True. One line conductor is grounded (conventionally it is BØ). 362K subscribers in the electricians community. If you have a 3-phase motor on a center-tap system, the grounded conductor does not come into the picture at all. g. 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. This question references Article 240. 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). 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). I think it also allows you to use single phase panel boards also. Some have argued that, because Rule 097B2 does not specifically mention the multi-grounded phase of a corner-grounded delta circuit, the multi-grounded phase cannot be A corner-grounded Delta system is a system in which the transformer secondary is grounded and one corner of the delta is solidly grounded. Installations with this system require a 480-120V transformer to supply 120V lighting. These are obsolete methods but can still be found, mostly in older industrial areas. Grounded Systems Ltd. But, what I could do is put an auto-transformer between center of one side and the opposite corner. So all of the breakers you. 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. When solving for phase current, don’t forget to divide the overall transformer kVA rating by 3. Rick It is both, ground and hot. Is this a corner grounded delta secondary as. 20, Informational Note. If such systems are grounded, they shall comply with the applicable provisions of this article. Corner-Grounded Delta System. Corner grounded Delta transformer systems are known to confuse people. (2) In ungrounded systems, impedance grounded systems, or corner-grounded delta systems unless listed specifically for use on these systems. Aquavar CPC For R4 or N4 frame size, remove EM3. move into 2008, as NEC-2005 requires Combination AF-. 12. 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. Corner Grounded Delta Solidly (effectively) grounded (LRG) Solidly (or effectively) grounded systems connect (bond) the system neutral directly to earth ground. This is coming from the corner grounded delta that is feeding the buss. Delta-connected systems can be solidly grounded using a few methods. Jul 4, 2023. The 277 volt is interesting but, not relevant. Section 250. Only for use with 480V Wye systems. Use of a slash rated breaker on a corner grounded delta is not ruled out by it not being solidly grounded but by the voltage to ground on the two ungrounded wires being greater than the second number in the rating. IN reference to. [/QU Corner Grounded. On a 240V 3 phase grounded delta system, the voltage to ground is 240V from 2 of the poles. 277V lighting is designed for a grounded system where the connection is to a hot and a neutral. Remote Operation (MN/MX Voltage Release) Let-Through Curves and Trip Curves. Corner Grounded Delta. Its incoming utility service is 480V, corner-grounded delta. 5. J. My question is on the secondary side I need to take a bonding conductor from any of the three phase to ground to created a corner grounded delta, I know I've done a set up like this in the past but grounding a phase always makes me. Thread starter thebigmt; Start date Nov 24, 2010; Status Not open for further replies. 3–Phase Corner-Grounded Delta System using 2-Pole Circuit Breakers. Running the 480 as ungrounded presents a whole other set of issues. That would be a fairly simple fix in the panel, assuming that the panel is. Corner-grounded delta. Another disadvantage, as given on page 33 of IEEE. A corner grounded delta power system is a configuration where one of the phases (typically B phase) is solidly grounded. Besoeker3 Senior Member. Go. Another variation is a "corner grounded" delta system, which is a closed delta that is. 3. Jun 21, 2023. By doing so, we are creating a split phase supply as well as a three-phase delta connected supply. B phase is bonded to ground at the transformer lugs, not in the switchgear. NEC expert Mike Holt explains how to properly ground a corner grounded delta system and the special characteristics of these rare systems. High leg delta has the mid point of one side. We have an old system in our plant that is the grounded B phase or the corner grounded delta. 2. Also be aware that your gear will have to be listed for use with corner grounded delta and some loads are not acceptable for use on a corner grounded supply. The current flowing in each circuit conductor to the load is ___ amps. The service is a corner grounded 240V delta. SPD requirements. "A" or "B" phase short and the the OCP operates. ® (UL®) Listed products for this application. There are circuits where grounding is prohibited. 120V. 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. 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. If corner grounded delta system, use outer switching poles for ungrounded conductors. 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. Introduction Corner-grounded delta systems are not re commended for new installations. 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. In a delta configuration, the three windings are connected end-to-end to form a closed path. This center tap is grounded to produce voltages of 120V, 208V, 120V. But read 480 A to N, 0 B to N, 480 C to N. I'm not familiar to this at all. I guess what I'm saying is that Delta seems never to be a good option. zbang Senior Member. Measuring current of the grounded conductor at load side of the meter socket gave. EPD circuit breakers may not be used in systems with phase to ground voltages other than 277 Vac. The generator cannot be configured to the 480 delta per manufacturer. The B phase to ground voltage should be 1/2 of the line voltage. It is a 240v CGD. Sep 4, 2019. NEC 430. Aside from the corner-grounding of the delta, this is a fairly common configuration for transmission substation transformer in the US. But guess what, any line to ground fault will be 480v. For use on 240 V systems, circuit breakers may be ordered as 480 V. 1. They based it on current measurements they took at the pole after checking and cleaning all connections. I have multiple 240v single phase loads and (1) 240v 3 phase load. I wasn't sure what issues it might cause having one of the phases to ground be 0 volts. 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. 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. 0 pf - 480/208. 6. Northern Virginia. Interrupting Rating. 1. NEC expert Mike Holt explains how to properly ground a corner grounded delta system and the special characteristics of these rare systems. The earth. K. grounded, corner grounded delta and ungrounded delta. You can determine if you have a corner grounded delta service by. 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. . Evans said: Yes, 3 phase/3 wire is used sometimes. Location. Such a system changes to a corner. Commercial buildings require 3P4W and ground. Unless you ground one of the legs, the reading will be zero on all legs to ground. On the utility side, the transformer can either be. My attached schematic is a center tapped phase (this creates a neutral point in secondary side of bank that can be tied to ground). 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. kclark8799 Member. The motors operate at a nominal supply voltage of 220 volts, 3 phase. Figure 11. Electric circuit : open & short circuits instrumentation toolsTransformer phase wiring 480v 208v diagram 480 delta wye 15kva vac Diagram of delta connectionThree phase transformer connections. rcarroll said: '08 nec 408. A 480v delta with a coil center taped for a grounded conductor (neutral) would be considered a 277/480 high leg. You must also bond the phase to the case with a jumper sized to 250. Corner grounded Delta (One phase conductor is connected to the grounding electrode system. Remember, voltage is a difference in potential. Lexington KY. When you open the secondary side of the 500kva transformers the center phase has a. e. 26(4) for conductor to be grounded. 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. The others will be your expected phase to phase voltage to eachother and ground. For use on 480 V systems, LH type circuit breakers must be ordered as 600 V versions and with a 5861 suffiix (i. Finally, an equipment grounding conductor is added as. There is no 120 or 277 volt lead, you will need to. 61 (A) Exception has a requirement for a 140% factor for calculating the neutral load from the unbalanced load on a 2-phase feeder. Just because your house has 240 single phase doesn't mean there isn't any 240 3 phase systems. There is no way of grounding a 480V system (or any over 260V L-L) to meet the 150V L-G standard. The leg that reads zero to ground is the grounded leg. See 250. And, without proper identification of the. 3-phase corner-grounded delta or single-phase circuits (NEC 240. For use on 480 V systems, LH type circuit breakers must be ordered as 600 V versions and with a 5861 suffiix (i. 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. Be careful when installing slash-rated breakers on a solidly grounded high-leg delta system. No neutral from POCO bank to service. If one phase is zero volts to ground, you probably have a corner grounded delta. One-line diagram symbol for a system- or equipment grounding connection _____ m. b. They have 3 phase delta 480. ATSman ATSman. Yeah a 3 pole on a corner ground delta system feeding 3ph equip. So when the disconnects are open, the B phase is no longer. 8kv/480V Y transformer. corner grounded delta systems, considers the circuit breakers’ individual pole interrupting capability. 408. Location NW Florida Occupation Electrical Jul 20, 2023 #8 Phase to neutral are 124, 214, 124. 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. (3) If the voltage rating of the SPD is less than the maximum continuous phase-to-ground voltage available at the point of connection. looking for advice on working on a 3 ph, 3 wire 480 delta that i believe fits the definition of a corner grounded delta. A ground fault in a floating delta circuit is a foreseeable event, no surprise, and ought to be protected against. A diagram of such a system is shown at __ in figure 304. 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. 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). 67A; secondary current will be 1. In a 240-volt corner-grounded delta, what is the voltage between C phase and ground? 0 volts. A corner grounded delta is not ungrounded. I hooked up 240v 3 phase motor to make sure and. #4 · Oct 2, 2020. Proper grounding reduces overvoltages, improves uptime, and isolates faults. A straight rated CB (such as 480V) can be applied on systems that have no more than 480V between any two conductors. L-G phase readings are L-L V. 430. Image used courtesy of Lorenzo Mari . I also have an older model Eurotherm VFD but I have not tested it. on corner grounded delta when using Class J or R fuses. one pole. Select one: a. 36 Overcurrent Protection > (C) Delta Breakers. • 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. I know each leg has 240v to another phase or to ground except for the "B" phase so its not like the. Its hard to visualize attaching 1 of 3 energized lines to ground. Small residential is normally single phase 2 wire or single phase 3 wire. 22 does not apply to the B phase of a center tapped 120/240 volt delta system. Mr. 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. ¿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. One method of grounding a three-phase, three-wire, delta-connected system is to ground one of the phase conductors. L. 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). 120/240 V, single-phase, 3 W, solidly grounded III. The purpose of grounding d. A corner-grounded delta transformer connection is an example of a system permitted to be grounded. LHL361005861). Not available in E04 or F04. The NEC® addresses slash voltage ratings for circuit breakers in 240. Installations with this system require a 480-120V transformer to supply 120V lighting. Retired Electrical Engineer - Power Systems. 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. The maximum continuous operating voltage is measured from phase to ground for solidly grounded systems. Schneider Electric has tested equipment for use on corner-grounded delta systems to provide Underwriters Laboratories Inc. C phase to ground you have 480V. 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. Perhaps it should be extended to cover the grounded conductor of a corner grounded delta with a 170% factor. 3 pole breakers may be used for 3 phase loads with grounded phase connected through a breaker pole. 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. 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. thebigmt Member. Another disadvantage, as given on page 33 of IEEE. 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. Does service entrance equipment still have to have neutral bus in this case? Steve. 480V. Could be the outlet is miswired or mis-breakered and has two of one line and one of a second. 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. A wye winding, with the wye point left unconnected, since there is nothing to connect it to. We have a industrial setting with a corner grounded delta system. For nominal 480 volts that high leg voltage is about 416 volts to ground, still 480 between all corners. You may have not intended it that way, but a 3 phase/3-wire service by definition would not have a neutral. 8]. (UL®) listed products for this application. 73=796. 10, and 680. Its corner ground Delta 3 phase , 208 V , 30 horsepower. 85 of the 2002 NEC was changed to read: 240. Yes, that is my understanding too. This is a violation of Section 240. It's 830 wye. The correct application is 480 V or 600 V straight voltage ratings. 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). 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. A corner grounded delta system will put more stress on the insulation between windings and ground. #2 · May 30, 2022 (Edited) If the system is to be a 208 or 480 grounded B and you have only 120 or 277 transformers, the corner grounded Y will work. 9A. So on A phase to ground you have straight 480V. The only loads are the pumps and a smaller transformer running heat and air, control and a light. rbulsara (Electrical) 16 Jun 05 20:28. That would imply using equipment that is wired the same way as center-tapped 1-phase. APPLICATION ON GROUNDED . An open Delta is (almost) always a high-leg added to a typical 120/240v 1ph to supply a smaller 3ph load. - All phase L-L voltages are normal and the same. ppsh41pro • 10 mo. Basic cheap plug-in breakers are “slash” rated, meaning 240/120V; they are rated 240V phase to phase, but 120V phase to ground. Grounded B-Phase Systems (Corner-Grounded Delta) PowerPacT B Electrical Accessory Wiring Diagrams. NEC 240. I recall the EE missed it, I didn't realize it (or. rbulsara (Electrical) 16 Jun 05 20:28. You will measure 480 volts from either A phase or C phase to ground, B phase to ground will measure 0 volts. They do have a +/-10% tolerance however. We would like to show you a description here but the site won’t allow us. I'm not familiar to this at all. Indication Contacts. Such a ground fault converts the HRG system to a sort of solidly grounded system (depending upon how solid the fault is) and you would want to reliably detect it. Corner Grounded Delta Solidly (effectively) grounded (LRG) Solidly (or effectively) grounded systems connect (bond) the system neutral directly to earth ground. A corner-grounded or an un-grounded. PowerPacT B-Frame Peak Let-Through Current Curve. We are doing this to avoid required ground fault protection in the breakers. Order Pendant Mount Stem accessory 5. The primary goal for a solidly grounded system is to open the circuit as quickly as possible to limit damage and risk to life. Almost as if the utility decided to run an EGC for giggles. This section requires a surge arrester connected to each. 85 permits one pole of a motor controller to be placed in a permanently grounded conductor provided the controller is designed for all conductors. 3, July 2022 -Corner-grounded delta grids not supported at voltages of 400V / 480V. primary. By "fail", it would have to mean a GROUND FAULT. NEC section 250. About Quizlet; How. –See Figure 4. Solidly (effectively) grounded (LRG) Solidly (or effectively) grounded systems connect (bond) the system neutral directly to earth ground. Delta grounded 240vSchematic diagram of (a) grounded and (b) ungrounded pv systems Grounded b phase wiring diagramPhase wire delta single grounded 480v transformer corner 480 ground system volt three 208 volts leg efficent than service open. 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. Leave EM1 connected. We're working in an old mine machine factory, recently converted to a gear shop. This feature, however, applies to ground faults, not short-circuit or line-to-line faults. Nov 24, 2010 #1. You are correct in that a corner grounded delta would have 240V L-L x3, the corner would have 0V to ground. System also requires a. This configuration goes by several names including grounded. PowerPacT B-Frame Peak Let-Through Current Curve. That corner grounded delta system still needs equipment grounding conductors run beyond the service disconnecting means, you do not bond any equipment to the current carrying B phase at equipment you run separate EGC like you do for other voltage systems. Abstract Many factors must be considered when designing the electrical system for critical facilities, especially the type of ground system used. CMP said: Sounds like you have an ungrounded delta system, and your getting a capacitive voltage reading to your ghost ground. roberius Member. ® (UL®) Listed products for this application. Other systems shall be permit‐ ted to be grounded. Circuit breakers marked “1-phase – 3-phase” or “10I – 30I “are suitable for use on are removed. There are certain restrictions when using a VFD on a corner grounded delta power system. Equipment ground bonds to disconnect and grounded phase connects to unfused pole. NEC 430. 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. A phase is connected to each corner of the delta. Trying to determine if I have a ground fault somewhere or a bad leg or breaker. Location: In the bothy, 7 chains down the line from Dodman's Lane level crossing, in the nation formerly known as Great Britain. Perhaps it should be extended to cover the grounded conductor of a corner grounded delta with a 170% factor. I had NEVER heard of corner grounded delta, so my head was full of confusion when line to line, and line to ground were equal. Other types of three-phase supplies are wye connections, ungrounded delta connections, or corner-grounded delta ("ghost" leg configuration) connections. High leg delta has one winding center tapped. Phase ab 240v, ac 240v, bc 240v, a to ground 120v, b to ground 0v, c to ground 120v. three-phase, 3-wire, corner-grounded delta system? 120V 240V 277V 480V Correct Answer: 480V. Neutral Conductor. The inverters may not like the elevated voltages to ground. 4. 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?. corner grounded delta systems, considers the circuit breakers’ individual pole interrupting capability. 2 requires a grounded conductor in all premises wiring. #1 · Feb 28, 2020. not smaller than the required grounding electrodeCorner grounded Delta. Me and a contractor were working on a pump station trying to get old fire pumps running that probably haven't run in 20 years. A ground fault in a floating delta circuit is a foreseeable event, no surprise, and ought to be protected against. 24(D)(4) This section covers impedance grounded services. not smaller than the size of the grounding electrode. #2 · Aug 15, 2015. What is the minimum size required for a copper grounded conductor of three phase, three wire, corner grounding delta system if the ungrounded. We have a 480 only corner grounded delta service. 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. BRB for 120/240, 120/208, 120 delta corner grounded (rare but have seen it), or 240 delta corner grounded, with grounded white or marked white, whether it be grounded corner phase, center tap ,or wye. 20. Schneider Electric has tested equipment for use on corner-grounded delta systems to provide Underwriters Laboratories Inc. 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. When connected to the no. 2) Adding a grounding autotransformer. Our PoCo will not supply it, but many factories install it currently. Assuming you adjusted the taps at 2. larz_6446 • 2 yr. Is this the same thing as a Corner Grounded system?Corner grounded delta was very popular. Frame size EMC filter (+E200) screw Ground-to-phase varistor screw R10, R11 EMC AC VAR Drive. Grounded Systems Ltd Company Profile | Victoria, BC, Canada | Competitors, Financials & Contacts - Dun & BradstreetHotel Pulitzer, Amsterdam; L’Hermitage Vancouver, BC; Four Season Nevis, BVI; Rosewood Miramar Montecito, CA; Residences at Little Nell Aspen, CO; St Regis Bal. No neutral comming in. On the secondary the voltage would be, if. "A" or "B" phase short and the the OCP operates. 36 (C) Equipment for General Use, Delta Breakers. Not sure if it is B or C phase that is corner grounded. 5 . Location Roughly 5346 miles from Earls Court. Aside from serving the step-down transformer, the 480V side is mostly going unused. Licensed Electrical Engineer, Licensed Electrical Contractor, Certified Master Electrician. Number Required. In most cases, the delta is "buried" with no leads. Usually different on each phase. In einem Delta – System werden alle angeschlossenen Komponenten direkt geerdet. Location. Another disadvantage, as given on page 33 of IEEE Std 142. The equipment itself may generate an undesirable amount of capacitive current to the shell of the bed if it is powered by either. A grounded wye system. Corner-grounded delta: One line conductor is grounded directly. Corner grounded delta (CGD) As the disadvantages of ungrounded systems became better known, simple, low-cost method of establishing a ground reference on an. The "wild leg" has a different voltage to ground, which can. Spend $75 to keep yourself safe. Thread starter domnic; Start date Nov 19, 2020; Status Not open for further replies. 2. You will read 480v from l1 and l2 to ground, 0 v on the neutral leg to ground. At the MV level corner grounded delta is exceptionally rare. I am in north Texas, where usually when I see a corner-grounded delta, it is really a pretty old ungrounded delta that has a ground fault or multiple faults on the same leg. Directions Advertisement. In this video, NEC expert Mike Holt explains how to properly ground a corner grounded delta system and the special characteristics of these rare systems…A delta secondary may be corner grounded, but that conductor, though grounded, is not a ``neutral``. 85 Applications. Also, you can save. The correct solution is to use a 208 Delta X 480Y xformer. For use on. . Introduction Grounded systems offer many benefits over ungrounded systems [1][2][3]. ago. 22, 2005 nec. A phase 490-ground B phase 490-ground C phase 0. Sparkle. A two-pole circuit breaker applied on a 3-phase, corner-grounded delta system must be marked 1Φ-3Φ. 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. No magic and no mysteries. Some devices will have multiple interrupting ratings, such as 14,000 amperes at 600 volts and 25,000 amperes at 480 volts. Slash marked circuit breakers such as 120/240V or 277/480V must not be used. I hooked up 240v 3 phase motor to make sure and. If all are zero to gnd, then probably a floating delta. Compared with the solidly-grounded wye system of Figure 1 this system grounding arrangement has a number of disadvantages. Abstract Many factors must be considered when designing the electrical system for critical facilities, especially the type of ground system used. I recently had and issue with a 240v three phase Delta system while on the job. 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.