Recently and in the past there have been numerous posts/questions re: corner ground delta systems and the responses have been quite varied. Wye-wyes are extremely rare in <600V systems. Corner Grounded Delta Transformer Bank. #1. It's a three-winding transformer - grounded wye primary, corner-grounded delta tertiary, grounded wye secondary with neutral grounding resistor. Aside from serving the step-down transformer, the 480V side is mostly going unused. BUT you have a 2 to 1 transformer (480/240=2 to 1) at 208 in you would get 416 out. Corner grounded delta securely references the other two phases to earth potential. These connections do not have a high leg and do not produce divided single-phase electricity. A new transformer was set for a motor load to step up to 480 volt. Japanese electricity is a dumpster fire since they have both 50 and 60 hz, depending on the island (and whether it was under German or US influence in ~1900), AND they use 100V since it is nominally. We can treat it just like a grounded neutral in our other conventional systems and make solid connections in distribution with no in-line OCPD. He has tied the grounded phase of the delta supply to the green. We own the transformer. 480V rated breakers are only available with 3-poles and special labeling. Question I have is I believe I need to utilize a corner grounded delta on the 480v side, otherwise the system is not grounded. Corner grounding a delta secondary, will most likely cause more equipment damage than you currently are having. BTW, this is a grounded system. Reply. So then tested phase to ground and found 235v phase to ground on both A and B phases. What exactly is an unbalanced delta system? Figure 3. 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. A corner grounded delta is not ungrounded. 362K subscribers in the electricians community. It requires connecting the impedance grounding conductor. The minimum size of the grounded service-entrance conductor is a. Phase ab 240v, ac 240v, bc 240v, a to ground 120v, b to ground 0v, c to ground 120v. About us. That is a corner-grounded delta system. MRG, Article 200. A corner grounded power system is a system that is fed from a delta transformer winding with one phase grounded. 5 . 36 Overcurrent Protection > (C) Delta Breakers. D1-D4 lumen packages only. IN reference to. Delta with Wild Leg. Location DFW, Texas. A phase is connected to each corner of the delta. Corner-Ground: The three corners of the delta arrangement are connected to the line conductors. The correct application is 480 V or 600 V straight voltage ratings. This system exists to keep voltages stable, limit or reduce surges, and/or be. - All Line to ground voltages read (L-L/1. Google a pic for corner grounded delta transformer. kclark8799 Member. . For use on 240 V systems, circuit breakers may be ordered as 480 V. Furthermore, 3-phase, corner-grounded, delta circuits can only use two-pole circuit. 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. Not available with HA option. The delta system has a phase-to-phase voltage of 240 V. Other systems shall be permit‐ ted to be grounded. If you have a 3-phase motor on a center-tap system, the grounded conductor does not come into the picture at all. 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. Another variation is a "corner grounded" delta system, which is a closed delta that is. Until the service is restored we need to get power to the facility. 480 x 1. Read also : what is an operational amplifier. , Where a system is grounded, the service must be supplied with a(n) ? conductor. Exactly what one would use for 13. Corysan said: 240V 3ph corner grounded delta will definitely yield: A-Grd: 240V. 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. 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. By doing so, we are creating a split phase supply as well as a three-phase delta connected supply. (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. For alarm switch, add the suffix BA. 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. 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. And Delta ground monitor. This is coming from the corner grounded delta that is feeding the buss. In the setup the OP describes, the maximum voltage to ground would be 240, so he must use a straight 240 V breaker. "C" phase carries current just like a ungrounded delta or a 3 phase 4-wire wye. So enter the corner grounded delta secondary. A two-pole circuit breaker applied on a 3-phase. #3. We have a industrial setting with a corner grounded delta system. You are required to have ground fault indication/alarms and need to take steps to find and repair it. Another disadvantage, as given on page 33 of IEEE. I actually ran into a corner grounded delta myself Friday or at least I think. 3. Corner Grounded Delta Solidly (effectively) grounded (LRG) Solidly (or effectively) grounded systems connect (bond) the system neutral directly to earth ground. For R5/N5 and R6/N6 leave the screws in F1/F2 installed (Refer to the “Corner grounded TN systems” column in the table below). Corner Grounded Delta Solidly (effectively) grounded (LRG) Solidly (or effectively) grounded systems connect (bond) the system neutral directly to earth ground. You must also bond the phase to the case with a jumper sized to 250. They do have a +/-10% tolerance however. If the source is a corner grounded delta, and you connect a zig-zag transformer, then the neutral of the zig-zag would be at 277V (presuming a 480V system). We have a industrial setting with a corner grounded delta system. The "wild leg" has a different voltage to ground, which can. 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. However this grounded leg will be 480 volts phase to phase but no voltage to ground at the service and the inverter. Rick- It sounds like you have a corner grounded delta service. In a corner grounded delta system, one of the three phase legs is intentionally grounded. The inverters may not like the elevated voltages to ground. 1KV breaker at nearby sub. You will read 480v from l1 and l2 to ground, 0 v on the neutral leg to ground. move into 2008, as NEC-2005 requires Combination AF-. 23(A)(2) show instances. 160, 668. Is this the same thing as a Corner Grounded system?Corner grounded delta was very popular. If you do ground one leg, you will only get zero on that one leg. 61, 517. If you don't have VFDs or servos to contend with, then the NEC requires that you have EITHER a continuous ground fault monitoring system on an ungrounded Delta service, or you must use a "corner grounded" Delta system, wherein you tie one leg of your 480V transformer output directly to ground. 3. Corner grounded delta bank is three wire, grounded delta. Circuit Breakers for Grounded B-Phase (BØ) (Corner-Grounded Delta) Systems. It's 830 wye. Lexington KY. What we have is 4160V feeding 4 step down transformers that step it down to 230V Grounded B. 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. Another disadvantage, as given on page 33 of IEEE. I pointed out that in industry it is quite common for an ungrounded delta secondary to allow continuous ops while the partial/total phase grnd. #1. Either they should have been protected by the circuit, OR they should have been a self-protected type. JimmySki23 Member. 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. 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. It is not a phase conductor, it is a grounded circuit conductor just like the neutral on the common 120/240 volt single phase system. 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 ungrounded delta system except the transformer windings are grounded. Utilities are trying hard to get rid of corner grounded delta systems. 5. Always wear your gloves. ) Only standard ampere rated fuses and circuit breakers found in 240. 480 3ø, 3W corner grounded delta (ground jumper goes from one of the phases to ground. D325NT, D325NTR, D326NT, D326NTR, T327N and T327NR accept only 300Vac Class T fuses. 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. Indication Contacts. Looking at a 120/208 wye system, the phase voltage would be 120V and the phase-to-phase voltage would be 208V. 4. LocationStudy with Quizlet and memorize flashcards containing terms like The practical safeguarding of persons and property from hazards arising from the use of electricity best describes which of the following? Select one: a. micromind · #7 · May 3, 2023. Perhaps it should be extended to cover the grounded conductor of a corner grounded delta with a 170% factor. A corner-grounded delta transformer connection is an example of a system permitted to be grounded. This panel runs a 20 ton air handler. No 120/240VAC circuit breakers may be used on any corner grounded delta system. 8. Question, when connecting a Wye generator to the Corner Grounded Delta, will. My recommendation on corner grounded delta is to bolt all three phases together and hire a monkey to throw the main switch! But seriously, you'll have nightmares with corner grounded delta, it causes wierd ground. SPD requirements. Not open for further replies. Another disadvantage, as given on page 33 of IEEE Std 142. This supply system configuration is often used where high power is required, for example for large mo-tors. #1 · Feb 28, 2020. 2 pole fusible disconnects and 120/240V panels are sometimes rated for 240V three phase. This will impact the selection of circuit breakers in a corner-grounded Delta power system. The primary can be grounded wye, ungrounded wye or delta while the. We would like to show you a description here but the site won’t allow us. Aside from the corner-grounding of the delta, this is a fairly common configuration for transmission substation transformer in the US. Hi, Our company rented an old warehouse and this is the first time I've ever seen corner ground delta (CGD) panel. Corner grounded Delta transformer systems are known to confuse people. . 85 of the 2002 NEC was changed to read: 240. Corner-grounded Delta One line conductor is grounded directly. This creates a three-phase, corner-grounded system, sometimes referred to as an end-grounded system. ® (UL®) Listed products for this application. 8]. 277V. However, just like the 120/240 split phase secondary, it does carry current despite having zero volts relative to ground. 3 pole breakers may be used for 3 phase loads with grounded phase connected through a breaker pole. Schneider Electric has tested equipment for use on corner-grounded delta systems to provide Underwriters Laboratories Inc. 120 V, 3-phase, corner-grounded delta. However, some utilities still provide this system, and many old installations still exist. SE Michigan. ” Following are sketches of what the voltage source looks like with a breaker applied. not smaller than the required grounding electrode Corner grounded Delta. Is the transformer output an ungrounded or corner grounded delta? If ungrounded, a ground detector must be provided. Now connect one corner of the triangle to ground. 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. CIs in bedrooms effective January 1, 2008 (NEC 210. APPLICATION ON GROUNDED . They sent me back readings for phase-phase at 480V, but phase-ground measured approximately 277V for. corner grounded Delta system. It is a Delta and Split-phase hybrid. While it is a grounded conductor, the grounded phase of a corner-grounded delta grid is not technically a neutral. Select one: a. , In addition to the grounding. I hooked up 240v 3 phase motor to make sure and. Best be taking some voltage readings and confirming what you have before making too many plans I would think. That would be a fairly simple fix in the panel, assuming that the panel is. . The secondary in this building is a 480V Corner Grounded Delta or Grounded "B" Phase Delta, whatever it is called. Only for use with 480V Wye systems. System grounding is the connection to the ground – solidly or through impedance – of current-carrying conductors – e. The correct application is 480 V or 600 V straight voltage ratings. Aug 14, 2018. Figure 2 – Corner-Grounded Delta System arrangement and voltage relationships. 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. When the bond is made from B phase to ground, you are simply creating a reference point. This system has multiple transformers that go from 480-208 delta-delta and also 480v delta-208/120v wye. The grounded line of the corner-grounded delta is safe to touch with or without load at the end of the line only when the line is properly bonded to ground. ppsh41pro • 10 mo. Other 2 phases = line voltage. For services they used to hook the 600 volt and under seondaries anyway you wanted. the panel has two bus bars and grounded bar. This Wikipedia article explains TT, IT and TN-S power distribution systems. A two-pole circuit breaker shall not be used for protecting a 3-phase, corner-grounded delta circuit unless the circuit breaker is marked 1f- 3fto indicate such suitability. 240. The maximum continuous operating voltage is measured from phase to phase for impedance grounded and ungrounded systems. might occur when Phase A goes to ground on a 480V, B-phase, corner grounded delta system. IESNA. A two-pole circuit breaker may not be used for protecting a 3-phase, corner-grounded delta circuit unless the circuit breaker is marked 1Φ—3Φ to indicate such suitability. 3–Phase Corner-Grounded Delta System using 2-Pole Circuit Breakers. 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). K. 480V. Another indicator is you say your VFD’s run fine, the vast majority of VFD’s have MOV surge. Also, you can save. The service is a corner grounded 240V delta. Location. Thus, the phase which is corner grounded has zero volts relative to ground because we have chosen to bond it. But again, you have a corner grounded delta system so that's fine. Occasionally, (especially in older facilities or in oil well and irrigation applications), you may encounter a three-phase delta service with one. A corner grounded delta service can be designed for any desired voltage, but 240 is most common. 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. Our PoCo will not supply it, but many factories install it currently. That is the key answer with open delta system and I know it is common used on some resdentail and a bit of small commercal location. EPD circuit breakers may not be used in systems with phase to ground voltages other than 277 Vac. I came across a code a while back about NEC not allowing circuits to. 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). Almost as if the utility decided to run an EGC for giggles. As with most other UPS systems, Cat UPS requires an upstr eam isolation transformer for the UPS and bypass before it can be connected to these power systems. Remember, voltage is a difference in potential. Doing this is technically challenging and expensive, however, the corner-grounded system offers. Do not install them on corner-grounded, resistance-grounded, or ungrounded systems. While the rail-rail DC component of the rectifier output is the same in both wye and corner. Perhaps some. Have to physically see the MBJ to. Similar to the methods used to Ground all other Solidly Grounded AC Power Systems, the "Corner Grounded" Delta has Ungrounded. Figure 11. No. Not sure if that's the technical name or not. When wiring up electrical service configured as 3-phase corner-grounded delta, it would seem that the appropriate way to connect overcurrent protection would be to make the 2 ungrounded wired breakable, and pass the grounded wire straight through. The B phase is a high leg not a grounded conductor so 240. 208V. We use our. Per the NEC, you need either GROUND FAULT MONITORING, OR you need to use a Corner Grounded Delta system. This section classifies the systems that must be grounded – unless prohibited elsewhere in the Code – into four categories. From there a grounded phase conductor and equipment ground go to the disconnect and remain separate. 3830 posts · Joined 2010. Directions Advertisement. The NEC® addresses slash voltage ratings for circuit breakers in 240. Occasionally you may have an application that is a delta voltage source with a grounded “B” phase, also known as corner grounded. There is no way of grounding a 480V system (or any over 260V L-L) to meet the 150V L-G standard. J. I-Line) often require special breakers for 240V which are built using 3-pole housings. "C" phase carries current just like a ungrounded delta or a 3 phase 4-wire wye. 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. Wye connections, ungrounded delta connections, and corner-grounded delta (“ghost”) leg configuration connections are all examples of three-phase supply. Corner Ground Delta. The MOV surge protectors in your drives will not like one or two legs of a higher voltage to ground. #1. Trying to determine if I have a ground fault somewhere or a bad leg or breaker. The purpose of bonding c. Three-phase — 4-wire 120/240 volt delta connected system (high-leg). Cause what is happening then is the 3ph load is seeing A,C,A or C,A,C. 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). So instead of 480VAC 3 phase being 277V to ground, it was also 480V to ground thus being a bigger risk if accidentally grounded during troubleshooting. 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). Industrial mostly, and irrigation pumps. I also have an older model Eurotherm VFD but I have not tested it. NEC 240. on corner grounded delta when using Class J or R fuses. There are certain restrictions when using a VFD on a corner grounded delta power system. On a standard wye transformer, you would read 277v to ground on all three legs. 85 of the 2002 NEC was changed to read: 240. For example, a corner-grounded delta system has a grounded phase conductor and no grounded neutral conductor present. The derived neutral connot operate at 0 volts as this would mean there is a short circuit to ground. Two wire systems - maybe a separately derived 120 volt control circuit, will have one conductor grounded, but technically that conductor is not a neutral though many will call it that. High Leg Delta Transformer Connectionmight occur when Phase A goes to ground on a 480V, B-phase, corner grounded delta system. Could be as jraef mentioned. It's a three-winding transformer - grounded wye primary, corner-grounded delta tertiary, grounded wye secondary with neutral grounding resistor. Then leg to ground 480 479 0. I have a job where they want to install a Dan Foss FC202 on a pump. 99 votes, 37 comments. I believe that you are not supposed to connect any single phase loads between the high leg and the neutral. Running the 480 as ungrounded presents a whole other set of issues. Location AIken SC. B-PHASE SYSTEMS . The earth. The ratings on the gen set are for 1 ph, 190 kVA - 240V 3 ph, 237 kVA 0. It consists of a maximum current and the voltage at which the device is rated to interrupt the circuit. The grounded conductor of a corner grounded delta system is covered by the rules in Article 200, just like any other grounded conductor. Such a system changes to a corner. Where a service is supplying from a corner – grounded system, and the ungrounded conductors are sized at 750 kcmil copper, What is the minimum size required for the grounded conductor?. The only equipment bonded together is the main panel board case to the cable tray. not smaller than the required grounding electrodeCorner grounded Delta. This is a violation of Section 240. 102(C)(1). T. More. ® (UL®) Listed products for this application. ® (UL®) Listed products for this application. I asked them to take voltage readings between phase-phase and phase-ground just to make sure it is an un-grounded delta secondary. T. NEMA Type 7/9 SCCR 10 kAIR 600 Vac maximum. (3) If the voltage rating of the SPD is less than the maximum continuous phase-to-ground voltage available at the point of connection. I believe it also allows you to save wire, but I am not sure. Every fuse and circuit breaker is assigned an interrupting rating. Perhaps it should be extended to cover the grounded conductor of a corner grounded delta with a 170% factor. hello. 24(D)(4) This section covers impedance grounded services. Grounded B-Phase Systems (Corner-Grounded Delta) PowerPacT B Electrical Accessory Wiring Diagrams. Corner-Grounded Delta System. L-N: 277V L-L: 480V 480V. For use on 240 V systems, circuit breakers may be ordered as 480 V. The phase load in VA of a 3-phase, 240V load is the line load divided by three (one third of. The center of the Y, which is usually grounded, must not be connected to anything. Apr 6, 2011. Might be more economical to just order 240V equipment and use whats there. 480V. Eaton Corporation literature states “for all 3 phase delta grounded B phase applications, refer to Eaton Corporation. 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. . Two of the most significant tests performed on a TVSS are the measured limiting voltage test and a series of abnormal overvoltage. Ground a suitable midpoint of that auto-transformer. 67 times 34. Centertap is an effective ground (Neutral) at 0V potential and each leg is +120VAC and -120VAC respectively for the full voltage of 240V. If you choose the corner grounded delta, you will lose. At the transformer, the grounding electrode conductor, grounded phase, and equipment grounding conductor all tie together. For that reason, 99% of people who HAD legacy ungrounded delta systems. Along with the 'slash rating', Corner Grounded (grounded B phase) systems can impact the AIC ratings of breakers. When the bond is made from B phase to ground, you are simply creating a reference point. 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 grounded, then a ground fault protector may be desirable although not required. b. Measured voltage on tenant panel 480 A-B, A-C, B-C. Occasionally you may have an application that is a delta voltage source with a grounded “B” phase, also known as corner grounded. See Figure 11. B to Earth = 0, C to Earth = 524Delta, open or ungrounded 230 (or 460) volt A to B 230 (460) B to C 230 (460) A to C 230 (460) Any phase to ground will read random values. Grounding center of one side (high leg 240/480 delta) might still be too high a voltage. (2) In ungrounded systems, impedance grounded systems, or corner-grounded delta systems unless listed specifically for use on these systems. 408. According to mike holt one random? corner phase is to be grounded and bonded to the case of the transformer. Z. If A to B = 240, B to C = 240, and B is grounded, then A to ground and C to ground is the same potential as A to B or B to C. There is no way of grounding a 480V system (or any over 260V L-L) to meet the 150V L-G standard. As such it allows the OCPD to trip and clear the fault. Why would a corner grounded Delta system have a 4 wire drop? SDG&E?s Service Standards book states: ? On overhead service installations the service ground conductor, provided as the redundant 4th wire corner ground conductor of a 480 volt delta service, will be connected to the customer?s identified equipment grounding conductor at. It requires connecting the impedance grounding conductor according to sections 250. 5. 3–Phase Corner-Grounded Delta System using 2-Pole Circuit Breakers. The equipment itself may generate an undesirable amount of capacitive current to the shell of the bed if it is powered by either. Otherwise the delta would be corner grounded (grounded 'B' phase). Location Roughly 5346 miles from Earls Court. The earth as a conductive body can serve as an effective ground-fault current path to facilitate the operation of fuses or circuit breakers protecting the system. 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. Open delta provides 57% (iirc) of the power that straight delta does with the same size transformers. Could be red leg delta at the pole but floating and corner grounded delta at the customer's equipment. Save. A grounded Delta would have one phase solidly grounded, as with any grounded neutral, but would supply only 3ph loads. ) 480 3ø, 3W Wye connected Impedance grounded system. A lot of drives have surge suppressors that are designed for standard line to neutral voltages and don’t work with. Sections 503. Electric circuit : open & short circuits instrumentation toolsTransformer phase wiring 480v 208v diagram 480 delta wye 15kva vac Diagram of delta connectionThree phase transformer connections. I have seen corner grounded deltas for 3 phase motors, but my situation is a bit different. For nominal 480 volts that high leg voltage is about 416 volts to ground, still 480 between all corners. Corner grounded delta (CGD) As the disadvantages of ungrounded systems became better known, simple, low-cost method of establishing a ground reference on an. 0V. PowerPacT B-Frame 15/20 A. On this latter type, one phase is indeed grounded and is 0 volts to ground. LHL361005861). A second fault, on a different phase, however, presents a problem. might occur when Phase A goes to ground on a 480V, B-phase, corner grounded delta system. Aside from the corner-grounding of the delta, this is a fairly common configuration for transmission substation transformer in the US. 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. You're describing "high leg" or "wild leg" delta. 100 % (3 ratings) for this solution. Jun 10, 2019 #5 B phase on the Delta system is grounded. IESNA Type III typical. They are available. This center tap is grounded to produce voltages of 120V, 208V, 120V. I would call the 4rth wire a ground wire unless it was used for load unbalance. The only solution i have come up with is pulling the pump, and changing them to 277/480 wye,. The CB panel fed by the transformer secondary (240/120V) has a grounding electrode where the secondary center tap (neutral) is connected but as stated the corner grounded delta supply is not connected to it. 2 requires a grounded conductor in all premises wiring. 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. If one phase is zero volts to ground, you probably have a corner grounded delta. The size of the step-down transformer is. 14. That 'neutral' is of course not a neutral, but a parallel 'grounded phase' conductor. 44. M. ChrisSeems like a trick question. Occupation Electrical Contractor Nov 19, 2020 #1 cain a use a 3 phase panel for a 3 phase corner grounded service ( just use 2 of the lugs on the 3 phase breaker ). I wasn't sure what issues it might cause having one of the phases to ground be 0 volts. If the phase line was solidly grounded you would be reading 0 volts. i agree. 1 of 2 Go to page. I would not worry about it, but don't buy into the "kit" concept, tell them you want a 240V drive, or just use a 480V drive. Circuit Breakers for Grounded B-Phase (BØ) (Corner-Grounded Delta) Systems. If you choose the corner grounded delta, you will lose your three phase power that you need. Nov 30, 2020. The grounded conductor will be the neutral connected to the center tap of one of the windings.