• 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. This supply system configuration is often used where high power is required, for example for large mo-tors. Measured voltage on tenant panel 480 A-B, A-C, B-C. looking for advice on working on a 3 ph, 3 wire 480 delta that i believe fits the definition of a corner grounded delta. (d) Separately Derived Systems. 85 permits one pole of a motor controller to be placed in a permanently grounded conductor provided the controller is designed for all conductors. Assuming you adjusted the taps at 2. Currently, the secondary of the transformer enters our switchgear which has a disconnect for each of the 2 sides of the switchgear. Read also : what is an operational amplifier. Not open for further replies. Unless you ground one of the legs, the reading will be zero on all legs to ground. 12,470/7200 grounded Wye primary and. 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. ppsh41pro • 10 mo. R. The phase-to-ground voltages are not equal, and therefore the system is not suitable for single-phase loads. Along with the 'slash rating', Corner Grounded (grounded B phase) systems can impact the AIC ratings of breakers. Be careful when installing slash-rated breakers on a solidly grounded high-leg delta system. ) Branch-circuit fuses do not have to be marked with their ampere rating. One of the phases, normally A phase, is connected to a grounding electrode. Location NW Florida Occupation Electrical Jul 20, 2023 #8 Phase to neutral are 124, 214, 124. If grounded, then a ground fault protector may be desirable although not required. For example, the grounded conductor, as previously defined, could be a corner-grounded phase conductor per 250. 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. A 120/240 breaker is intended for use on a system where the maximum voltage to ground is 120, and the maximum voltage line to line is 240. Scanning through 250. One method of grounding a three-phase, three-wire, delta-connected system is to ground one of the phase conductors. Corner-Grounded Delta System. Although delta. I recall the EE missed it, I didn't realize it (or. I-Line) often require special breakers for 240V which are built using 3-pole housings. teal854t Discussion starter · Oct 13, 2010. A straight rated CB (such as 480V) can be applied on systems that have no more than 480V between any two conductors. 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”. By doing so, we are creating a split phase supply as well as a three-phase delta connected supply. The delta system can also be grounded, as shown in Figure 2 below. The grounded conductor is treated like a neutral in 120 V and 240 V single-phase systems. If that isn't possible, then the drive should be labeled as unsuitable for the floating delta and/or corner grounded delta. These interrupting. What you have is a center tapped delta 120/240 volt 3 phase system. An ungrounded (floating) delta should have a ground indicator to alert maintenance personnel because a second ground may be catastrophic. three-phase, 3-wire, corner-grounded delta system? 120V 240V 277V 480V Correct Answer: 480V. I know each leg has 240v to another phase or to ground except for the "B" phase so its not like the. 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). No magic and no mysteries. Most utilities would require for you to request a variance to get ungrounded Delta now, so if you don't ask for it, you get corner grounded. Corner grounded delta systems are very common here, we have them with 220V and 440V, but 440V is rather seldom. 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. zbang Senior Member. Hi, Our company rented an old warehouse and this is the first time I've ever seen corner ground delta (CGD) panel. 3 pole breakers may be used for 3 phase loads with grounded phase connected through a breaker pole. Furthermore, 3-phase, corner-grounded, delta circuits can only use two-pole circuit. I recently had and issue with a 240v three phase Delta system while on the job. Open delta, also known as corner-grounded or ungrounded delta, is an electrical configuration of a 3-phase system that provides individual phase to ground connections without a single selected neutral point. A corner grounded delta system is a common way to establish a reference to safety ground when dealing with an otherwise floating output from a delta secondary transformer. Voltage between phase A and C to ground would be 277v while Phase B to ground would be something like 347v (I'm just guessing on that number) This would all be on the primary side. In the setup the OP describes, the maximum voltage to ground would be 240, so he must use a straight 240 V breaker. the breakers in the panel are. Because of the size and complexity of Grounding and Bonding, Article 250 is subdivided into the. Perhaps it should be extended to cover the grounded conductor of a corner grounded delta with a 170% factor. However, the grounded phase is still current carrying just like a neutral is current carrying and is grounded. You are correct in that a corner grounded delta would have 240V L-L x3, the corner would have 0V to ground. A lot of drives have surge suppressors that are designed for standard line to neutral voltages and don’t work with. Version 1. . 5. False Nec Ref:240. A circuit breaker with a slash rating, such as 120/240V or 480Y/277, shall be permitted to be applied in a solidly grounded circuit where the nominal voltage of any conductor to ground does not exceed theThe system is “corner grounded”, one leg of three phase delta is tied to ground. The leg that reads zero to ground is the grounded leg. On BOLTED faults the first fault to ground turns it into a corner grounded delta system but doesn’t trip anything. There is no way of grounding a 480V system (or any over 260V L-L) to meet the 150V L-G standard. 90 posts · Joined 2007. CryptoDelta has no obvious grounding location; the AC lines are generally all floating relative to earth. The Corner Grounded Delta system is a 3Ø 3 Wire configuration, of which has one of the Secondary output Lines (AKA "Phases") intentionally connected to "Ground" via the Grounding Electrode System. I'm not familiar to this at all. Corner grounded delta. A corner-grounded delta transformer connection is an example of a system permitted to be grounded. , Premises wiring systems generally are required to be supplied by a system that is ? and includes a grounded conductor. Ground B phase systems, grounded phase services, and end-grounded delta systems are all examples of corner-grounded delta systems. I have seen highly trained electricians freak out at a corner grounded delta in a power plant by me. 13. In a 240-volt corner-grounded delta, what is the voltage between C phase and ground? 0 volts. A circuit breaker with a slash rating, such as 120/240V or 480Y/277, shall be permitted to be applied in a solidly grounded circuit where the nominal voltage of any conductor to ground does not exceed theOne thing I think would work is if the 480V delta had center-tapped windings, 240/480V. 208V. Corner grounded delta systems produce crazy voltages, and crazy ground faults. A corner ground is used on a strait 3 phase, 3 wire Delta system, that has no neutral. 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. There is no way of grounding a 480V system (or any over 260V L-L) to meet the 150V L-G standard. D. Another disadvantage, as given on page 33 of IEEE. 85 permits one pole of a motor controller to be placed in a permanently grounded conductor provided the controller is designed for all conductors. 2) ABB does not guarantee the EMC category or the operation of the ground leakage detector. 22 does not apply to the B phase of a center tapped 120/240 volt delta system. Solidly-Grounded wye or star configuration : Yes: High resistance grounded wye or star configuration : No: Ungrounded wye or star configuration : Asymmetrical: Grounded at the corner of the delta connection : Grounded at the middle of the side : Single-phase, grounded at the end point : Three-phase variable transformer without. We have an old system in our plant that is the grounded B phase or the corner grounded delta. We have a industrial setting with a corner grounded delta system. I actually ran into a corner grounded delta myself Friday or at least I think. Delta-connected systems can be solidly grounded using a few methods. Yes, that is my understanding too. No magic and no mysteries. Proper grounding reduces overvoltages, improves uptime, and isolates faults. However, just like the 120/240 split phase secondary, it does carry current despite having zero volts relative to ground. They are available. 24, 250. Section 250. ® (UL®) Listed products for this application. 26. B phase is bonded to ground at the transformer lugs, not in the switchgear. The grounded conductor will be the neutral connected to the center tap of one of the windings. The MOV surge protectors in your drives will not like one or two legs of a higher voltage to ground. 480v, corner-grounded delta. 8]. In case of a power failure, when the generator motor reaches the correct speed, a set of ___ is energized to disconnect the load from its normal source and to connect it to the generator output. The grounded neutral conductors typically carry the maximum. However, some utilities still provide this system, and many old installations still exist. Three-Phase, 240 Volt, 3-Wire Corner Grounded Delta: The 3-phase, 3-wire, delta corner grounded electrical system is used generally for the same applications as the. Remove EMC AC, VAR. An open Delta is (almost) always a high-leg added to a typical 120/240v 1ph to supply a smaller 3ph load. Other 2 phases = line voltage. LHL361005861). Introduction Corner-grounded delta systems are not re commended for new installations. 250. However, some utilities still provide this system, and many old installations still exist. Grounding center of one side (high leg 240/480 delta) might still be too high a voltage. 480V – 3-Phase, 2-Wire – Corner Grounded – Delta. Corner ground is exactly what the name says - one corner of the delta is grounded, the other two corners will be 480 volts to ground on such system. For use on 480 V systems, LH type circuit breakers must be ordered as 600 V versions and with a 5861 suffiix (i. "A" or "B" phase short and the the OCP operates. Figure 2 – Corner-Grounded Delta System arrangement and voltage relationships. PowerPacT B-Frame Let-Through Energy Curve. 480V. NEC 430. T. Each test evaluates a different function or potential failure mode of a TVSS. 67A; secondary current will be 1. Looking at a 120/208 wye system, the phase voltage would be 120V and the phase-to-phase voltage would be 208V. In a delta configuration, the three windings are connected end-to-end to form a closed path. , a zero sequence voltage). Corner grounded delta is cheap. micromind · #7 · May 3, 2023. On this latter type, one phase is indeed grounded and is 0 volts to ground. gap, is maximum. For that reason, 99% of people who HAD legacy ungrounded delta systems. 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. Glenwood landings for lipa has one. There is no grounding of any kind on the panel boards, transformers or disconnects. A corner grounded delta system is a three-phase delta service with one phase having the ground connection. You're describing "high leg" or "wild leg" delta. There are circuits where grounding is prohibited. A high leg delta connection is a configuration in which one of the windings in a delta connected secondary of a transformer is centre-tapped and grounded. Ampere rating of fuse or circuit breaker not to exceed switch ampere rating. About us. It is a 240v CGD. Basic cheap plug-in breakers are “slash” rated, meaning 240/120V; they are rated 240V phase to phase, but 120V phase to ground. I wasn't sure what issues it might cause having one of the phases to ground be 0 volts. Therefore, it is not correct to refer to all grounded conductors as neutral conductors, although that is the case in the majority of electrical distribution systems. NEC 240. UL Listed for use on 240 V Corner-grounded Delta Systems (Grounded B Phase). One method of grounding a three-phase, three-wire, delta-connected system is to ground one of the phase conductors. I have a job where they want to install a Dan Foss FC202 on a pump. 1) The neutral system has lower line-ground voltages 2) In a corner grounded HRG system, detecting ground faults in the grounded circuit conductor would be more difficult. Aside from serving the step-down transformer, the 480V side is mostly going unused. This creates a three. 1; 2; Next. Aprenda cómo usar la pantalla y el teclado integrados, así como las opciones de comunicación y control. 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 ? . T. Once wired up as a delta bank, the system is now a three phase system and has a phase-to-phase voltage of 240V, the same voltage as the phase voltage. 480 x 1. 7 taps I am getting 439 volts, but If I need higher voltage the connection can be. Remote Operation (MN/MX Voltage Release) Let-Through Curves and Trip Curves. 20 informational not refers to a corner grounded delta tranformer. This supply system configuration is not used in Europe. 24(D)(4) This section covers impedance grounded services. Another disadvantage, as given on page 33 of IEEE Std 142. Phase readings as follows: A to…By grounding a corner of the delta, you help stabilize the phase to ground voltages and the phase to phase voltages will also be stable. Snap. Therefore, many historic structures still have operating delta-delta service transformers where one corner of the transformer has been grounded to provide 120 V/240 V power within the facility. 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. This includes the rules in 230. A grounded wye system. Aquavar CPC For R4 or N4 frame size, remove EM3. We have a project where we are changing the service from 480/277V, 3-phase, 4-wire wye to 480V, 3-phase, 3-wire, corner grounded delta. thebigmt Member. It kind of freaks me out measuring 0 volts to ground on a open buss 4-5 thousand amps switchgear in the powerplant. The system has accidentally become a corner-grounded delta system with little, if any, current flow. [/QU Corner Grounded. 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. The motors operate at a nominal supply voltage of 220 volts, 3 phase. 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. High-leg Delta "HLD" B/HL A N C G High-leg Delta This supply system configuration is not used in Europe. Corner grounded is normally in industrial and commercial applications. The NEC® addresses slash voltage ratings for circuit breakers in 240. 3 Phase grounded delta three wire 480 volt to single phase 240/120 volt transformer to 200 amp panel , does the 480 volt grounded phase always come in. If the available line-to-ground fault current exceeds 8,660 amps at 480 volts, such as might occur on the secondary of a 1000 KVA, 480 volt, corner-grounded delta transformer, the circuit breaker may be misapplied. IN reference to. If such systems are grounded, they shall comply with the applicable provisions of this article. 2778 posts · Joined 2014. Grounded B-Phase Systems (Corner-Grounded Delta) PowerPacT B Electrical Accessory Wiring Diagrams. Introduction Grounded systems offer many benefits over ungrounded systems [1][2][3]. The service is a corner grounded 240V delta. Thread starter thebigmt; Start date Nov 24, 2010; Status Not open for further replies. A grounded wye system has each phase at line voltage divided by the square root of three above ground. 85 covers the requirements for straight rated and slash rated CBs. 8kv/480V Y transformer. 1) The neutral system has lower line-ground voltages 2) In a corner grounded HRG system, detecting ground faults in the grounded circuit conductor would be more difficult. If you choose the high leg delta, you'll need to pull a grounded conductor anyway. Open delta 480 volt service. Cause what is happening then is the 3ph load is seeing A,C,A or C,A,C. #1. From there a grounded phase conductor and equipment ground go to the disconnect and remain separate. Perhaps some. You will read 480v from l1 and l2 to ground, 0 v on the neutral leg to ground. The grounded conductor is defined in Article 100 in the National Electrical Code (NEC), but this definition can cause confusion when it’s used in an electrical system. This question references Article 240. More. What exactly is an unbalanced delta system? Figure 3. Corner grounded delta securely references the other two phases to earth potential. Fig. In addition, if you have any sort of rectification stage, for example in a VSD, then the DC rail voltages relative to ground will be very different. If you choose the high leg delta, you'll need to pull a grounded conductor anyway. They have 3 phase delta 480. Remember, voltage is a difference in potential. The only equipment bonded together is the main panel board case to the cable tray. L. might occur when Phase A goes to ground on a 480V, B-phase, corner grounded delta system. Trust is hard to come by in St. 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). My attached schematic is a center tapped phase (this creates a neutral point in secondary side of bank that can be tied to ground). [9] 22 k AIR main circuit breaker UL Listed for use ahead of QO, QOT and QO-PL 10 k AIR branch circuit breakers to permit their application on systems with up to 22 kA available fault current. Thus, the phase which is corner grounded has zero volts relative to ground because we have chosen to bond it. Industrial mostly, and irrigation pumps. What is the minimum size required for a copper grounded conductor of three phase, three wire, corner grounding delta system if the ungrounded. We own the transformer. Never ran into that before. The purpose of a corner ground is equipment and personnel protection. PowerPacT B-Frame Peak Let-Through Current Curve. Use QO-H circuit breakers only. If such systems are grounded, they shall comply with the applicable provisions of this article. Introduction Corner-grounded delta systems are not re commended for new installations. This is a system where one of the phase conductors of the 3-phase delta bank is intentionally grounded. "C" phase carries current just like a ungrounded delta or a 3 phase 4-wire wye. The corner grounded delta (CGD) is one of the earliest forms of grounded systems in electrical installations. 3-phase corner-grounded delta or single-phase circuits (NEC 240. One-line diagram symbol for a system- or equipment grounding connection _____ m. 242. The current flowing in each circuit conductor to the load is ___ amps. Image used courtesy of Lorenzo Mari . Our instructor made a point to warn of corner grounded Delta transformers, since you get your "phase-to-phase" voltage present "phase-to-ground". is located/eliminated asap. A wye winding, with the wye point left unconnected, since there is nothing to connect it to. 3131 Delta St Victoria BC V8Z 1A6 (250) 884-1942. 480V. 100 % (3 ratings) for this solution. 23(A)(2) show instances. to ground on a 480 volt corner grounded delta system. When you open the secondary side of the 500kva transformers the center phase has a. Corner Grounded Delta Aquavar SPD Follow procedure: Disconnecting EMC Filter and MOV's per IM213. 85 Applications. 73 =830v; I don’t think it’s a wye system, could just be an oddball system. (2) A circuit breaker with a slash rating, such as 120/240 V or 480Y/277 V, shall only be installed in a circuit where the nominal voltage of any conductor to ground does. . This video covers voltage relationship for a Delta source or load. I guess what I'm saying is that Delta seems never to be a good option. - All Line to ground voltages read (L-L/1. The ratings on the gen set are for 1 ph, 190 kVA - 240V 3 ph, 237 kVA 0. NEC 430. It does NOT carry current like a neutral, a neutral carries the unbalance of the load. Jun 10, 2019 #5 B phase on the Delta system is grounded. 9A. Corner grounded delta systems are common in old industrial facilities around St. The conductor connected to the neutral point of a system that is intended to carry current under normal. 9. What we have is 4160V feeding 4 step down transformers that step it down to 230V Grounded B. A phase is connected to each corner of the delta. However this grounded leg will be 480 volts phase to phase but no voltage to ground at the service and the inverter. Agreed, corner grounded delta, but strange that they have two separate conductors for 'grounded phase conductor' and 'neutral conductor'. Could be the outlet is miswired or mis-breakered and has two of one line and one of a second. 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. 8. As far as marking, I have never seen a corner grounded system where the grounded conductor was identified as required by the rules in 200. The primary can be grounded wye, ungrounded wye or delta while the. Fusible switch for corner-grounded delta system. The maximum continuous operating voltage is measured from phase to ground for solidly grounded systems. You will measure 480 volts from either A phase or C phase to ground, B phase to ground will measure 0 volts. not smaller than the required grounding electrodeCorner grounded Delta. For example, a 480 V, 3-phase, corner-grounded, delta-connected system cannot use a 480Y/277 V circuit breaker because the voltage of two phases to the ground exceeds 277 V. L-G phase readings are L-L V. Have to physically see the MBJ to. It's not exactly common, and maybe has no goo purpose, but a corner grounded delta and a center grounded wye can be wired as an SDS simply by connecting the two grounded conductors. It then goes on to discuss performing an open corner test to ensure proper polarity when c. This wire must be white or grey, because it is a grounded conductor, even though it isn’t a neutral. Three single phase 480 transformers in a wye configuration. roberius Member. Section 242. Now, there are exceptions. When the bond is made from B phase to ground, you are simply creating a reference point. If the leg chosen is the B phase, then the voltage to ground for A and C will be 240 volts, while for B it will be zero. Location UK Occupation Retired Electrical EngineerThe loads don’t know the difference. Also, you can save. Similar to the methods used to Ground all other Solidly Grounded AC Power Systems, the "Corner Grounded" Delta has Ungrounded. This video is based on the 2020 NEC and was extracted. PowerPacT B-Frame Peak Let-Through Current Curve. Then any corner of the delta arrangement is grounded (the B-corner-ground is customary) to create a neutral in the winding (labeled and colored usually gray and white as a neutral). Installations with this system require a 480-120V transformer to supply 120V lighting. Frame size EMC filter (+E200) screw Ground-to-phase varistor screw R10, R11 EMC AC VAR Drive. Occupation. 2) Adding a grounding autotransformer. Not a corner grounded delta. Business, Economics, and Finance. If it is a 480 volt system, you should read 480 v between each phase. The neutral is by definition a grounded conductor but if you had a corner grounded delta system the grounded conductor would not be a neutral. CMP said: Sounds like you have an ungrounded delta system, and your getting a capacitive voltage reading to your ghost ground. Wye connections, ungrounded delta connections, and corner-grounded delta (“ghost”) leg configuration connections are all examples of three-phase supply. e. Corner grounded delta. PowerPacT B-Frame Let-Through Energy Curve. A vendor recommended it for their equipment (all motor loads), to use a step down delta-delta transformer, from 480 volts down to 240 volts. A new transformer was set for a motor load to step up to 480 volt. MRG, Article 200. 2 pole fusible disconnects and 120/240V panels are sometimes rated for 240V three phase. 'power' panels (e. It is both, ground and hot. You can determine if you have a corner grounded delta service by. Typically in my area BOY is used for any 480 volt power and if a grounded conductor involved, it is grey or marked grey. It is a 240v CGD. The problems found include: dangerous step and touch. I got a call today from dry cleaners he wants to add new washer. Power company recently replaced transformers and now that businesses are opening back up. NEC 430. See Figure 11. Small residential is normally single phase 2 wire or single phase 3 wire. 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. Mr. Running the 480 as ungrounded presents a whole other set of issues. Louis. domnic Senior Member. Areas of concern converting a corner ground to a wye include: In a properly installed corner grounded system, the corner conductor should be white or gray. The only time you will see delta B corner grounded is when original older system was ungrounded and it was modified to be grounded by taking B phase and intentionally grounding it. kclark8799 Member. But the key issue with any delta sytem is grounding that will get ya due there is a corner grounded delta. Mr. I think it also allows you to use single phase panel boards also. As detailed above, a delta secondary Transformer cannot have a neutral, while a center-tapped delta secondary Transformer, once the center-tap is bonded to the nearest earth ground per the NEC by the installer, can have a limited. One-line diagram symbol for a start push button _____ and a stop push button _____ Step-by-step solution. Could be red leg delta at the pole but floating and corner grounded delta at the customer's equipment. 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. 120/240 V, single-phase, 3 W, solidly grounded III. Subsection 250. These connections do. Basic cheap plug-in breakers are “slash” rated, meaning 240/120V; they are rated 240V phase to phase, but 120V phase to ground. However, some utilities still provide this system, and many old installations still exist. it is three phase 240 volt the panel is 200 amp three phase corner grounded the listing in the panel 120/240 volt single phase or 240 volt three phase delta. . Master Electrician / Electrical Engineer. It is a Delta and Split-phase hybrid. 26(4) for conductor to be grounded. Next Last. - All phase L-L voltages are normal and the same. That 'neutral' is of course not a neutral, but a parallel 'grounded phase' conductor. This parasitic capacitance appears in the zero sequence network as an impedance (XC) connected to the neutral bus. 277V. Could be the outlet is miswired or mis-breakered and has two of one line and one of a second. To visualize this, imagine the voltage triangle with all three sides = 480V and the phase connections at the three corners. No 120/240VAC circuit breakers may be used on any corner grounded delta system. With the corner grounded, you'll wind up with two phase to ground voltages equal to the phase to phase voltage and the third will be equal to zero. Other systems shall be permit‐ ted to be grounded. If the leg chosen is the B phase, then the voltage to ground for A and C will be 240 volts, while for B it will be zero. You will measure 480 volts from either A phase or C phase to ground, B phase to ground will measure 0 volts. High leg delta has one winding center tapped. But again, you have a corner grounded delta system so that's fine. I have seen corner grounded deltas for 3 phase motors, but my situation is a bit different. See a problem? Let us know. A two-pole circuit breaker shall not be used for protecting a 3-phase, corner-grounded delta circuit unless the circuit breaker is marked 1Φ–3Φ (see figure 13). 120 V, single-phase, 2 W, solidly grounded II. (UL®) listed products for this application. It consists of a maximum current and the voltage at which the device is rated to interrupt the circuit. If the phase that is grounded shorts to the equipment frame there. They do have a +/-10% tolerance however. Corner grounded delta. 1. 85 of the 2002 NEC was changed to read: 240. A 480 volt corner ground delta does not have any portion of the supply that operates below 277 volts to ground (aside from the grounded conductor itself) - you can not connect any load in a way that gives you less then 277 volts between conductors or ground on this sytem - a 277/480 rated breaker can not be used on this system.