circuit panelboard.
 
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Old 01-01-07, 12:29 AM
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So they would shunt the grounded leg at the fuse block ....hmmm interesting Nap.

Heck I started all this by not noticing my error in the first place. So I never felt you muddied the waters but were just clarifiing my incorrect phrasing of corner grounded delta.

I still contend that the statement that corner grounded delta cannot supply phase to neutral loads is accurate. I do not consider that confusing or puzzling. If I could supply phase to neutral then I could supply some other voltage besides 240 volts which is not the case with corner grounded delta. I can only supply single phase 240 or 3 phase 240 with corner grounded 3 wire delta.

Roger
 
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Old 01-01-07, 12:35 AM
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We have been using the color purple in place of orange for 480/277 wye connected B phase for a while now*
Thats the only color I've seen for this app.

Delta,right? I don't like the orange,for reasons stated. Even though 480/277 BOY not code. It is industry standard.

I'm at a college now. A portion of campus is still the 2300 (delta) 500V.

What fun this is for a quick modification. Your never sure were/how to start.
 
  #21  
Old 01-01-07, 03:45 AM
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I still contend that the statement that corner grounded delta cannot supply phase to neutral loads is accurate. I do not consider that confusing or puzzling. If I could supply phase to neutral then I could supply some other voltage besides 240 volts which is not the case with corner grounded delta. I can only supply single phase 240 or 3 phase 240 with corner grounded 3 wire delta.
==========================================================

you are correct Roger. I am confusing somebody somewhere. Sorry 'bout that.


==================

If any of you guys are really into the code, why don;t you write a proposal to alter the requirement for marking high leg delta. I believe it would be easier and more correct to change the high leg marking rather than restrict the common practice marking of BOY. Since there is so much more marking using the BOY color coding (although there is no code requirement) that it would be simpler to alter the high leg to something like purple.
 
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Old 01-01-07, 09:33 AM
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You all have got me confused. It seems like you are saying that BOY is used for a center tap delta. (i agree this is not code but standards, and spec on most larger jobs)

BOY is 480 v. I for one have never seen a center tap delta in a 480 v system. Center tap delta is seen on 120/240 V systems where the color code is BRB. The code does tell us that the high leg must be the center leg and that it must be marked orange. (408.2 (E) and 110.15)

This means that if we use the industry standard and follow the NEC, the colors for a center tap delta will be black, orange, Blue. A 120/240 delta no ground would have Black, Red, Blue and no White or Bare. A 120/240 Wye would have Black, Red, Blue, White. A 240 volt corner ground delta would have Black, Red, White all tied to the hot buss bars.

I do not see where this gets confusing till we get to the field devices. A box with black, blue, white could be either corner ground delta, center tap delta, or wye.

(some utility companies require the high leg in a delta service to be the third leg, not the center leg. this is because of the type of meters that they use. Most inspectors will say that if this is the case you should keep the high leg on the third phase throughout the building. Ask to be sure what your inspector will require.)
 
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Old 01-01-07, 10:55 AM
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Typically in my area BOY is used for any 480 volt power and if a grounded conductor involved, it is grey or marked grey. BRB for 120/240, 120/208, 120 delta corner grounded (rare but have seen it), or 240 delta corner grounded, with grounded white or marked white, whether it be grounded corner phase, center tap ,or wye.

What code requires is orange in place of the red (if installed correctly) on the "B" phase of the center tap delta. Hate to say it but not often followed in my area.

Since either white or grey is a possibility for a neutral, if you open a j box with a white neutral and an orange or orange marked wire, it tends to make one think 277 volt.

Now you may ask why you would be runnning the high leg with a neut. Sometimes it is just part of the combination in the j-box but occasionally the 208 actually can be used. As your examples as well, the electrician needs to be aware of the service type of the facility and ALWAYS check, not rely on a guess.



With at least one of the POCO's in my area, they too require highleg to be "C" phase. I have had to carry C phase at meter to B phase in panel when upgrading a service. The alternative would have been a lot of time swapping circuits around. Not practical.

Now are you telling us the inspector actually recommends practice contrary to code (high leg not on "B" phase)? Although it does allow a possibility of confusion, I have no real problem with having the phases in the meter not match the panel. If they are marked, it usually is self evident to those that need to know when it is neccessary. It can be misleading until the meter is opened though and just relying on the digital readouts of the meter to diagnose.

You never answered me about the mod status Jeff. Hopefully that isn't a sore spot. If so, ignore the inquisitiveness.
 
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Old 01-01-07, 11:07 AM
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Most of my confusion is with regard to this post:

=====================
"We have been using the color purple in place of orange for 480/277 wye connected B phase for a while now*
Thats the only color I've seen for this app.

Delta,right? I don't like the orange,for reasons stated. Even though 480/277 BOY not code. It is industry standard."
=====================

I do not understand the connection between orange high leg and 480/277 volt service. 480/277 is a wye service not a delta. There is no high leg. A high leg would be on a 120/240v three phase service.
 
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Old 01-01-07, 11:38 AM
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Ya, this has taken on a life of its own.

I'll try to reel in my comment.

All the delta High legs I have seen are purple. regardless of location.
(@ distribution, or in the feild)
Code states now,use orange.

In the feild, most would assume (bad I know)orange, to be part of a 480/277 system.

Thats all, sorry for the spin.
 
  #26  
Old 01-01-07, 11:45 AM
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After giving this some thought, I like the idea of using purple for 480v center leg. This would leave the only wire commonly colored Orange to be the high leg on a center tap delta. That would make things much faster to figure out.

On another note: this is a DIY site, and IMHO anything three phase is not a DIY subject.
 
 

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