Installations with this system require a 480-120V transformer to supply 120V lighting. Systems from Intermittent Ground Faults Introduction Many papers and standards [1][2][3][4][5][6] have discussed grounding of an electrical distribution system. High-Leg Delta power is only available in 120/208/240, and is not put in any longer as Wye circuits are. Refer to the Digest, CAD drawings, or device wiring diagram(s. 86 restricting their use to solidly grounded systems where the line to ground voltage does not exceed the lower of the two values and the line voltage does not exceed the higher value. 12,470/7200 grounded Wye primary and. On a 240V 3 phase grounded delta system, the voltage to ground is 240V from 2 of the poles. There are certain restrictions when using a VFD on a corner grounded delta power system. For example, the grounded conductor, as previously defined, could be a corner-grounded phase conductor per 250. However, some utilities still provide this system, and many old installations still exist. 3–Phase Corner-Grounded Delta System using 2-Pole Circuit Breakers. CIs in bedrooms effective January 1, 2008 (NEC 210. 44. 26(4) for conductor to be grounded. D325NT, D325NTR, D326NT, D326NTR, T327N and T327NR accept only 300Vac Class T fuses. 230 is also a 3 phase system voltage that comes in a couple of different flavors: Corner grounded Delta, or a mid point grounded Delta with the B phase bastard leg. The uncommon grounded system is a 3-phase, 3-wire corner-grounded delta system. 3830 posts · Joined 2010. The corner grounded delta (CGD) is one of the earliest forms of grounded systems in electrical installations. 3. The purpose of grounding one phase is to provide a return path to clear a ground fault on the either of the other 2 phases. #1. #4. Some connections like ungrounded wye grounded wye are not feasible, but something like delta grounded wye or ungrounded wye corner grounded delta is doable and operational. - One phase is intentionally grounded. No, it is not showing the high side delta winding is corner grounded. a delta winding, with the corner ground not causing any difference to actual operation unless the higher voltage from tap to ground is a specification issue, or. If you had a corner grounded delta, B phase grounded and A phase shorts assuming you protected everything per the NEC you would have a ground fault and the fuses would blow or the CB open. if a guy happens to pick the corner-grounded leg to test to ground to verify that the line is off, then there is the potential for mayhem. For safety reasons the tank would need to be grounded, and for symmetry reasons it would need to be a neutral. Electrically, the grounded conductor in a corner-grounded delta system operates identically to a multi-grounded neutral conductor on a wye system meeting Rule 230E1. So put in a 2 pole and land B on the bus bar and I. 3, July 2022 -Corner-grounded delta grids not supported at voltages of 400V / 480V. Louis. As the project is presently designed, we are stepping this down to 208/120Y and serving all of the building's loads via the 208/120V distribution system. 120 V, 3-phase, corner-grounded delta. High leg deltaGrounded solidly system delta ground wye electrical fault engineering phase grounding systems portal circuit overview short Corner-grounded delta (grounded b phase) systems data bulletinGrounded b phase. That’s why you get 0volts from it to ground because it’s at the same potential. NEC actually calls it the "grounded conductor" which would seem to open up the possibility of corner grounding one of the three phase conductors. We're working in an old mine machine factory, recently converted to a gear shop. 02. Thread starter domnic; Start date Nov 19, 2020; Status Not open for further replies. The B phase is a high leg not a grounded conductor so 240. Figure 4 – Fault to Ground on a Corner-Grounded Delta System A disadvantage of Corner-Grounded Delta systems is the inability to readily supply voltage levels for fluorescent or HID lighting (277V). A wye winding, with the wye point left unconnected, since there is nothing to connect it to. 220. The grounded conductor of a service is usually a neutral conductor, but it can also be a phase conductor, depending on the type of system supplied. 60% of these I run across are done incorrectly. A corner grounded delta system is a three-phase delta service with one phase having the ground connection. What we have is 4160V feeding 4 step down transformers that step it down to 230V Grounded B. If you choose the high leg delta, you'll need to pull a grounded conductor anyway. See Figure 4. Reply. Occasionally you may have an application that is a delta voltage source with a grounded “B” phase, also known as corner grounded. The minimum size of the grounded service-entrance conductor is a. Get a new disconnect with a neutral bar and run the incoming corner grounded phase into the neutral bar. Corner grounded is normally in industrial and commercial applications. This creates a three. For starters the xformer 480 side, if grounded, all the load side gear and equipment must be approved for corner grounding-not likely. The cost of running a neutral to the service disconnect seems like a cheap way to save expensive headaches. Subsection 250. move into 2008, as NEC-2005 requires Combination AF-. See Figure 11. They sent me back readings for phase-phase at 480V, but phase-ground measured approximately 277V for. Order Pendant Mount Stem accessory 5. 2778 posts · Joined 2014. Location UK Occupation Retired Electrical EngineerThe loads don’t know the difference. Location. Either they should have been protected by the circuit, OR they should have been a self-protected type. If the phase line was solidly grounded you would be reading 0 volts. The utility company says it is an un-grounded delta secondary at 480V/3-phase/3-wire system. 6 are permitted to be used in services, feeders. gap, is maximum. Grounded B-Phase Systems (Corner-Grounded Delta) PowerPacT B Electrical Accessory Wiring Diagrams. Go. , In addition to the grounding. #4 · Oct 2, 2020. Other types of three-phase supplies are wye connections, ungrounded delta connections, or corner-grounded delta ("ghost" leg configuration) connections. If you do not ground one of the. Figure 11. I actually ran into a corner grounded delta myself Friday or at least I think. 36 requires where fuses are used for motor overload protection that a fuse be also inserted in the grounded conductor if the supply system is a corner-grounded delta system. The Delta system has aThe NEC requires EITHER that a delta system be corner grounded OR you must have a "ground monitoring system" in place. 67, or 57. Other systems shall be permit‐ ted to be grounded. Study with Quizlet and memorize flashcards containing terms like The first point of grounding for a building or structure supplied by a utility service is usually within the service equipment enclosure(s). Another disadvantage, as given on page 33 of IEEE. Lexington KY. three-phase, 3-wire, corner-grounded delta system? 120V 240V 277V 480V Correct Answer: 480V. Number Required. In the setup the OP describes, the maximum voltage to ground would be 240, so he must use a straight 240 V breaker. Informational Note: An example of a system permitted to be grounded is a corner-grounded delta transformer connection. The other two phased are at the line voltage above ground. We did an upgrade at a plant that had a corner grounded delta service. 13. You only need two current transformers to monitor the power in a 3 phase, 3 wire system. Retired Electrical Engineer - Power Systems. grounded TN-S systems (center-grounded wye) Corner-grounded delta and midpoint-grounded delta systems IT systems (ungrounded or high-resistance grounded) TT systems 1) 2) 1) A residual current device must be installed in the supply system. Terms in this set (83) In the case of a delta, 3 phase, corner grounded "B" phase system, a device called a ___ can be installed in the "B" phase. 277V lighting is designed for a grounded system where the connection is to a hot and a neutral. This center tap is grounded to produce voltages of 120V, 208V, 120V. The correct solution is to use a 208 Delta X 480Y xformer. The grounded leg is no more dangerous than the grounded neutral leg in a 120 volt circuit. It's 830 wye. If he has corner grounded delta then I could see misunderstanding ~500 volts to ground as a stinger leg - but there should be two legs that are ~500 volts to ground. If grounded, then a ground fault protector may be desirable although not required. In Figure 4 below, we model an ungrounded (capacitively grounded) delta-connected power system connected through a single-phase fault to ground using a. Corysan said: 240V 3ph corner grounded delta will definitely yield: A-Grd: 240V. Question, when connecting a Wye generator to the Corner Grounded Delta, will it work without any abnormalities. Leave EM1 connected. Can’t do line to neutral loads but phase to phase single or three phase loads are fine. A straight rated CB (such as 480V) can be applied on systems that have no more than 480V between any two conductors. A high-leg system is a hybrid between a standard 3-wire single phase and a 3-phase system. larz_6446 • 2 yr. JimmySki23 Member. If such systems are grounded, they shall comply with the applicable provisions of this article. D1-D4 lumen packages only. I came across a code a while back about NEC not allowing circuits to. Do not remove EMC AC or VAR. Remember that all the rules in the NEC that apply to grounded conductors are applicable to a grounded phase conductor in this case as well. This is a violation of Section 240. Could be as jraef mentioned. Delta grounded 240vSchematic diagram of (a) grounded and (b) ungrounded pv systems Grounded b phase wiring diagramPhase wire delta single grounded 480v transformer corner 480 ground system volt three 208 volts leg efficent than service open. Think about this a little more. You need transformers with a wye secondary and ground the center of the wye. Along with the 'slash rating', Corner Grounded (grounded B phase) systems can impact the AIC ratings of breakers. Aug 14, 2018. In this video, NEC expert Mike Holt explains how to properly ground a corner grounded delta system and the special characteristics of these rare systems…A delta secondary may be corner grounded, but that conductor, though grounded, is not a ``neutral``. 'power' panels (e. In the setup the OP describes, the maximum voltage to ground would be 240, so he must use a straight 240 V breaker. Hi, Our company rented an old warehouse and this is the first time I've ever seen corner ground delta (CGD) panel. In most cases, the delta is "buried" with no leads. A ground fault in a floating delta circuit is a foreseeable event, no surprise, and ought to be protected against. Menu. A circuit breaker with a special “straight” rating of 277/480 volts may be used on a corner-grounded delta system. Because of the disadvantages of not grounding systems, electrical designers had to integrate a ground reference to existing configurations. If it is a corner grounded delta, the grounded phase must be* grounded AT the transformer terminal, meaning you will be able to SEE the ground. It states that when grounding a circuit where grounding is permitted, it must follow the rules of Article 250. A corner-grounded delta transformer connection is an example of a system permitted to be grounded. Corner Grounded Delta Solidly (effectively) grounded (LRG) Solidly (or effectively) grounded systems connect (bond) the system neutral directly to earth ground. Version 1. Delta with Wild Leg. 20, Informational Note. The grounded phase is a "grounded conductor" that carries current. test Learn with flashcards, games, and more — for free. The only loads are the pumps and a smaller transformer running heat and air, control and a light. Schneider Electric has tested equipment for use on corner-grounded delta systems to provide Underwriters Laboratories Inc. By doing so, we are creating a split phase supply as well as a three-phase delta connected supply. Corner-Grounded Delta System. A 480 Δ — 240-volt 3-wire Δ transformer is delivering power to a 3Ø load and has 75 amps of coil current flowing through each winding. BTW, this is a grounded system. 208, 240 and 480 are all common 3 phase systems. If you corner ground make sure the customer knows that the transformers will need to be upgraded when the RTUs get changed, since modern RTUs often use variable speed drives. On this latter type, one phase is indeed grounded and is 0 volts to ground. In a Delta system, you must either have one corner grounded, or you must have ground current monitoring if it is an ungrounded Delta system. The grounded conductor is treated like a neutral in 120 V and 240 V single-phase systems. Use QO-H circuit breakers only. ” Following areYou are correct in that a corner grounded delta would have 240V L-L x3, the corner would have 0V to ground. A corner grounded delta is not ungrounded. Aside from the corner-grounding of the delta, this is a fairly common configuration for transmission substation transformer in the US. 85. Apparently, code requires this conductor to be phased white or gray but many People outside of code apply alternate color tape to the conductor because this. Trying to determine if I have a ground fault somewhere or a bad leg or breaker. Introduction Corner-grounded delta systems are not re commended for new installations. OccupationHey this happens all the time. PowerPacT B-Frame Peak Let-Through Current Curve. not smaller than the required grounding electrodeCorner grounded Delta. Equipment ground bonds to disconnect and grounded phase connects to unfused pole. 73=796. For use on 480 V systems, LH type circuit breakers must be ordered as 600 V versions and with a 5861 suffiix (i. 480 V, 3-phase, 3 W, ungrounded or high resistance grounded VII. I would think if at a school there would be a system with 120 volts somewhere and not just corner ground delta everywhere. This is a "Corner Grounded Delta" system and is found in older facilities that have no need for 277 volt service such as a manufacturing facility or a central plant in an apartment complex. See a problem? Let us know. Sections 503. g. 12. ago. Corner grounded delta. Corner-grounded delta: One line conductor is grounded directly. The center of the Y, which is usually grounded, must not be connected to anything. Is the transformer output an ungrounded or corner grounded delta? If ungrounded, a ground detector must be provided. 61, 517. You still must run a separate grounding conductor to bond non current carrying components - so you are running 4 wire circuits either way you do it. Other 2 phases = line voltage. 52(C)(6) FPN: Proper application of self protected combination controllers on 3-phase systems, other than solidly grounded wye, particularly on corner grounded delta systems, considers the A 100A, 240V corner grounded Delta three phase supply needed to power the large VFDs for ventilation fans, as well as a 30A, 120V single phase supply (fed from a separate 208/120V panel) to separately feed control needs and lighting (this thing is rather strangely designed). High-leg Delta. Directions Advertisement. not smaller than the size of the grounding electrode. I hooked up 240v 3 phase motor to make sure and. 480 3ø, 3W corner grounded delta (ground jumper goes from one of the phases to ground. The problems found include: dangerous step and touch. 61 (A) Exception has a requirement for a 140% factor for calculating the neutral load from the unbalanced load on a 2-phase feeder. A corner grounded delta is not ungrounded. Looking at a 120/208 wye system, the phase voltage would be 120V and the phase-to-phase voltage would be 208V. As the project is presently designed, we are stepping this down to 208/120Y and serving all of the building's loads via the 208/120V distribution system. The grounded conductor of a corner grounded delta system is covered by the rules in Article 200, just like any other grounded conductor. 3 (f) This is applicable, only if it is a center tapped delta, 240/120 3P 4W. Aside from serving the step-down transformer, the 480V side is mostly going unused. PowerPacT B-Frame Let-Through Energy Curve. A corner-grounded or an un-grounded. One method of grounding a three-phase, three-wire, delta-connected system is to ground one of the phase conductors. For use on 480 V systems, LH type circuit breakers must be ordered as 600 V versions and with a 5861 suffiix (i. A to Earth = 524. Corner ground Delta, A higher line to ground voltage exists on the other two phase in a neutral - grounded system along with fault switching (opening) is much more severe for cleaning devices and ratings may be greatly reduced, and stabilizing voltages of the ungrounded phases to ground . Rick- It sounds like you have a corner grounded delta service. Corner grounded delta systems are common in old industrial facilities around St. One certainly would not corner ground a primary delta. So when the disconnects are open, the B phase is no longer. By "fail", it would have to mean a GROUND FAULT. Read also : what is an operational amplifier. J. . zbang Senior Member. I believe it also allows you to save wire, but I am not sure. T. When connected to the no. Warning: If two-pole circuit breakers are installed in a corner-grounded delta system, they must be marked to indicate such suitability. This creates a three-phase, corner-grounded system, sometimes referred to as an end-grounded system. Remember, voltage is a difference in potential. [/QU Corner Grounded. teal854t Discussion starter · Oct 13, 2010. For starters the xformer 480 side, if grounded, all the load side gear and equipment must be approved for corner grounding-not likely. Author's Comment: Other systems such as a corner-grounded delta system are permitted to be grounded, see Section 250-26(4). Home. optional based on the design of the electrical engineer. Occasionally, (especially in older facilities or in oil well and irrigation applications), you may encounter a three-phase delta service with one phase (leg) connected to ground, called a “corner grounded delta” or “grounded leg service”. Save. Measured voltage on tenant panel 480 A-B, A-C, B-C. You are now operating on a corner grounded delta unintentionally. Use dedicated IES files on product website for non-standard CCTs. 30 (A) (1) (3) (c) in the 2020 NEC pertains to Delta-Connected Systems, in particular 3-phase, 3-wire delta systems with a grounded conductor. Solidly (effectively) grounded (LRG) Solidly (or effectively) grounded systems connect (bond) the system neutral directly to earth ground. 86 restricting their use to solidly grounded systems where the line to ground voltage does not exceed the lower of the two values and the line voltage does not exceed the higher value. Section 250. The correct application is 480 V or 600 V straight voltage ratings. My attached schematic is a center tapped phase (this creates a neutral point in secondary side of bank that can be tied to ground). The corner-grounded phase acts in much the same way as the grounded neutral of the single-phase Edison system, carrying current and maintaining ground potential. There are circuits where grounding is prohibited. The maximum continuous operating voltage is measured from phase to phase for impedance grounded and ungrounded systems. I figured at the least it would cause a phase loss alarm, but wasn't sure if there. 362K subscribers in the electricians community. I also have an older model Eurotherm VFD but I have not tested it. When the bond is made from B phase to ground, you are simply creating a reference point. However, some utilities still provide this system, and many old installations still exist. The delta system has a phase-to-phase voltage of 240 V. Grouch1980 said: Actually I didn't specify it. The secondary in this building is a 480V Corner Grounded Delta or Grounded "B" Phase Delta, whatever it is called. Best be taking some voltage readings and confirming what you have before making too many plans I would think. There are multi-tap ballast units, which can be 480V, 240V, or 208V, in addition to 277V, all of which are Line-to-Line connections. 20(A). Electrical. It is the best way to connect two transformers with different voltage ratings when a 4-wire or a wye connection is not viable or practical. These connections do not supply split single-phase power, and do not have a high leg. For alarm switch, add the suffix BA. Look for 2 xformer cans on the power pole! Open Delta. The ratings on the gen set are for 1 ph, 190 kVA - 240V 3 ph, 237 kVA 0. Since one phase is already grounded this 4th wire is somewhat redundant. You can determine if you have a corner grounded delta service by. It would seem to me, that there is no difference in principle between the grounded conductor in a 3 phase, 4 wire delta system, the grounded conductor in a 3 phase, 4 wire Y system, or the grounded conductor of of a 3 wire 240/120 volt system, or the grounded corner of a delta system as being disscussed. It is implemented by grounding any one of the three phases of the transformer secondary (corners of the delta). Jul 20, 2023Other system configurations, such as 3-wire corner-grounded delta system, ungrounded system, or high resistance grounding system are permitted by the National Electrical Code, but they are rarely installed, except in industrial applications. When you open the secondary side of the 500kva transformers the center phase has a 500mcm bare. Aside from the corner-grounding of the delta, this is a fairly common configuration for transmission substation transformer in the US. If the phase that is grounded shorts to the equipment frame there. For 240V delta corner ground, it's 240V three phase, or 240V single phase, what I said was that you can't use the B phase as a single phase anyway, because it's ground, therefore your potential is zero! For 240V delta high leg, you can get 120V, 240V, and 208V (only single pole). rcarroll said: '08 nec 408. grounded, corner grounded delta and ungrounded delta. Similar to the methods used to Ground all other Solidly Grounded AC Power Systems, the "Corner Grounded" Delta has Ungrounded. Phase ab 240v, ac 240v, bc 240v, a to ground 120v, b to ground 0v, c to ground 120v. "C" phase is solidly bonded to ground. The correct solution is to use a 208 Delta X 480Y xformer. This feature, however, applies to ground faults, not short-circuit or line-to-line faults. Thus, the phase which is corner grounded has zero volts relative to ground because we have chosen to bond it. One of the phases, normally A phase, is connected to a grounding electrode. 415V. A phase 490-ground B phase 490-ground C phase 0. Each test evaluates a different function or potential failure mode of a TVSS. High Leg Delta Transformer Connectionmight occur when Phase A goes to ground on a 480V, B-phase, corner grounded delta system. That corner grounded delta system still needs equipment grounding conductors run beyond the service disconnecting means, you do not bond any equipment to the current carrying B phase at equipment you run separate EGC like you do for other voltage systems. 4. #2 · Aug 15, 2015. I've been given two different answers for the same set-up. #1. A grounded conductor is to be pulled in with 500 kcmil THHN/THWN aluminum conductors as parts of a 277/480 volt 3phase 4w servioce to a 300 amp fused safety switch. The VFD's and motors we had installed didn't seem to mind. The phase load in VA of a 3-phase, 240V load is the line load divided by three (one third of. Applying a slash-rated breaker in such a system may result in complete device failure when a full voltage fault exceeds the circuit breaker rating. 20. Location. 20. The only solution i have come up with is pulling the pump, and changing them to 277/480 wye,. Being that a GF would. 85 covers the requirements for straight rated and slash rated CBs. Circuit Breakers for Grounded B-Phase (BØ) (Corner-Grounded Delta) Systems. (2) In ungrounded systems, impedance grounded systems, or corner-grounded delta systems unless listed specifically for use on these systems. 242. The only equipment bonded together is the main panel board case to the cable tray. 2 requires a grounded conductor in all premises wiring. The delta system can also be grounded, as shown in Figure 2 below. CMP said: Sounds like you have an ungrounded delta system, and your getting a capacitive voltage reading to your ghost ground. 36 (C) Equipment for General Use, Delta Breakers. PowerPacT B-Frame 15/20 A Thermal-Magnetic Trip. “A circuit breaker with a slash rating, such as 120/240V or 480Y/277V, shall be permitted to be applied in a solidly grounded circuit where the nominal voltage of any. Unless its to. 85 of the 2002 NEC was changed to read: 240. They have 3 phase delta 480. A second fault, on a different phase, however, presents a problem. looking for advice on working on a 3 ph, 3 wire 480 delta that i believe fits the definition of a corner grounded delta. It requires connecting the impedance grounding conductor according to sections 250. 85 of the 2002 NEC was changed to read: 240. Safety Switches Table 4 lists two-pole safety switches that are UL Listed for use on 240 and 480 Vac grounded B phase systems. To visualize this, imagine the voltage triangle with all three sides = 480V and the phase connections at the three corners. So on A phase to ground you have straight 480V. i agree. Per NEC, not for use with ungrounded systems, impedance grounded systems or corner grounded systems (commonly known as Three Phase Three Wire Delta, Three Phase High Leg Delta and Three Phase Corner Grounded Delta systems). Also explains your 480v to ground readings. It could also prohibit a corner grounded 240V delta since using a grounding transformer a 240V system could be grounded with a L-G voltage of only 139V. Informational Note: An example of a system permitted to be grounded is a corner-grounded delta transformer connection. NEC expert Mike Holt explains how to properly ground a corner grounded delta system and the special characteristics of these rare systems. One phase connected to ground. Now, there are exceptions. • Ground fault sensing is undefined for the grounded phase, so typically cannot be used at locations where GF is required, such as healthcare facilities Figure 2. False Nec Ref:240. False Note: “Straight” rated circuit breakers are rated at 240, 480, or 600 volts and not 277/480 volts; which is a slash rating: Interrupting ratings on AC rated circuit breakers are used for ? . 7. The motor will. Cause what is happening then is the 3ph load is seeing A,C,A or C,A,C. Used to be more corner ground around, but some POCO don't offer it at all anymore and have even converted any they had to three phase 4 wire whether it be. A new transformer was set for a motor load to step up to 480 volt. Grounding center of one side (high leg 240/480 delta) might still be too high a voltage. Introduction Corner-grounded delta systems are not re commended for new installations. Its corner ground Delta 3 phase , 208 V , 30 horsepower. 5869 posts · Joined 2009. - All phase L-L voltages are normal and the same. See 250. Could be red leg delta at the pole but floating and corner grounded delta at the customer's equipment. That would be a fairly simple fix in the panel, assuming that the panel is 3ph, not 1ph. Corner grounded delta securely references the other two phases to earth potential. CryptoDelta has no obvious grounding location; the AC lines are generally all floating relative to earth. R. The frst ground fault makes the ungrounded Delta into a Corner Grounded Delta, so the plant continues to run. W. A corner-grounded delta transformer connection is an example of a system permitted to be grounded. 2, the transformation ratio is 4160 divided by 120, or 34. The NEC technically still allows for this, but the system must be EITHER: 1) Grounded, meaning "corner grounded delta"; or 2) Monitored, meaning a Ground Fault Monitoring system. to ground on a 480 volt corner grounded delta system. 26(4) and 250. This question references Article 240. Use of a slash rated breaker on a corner grounded delta is not ruled out by it not being solidly grounded but by the voltage to ground on the two ungrounded wires being greater than the second number in the rating. 90 posts · Joined 2007. False. At the MV level corner grounded delta is exceptionally rare. The purposes are to: limit overvoltages due to lightning, line surges, or accidental contacts with higher-voltage. It could also prohibit a corner grounded 240V delta since using a grounding transformer a 240V system could be grounded with a L-G voltage of only 139V. The grounded conductor is treated like a neutral in 120 V and 240 V single-phase systems. It does NOT carry current like a neutral, a neutral carries the unbalance of the load. A diagram of such a system is shown at __ in figure 304. The generator cannot be configured to the 480 delta per manufacturer. 4. You will measure 480 volts from either A phase or C phase to ground, B phase to ground will measure 0 volts. If you choose the corner grounded delta, you will lose your three phase power that you need. Not a corner grounded delta. Although delta windings are often operated ungrounded, a leg of the delta can be center tapped and grounded, or a corner of the delta can be grounded. kclark8799 Member. Figure 2 – Corner-Grounded Delta System arrangement and voltage relationships. AC systems of less than 50 V. They were very popular on rural farms where the predominant building load was single phase, but the milking parlor. Occupation. EPD circuit breakers may not be used in systems with phase to ground voltages other than 277 Vac. Schneider Electric has tested equipment for use on corner-grounded delta systems to provide Underwriters Laboratories Inc. 3 phase 480 corner grounded delta. Location North of the 65 parallel Occupation EE (Field - as little design as possible)Most 480 volt delta systems are corner grounded by the utility and a 4th ground wire is brought to the service.