Small residential is normally single phase 2 wire or single phase 3 wire. The motor will. 3 pole breakers may also be used for single phase loads which will be connected through the outside poles. This demonstration video shares the wiring, voltage and history of a corner grounded delta bank. 60% of these I run across are done incorrectly. 155, 517. A phase 490-ground B phase 490-ground C phase 0. IESNA. 120/240 V, single-phase, 3 W, solidly grounded III. 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. might occur when Phase A goes to ground on a 480V, B-phase, corner grounded delta system. Never ran into that before. Otherwise the delta would be corner grounded (grounded 'B' phase). Doing this is technically challenging and expensive, however, the corner-grounded system offers. There is no way of grounding a 480V system (or any over 260V L-L) to meet the 150V L-G standard. My proposed fix is: 1). 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. 23(A)(2) show instances. Sounds like you know you have three supply conductors but don't exactly know what they are. Its corner ground Delta 3 phase , 208 V , 30 horsepower. three-phase, 3-wire, corner-grounded delta system? 120V 240V 277V 480V Correct Answer: 480V. 5% each you coould. 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). Introduction Corner-grounded delta systems are not re commended for new installations. This is a violation of Section 240. CryptoDelta has no obvious grounding location; the AC lines are generally all floating relative to earth. to ground on a 480 volt corner grounded delta system. might occur when Phase A goes to ground on a 480V, B-phase, corner grounded delta system. A corner grounded power system is a system that is fed from a delta transformer winding with one phase grounded. So on A phase to ground you have straight 480V. Two of the most significant tests performed on a TVSS are the measured limiting voltage test and a series of abnormal overvoltage. 480V. (Read the same voltage measured to Ground)Corner grounded delta systems have a grounded conductor but it is not a neutral conductor. Re: Ground Fault Protection in Corner Grounded Delta System. Jul 4, 2023. 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). It's a three-winding transformer - grounded wye primary, corner-grounded delta tertiary, grounded wye secondary with neutral grounding resistor. I've seen corner-grounded systems where one phase is tied to earth. 240. Remember, voltage is a difference in potential. Running the 480 as ungrounded presents a whole other set of issues. Corner grounded delta. looking for advice on working on a 3 ph, 3 wire 480 delta that i believe fits the definition of a corner grounded delta. In most cases, the delta is "buried" with no leads. So all of the breakers you. A ground fault in a floating delta circuit is a foreseeable event, no surprise, and ought to be protected against. . 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. This would be a service like an ungrounded delta or a corner-grounded delta. Location UK Occupation Retired Electrical EngineerThe loads don’t know the difference. 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. The only loads are the pumps and a smaller transformer running heat and air, control and a light. It has (in this instance) 480v relative to the two other phases, and is 1/3 of the 3 phase circuit. When I look at the bank on the pole I see 2 primary and 1 primary neutral conductors and 2 transformers. 20(B)(1) and avoid an NEC violation. No neutral from POCO bank to service. IN reference to. 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. 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. 240 V, 3-phase, 3 W, ungrounded or corner grounded delta V. In a 480V, three-phase, 3-wire delta system, the voltage-to-ground is always 480V whether it is ungrounded or corner-grounded. I-Line) often require special breakers for 240V which are built using 3-pole housings. 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. From there a grounded phase conductor and equipment ground go to the disconnect and remain separate. 0 pf - 480/208. Question, when connecting a Wye generator to the Corner Grounded Delta, will it work without any abnormalities. K. Claim this business (250) 884-1942. Business, Economics, and Finance. 796v is what's marked on a motor used on these 830 systems. However, some utilities still provide this system, and many old installations still exist. Delta system. Also explains your 480v to ground readings. The two pole breakers can handle 240V or more to ground, as would be seen in a 416Y/240 system or a 240/480 three wire single phase or a corner grounded 240 delta, but not the 480V to ground seen in a corner grounded delta. An ungrounded (floating) delta should have a ground indicator to alert maintenance personnel because a second ground may be catastrophic. UL Listed for use on 240 V Corner-grounded Delta Systems (Grounded B Phase). 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. Hi, Our company rented an old warehouse and this is the first time I've ever seen corner ground delta (CGD) panel. 3–Phase Corner-Grounded Delta System using 2-Pole Circuit Breakers. 2) ABB does not guarantee the EMC category or the operation of the ground leakage detector. 26(4) for conductor to be grounded. the title of the thread is appropriate because theres only 3 wires marked for each phase and no neutral going into the customers main disconnect switch which powers a 3 phase 480v motor control circuit. zbang Senior Member. corner grounded delta systems, considers the circuit breakers’ individual pole interrupting capability. NEC expert Mike Holt explains how to properly ground a corner grounded delta system and the special characteristics of these rare 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. No magic and no mysteries. micromind · #7 · May 3, 2023. - All phase L-L voltages are normal and the same. Do not remove EMC AC or VAR. PowerPacT B-Frame Let-Through Energy Curve. 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. Only the high leg will produces 120V, single pole power. #1. More. ® (UL®) Listed products for this application. Looking at a 120/208 wye system, the phase voltage would be 120V and the phase-to-phase voltage would be 208V. When electrical systems or equipment are grounded, the ground (earth) is part of the electrical circuit. There is no grounding of any kind on the panel boards, transformers or disconnects. Refer to the Digest, CAD drawings, or device wiring diagram(s. 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). For me, its a textbook corner grounded delta. However, some utilities still provide this system, and many old installations still exist. The grounded conductor of a service is usually a neutral conductor, but it can also be a phase conductor, depending on the type of system supplied. Particularly common if only building open delta, though there is still some existing full delta, but most new systems with three transformers are going to be 480/277 anymore. You must also bond the phase to the case with a jumper sized to 250. Could be the outlet is miswired or mis-breakered and has two of one line and one of a second. Northern Virginia. 85 Applications. Same with "wild leg" center grounded delta, which is also becoming obsolete. Also, with the same KVA and impedance transformers, the available fault. Aside from the corner-grounding of the delta, this is a fairly common configuration for transmission substation transformer in the US. 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. 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). a Split Phase circuit with 120V from each respective leg to Neutral (residential power tap - grin). You have a different problem. 20. This supply system configuration is often used where high power is required, for example for large mo-tors. ”The VFD that I have now is an older model Woods E-trac X2C-40150 and the manual does not say anything about corner grounded delta. 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. The size of the step-down transformer is. See Figure 11. 208, 240 and 480 are all common 3 phase systems. 430. rbulsara (Electrical) 16 Jun 05 20:28. One line conductor is grounded (conventionally it is BØ). 8kv/480V Y transformer. PowerPacT B-Frame Peak Let-Through Current Curve. If all are zero to gnd, then probably a floating delta. 242. A circuit breaker with a special “straight” rating of 277/480 volts may be used on a corner-grounded delta system. Only for use with 480V Wye systems. Indication Contacts. See 250. This question references Article 240. 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. At first we were having trouble getting the motor to start in auto and just out of habit I checked power in. Occasionally you may have an application that is a delta voltage source with a grounded “B” phase, also known as corner grounded. Not available in E04 or F04. A corner grounded delta service can be designed for any desired voltage, but 240 is most common. It is implemented by grounding any one of the three phases of the transformer secondary (corners of the delta). D. So put in a 2 pole and land B on the bus bar and I. A new transformer was set for a motor load to step up to 480 volt. 600 Y/347 V, 3. Sparkle. Corner-grounded delta: One line conductor is grounded directly. The system is a 240v 3phase corner grounded delta system with "B" phase intensionally grounded. When connected to the no. High-leg Delta. B-Grd: 0V (assuming B ph is the grounded phase) C-Grd: 240V. Furthermore, 3-phase, corner-grounded, delta circuits can only use two-pole circuit breakers marked 1ɸ-3ɸ. 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. Apr 28, 2020. Areas of concern converting a corner ground to a wye include: In a properly installed corner grounded system, the corner conductor should be white or gray. Red leg 240 delta four wire was also a standard system and if that was floating (or maybe even grounded at the pole) you would get 120, 120, 183, *or* 0, 240, 240 if A was faulted without being noticed. 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. Besoeker3 Senior Member. Phase ab 240v, ac 240v, bc 240v, a to ground 120v, b to ground 0v, c to ground 120v. When people pass the grounded phase through a disconnect, one of the solutions is to put in a dummy fuse link that would look very similar to this. ¿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. Also don't forget that NEC doesn't apply on the utility side of the interconnection point. –See Figure 4. Section 250. For starters the xformer 480 side, if grounded, all the load side gear and equipment must be approved for corner grounding-not likely. Yeah a 3 pole on a corner ground delta system feeding 3ph equip. 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. Introduction Corner-grounded delta systems are not re commended for new installations. Corner-Grounded Delta System. 85 covers the requirements for straight rated and slash rated CBs. Delta with Wild Leg. 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. 5869 posts · Joined 2009. 480 x 1. Equipment ground bonds to disconnect and grounded phase connects to unfused pole. 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. #1. High leg delta has one winding center tapped. NEMA Type 7/9 SCCR 10 kAIR 600 Vac maximum. Leave EM1 connected. 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. A corner grounded power system is a system that is fed from a delta transformer winding with one phase grounded. 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. [/QU Corner Grounded. AC systems of less than 50 V. This is the problem. One method of grounding a three-phase, three-wire, delta-connected system is to ground one of the phase conductors. 208 Y/120 V, 3-phase, 4 W, solidly grounded IV. It's 830 wye. That would be a fairly simple fix in the panel, assuming that the panel is. So enter the corner grounded delta secondary. Section 242. Another disadvantage, as given on page 33 of IEEE Std 142. For use on. gap, is maximum. This section requires a surge arrester connected to each. b. Nov 30, 2020. Such a system changes to a corner. D1-D4 lumen packages only. This is a delta - delta transformer. 36 (C) Equipment for General Use, Delta Breakers. 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. We did an upgrade at a plant that had a corner grounded delta service. (3) If the voltage rating of the SPD is less than the maximum continuous phase-to-ground voltage available at the point of connection. Measuring current of the grounded conductor at load side of the meter socket gave. 250. The correct solution is to use a 208 Delta X 480Y xformer. Interrupting Rating. move into 2008, as NEC-2005 requires Combination AF-. corner grounded delta systems, considers the circuit breakers’ individual pole interrupting capability. The grounded conductor of a corner grounded delta system is covered by the rules in Article 200, just like any other grounded conductor. 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. A and C to ground could be 120 (ish), 128. Commercial buildings require 3P4W and ground. The other two phased are at the line voltage above ground. Recently and in the past there have been numerous posts/questions re: corner ground delta systems and the responses have been quite varied. I believe that you are not supposed to connect any single phase loads between the high leg and the neutral. - All Line to ground voltages read (L-L/1. Is this a corner grounded delta secondary as. SPD requirements. The earth. The purpose of grounding d. Utilities are trying hard to get rid of corner grounded delta systems. A ground fault in a floating delta circuit is a foreseeable event, no surprise, and ought to be protected against. For the example shown in Fig. not smaller than the size of the grounding electrode. 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. 22, 2005 nec. It does NOT carry current like a neutral, a neutral carries the unbalance of the load. One method of grounding a three-phase, three-wire, delta-connected system is to ground one of the phase conductors. Introduction Grounded systems offer many benefits over ungrounded systems [1][2][3]. 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. I know you cannot get any 120v loads but what about single phase 240v loads. Schneider Electric has tested equipment for use on corner-grounded delta systems to provide Underwriters Laboratories Inc. Corner grounded is normally in industrial and commercial applications. For starters the xformer 480 side, if grounded, all the load side gear and equipment must be approved for corner grounding-not likely. The "wild leg" has a different voltage to ground, which can. The purpose of a corner ground is equipment and personnel protection. 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 theA 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). 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. Three pole breakers are allowed, because you are opening all three phases at once. Warning: If two-pole circuit breakers are installed in a corner-grounded delta system, they must be marked to indicate such suitability. But read 480 A to N, 0 B to N, 480 C to N. True False. 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. Abstract Many factors must be considered when designing the electrical system for critical facilities, especially the type of ground system used. One phase center tapped to derive a different voltage. 26(4) and 250. domnic Senior Member. 120 V, 3-phase, corner-grounded delta. I hooked up 240v 3 phase motor to make sure and. Location Roughly 5346 miles from Earls Court. Corner grounded delta systems are common in old industrial facilities around St. Fig. Solidly (effectively) grounded (LRG) Solidly (or effectively) grounded systems connect (bond) the system neutral directly to earth ground. 1. Sparkle. one pole. The utility company says it is an un-grounded delta secondary at 480V/3-phase/3-wire system. Corner grounded Delta transformer systems are known to confuse people. I was planning on reverse feeding it with 208v, and getting 480v. ® (UL®) Listed products for this application. g. corner grounded Delta system. 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``. 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. In a delta configuration, the three windings are connected end-to-end to form a closed path. iceworm Curmudgeon still using printed IEEE Color Books. 480 3ø, 3W corner grounded delta (ground jumper goes from one of the phases to ground. 480V rated breakers are only available with 3-poles and special labeling. 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. The delta system is grounded through parasitic capacitance from each phase to ground. Some devices will have multiple interrupting ratings, such as 14,000 amperes at 600 volts and 25,000 amperes at 480 volts. I've been given two different answers for the same set-up. (2) In ungrounded systems, impedance grounded systems, or corner-grounded delta systems unless listed specifically for use on these systems. The delta system has a phase-to-phase voltage of 240 V. 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. I know each leg has 240v to another phase or to ground except for the "B" phase so its not like the. Spend $75 to keep yourself safe. 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. Corner Grounded Delta Solidly (effectively) grounded (LRG) Solidly (or effectively) grounded systems connect (bond) the system neutral directly to earth ground. Thread starter domnic; Start date Apr 4, 2016; Status Not open for further replies. Basic cheap plug-in breakers are “slash” rated, meaning 240/120V; they are rated 240V phase to phase, but 120V phase to ground. Sections 503. Slash marked circuit breakers such as 120/240V or 277/480V must not be used. domnic Senior Member. Pretty curious though. 2) Adding a grounding autotransformer. corner grounded delta service. grounded, corner grounded delta and ungrounded delta. Furthermore, 3-phase, corner-grounded, delta circuits can only use two-pole circuit. Figure 11. Frame size EMC filter (+E200) screw Ground-to-phase varistor screw R10, R11 EMC AC VAR Drive. It's a three-winding transformer - grounded wye primary, corner-grounded delta tertiary, grounded wye secondary with neutral grounding resistor. In a corner grounded delta system, one of the three phase legs is intentionally grounded. Our PoCo will not supply it, but many factories install it currently. Ungrounded Delta: - No phase is intentioally grounded. M. 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. corner grounded Delta system. I have seen highly trained electricians freak out at a corner grounded delta in a power plant by me. A grounded wye system has each phase at line voltage divided by the square root of three above ground. BUT you have a 2 to 1 transformer (480/240=2 to 1) at 208 in you would get 416 out. Schneider Electric has tested equipment for use on corner-grounded delta systems to provide Underwriters Laboratories Inc. 208V. Google a pic for corner grounded delta transformer. "A" or "B" phase short and the the OCP operates. Ground a suitable midpoint of that auto-transformer. I figured at the least it would cause a phase loss alarm, but wasn't sure if there was. And Delta ground monitor. #3. 4. Best be taking some voltage readings and confirming what you have before making too many plans I would think. The earth. The maximum continuous operating voltage is measured from phase to phase for impedance grounded and ungrounded systems. At the MV level corner grounded delta is exceptionally rare. Technologic & IPC Set Parameter 14. The three pole breakers are designed for the higher voltage to ground found in a corner grounded. 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 corner grounded delta system is a three-phase delta service with one phase having the ground connection. For alarm switch, add the suffix BA. Circuit Breakers for Grounded B-Phase (BØ) (Corner-Grounded Delta) Systems. You have a different problem. The plant maintenance manager has said, " That delta will go away and I will get wye or I will go away. It requires connecting the impedance grounding conductor. Is this the same thing as a Corner Grounded system?Corner grounded delta was very popular. The uncommon grounded system is a 3-phase, 3-wire corner-grounded delta system. At the risk of repeating myself, I'll try to illustrate the difference with a few examples. It is very dangerous to touch the grounded line in a corner-grounded delta when the line. Other systems shall be permit‐ ted to be grounded. b. Circuit Breakers for Grounded B-Phase (BØ) (Corner-Grounded Delta) Systems. Look for 2 xformer cans on the power pole! Open Delta. 4. Although delta. Jun 10, 2019 #5 B phase on the Delta system is grounded. 6. 3, July 2022 -Corner-grounded delta grids not supported at voltages of 400V / 480V Version 1. 26(4) for conductor to be grounded. Neutral Conductor. not smaller than the size of the grounding electrode. IESNA Type III typical. In the setup the OP describes, the maximum voltage to ground would be 240, so he must use a straight 240 V breaker. The corner grounded delta (CGD) is one of the earliest forms of grounded systems in electrical installations. This system exists to keep voltages stable, limit or reduce surges, and/or be required in compliance with electrical code. If the phase that is grounded shorts to the equipment frame there. A corner grounded delta is not ungrounded. 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. Image used courtesy of Lorenzo Mari . 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. This Wikipedia article explains TT, IT and TN-S power distribution systems. The motors operate at a nominal supply voltage of 220 volts, 3 phase. Being that a GF would. So when the disconnects are open, the B phase is no longer. Its a separately derived system. Cause what is happening then is the 3ph load is seeing A,C,A or C,A,C. The other two will be 240v to ground. Location DFW, Texas. 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. Then leg to ground 480 479 0. scriverman. NEC 430. 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 such systems are grounded, they shall comply with the applicable provisions of this article. If you have a 3-phase motor on a center-tap system, the grounded conductor does not come into the picture at all. By "fail", it would have to mean a GROUND FAULT. is located/eliminated asap. Not a 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. Most utilities will not longer accept the 3 "ground lights" as a monitoring system, they will insist on an expensive electronic ground monitor. 5. Der PE-Schutzleiter (GND) darf keinen Strom tragen! Der Neutralleiter N (Grounded Conductor) ist dabei als getrennter Leiter anzulegen und erst innerhalb der Verbraucherablage abzugreifen. False. Mr. J. The service is a corner grounded 240V delta. B would be 180 (ish) to ground. 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”. A grounded wye system. Jun 21, 2023. 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. 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. Number Required. Corner grounded delta systems are very common here, we have them with 220V and 440V, but 440V is rather seldom. 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). System grounding is the connection to the ground – solidly or through impedance – of current-carrying conductors – e. You are required to have ground fault indication/alarms and need to take steps to find and repair it. Corner-grounded delta. Other types of three-phase supplies are wye connections, ungrounded delta connections, or corner-grounded delta ("ghost" leg configuration) connections. This supply system configuration is often used where high powers are required, for example for large motors. Measured voltage on tenant panel 480 A-B, A-C, B-C. 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. Jan 26, 2017. Its hard to visualize attaching 1 of 3 energized lines to ground. Unless its to.