ground continuity, enclosure impact, adequacy of mounting, and many others. Abstract Many factors must be considered when designing the electrical system for critical facilities, especially the type of ground system used. Also, with the same KVA and impedance transformers, the available fault. This system exists to keep voltages stable, limit or reduce surges, and/or be required in compliance with electrical code. NEC expert Mike Holt explains how to properly ground a corner grounded delta system and the special characteristics of these rare systems. Unless its to. A corner grounded delta is not ungrounded. . Louis, and they are a nightmare. The NEC® addresses slash voltage ratings for circuit breakers in 240. 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. A high-leg system is a hybrid between a standard 3-wire single phase and a 3-phase system. They do make a reference to issues with control circuit isolation on corner grounded 400-500VAC systems, but no issue mentioned on a 240V delta. They based it on current measurements they took at the pole after checking and cleaning all connections. What you have is a center tapped delta 120/240 volt 3 phase system. You will measure 480 volts from either A phase or C phase to ground, B phase to ground will measure 0 volts. The size of the step-down transformer is. 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 . The equipment itself may generate an undesirable amount of capacitive current to the shell of the bed if it is powered by either. That 'neutral' is of course not a neutral, but a parallel 'grounded phase' conductor. Such faults are typically high impedance and at unspecified locations. The objectives of the National Electrical Safety Code b. He has tied the grounded phase of the delta supply to the green. (2) In ungrounded systems, impedance grounded systems, or corner-grounded delta systems unless listed specifically for use on these systems. You're describing "high leg" or "wild leg" delta. . 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. Aside from the corner-grounding of the delta, this is a fairly common configuration for transmission substation transformer in the US. They do have a +/-10% tolerance however. 3–Phase Corner-Grounded Delta System using 2-Pole Circuit Breakers. Thread starter thebigmt; Start date Nov 24, 2010; Status Not open for further replies. PowerPacT B-Frame Peak Let-Through Current Curve. The system has accidentally become a corner-grounded delta system with little, if any, current flow. In my experience, there always seems to be a higher current on the. 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. 120 V, 3-phase, corner-grounded delta. Systems from Intermittent Ground Faults Introduction Many papers and standards [1][2][3][4][5][6] have discussed grounding of an electrical distribution system. Only for use with 480V Wye systems. 6. This is a non sequitur. If you choose the high leg delta, you'll need to pull a grounded conductor anyway. 220. 102(C)(1) for sizing the grounded conductor. High-leg Delta "HLD" B/HL A N C G High-leg Delta This supply system configuration is not used in Europe. A. IESNA Type III typical. When you look up Conductors, then Grounded you will find the first reference given is Alternating current systems, 250. 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. 480V. 6 are permitted to be used in services, feeders. But the key issue with any delta sytem is grounding that will get ya due there is a corner grounded delta. On the primary side, what is the voltage to ground on each phase? If one is zero and the other two are 480 or 525 then yes it is a corner grounded system. 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. Delta-connected systems can be solidly grounded using a few methods. 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. Looking at a 120/208 wye system, the phase voltage would be 120V and the phase-to-phase voltage would be 208V. They could have a neighboring property causing that or could be monitoring lamp or relay seeking a fault. NEC actually calls it the "grounded conductor" which would seem to open up the possibility of corner grounding one of the three phase conductors. For that reason, 99% of people who HAD legacy ungrounded delta systems. You can determine if you have a corner grounded delta service by. Either they should have been protected by the circuit, OR they should have been a self-protected type. Ground B phase systems, grounded phase services, and end-grounded delta systems are all examples of corner-grounded delta systems. Introduction Corner-grounded delta systems are not re commended for new installations. 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. 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. Each test evaluates a different function or potential failure mode of a TVSS. Ampere rating of fuse or circuit breaker not to exceed switch ampere rating. That is a corner-grounded delta system. ATSman ATSman. 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. 240. "C" phase carries current just like a ungrounded delta or a 3 phase 4-wire wye. You only need two current transformers to monitor the power in a 3 phase, 3 wire system. e. 24 I see 250. Ground a suitable midpoint of that auto-transformer. Trying to determine if I have a ground fault somewhere or a bad leg or breaker. 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. Location: In the bothy, 7 chains down the line from Dodman's Lane level crossing, in the nation formerly known as Great Britain. 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. Mr. Rick It is both, ground and hot. Two ways to use the Grounded Conductor on 3Ph 3W Delta Two ways to use the Grounded Conductor on 3Ph 3W Delta Check out these Schematics, regarding a 3 Phase 3 Wire Corner-Grounded Delta, and the Two ways the. It does NOT carry current like a neutral, a neutral carries the unbalance of the load. 120/240 V, single-phase, 3 W, solidly grounded III. Version 1. On the secondary the voltage would be, if. corner grounded delta service. A building needs to be taken off it's primary feed, so we can service it's 4. 90(B). 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. Corner grounded systems often employ 2 pole circuit breakers and distribution panels which would need to. I wasn't sure what issues it might cause having one of the phases to ground be 0 volts. Perhaps it should be extended to cover the grounded conductor of a corner grounded delta with a 170% factor. 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). However, some utilities still provide this system, and many old installations still exist. I would call the 4rth wire a ground wire unless it was used for load unbalance. Could be the outlet is miswired or mis-breakered and has two of one line and one of a second. The grounded phase has no voltage to ground (at the service) and 240 or 480 volts to the other two phases. These connections do not supply split single-phase power, and do not have a high leg. The voltages are 480 volts between phases, 480 volts between phase a and ground, 480 volts between phase c and ground and 0 volts between phase b and ground. You can run a typical two-wire line-to-line load off just a single pole breaker because on this. Agreed, corner grounded delta, but strange that they have two separate conductors for 'grounded phase conductor' and 'neutral conductor'. 220. Similar to the methods used to Ground all other Solidly Grounded AC Power Systems, the "Corner Grounded" Delta has Ungrounded. 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. 61 (A) Exception has a requirement for a 140% factor for calculating the neutral load from the unbalanced load on a 2-phase feeder. So when the disconnects are open, the B phase is no longer. 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 maximum continuous operating voltage is measured from phase to ground for solidly grounded systems. Class R fuses are rated for 100 kA, however without the rejection fuse clips - system is limited to 10 kA since Class H or K fused could be installed in the future. The grounded conductor of a corner grounded delta system is covered by the rules in Article 200, just like any other grounded conductor. a Split Phase circuit with 120V from each respective leg to Neutral (residential power tap - grin). This supply system configuration is often used where high powers are required, for example for large motors. Image used courtesy of Lorenzo Mari . A grounded Delta would have one phase solidly grounded, as with any grounded neutral, but would supply only 3ph loads. These connections do. - All phase L-L voltages are normal and the same. #5. Snap. R. Electrical. No, it is not showing the high side delta winding is corner grounded. This demonstration video shares the wiring, voltage and history of a corner grounded delta bank. "A" or "B" phase short and the the OCP operates. Hi, Our company rented an old warehouse and this is the first time I've ever seen corner ground delta (CGD) panel. The correct application is 480 V or 600 V straight voltage ratings. I can see 1 phase of the secondary is grounded to the common primary neutral. I've seen a center-tap on one phase that's tied to earth. 23(A)(2) show instances. Furthermore, 3-phase, corner-grounded, delta circuits can only use two-pole circuit breakers marked 1ɸ-3ɸ. Finally, an equipment grounding conductor is added as. You cannot use a slash-rated 480/277V breaker on a 480V corner-grounded delta circuit because the line-to-ground voltage from two of the conductors. 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. the breakers in the panel are. 796v is what's marked on a motor used on these 830 systems. Besoeker3 Senior Member. 5869 posts · Joined 2009. 60% of these I run across are done incorrectly. Whichever you want to call it. Perhaps it was intended to be connected to a transformer. A corner-grounded delta transformer connection is an example of a system permitted to be grounded. 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. ) A 480/277-volt, 3-pole circuit breaker can be applied on a 480-volt corner-grounded delta. For me, its a textbook corner grounded delta. False. NEC 430. The easiest way to ground a delta is at a corner, which also happens to be convenient in converting/upgrading ungrounded systems. Corner Grounded Delta You don't see this on new services much these days, but it is very common on older industrial buildings. The delta system has a phase-to-phase voltage of 240 V. 3131 Delta St Victoria BC V8Z 1A6 (250) 884-1942. Check Details. What exactly is an unbalanced delta system? Figure 3. We have a industrial setting with a corner grounded delta system. Corner grounded delta. one pole. Mr. Trust is hard to come by in St. 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. Solidly (effectively) grounded (LRG) Solidly (or effectively) grounded systems connect (bond) the system neutral directly to earth ground. Its corner ground Delta 3 phase , 208 V , 30 horsepower. Corner grounded delta systems are good in theory, but only with older types of loads. Introduction Corner-grounded delta systems are not re commended for new installations. Corner grounded delta (CGD) As the disadvantages of ungrounded systems became better known, simple, low-cost method of establishing a ground reference on an. It is very dangerous to touch the grounded line in a corner-grounded delta when the line. The corner grounded delta (CGD) is one of the earliest forms of grounded systems in electrical installations. Currently, the secondary of the transformer enters our switchgear which has a disconnect for each of the 2 sides of the switchgear. Schneider Electric has tested equipment for use on corner-grounded delta systems to provide Underwriters Laboratories Inc. 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. 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. Such a system changes to a corner. The other two will be 240v to ground. Also, you can save. . PowerPacT B-Frame 15/20 A. Its incoming utility service is 480V, corner-grounded delta. Consider the relative sizes of the tank and the electrodes. A corner grounded delta system will put more stress on the insulation between windings and ground. Could be as jraef mentioned. Perhaps it should be extended to cover the grounded conductor of a corner grounded delta with a 170% factor. In the setup the OP describes, the maximum voltage to ground would be 240, so he must use a straight 240 V breaker. Eaton Corporation literature states “for all 3 phase delta grounded B phase applications, refer to Eaton Corporation. 12. 242. Schneider Electric has tested equipment for use on corner-grounded delta systems to provide Underwriters Laboratories Inc. That is a corner-grounded delta system. . I know right now there is a customer that is served by the POCO with ungrounded wye primary - corner ground 480 volt delta secondary, three transformers totaling 1000kVA. See. (UL®) listed products for this application. CMP said: Sounds like you have an ungrounded delta system, and your getting a capacitive voltage reading to your ghost ground. The primary can be grounded wye, ungrounded wye or delta while the secondary can be anyone one of those not having to match. This creates a three-phase, corner-grounded system, sometimes referred to as an end-grounded system. #4. Being that a GF would. Open delta provides 57% (iirc) of the power that straight delta does with the same size transformers. Other 2 phases = line voltage. Leave EM1 connected. 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. NEC section 250. 8]. Figure 2. . 2778 posts · Joined 2014. However, some utilities still provide this system, and many old installations still exist. The inverters may not like the elevated voltages to ground. 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. A corner grounded delta power system is a configuration where one of the phases (typically B phase) is solidly grounded. The grounding resistance required can be determined from these values of current and voltage. 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. The frst ground fault makes the ungrounded Delta into a Corner Grounded Delta, so the plant continues to run. The transformer has multiple taps . Grounding center of one side (high leg 240/480 delta) might still be too high a voltage. 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. Installations with this system require a 480-120V transformer to supply 120V lighting. You will measure 480 volts from either A phase or C phase to ground, B phase to ground will measure 0 volts. Save. 73) - Upon ground fault, the faulted phase L-G reading is zero and the other two. 2. Welcome to /r/Electricians In solidarity with 3rd party developers…Only for use with 480V Wye systems. 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. It is implemented by grounding any one of the three phases of the transformer secondary (corners of the delta). Select one: a. Other standard delta is one with mid point of one phase grounded - this leaves you with a high leg to ground on the opposite corner of the grounded point. It is both, ground and hot. Jul 26, 2017. Corner-Grounded Delta System. -John. 5. PowerPacT B-Frame Let-Through Energy Curve. 9A. Figure 11. 480V. A ground fault in a floating delta circuit is a foreseeable event, no surprise, and ought to be protected against. Not open for further replies. Pretty curious though. optional based on the design of the electrical engineer. 44. #1. The only solution i have come up with is pulling the pump, and changing them to 277/480 wye,. This question references Article 240. the panel has two bus bars and grounded bar. 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. Circuit Breakers for Grounded B-Phase (BØ) (Corner-Grounded Delta) Systems. The NEC® addresses slash voltage ratings for circuit breakers in 240. A 120 V, 3-phase, 3-wire delta requires the grounding of one of the corners to comply with NEC 250. 73 =830v; I don’t think it’s a wye system, could just be an oddball system. This question references Article 240. False. 67, or 57. 2, the transformation ratio is 4160 divided by 120, or 34. Customer had lost some lights. This is a delta - delta transformer. Best be taking some voltage readings and confirming what you have before making too many plans I would think. A two-pole circuit breaker applied on a 3-phase, corner-grounded delta system must be marked 1Φ-3Φ. 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. 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. The correct solution is to use a 208 Delta X 480Y xformer. Corner-grounded delta system. If you do not ground one of the. Our instructor made a point to warn of corner grounded Delta transformers, since you get your "phase-to-phase" voltage present "phase-to-ground". We have a 480 only corner grounded delta service. Corner grounded delta systems are very common here, we have them with 220V and 440V, but 440V is rather seldom. Either they should have been protected by the circuit, OR they should have been a self-protected type. 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. "C" phase is solidly bonded to ground. 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. This is a 277/480 volt system. 2) ABB does not guarantee the EMC category or the operation of the ground leakage detector. Not open for further replies. #20. The corner grounded delta (CGD) is one of the earliest forms of grounded systems in electrical installations. When you open the secondary side of the 500kva transformers the center phase has a 500mcm bare. "A" or "B" phase short and the the OCP operates. 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. 73=796. Just speculation: Probably not really a neutral, but they likely had one leg of the delta winding grounded (corner grounded delta) because if not, they would have needed to add ground fault monitoring to that circuit, and at 4160V, that would have been expensive. 277V. This demonstration video shares the wiring, voltage and history of a corner grounded delta bank. Although delta. There are circuits where grounding is prohibited. Wye-wyes are extremely rare in <600V systems. Circuit Breakers for Grounded B-Phase (BØ) (Corner-Grounded Delta) Systems. #1. T. You are correct in that a corner grounded delta would have 240V L-L x3, the corner would have 0V to ground. 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. You are now operating on a corner grounded delta unintentionally. 120 V, single-phase, 2 W, solidly grounded II. Otherwise the delta would be corner grounded (grounded 'B' phase). NEMA Type 7/9 SCCR 10 kAIR 600 Vac maximum. 160, 668. 240V. When electrical systems or equipment are grounded, the ground (earth) is part of the electrical circuit. The VFD's and motors we had installed didn't seem to mind. What is the minimum size required for a copper grounded conductor of three phase, three wire, corner grounding delta system if the ungrounded phase conductors are sized at 500 kcmil copper 500 kcmil Delta-connected systems can be solidly grounded using a few methods. Informational Note: An example of a system permitted to be grounded is a corner-grounded delta transformer connection. Corner Ground Delta. Question, when connecting a Wye generator to the Corner Grounded Delta, will. to ground on a 480 volt corner grounded delta system. The delta system is grounded through parasitic capacitance from each phase to ground. 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?. A phase is connected to each corner of the delta. This is a violation of Section 240. When you open the secondary side of the 500kva transformers the center phase has a. I came across a code a while back about NEC not allowing circuits to. The minimum size of the grounded service-entrance conductor is a. Corner grounded delta. 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). Abstract Many factors must be considered when designing the electrical system for critical facilities, especially the type of ground system used. (3) If the voltage rating of the SPD is less than the maximum continuous phase-to-ground voltage available at the point of connection. Corner-grounded delta. In Figure 4 below, we model an ungrounded (capacitively grounded) delta-connected power system connected through a single-phase fault to ground using a. 13. 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 is also a. 20, Informational Note. For nominal 480 volts that high leg voltage is about 416 volts to ground, still 480 between all corners. Fig. The corner-grounded Delta system has an obvious economy in wiring costs, and the grounded phase can be used to physically protect the other two phases from accidental grounding. Its a separately derived system. NEC 240. Exactly what one would use for 13. The delta system can also be grounded, as shown in Figure 2 below. There are certain restrictions when using a VFD on a corner grounded delta power system. If you built the system using say a corner grounded delta (say B phase grounded) then you would see high current from A to B and from C to B but I suspect. 480V rated breakers are only available with 3-poles and special labeling. IESNA Type IV typical. 1KV breaker at nearby sub. This Wikipedia article explains TT, IT and TN-S power distribution systems. For NEMA Type 4X Fiberglass Reinforced Polyester switches, see Fiberglass Reinforced Polyester Enclosures—NEMA 4X. Good points. What is the minimum size required for a copper grounded conductor of three phase, three wire, corner grounding delta system if the ungrounded. Apr 28, 2020. 4. L. NEC 430. , In addition to the grounding. Phase ab 240v, ac 240v, bc 240v, a to ground 120v, b to ground 0v, c to ground 120v. Wye connections, ungrounded delta connections, and corner-grounded delta (“ghost”) leg configuration connections are all examples of three-phase supply. & below. Corner-Grounded Delta (Grounded B Phase) Systems 2700DB0202R2/09 Data Bulletin 02/2009. Perhaps some. Equivalently what happens when the corner of the delta is grounded is that the voltage at each phase is offset by the same AC voltage (i. 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. Whichever you want to call it. A review is given of 480 V corner-grounded delta service for oil fields. My attached schematic is a center tapped phase (this creates a neutral point in secondary side of bank that can be tied to ground). e. The generator cannot be configured to the 480 delta per manufacturer. 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). C orner-grounded delta grids are not supported at these voltages. 3 phase 480 corner grounded delta. It is also known as red leg connection or wild leg connection or orange leg connection. B phase to ground you have 0V. These are obsolete methods but can still be found, mostly in older industrial areas. The secondary in this building is a 480V Corner Grounded Delta or Grounded "B" Phase Delta, whatever it is called. One method of grounding a three-phase, three-wire, delta-connected system is to ground one of the phase conductors. But guess what, any line to ground fault will be 480v. g. Also explains your 480v to ground readings. We didn't add a transfer switch however; but there were existing generators and transfer switches present that were much newer than the existing electrical service. Scanning through 250. This panel runs a 20 ton air handler. The grounded conductor is treated like a neutral in 120 V and 240 V single-phase systems. IESNA. 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 ). 4kV service right into the customers plant, where the customer has a transformer (in our company it's a 600kVA delta-delta) to decrease the voltage. NEC 430. 12). LHL361005861). This is a system where one of the phase conductors of the 3-phase delta. 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). The B phase to ground voltage should be 1/2 of the line voltage. #5. rcarroll said: '08 nec 408. g. Measured voltage on tenant panel 480 A-B, A-C, B-C. About us. See data bulletin 2700DB0202. 67A; secondary current will be 1. I hooked up 240v 3 phase motor to make sure and. The others will be your expected phase to phase voltage to eachother and ground. 240 V, 3-phase, 3 W, ungrounded or corner grounded delta V. #4 · Oct 2, 2020. There is no grounding of any kind on the panel boards, transformers or disconnects. 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). You can calculate the phase current of a delta transformer winding by dividing the phase VA by the phase volts: I Phase = VA Phase ÷E Phase. If all are zero to gnd, then probably a floating delta. “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. Aside from serving the step-down transformer, the 480V side is mostly going unused. 480v, corner-grounded delta. not smaller than the size of the grounding electrode. Running the 480 as ungrounded presents a whole other set of issues.