The purpose of a corner ground is equipment and personnel protection. Corner Grounded Delta Transformer Bank. We have addressed neutral loads using individual 480V x 480/277V. J. 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. Whichever you want to call it. A. , What is the minimum-size aluminum or copper-clad aluminum. But guess what, any line to ground fault will be 480v. Question I have is I believe I need to utilize a corner grounded delta on the 480v side, otherwise the system is not grounded. Typically in my area BOY is used for any 480 volt power and if a grounded conductor involved, it is grey or marked grey. Use QO-H circuit breakers only. 8 pf - 480/208 3 ph, 190 kVA 1. They do have a +/-10% tolerance however. 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. Is this the same thing as a Corner Grounded system?Corner grounded delta was very popular. For use on. The manufacturing plant that I worked for always bonded the X0 of a 480v delta -208y/120 to the frame but as I understand it not all manufactures do this I picked up upon when using one as a step up transformer. While testing a condensing units 3 pole breaker for voltage I found 235v A phase to B phase and 0v C phase. might occur when Phase A goes to ground on a 480V, B-phase, corner grounded delta system. When you look up Conductors, then Grounded you will find the first reference given is Alternating current systems, 250. A corner grounded power system is a system that is fed from a delta transformer winding with one phase grounded. 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 to indicate such suitability. Remote Operation (MN/MX Voltage Release) Let-Through Curves and Trip Curves. 3 pole breakers may also be used for single phase loads which will be connected through the outside poles. Aside from the corner-grounding of the delta, this is a fairly common configuration for transmission substation transformer in the US. Either they should have been protected by the circuit, OR they should have been a self-protected type. False. D. 240. Introduction Corner-grounded delta systems are not re commended for new installations. Home. ¿Busca un manual de instalación rápida para el convertidor de frecuencia ACH580-01 de ABB? Descargue este documento en formato PDF y siga las instrucciones paso a paso para configurar el dispositivo y conectarlo a su sistema HVAC. Corner grounded delta systems produce crazy voltages, and crazy ground faults. corner grounded Delta system. the panel has two bus bars and grounded bar. ain't going to end well. -John. 208, 240 and 480 are all common 3 phase systems. 3 (f) This is applicable, only if it is a center tapped delta, 240/120 3P 4W. i agree. If you choose the high leg delta, you'll need to pull a grounded conductor anyway. There is no 120 or 277 volt lead, you will need to. Frame size EMC filter (+E200) screw Ground-to-phase varistor screw R10, R11 EMC AC VAR Drive. If the phase that is grounded shorts to the equipment frame there. Figure 11. a Split Phase circuit with 120V from each respective leg to Neutral (residential power tap - grin). A building needs to be taken off it's primary feed, so we can service it's 4. zbang Senior Member. 5869 posts · Joined 2009. Ungrounded Delta: - No phase is intentioally grounded. 1. 90 posts · Joined 2007. Along with the 'slash rating', Corner Grounded (grounded B phase) systems can impact the AIC ratings of breakers. "C" phase is solidly bonded to ground. Not open for further replies. I would normally only use a solid corner ground on a. 85 permits one pole of a motor controller to be placed in a permanently grounded conductor provided the controller is designed for all conductors. test Learn with flashcards, games, and more — for free. Other 2 phases = line voltage. It has (in this instance) 480v relative to the two other phases, and is 1/3 of the 3 phase circuit. 3–Phase Corner-Grounded Delta System using 2-Pole Circuit Breakers. If that isn't possible, then the drive should be labeled as unsuitable for the floating delta and/or corner grounded delta. 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. No. . The grounded conductor of a corner grounded delta system is covered by the rules in Article 200, just like any other grounded conductor. This type of grounded system is 3-phase, delta-connected and is called a corner-grounded system, because one corner of the delta is grounded (figure 1). One method of grounding a three-phase, three-wire, delta-connected system is to ground one of the phase conductors. IESNA Type III typical. This is a diagram of a normal (North American Standard), delta primary, wye secondary, transformer. Grounded Systems Ltd. At the MV level corner grounded delta is exceptionally rare. not smaller than the required grounding electrode Corner grounded Delta. Louis. We have a 480 only corner grounded delta service. L-G phase readings are L-L V. 61 (A) Exception has a requirement for a 140% factor for calculating the neutral load from the unbalanced load on a 2-phase feeder. The minimum size of the grounded service-entrance conductor is a. Joined Jan 25, 2011. Ground Fault Circuit InterruptersUL Listed 5000 A short circuit current rating for corner grounded Delta systems. (2) In ungrounded systems, impedance grounded systems, or corner-grounded delta systems unless listed specifically for use on these systems. This system exists to keep voltages stable, limit or reduce surges, and/or be. SPDs must be listed [Sec. One method of grounding a three-phase, three-wire, delta-connected system is to ground one of the phase conductors. 240 V, 3-phase, 3 W, ungrounded or corner grounded delta V. These connections do. 61, 517. 12. Small residential is normally single phase 2 wire or single phase 3 wire. Safety Switches Table 4 lists two-pole safety switches that are UL Listed for use on 240 and 480 Vac grounded B phase systems. Now if your delta distribution system is corner grounded or ungrounded with an unrepaired ground fault you will have serious problems. Pretty curious though. We use our trainer model made by Three Phase Innovations to. The ratings on the gen set are for 1 ph, 190 kVA - 240V 3 ph, 237 kVA 0. 102(C)(1). The delta system is grounded through parasitic capacitance from each phase to ground. You can determine if you have a corner grounded delta service by. On the secondary the voltage would be, if. Unless its to. For services they used to hook the 600 volt and under seondaries anyway you wanted. 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. Sparkle. Version 1. Remote Operation (MN/MX Voltage Release) Let-Through Curves and Trip Curves. Installations with this system require a 480-120V transformer to supply 120V lighting. 2. Other types of three-phase supplies are wye connections, ungrounded delta connections, or corner-grounded delta ("ghost" leg configuration) connections. Corner grounded delta bank is three wire, grounded delta. Doing this is technically challenging and expensive, however, the corner-grounded system offers. thebigmt Member. For use on 240 V systems, circuit breakers may be ordered as 480 V. . Corner-Grounded Delta (Grounded B Phase) Systems 2700DB0202R2/09 Data Bulletin 02/2009. system in which the transformer secondary is delta-connected with one corner of the delta solidly grounded. kclark8799 Member. 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. Listed means one follow the instructions. Another disadvantage, as given on page 33 of IEEE. 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. If you choose the high leg delta, you'll need to pull a grounded conductor anyway. Licensed Electrical Engineer, Licensed Electrical Contractor, Certified Master Electrician. MRG, Article 200. 3 hots and a neutral wire. 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. High leg delta has the mid point of one side. Introduction Corner-grounded delta systems are not re commended for new installations. 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. 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. See 250. For nominal 480 volts that high leg voltage is about 416. Jul 4, 2023. For use on 480 V systems, LH type circuit breakers must be ordered as 600 V versions and with a 5861 suffiix (i. Corner-Grounded Delta Circuits. Good points. ® (UL®) Listed products for this application. might occur when Phase A goes to ground on a 480V, B-phase, corner grounded delta system. 480V. Remember, voltage is a difference in potential. J. 362K subscribers in the electricians community. My attached schematic is a center tapped phase (this creates a neutral point in secondary side of bank that can be tied to ground). • 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. 85 Applications. hello. I believe that you are not supposed to connect any single phase loads between the high leg and the neutral. 85 covers the requirements for straight rated and slash rated CBs. Only for use with 480V Wye systems. The grounded phase is a "grounded conductor" that carries current. Not available in E04 or F04. Eaton Corporation literature states “for all 3 phase delta grounded B phase applications, refer to Eaton Corporation. 12). Fig. Trust is hard to come by in St. 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. Agreed, corner grounded delta, but strange that they have two separate conductors for 'grounded phase conductor' and 'neutral conductor'. Just because your house has 240 single phase doesn't mean there isn't any 240 3 phase systems. In most cases a corner grounded delta is a very poor choice of supply as it has a. However, some utilities still provide this system, and many old installations still exist. 220. 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. Systems from Intermittent Ground Faults Introduction Many papers and standards [1][2][3][4][5][6] have discussed grounding of an electrical distribution system. 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. This section requires a surge arrester connected to each. 480 Y/277 V, 3-phase, 4 W, solidly grounded VI. Think about this a little more. The other two phased are at the line voltage above ground. Also note the one can use a slash rated breaker on a corner grounded 240 delta, it just has to be a 480/277 rated breaker. #4. The utility company says it is an un-grounded delta secondary at 480V/3-phase/3-wire system. 36 Overcurrent Protection > (C) Delta Breakers. I hooked up 240v 3 phase motor to make sure and. If such systems are grounded, they shall comply with the applicable provisions of this article. 24 I see 250. He said that it's about 240 volts so 128 volts to ground isn't that far off for a corner grounded Delta. A and C to ground could be 120 (ish), 128. PowerPacT B-Frame 15/20 A. On this latter type, one phase is indeed grounded and is 0 volts to ground. The NEC® addresses slash voltage ratings for circuit breakers in 240. Re: Ground Fault Protection in Corner Grounded Delta System. Can’t do line to neutral loads but phase to phase single or three phase loads are fine. (d) Separately Derived Systems. Corner Ground Delta. In the setup the OP describes, the maximum voltage to ground would be 240, so he must use a straight 240 V breaker. 85). If such systems are grounded, they shall comply with the applicable provisions of this article. Image used courtesy of Lorenzo Mari . Corner Grounded Delta. "C" phase is solidly bonded to ground. Marking on 3 phase matters especially with corner grounded delta as this sets up a wild leg that is required to be marked B leg and identified with orange phase tape the phases are 120 degrees out of phase so it matters how they are connected. Some connections like ungrounded wye grounded wye are not feasible, but something like delta grounded wye or ungrounded wye corner grounded delta is doable and operational. False Nec Ref:240. L-N: 277V L-L: 480V 480V. Corner-Ground: The three corners of the delta arrangement are connected to the line conductors. I figured at the least it would cause a phase loss alarm, but wasn't sure if there. A corner ground is used on a strait 3 phase, 3 wire Delta system, that has no neutral. The grounded phase has no voltage to ground (at the service) and 240 or 480 volts to the other two phases. There is no grounding of any kind on the panel boards, transformers or disconnects. Welcome to /r/Electricians In solidarity with 3rd party developers…Only for use with 480V Wye systems. In Figure 4 below, we model an ungrounded (capacitively grounded) delta-connected power system connected through a single-phase fault to ground using a. 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 . 36 requires where fuses are used for motor overload protection that a fuse be also inserted in the grounded conductor if the supply system is a corner-grounded delta system. What we have is 4160V feeding 4 step down transformers that step it down to 230V Grounded B. Running the 480 as ungrounded presents a whole other set of issues. 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. The motors operate at a nominal supply voltage of 220 volts, 3 phase. 90(B). Running the 480 as ungrounded presents a whole other set of issues. The system has accidentally become a corner-grounded delta system with little, if any, current flow. 85 of the 2002 NEC was changed to read: 240. A circuit breaker with a special “straight” rating of 277/480 volts may be used on a corner-grounded delta system. It does NOT carry current like a neutral, a neutral carries the unbalance of the load. 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. We're working in an old mine machine factory, recently converted to a gear shop. . 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. I guess what I'm saying is that Delta seems never to be a good option. ) A 480/277-volt, 3-pole circuit breaker can be applied on a 480-volt corner-grounded delta. Aquavar CPC For R4 or N4 frame size, remove EM3. e. domnic Senior Member. A 480 Δ — 240-volt 3-wire Δ transformer is delivering power to a 3Ø load and has 75 amps of coil current flowing through each winding. 13. PowerPacT B-Frame Let-Through Energy Curve. 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. not smaller than the size of the grounding electrode. It's a three-winding transformer - grounded wye primary, corner-grounded delta tertiary, grounded wye secondary with neutral grounding resistor. 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. They were very popular on rural farms where the predominant building load was single phase, but the milking parlor. Phase ab 240v, ac 240v, bc 240v, a to ground 120v, b to ground 0v, c to ground 120v. IN reference to. About us. From there a grounded phase conductor and equipment ground go to the disconnect and remain separate. Such a system changes to a corner. 20(A). 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. 61 (A) Exception has a requirement for a 140% factor for calculating the neutral load from the unbalanced load on a 2-phase feeder. 26(4) for conductor to be grounded. Usually different on each phase. Corner grounded Delta transformer systems are known to confuse people. Finally, an equipment grounding conductor is added as. 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. If the phase line was solidly grounded you would be reading 0 volts. Not sure what you mean by “normal”. If you have a 3-phase motor on a center-tap system, the grounded conductor does not come into the picture at all. It then goes on to discuss performing an open corner test to ensure proper polarity when c. JimmySki23 Member. If one phase is zero volts to ground, you probably have a corner grounded delta. Sections 503. 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. 100 % (3 ratings) for this solution. B phase is bonded to ground at the transformer lugs, not in the switchgear. NEC 240. Perhaps it was intended to be connected to a transformer. True False. T. 1KV breaker at nearby sub. The uncommon grounded system is a 3-phase, 3-wire corner-grounded delta system. When you open the secondary side of the 500kva transformers the center phase has a. Also, you can save. Delta with Wild Leg. . Thread starter William Robertson; Start date Jan 21, 2021; Status Not open for further replies. While it is a grounded conductor, the grounded phase of a corner-grounded delta grid is not technically a neutral. 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. 430. Kettle's on. ® (UL®) Listed products for this application. Feb 3, 2009. When electrical systems or equipment are grounded, the ground (earth) is part of the electrical circuit. 480V – 3-Phase, 2-Wire – Corner Grounded – Delta. 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. 240V. On the utility side, the transformer can either be. This can be avoided by simply checking more than one leg, but the plain fact is that the customer doesn't like corner-grounded delta, and doesn't want it used. Corner grounded Delta transformer systems are known to confuse people. Start shipping your package by locating a Purolator drop box, Purolator Shipping Centre, or Purolator Authorized Shipping Agent near you. on corner grounded delta when using Class J or R fuses. 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. A new transformer was set for a motor load to step up to 480 volt. However, some utilities still provide this system, and many old installations still exist. For me, its a textbook corner grounded delta. The purposes are to: limit overvoltages due to lightning, line surges, or accidental contacts with higher-voltage. Circuit Breakers for Grounded B-Phase (BØ) (Corner-Grounded Delta) Systems. See 250. Another variation is a "corner grounded" delta system, which is a closed delta that is. #5. It's 830 wye. 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. 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. The B phase to ground voltage should be 1/2 of the line voltage. 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. 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”. Besoeker3 Senior Member. If a solidly grounded neutral conductor is also being brought to the MCC, the power system is a 4-wire. gap, is maximum. The primary goal for a solidly grounded system is to open the circuit as quickly as possible to limit damage and risk to life. 277V lighting is designed for a grounded system where the connection is to a hot and a neutral. Subsection 250. 2 pole fusible disconnects and 120/240V panels are sometimes rated for 240V three phase. Schneider Electric has tested equipment for use on corner-grounded delta systems to provide Underwriters Laboratories Inc. 5. Since one phase is already grounded this 4th wire is somewhat redundant. I partially agree. D. A phase is connected to each corner of the delta. Could be the outlet is miswired or mis-breakered and has two of one line and one of a second. The delta system can also be grounded, as shown in Figure 2 below. #1 · Feb 28, 2020. Could be red leg delta at the pole but floating and corner grounded delta at the customer's equipment. I was planning on reverse feeding it with 208v, and getting 480v. #4 · Oct 2, 2020. In a 480V, three-phase, 3-wire delta system, the voltage-to-ground is always 480V whether it is ungrounded or corner-grounded. 1 of 2 Go to page. Mr. Corner grounded delta. ” Following areYou are correct in that a corner grounded delta would have 240V L-L x3, the corner would have 0V to ground. 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. 85, which requires a circuit breaker. Most utilities will not longer accept the 3 "ground lights" as a monitoring system, they will insist on an expensive electronic ground monitor. I actually ran into a corner grounded delta myself Friday or at least I think. Three-phase — 4-wire 120/240 volt delta connected system (high-leg). 240V. 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. 2) ABB does not guarantee the EMC category or the operation of the ground leakage detector. But read 480 A to N, 0 B to N, 480 C to N. 'power' panels (e. Its corner ground Delta 3 phase , 208 V , 30 horsepower. The derived neutral connot operate at 0 volts as this would mean there is a short circuit to ground. The center of the Y, which is usually grounded, must not be connected to anything. However, some utilities still provide this system, and many old installations still exist. Its hard to visualize attaching 1 of 3 energized lines to ground. System grounding is the connection to the ground – solidly or through impedance – of current-carrying conductors – e. According to mike holt one random? corner phase is to be grounded and bonded to the case of the transformer. It does NOT carry current like a neutral, a neutral carries the unbalance of the load. “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. No neutral comming in. The only loads are the pumps and a smaller transformer running heat and air, control and a light. For starters the xformer 480 side, if grounded, all the load side gear and equipment must be approved for corner grounding-not likely. Utilities are trying hard to get rid of corner grounded delta systems. Neutral Conductor. 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. Perhaps some. This system can operate either at 480 volts or at 240 volts. 120 V, 3-phase, corner-grounded delta. 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. Ungrounded Delta: - No phase is intentioally grounded. Also don't forget that NEC doesn't apply on the utility side of the interconnection point. By doing so, we are creating a split phase supply as well as a three-phase delta connected supply. Corner grounded Delta (One phase conductor is connected to the grounding electrode system. 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. Corner grounded delta systems are common in old industrial facilities around St. This will impact the selection of circuit breakers in a corner-grounded Delta power system. A corner grounded delta system is a three-phase delta service with one phase having the ground connection. ® (UL®) Listed products for this application. ) Branch-circuit fuses do not have to be marked with their ampere rating. It consists of a maximum current and the voltage at which the device is rated to interrupt the circuit. 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?. 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). Basic cheap plug-in breakers are “slash” rated, meaning 240/120V; they are rated 240V phase to phase, but 120V phase to ground. Select one: True. I will not continue to be served by the corner grounded. #2 · Aug 15, 2015. T. Section 250. It's a three-winding transformer - grounded wye primary, corner-grounded delta tertiary, grounded wye secondary with neutral grounding resistor. Square D carries a 2 pole breaker rated at 240V ( not slash. g. The corner grounded delta (CGD) is one of the earliest forms of grounded systems in electrical installations. This is a violation of Section 240. 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. (3) If the voltage rating of the SPD is less than the maximum continuous phase-to-ground voltage available at the point of connection. No magic and no mysteries. 99 votes, 37 comments. Question, when connecting a Wye generator to the Corner Grounded Delta, will it work without any abnormalities. A corner grounded power system is a system that is fed from a delta transformer winding with one phase grounded. Just be aware: There is a very distant possibility that this electrical service is a corner-grounded delta, which has a grounded phase that cannot be fused by code. If you choose the corner grounded delta, you will lose. waross (Electrical) 6 May 15 10:54. We have an old system in our plant that is the grounded B phase or the corner grounded delta. grounded TN systems (TN-S systems) 1 Corner-grounded and midpoint-grounded delta systems 2 (< 600 V) IT systems (ungrounded or high-resistance-grounded [>30 ohms]) 3 R10, R11 Do not remove EMC AC or VAR. Best be taking some voltage readings and confirming what you have before making too many plans I would think. Because of the disadvantages of not grounding systems, electrical designers had to integrate a ground reference to existing configurations. The VFD's and motors we had installed didn't seem to mind. Could be as jraef mentioned. Informational Note: An example of a system permitted to be grounded is a corner-grounded delta transformer connection. The plant maintenance manager has said, " That delta will go away and I will get wye or I will go away. The conductor connected to the neutral point of a system that is intended to carry current under normal. This panel runs a 20 ton air handler.