Might be more economical to just order 240V equipment and use whats there. He said that it's about 240 volts so 128 volts to ground isn't that far off for a corner grounded Delta. Corner-Grounded Delta System. 26(4) and 250. 250. 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). Apr 28, 2020. if a guy happens to pick the corner-grounded leg to test to ground to verify that the line is off, then there is the potential for mayhem. I also have an older model Eurotherm VFD but I have not tested it. larz_6446 • 2 yr. Unless its to. In another thread about imbalanced voltages and currents the POCO decided to change a corner grounded delta well service to a delta with high leg. The correct application is 480 V or 600 V straight voltage ratings. 24, 250. gap, is maximum. Now, there are exceptions. 8]. Whichever you want to call it. If A to B = 240, B to C = 240, and B is grounded, then A to ground and C to ground is the same potential as A to B or B to C. I guess what I'm saying is that Delta seems never to be a good option. 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. Delta wye transformer wiring arrangementDelta wiring diagram 4 wire 240 volt wiring diagramDelta phase system wiring wire three grounded corner. Customer had lost some lights. 8. I've seen corner-grounded systems where one phase is tied to earth. 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. It does NOT carry current like a neutral, a neutral carries the unbalance of the load. Is this the same thing as a Corner Grounded system?Corner grounded delta was very popular. Leave EM1 connected. Use dedicated IES files on product website for non-standard CCTs. Corner Grounded Delta Transformer Bank. Corner-Ground: The three corners of the delta arrangement are connected to the line conductors. NEC Article 100 defines interrupting rating as “The highest current at rated voltage that a device is intended to interrupt under standard test conditions. The other two phased are at the line voltage above ground. Because of the size and complexity of Grounding and Bonding, Article 250 is subdivided into the. 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 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. 120 V, 3-phase, corner-grounded delta. SSDriver said: I have a job that is 240v open Delta with B phase grounded . This freaks people out, but it is totally legit. 10, and 680. If you choose the corner grounded delta, you will lose. Also explains your 480v to ground readings. APPLICATION ON GROUNDED . Abstract Many factors must be considered when designing the electrical system for critical facilities, especially the type of ground system used. Schneider Electric has tested equipment for use on corner-grounded delta systems to provide Underwriters Laboratories Inc. There is no 120 or 277 volt lead, you will need to. Dies geschieht unabhängig von der Erdung der Stromquelle. 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). Location AIken SC. So enter the corner grounded delta secondary. Per NEC, not for use with ungrounded systems, impedance grounded systems or corner grounded systems (com-monly known as Three Phase Three Wire Delta, Three Phase High Leg Delta and Three Phase Corner Grounded Delta systems). Location Michigan Occupation Electrician Feb 24, 2023 #4 This is a 4 wire 3 phase delta high leg system. Slash marked circuit breakers such as 120/240V or 277/480V must not be used. ® (UL®) Listed products for this application. Along with the 'slash rating', Corner Grounded (grounded B phase) systems can impact the AIC ratings of breakers. #1. It kind of freaks me out measuring 0 volts to ground on a open buss 4-5 thousand amps switchgear in the powerplant. My proposed fix is: 1). 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. If you corner ground make sure the customer knows that the transformers will need to be upgraded when the RTUs get changed, since modern RTUs often use variable speed drives. 2778 posts · Joined 2014. If one phase is zero volts to ground, you probably have a corner grounded delta. SPDs must be listed [Sec. 1 of 2 Go to page. You will read 480v from l1 and l2 to ground, 0 v on the neutral leg to ground. This will impact the selection of circuit breakers in a corner-grounded Delta power system. This is coming from the corner grounded delta that is feeding the buss. Its incoming utility service is 480V, corner-grounded delta. Almost as if the utility decided to run an EGC for giggles. Agreed, corner grounded delta, but strange that they have two separate conductors for 'grounded phase conductor' and 'neutral conductor'. CIs in bedrooms effective January 1, 2008 (NEC 210. 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. Recently and in the past there have been numerous posts/questions re: corner ground delta systems and the responses have been quite varied. 102(C)(1) for sizing the grounded conductor. e. the panel has two bus bars and grounded bar. Delta-connected systems can be solidly grounded using a few methods. 480 Y/277 V, 3-phase, 4 W, solidly grounded VI. 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. Evans said: Yes, 3 phase/3 wire is used sometimes. 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). Not sure what you mean by “normal”. The other two will be 240v to ground. 120V. Same with "wild leg" center grounded delta, which is also becoming obsolete. 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. Listed means one follow the instructions. Location DFW, Texas. The center of the Y, which is usually grounded, must not be connected to anything. A circuit breaker with a slash rating, such as 120/240V or 480Y/277, shall be permitted to be applied in a solidly grounded circuit where the nominal voltage of any conductor to ground does not exceed theThe system is “corner grounded”, one leg of three phase delta is tied to ground. Go. The NEC® addresses slash voltage ratings for circuit breakers in 240. 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. Wye connections, ungrounded delta connections, and corner-grounded delta (“ghost”) leg configuration connections are all examples of three-phase supply. 85 Applications. BTW, this is a grounded system. J. Proper grounding reduces overvoltages, improves uptime, and isolates faults. 3. 208 Y/120 V, 3-phase, 4 W, solidly grounded IV. might occur when Phase A goes to ground on a 480V, B-phase, corner grounded delta system. So put in a 2 pole and land B on the bus bar and I. Section 250. That would be a fairly simple fix in the panel, assuming that the panel is. I think it also allows you to use single phase panel boards also. 240V. Grounded Systems Ltd. The purpose of a corner ground is equipment and personnel protection. Three-phase — 4-wire 120/240 volt delta connected system (high-leg). UL Listed for use on 240 V Corner-grounded Delta Systems (Grounded B Phase). Occasionally, (especially in older facilities or in oil well and irrigation applications), you may encounter a three-phase delta service with one. In a 240-volt corner-grounded delta, what is the voltage between C phase and ground? 0 volts. Corner grounded delta. corner grounded Delta system. 85). 4. scriverman. Not open for further replies. Perhaps some. to ground on a 480 volt corner grounded delta system. . And Delta ground monitor. 85 permits one pole of a motor controller to be placed in a permanently grounded conductor provided the controller is designed for all conductors. It is implemented by grounding any one of the three phases of the transformer secondary (corners of the delta). Mr. For services they used to hook the 600 volt and under seondaries anyway you wanted. Typically in my area BOY is used for any 480 volt power and if a grounded conductor involved, it is grey or marked grey. 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. Ampere rating of fuse or circuit breaker not to exceed switch ampere rating. ® (UL®) Listed products for this application. False. 24 I see 250. BUT you have a 2 to 1 transformer (480/240=2 to 1) at 208 in you would get 416 out. No, it is not showing the high side delta winding is corner grounded. Delta with Wild Leg. A 480v delta with a coil center taped for a grounded conductor (neutral) would be considered a 277/480 high leg. 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”. Version 1. 9. Snap. ) Branch-circuit fuses do not have to be marked with their ampere rating. b. CryptoDelta has no obvious grounding location; the AC lines are generally all floating relative to earth. 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. T. NEC expert Mike Holt explains how to properly ground a corner grounded delta system and the special characteristics of these rare systems. 7. 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. Schneider Electric has tested equipment for use on corner-grounded delta systems to provide Underwriters Laboratories Inc. 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 ). 5% each you coould. 20(A). Never ran into that before. Corner-Grounded Delta Circuits. The solidly-grounded wye secondary is the modern way to go for 600V. Save. 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. 6. The primary can be grounded wye, ungrounded wye or delta while the. "C" phase carries current just like a ungrounded delta or a 3 phase 4-wire wye. The leg that reads zero to ground is the grounded leg. Does service entrance equipment still have to have neutral bus in this case? Steve. micromind · #7 · May 3, 2023. 1. 155, 517. 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. 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. Claim this business (250) 884-1942. Doing this is technically challenging and expensive, however, the corner-grounded system offers. 20, Informational Note. One method of grounding a three-phase, three-wire, delta-connected system is to ground one of the phase conductors. A to Earth = 524. Could be as jraef mentioned. One phase center tapped to derive a different voltage. Such faults are typically high impedance and at unspecified locations. roberius Member. 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. SE Michigan. 60% of these I run across are done incorrectly. [9] 22 k AIR main circuit breaker UL Listed for use ahead of QO, QOT and QO-PL 10 k AIR branch circuit breakers to permit their application on systems with up to 22 kA available fault current. 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. This wire must be white or grey, because it is a grounded conductor, even though it isn’t a neutral. Per the NEC, you need either GROUND FAULT MONITORING, OR you need to use a Corner Grounded Delta system. All EPDs occupy two spaces, with or without Alarm Switch option. 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. Schneider Electric has tested equipment for use on corner-grounded delta systems to provide Underwriters Laboratories Inc. Aug 14, 2018. Aside from serving the step-down transformer, the 480V side is mostly going unused. You have a different problem. The NEC® addresses slash voltage ratings for circuit breakers in 240. Aside from the corner-grounding of the delta, this is a fairly common configuration for transmission substation transformer in the US. I hooked up 240v 3 phase motor to make sure and. 480V rated breakers are only available with 3-poles and special labeling. Looking at a 120/208 wye system, the phase voltage would be 120V and the phase-to-phase voltage would be 208V. But how is the corner grounded of a Δ. If the available line-to-ground fault current exceeds 8,660 amps at 480 volts, such as might occur on the secondary of a 1000 KVA, 480 volt, corner-grounded delta transformer, the circuit breaker may be misapplied. Corner grounded delta bank is three wire, grounded delta. 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. You're describing "high leg" or "wild leg" delta. Location Kentucky Occupation Electrician Jan 21, 2021 #1 Our system had 490 phase to phase. Open delta 480 volt service. That is a corner-grounded delta system. Exactly what one would use for 13. Centertap is an effective ground (Neutral) at 0V potential and each leg is +120VAC and -120VAC respectively for the full voltage of 240V. This question references Article 240. The grounded conductor is treated like a neutral in 120 V and 240 V single-phase systems. 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. For alarm switch, add the suffix BA. If we started off with 277V symmetrically to ground on phases A, B, C with phase A at 0°, then grounding phase A effectively adds 277V at 180° to each of the three phases so. ain't going to end well. I have seen highly trained electricians freak out at a corner grounded delta in a power plant by me. While it is a grounded conductor, the grounded phase of a corner-grounded delta grid is not technically a neutral. Introduction Corner-grounded delta systems are not re commended for new installations. A and C to ground could be 120 (ish), 128. The conductor connected to the neutral point of a system that is intended to carry current under normal. Its incoming utility service is 480V, corner-grounded delta. A grounded wye system has each phase at line voltage divided by the square root of three above ground. He has tied the grounded phase of the delta supply to the green. "A" or "B" phase short and the the OCP operates. Phase ab 240v, ac 240v, bc 240v, a to ground 120v, b to ground 0v, c to ground 120v. Sounds like you know you have three supply conductors but don't exactly know what they are. 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. D. Corner-Grounded Delta System. The delta system is grounded through parasitic capacitance from each phase to ground. Interrupting Rating. This video is based on the 2020 NEC and was extracted. Use QO-H circuit breakers only. For a fault current of 5A, primary current will be 5 divided by 3, or 1. Unless you ground one of the legs, the reading will be zero on all legs to ground. 3-phase corner-grounded delta or single-phase circuits (NEC 240. 480V rated breakers are only available with 3-poles and special labeling. 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. Circuit Breakers for Grounded B-Phase (BØ) (Corner-Grounded Delta) Systems. When the bond is made from B phase to ground, you are simply creating a reference point. Check Details. Directions Advertisement. I wasn't sure what issues it might cause having one of the phases to ground be 0 volts. 3131 Delta St Victoria BC V8Z 1A6 (250) 884-1942. Corner grounded Delta (One phase conductor is connected to the grounding electrode system. A new transformer was set for a motor load to step up to 480 volt. The inverters may not like the elevated voltages to ground. A wye winding, with the wye point left unconnected, since there is nothing to connect it to. The only equipment bonded together is the main panel board case to the cable tray. 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. 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. 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). For a red leg delta with one winding center tapped and grounded at the center tap, yes. Schneider Electric has tested equipment for use on corner-grounded delta systems to provide Underwriters Laboratories Inc. True False. 36 (C) Equipment for General Use, Delta Breakers. The grounded leg of a corner grounded delta simply cannot be the 'same' as the grounded conductor of a center-tap delta. 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. On a 240V 3 phase grounded delta system, the voltage to ground is 240V from 2 of the poles. This is the problem. When the bond is made from B phase to ground, you are simply creating a reference point. #1. You will measure 480 volts from either A phase or C phase to ground, B phase to ground will measure 0 volts. Because of the disadvantages of not grounding systems, electrical designers had to integrate a ground reference to existing configurations. 102(C)(1). A. Thread starter thebigmt; Start date Nov 24, 2010; Status Not open for further replies. Usually different on each phase. Location: In the bothy, 7 chains down the line from Dodman's Lane level crossing, in the nation formerly known as Great Britain. On the secondary the voltage would be, if. 8. The frst ground fault makes the ungrounded Delta into a Corner Grounded Delta, so the plant continues to run. B-Grd: 0V (assuming B ph is the grounded phase) C-Grd: 240V. But read 480 A to N, 0 B to N, 480 C to N. 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. A ground fault in a floating delta circuit is a foreseeable event, no surprise, and ought to be protected against. 480v, corner-grounded delta. NEC 430. 85 Applications. move into 2008, as NEC-2005 requires Combination AF-. Corner grounded delta securely references the other two phases to earth potential. Have to physically see the MBJ to. Its hard to visualize attaching 1 of 3 energized lines to ground. 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. 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. 20. I asked them to take voltage readings between phase-phase and phase-ground just to make sure it is an un-grounded delta secondary. PowerPacT B-Frame Peak Let-Through Current Curve. . Perhaps it should be extended to cover the grounded conductor of a corner grounded delta with a 170% factor. Nov 30, 2020. A grounded Delta would have one phase solidly grounded, as with any grounded neutral, but would supply only 3ph loads. #3. All phase-to-phase voltages are still = 480V. , In addition to the grounding. 277V. 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. More. 44. This system can operate either at 480 volts or at 240 volts. Sounds to me like it’s a corner grounded delta with no 120V tap. 8 pf - 480/208 3 ph, 190 kVA 1. 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. Consider the relative sizes of the tank and the electrodes. The grounded neutral conductors typically carry the maximum. 67A; secondary current will be 1. 22, 2005 nec. Corner Grounded Delta Aquavar SPD Follow procedure: Disconnecting EMC Filter and MOV's per IM213. For use on. Another disadvantage, as given on page 33 of IEEE. Retired Electrical Engineer - Power Systems. This system has multiple transformers that go from 480-208 delta-delta and also 480v delta-208/120v wye. This video is based. I came across a code a while back about NEC not allowing circuits to. For example, corner-grounded delta systems contain a grounded conductor that is not a neutral conductor. 120V. Ungrounded Delta: - No phase is intentioally grounded. . For example, a corner-grounded delta system has a grounded phase conductor and no grounded neutral conductor present. In einem Delta – System werden alle angeschlossenen Komponenten direkt geerdet. #5. M. it is three phase 240 volt the panel is 200 amp three phase corner grounded the listing in the panel 120/240 volt single phase or 240 volt three phase delta. The delta system can also be grounded, as shown in Figure 2 below. Pretty curious though. Aside from the corner-grounding of the delta, this is a fairly common configuration for transmission substation transformer in the US. I have a job where they want to install a Dan Foss FC202 on a pump. ® (UL®) Listed products for this application. 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 . 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. It's a three-winding transformer - grounded wye primary, corner-grounded delta tertiary, grounded wye secondary with neutral grounding resistor. ) Only standard ampere rated fuses and circuit breakers found in 240. The VFD's and motors we had installed didn't seem to mind. This is a "Corner Grounded Delta" system and is found in older facilities that have no need for 277 volt service such as a manufacturing facility or a central plant in an apartment complex. Another disadvantage, as given on page 33 of IEEE. "C" phase carries current just like a ungrounded delta or a 3 phase 4-wire wye. 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). 430. 2778 posts · Joined 2014. 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. That is a corner-grounded delta system. e. D1-D4 lumen packages only. . Currently, the secondary of the transformer enters our switchgear which has a disconnect for each of the 2 sides of the switchgear. Besoeker3 Senior Member. 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. #2 · Aug 15, 2015. Furthermore, 3-phase, corner-grounded, delta circuits can only use two-pole circuit breakers marked 1ɸ-3ɸ. I've been given two different answers for the same set-up. High-leg Delta "HLD" B/HL A N C G High-leg Delta This supply system configuration is not used in Europe. But the key issue with any delta sytem is grounding that will get ya due there is a corner grounded delta. Sections 503. The utilty provider is coming in with 480 delta corner grounded c phase. In a corner grounded delta system, one of the three phase legs is intentionally grounded. 1. This is a violation of Section 240. I believe it also allows you to save wire, but I am not sure. A phase 490-ground B phase 490-ground C phase 0. They do have a +/-10% tolerance however. 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). Occupation. You may have not intended it that way, but a 3 phase/3-wire service by definition would not have a neutral. B would be 180 (ish) to ground. ® (UL®) Listed products for this application. 24(D)(4) This section covers impedance grounded services. The uncommon grounded system is a 3-phase, 3-wire corner-grounded delta system. The derived neutral connot operate at 0 volts as this would mean there is a short circuit to ground. A straight rated CB (such as 480V) can be applied on systems that have no more than 480V between any two conductors. Corner grounded delta systems are common in old industrial facilities around St. 362K subscribers in the electricians community. Apr 6, 2011. You are required to have ground fault indication/alarms and need to take steps to find and repair it. 85 covers the requirements for straight rated and slash rated CBs. • 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. Corner-Grounded Delta Circuits. , the neutral point of a wye-connected transformer and the phase on a corner-grounded delta connection. Otherwise the delta would be corner grounded (grounded 'B' phase). ® (UL®) Listed products for this application. Good points. 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. 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. might occur when Phase A goes to ground on a 480V, B-phase, corner grounded delta system. IN reference to. The size of the step-down transformer is. 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. I recently had and issue with a 240v three phase Delta system while on the job. However, the grounded phase is still current carrying just like a neutral is current carrying and is grounded. rcarroll said: '08 nec 408. 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). Being that a GF would. A corner grounded delta is not ungrounded. Can’t do line to neutral loads but phase to phase single or three phase loads are fine.