Grounded B-Phase Systems (Corner-Grounded Delta) PowerPacT B Electrical Accessory Wiring Diagrams. Corner grounded systems often employ 2 pole circuit breakers and distribution panels which would need to. 85 Applications. Menu. Location Michigan Occupation Electrician Feb 24, 2023 #4 This is a 4 wire 3 phase delta high leg system. 61, 517. Thread starter domnic; Start date Nov 19, 2020; Status Not open for further replies. It is quite common as a separately derived system for 230 volt equipment in a plant with a 480 volt service. If such systems are grounded, they shall comply with the applicable provisions of this article. This question references Article 240. 3–Phase Corner-Grounded Delta System using 2-Pole Circuit Breakers. roberius Member. B would be 180 (ish) to ground. We are doing this to avoid required ground fault protection in the breakers. not smaller than the size of the grounding electrode. Indication Contacts. However, some utilities still provide this system, and many old installations still exist. The NEC® addresses slash voltage ratings for circuit breakers in 240. UL Listed for use on 240 V Corner-grounded Delta Systems (Grounded B Phase). The line is also safe to touch even when it is not properly bonded only when the load is shut off. I would normally only use a solid corner ground on a. Section 250. 24(D)(4) This section covers impedance grounded services. gap, is maximum. Installations with this system require a 480-120V transformer to supply 120V lighting. Question, when connecting a Wye generator to the Corner Grounded Delta, will it work without any abnormalities. The size of the step-down transformer is. This Wikipedia article explains TT, IT and TN-S power distribution systems. corner grounded delta systems, considers the circuit breakers’ individual pole interrupting capability. "A" or "B" phase short and the the OCP operates. 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. However, some utilities still provide this system, and many old installations still exist. Could be the outlet is miswired or mis-breakered and has two of one line and one of a second. The conductor connected to the neutral point of a system that is intended to carry current under normal. If one phase is zero volts to ground, you probably have a corner grounded delta. Phase ab 240v, ac 240v, bc 240v, a to ground 120v, b to ground 0v, c to ground 120v. Sparkle. A circuit breaker with a slash rating, such as 120/240 V or 480Y/277 V, may only be installed in a circuit where the nominal voltage of any conductor to ground does not. Corner grounded Delta transformer systems are known to confuse people. 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. 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). Thread starter domnic; Start date Apr 4, 2016; Status Not open for further replies. Electrically, the grounded conductor in a corner-grounded delta system operates identically to a multi-grounded neutral conductor on a wye system meeting Rule 230E1. The NEC technically still allows for this, but the system must be EITHER: 1) Grounded, meaning "corner grounded delta"; or 2) Monitored, meaning a Ground Fault Monitoring system. They based it on current measurements they took at the pole after checking and cleaning all connections. optional based on the design of the electrical engineer. ® (UL®) Listed products for this application. Yeah a 3 pole on a corner ground delta system feeding 3ph equip. Hi, Our company rented an old warehouse and this is the first time I've ever seen corner ground delta (CGD) panel. Do not remove EMC AC or VAR. 480 x 1. Occupation. Figure 4 – Fault to Ground on a Corner-Grounded Delta System A disadvantage of Corner-Grounded Delta systems is the inability to readily supply voltage levels for fluorescent or HID lighting (277V). The grounded neutral conductors typically carry the maximum. My proposed fix is: 1). The purpose of grounding d. 8kv/480V Y transformer. Schneider Electric has tested equipment for use on corner-grounded delta systems to provide Underwriters Laboratories Inc. True. 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). 10656 posts · Joined 2007. These connections do not supply split single-phase power, and do not have a high leg. , In addition to the grounding. Circuit Breakers for Grounded B-Phase (BØ) (Corner-Grounded Delta) Systems. "C" phase is solidly bonded to ground. Is this the same thing as a Corner Grounded system?Corner grounded delta was very popular. Thread starter William Robertson; Start date Jan 21, 2021; Status Not open for further replies. #4 · Oct 2, 2020. Phase ab 240v, ac 240v, bc 240v, a to ground 120v, b to ground 0v, c to ground 120v. Its incoming utility service is 480V, corner-grounded delta. Corner Grounded Delta. 24 I see 250. 5869 posts · Joined 2009. When I look at the bank on the pole I see 2 primary and 1 primary neutral conductors and 2 transformers. Study with Quizlet and memorize flashcards containing terms like ? is/are defined as the conductors and equipment for delivering electric energy from the serving utility to the wiring system of the premises served. might occur when Phase A goes to ground on a 480V, B-phase, corner grounded delta system. Schneider Electric has tested equipment for use on corner-grounded delta systems to provide Underwriters Laboratories Inc. They sent me back readings for phase-phase at 480V, but phase-ground measured approximately 277V for. Two of the most significant tests performed on a TVSS are the measured limiting voltage test and a series of abnormal overvoltage. A circuit breaker with a special “straight” rating of 277/480 volts may be used on a corner-grounded delta system. IESNA Type III typical. 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. 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. Corner-grounded systems were used to supply services serving only a 3-phase load such as a well pump. For use on. It requires connecting the impedance grounding conductor according to sections 250. Location: In the bothy, 7 chains down the line from Dodman's Lane level crossing, in the nation formerly known as Great Britain. Corner Grounded Delta Transformer Bank. A straight rated CB (such as 480V) can be applied on systems that have no more than 480V between any two conductors. The grounding resistance required can be determined from these values of current and voltage. A ground fault in a floating delta circuit is a foreseeable event, no surprise, and ought to be protected against. It is both, ground and hot. A corner grounded delta service can be designed for any desired voltage, but 240 is most common. Aug 14, 2018. A corner-grounded delta transformer connection is an example of a system permitted to be grounded. There is no 120 or 277 volt lead, you will need to. Also explains your 480v to ground readings. #3. joethemechanic. That would imply using equipment that is wired the same way as center-tapped 1-phase. 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. The service is a corner grounded 240V delta. 20 informational not refers to a corner grounded delta tranformer. For services they used to hook the 600 volt and under seondaries anyway you wanted. A wye winding, with the wye point left unconnected, since there is nothing to connect it to. 480V – 3-Phase, 2-Wire – Corner Grounded – Delta. 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. L-N: 277V L-L: 480V 480V. Normally the grounded conductor is A or B phase- but you never. Could be as jraef mentioned. Basic cheap plug-in breakers are “slash” rated, meaning 240/120V; they are rated 240V phase to phase, but 120V phase to ground. The phase load in VA of a 3-phase, 240V load is the line load divided by three (one third of. I would not worry about it, but don't buy into the "kit" concept, tell them you want a 240V drive, or just use a 480V drive. NEC 240. Each test evaluates a different function or potential failure mode of a TVSS. 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. I think it also allows you to use single phase panel boards also. Business, Economics, and Finance. Question I have is I believe I need to utilize a corner grounded delta on the 480v side, otherwise the system is not grounded. IN reference to. The inverters may not like the elevated voltages to ground. Assuming you adjusted the taps at 2. 20(B)(1) and avoid an NEC violation. I pointed out that in industry it is quite common for an ungrounded delta secondary to allow continuous ops while the partial/total phase grnd. William Robertson Member. This section classifies the systems that must be grounded – unless prohibited elsewhere in the Code – into four categories. Figure 2. It is used to reduce wiring expenses by utilizing a service cable that has only two insulated conductors instead of the three insulated conductors typically. To obtain UL certification, the TVSS unit must pass all tests. zbang Senior Member. Its corner ground Delta 3 phase , 208 V , 30 horsepower. R. We own the transformer. There is absolutely zero reason to design B phase cornered system if you designing a new system. Grouch1980 said: Actually I didn't specify it. An ungrounded (floating) delta should have a ground indicator to alert maintenance personnel because a second ground may be catastrophic. Looking at a 120/208 wye system, the phase voltage would be 120V and the phase-to-phase voltage would be 208V. If you do ground one leg, you will only get zero on that one leg. The solidly-grounded wye secondary is the modern way to go for 600V. teal854t Discussion starter · Oct 13, 2010. domnic Senior Member. Study with Quizlet and memorize flashcards containing terms like The first point of grounding for a building or structure supplied by a utility service is usually within the service equipment enclosure(s). Select one: a. A-B: 240V. Corner grounded is normally in industrial and commercial applications. The easiest way to ground a delta is at a corner, which also happens to be convenient in converting/upgrading ungrounded systems. 2778 posts · Joined 2014. 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. C orner-grounded delta grids are not supported at these voltages. Recently and in the past there have been numerous posts/questions re: corner ground delta systems and the responses have been quite varied. It's a three-winding transformer - grounded wye primary, corner-grounded delta tertiary, grounded wye secondary with neutral grounding resistor. IESNA Type IV typical. We use our. 3 pole breakers may be used for 3 phase loads with grounded phase connected through a breaker pole. 480 V, 3-phase, 3 W, ungrounded or high resistance grounded VII. 13. Go. 36 (C) Equipment for General Use, Delta Breakers. 22, 2005 nec. - One phase is intentionally grounded. He said that it's about 240 volts so 128 volts to ground isn't that far off for a corner grounded Delta. Solidly (effectively) grounded (LRG) Solidly (or effectively) grounded systems connect (bond) the system neutral directly to earth ground. Another disadvantage, as given on page 33 of IEEE Std 142. 480 3ø, 3W corner grounded delta (ground jumper goes from one of the phases to ground. Perhaps it should be extended to cover the grounded conductor of a corner grounded delta with a 170% factor. . Corner Grounded Delta Aquavar SPD Follow procedure: Disconnecting EMC Filter and MOV's per IM213. Equipment ground bonds to disconnect and grounded phase connects to unfused pole. 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. 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. 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. 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. I have seen corner grounded deltas for 3 phase motors, but my situation is a bit different. Save. 120/240 V, single-phase, 3 W, solidly grounded III. Corner grounded delta securely references the other two phases to earth potential. 2, the transformation ratio is 4160 divided by 120, or 34. 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. , a zero sequence voltage). For example, corner-grounded delta systems contain a grounded conductor that is not a neutral conductor. If the phase that is grounded shorts to the equipment frame there. Jun 21, 2023. Schneider Electric has tested equipment for use on corner-grounded delta systems to provide Underwriters Laboratories Inc. - All Line to ground voltages read (L-L/1. Introduction Corner-grounded delta systems are not re commended for new installations. Not sure if that's the technical name or not. Remote Operation (MN/MX Voltage Release) Let-Through Curves and Trip Curves. The minimum size of the grounded conductor for a 3-phase, 3-wire, corner-grounded, delta connected service is a. Read also : what is an operational amplifier. 0V. NEC 430. The grounded leg is no more dangerous than the grounded neutral leg in a 120 volt circuit. Welcome to /r/Electricians In solidarity with 3rd party developers…Only for use with 480V Wye systems. T. There is no grounding of any kind on the panel boards, transformers or disconnects. Not available in E04 or F04. 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. Delta-connected systems can be solidly grounded using a few methods. However, some utilities still provide this system, and many old installations still exist. 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). A 480v delta with a coil center taped for a grounded conductor (neutral) would be considered a 277/480 high leg. But the key issue with any delta sytem is grounding that will get ya due there is a corner grounded delta. 1 of 2 Go to page. According to mike holt one random? corner phase is to be grounded and bonded to the case of the transformer. domnic Senior Member. It is very uncommon to have 3 phase in residential in the US but other parts of the world it is. Northern Virginia. The VFD's and motors we had installed didn't seem to mind. It's 830 wye. 120 V, 3-phase, corner-grounded delta. 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. We would like to show you a description here but the site won’t allow us. You will measure 480 volts from either A phase or C phase to ground, B phase to ground will measure 0 volts. At first we were having trouble getting the motor to start in auto and just out of habit I checked power in. SSDriver said: I have a job that is 240v open Delta with B phase grounded . LHL361005861). A corner grounded delta power system is a configuration where one of the phases (typically B phase) is solidly grounded. 250. A two-pole circuit breaker applied on a 3-phase, corner-grounded delta system must be marked 1Φ-3Φ. I wasn't sure what issues it might cause having one of the phases to ground be 0 volts. More. 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. This is the problem. OccupationHey this happens all the time. 67A; secondary current will be 1. 100 % (3 ratings) for this solution. 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. 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. 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. , the neutral point of a wye-connected transformer and the phase on a corner-grounded delta connection. The B phase to ground voltage should be 1/2 of the line voltage. 4. Compared with the solidly-grounded wye system of Figure 1 this system grounding arrangement has a number of disadvantages. On this latter type, one phase is indeed grounded and is 0 volts to ground. The plant maintenance manager has said, " That delta will go away and I will get wye or I will go away. larz_6446 • 2 yr. ago. Not open for further replies. 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. 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). JimmySki23 Member. Only for use with 480V Wye systems. I have seen highly trained electricians freak out at a corner grounded delta in a power plant by me. If that isn't possible, then the drive should be labeled as unsuitable for the floating delta and/or corner grounded delta. What you have is a center tapped delta 120/240 volt 3 phase system. Perhaps it should be extended to cover the grounded conductor of a corner grounded delta with a 170% factor. Start shipping your package by locating a Purolator drop box, Purolator Shipping Centre, or Purolator Authorized Shipping Agent near you. This creates a three. See Figure 11. NEC 430. Corner grounded Delta (One phase conductor is connected to the grounding electrode system. Per the NEC, you need either GROUND FAULT MONITORING, OR you need to use a Corner Grounded Delta system. Eaton Corporation literature states “for all 3 phase delta grounded B phase applications, refer to Eaton Corporation. 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. Never ran into that before. That 'neutral' is of course not a neutral, but a parallel 'grounded phase' conductor. No. The ratings on the gen set are for 1 ph, 190 kVA - 240V 3 ph, 237 kVA 0. 85). - All Line to ground voltages read (L-L/1. Joined Jan 25, 2011. 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. I have a job where they want to install a Dan Foss FC202 on a pump. LHL361005861). [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. three-phase, 3-wire, corner-grounded delta system? 120V 240V 277V 480V Correct Answer: 480V. System grounding is the connection to the ground – solidly or through impedance – of current-carrying conductors – e. False. One-line diagram symbol for a system- or equipment grounding connection _____ m. Snap. Look for 2 xformer cans on the power pole! Open Delta. System also requires a. The 277 volt is interesting but, not relevant. Utilities are trying hard to get rid of corner grounded delta systems. Aside from the corner-grounding of the delta, this is a fairly common configuration for transmission substation transformer in the US. teal854t Discussion starter · Oct 13, 2010. In a corner grounded delta system, one of the three phase legs is intentionally grounded. #4. 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. move into 2008, as NEC-2005 requires Combination AF-. Directions Advertisement. 6. A phase is connected to each corner of the delta. Almost as if the utility decided to run an EGC for giggles. Systems from Intermittent Ground Faults Introduction Many papers and standards [1][2][3][4][5][6] have discussed grounding of an electrical distribution system. ® (UL®) Listed products for this application. 99 votes, 37 comments. One of the phases, normally A phase, is connected to a grounding electrode. I will not continue to be served by the corner grounded. For me, its a textbook corner grounded delta. In a delta configuration, the three windings are connected end-to-end to form a closed path. the breakers in the panel are. IESNA. Technical Note – Grids Supported by. Sections 503. e. In a delta configuration, the three windings are connected end-to-end to form a closed path. See a problem? Let us know. Ground B phase systems, grounded phase services, and end-grounded delta systems are all examples of corner-grounded delta systems. Another variation is a "corner grounded" delta system, which is a closed delta that is. Because of the disadvantages of not grounding systems, electrical designers had to integrate a ground reference to existing configurations. Corner grounded delta. The other two will be 240v to ground. ) Branch-circuit fuses do not have to be marked with their ampere rating. Corner Grounded Delta You don't see this on new services much these days, but it is very common on older industrial buildings. It is found that, although this type of service is less expensive than solidly grounded wye service, 480 V corner-grounded delta service may not provide a safe working environment if used for oil-field service. It is a 240v CGD. Every fuse and circuit breaker is assigned an interrupting rating. You need transformers with a wye secondary and ground the center of the wye. Remember, voltage is a difference in potential. 12). They could have a neighboring property causing that or could be monitoring lamp or relay seeking a fault. However this grounded leg will be 480 volts phase to phase but no voltage to ground at the service and the inverter. g. Section 250. 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. 7 taps I am getting 439 volts, but If I need higher voltage the connection can be. 4. They are available. The only solution i have come up with is pulling the pump, and changing them to 277/480 wye,. 85 permits one pole of a motor controller to be placed in a permanently grounded conductor provided the controller is designed for all conductors. 415V. It is a Delta and Split-phase hybrid. Spend $75 to keep yourself safe. 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. But read 480 A to N, 0 B to N, 480 C to N. 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. 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). A corner grounded delta system is a common way to establish a reference to safety ground when dealing with an otherwise floating output from a delta secondary. 20, Informational Note. It is a 240v CGD. So when the disconnects are open, the B phase is no longer. 85 of the 2002 NEC was changed to read: 240. Occasionally, (especially in older facilities or in oil well and irrigation applications), you may encounter a three-phase delta service with one. Is this a corner grounded delta secondary as. Ungrounded Delta: - No phase is intentioally grounded. For that reason, 99% of people who HAD legacy ungrounded delta systems. This is a non sequitur. Sparkle. Evans said: Yes, 3 phase/3 wire is used sometimes. • 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. waross (Electrical) 6 May 15 10:54. All EPDs occupy two spaces, with or without Alarm Switch option. APPLICATION ON GROUNDED . T. A building needs to be taken off it's primary feed, so we can service it's 4. Its a separately derived system. 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. There is no way of grounding a 480V system (or any over 260V L-L) to meet the 150V L-G standard. 3, July 2022 -Corner-grounded delta grids not supported at voltages of 400V / 480V Version 1. Our instructor made a point to warn of corner grounded Delta transformers, since you get your "phase-to-phase" voltage present "phase-to-ground". I actually ran into a corner grounded delta myself Friday or at least I think. 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. 10, and 680. 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. 02. Now that I’ve wrote all this, if it’s truly an ungrounded system there should be ground fault monitoring somewhere to alarm of such ground fault. 240. If you had a corner grounded delta, B phase grounded and A phase shorts assuming you protected everything per the NEC you would have a ground fault and the fuses would blow or the CB open. Aside from serving the step-down transformer, the 480V side is mostly going unused. This would be a service like an ungrounded delta or a corner-grounded delta. Location. 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. 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. "C" phase is solidly bonded to ground. In addition, if you have any sort of rectification stage, for example in a VSD, then the DC rail voltages relative to ground will be very different. At the transformer, the grounding electrode conductor, grounded phase, and equipment grounding conductor all tie together. Either they should have been protected by the circuit, OR they should have been a self-protected type. You must also bond the phase to the case with a jumper sized to 250. Thus, the phase which is corner grounded has zero volts relative to ground because we have chosen to bond it. A grounded wye system. Ground a suitable midpoint of that auto-transformer. 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 grounded leg of a corner grounded delta simply cannot be the 'same' as the grounded conductor of a center-tap delta. ground continuity, enclosure impact, adequacy of mounting, and many others. Cause what is happening then is the 3ph load is seeing A,C,A or C,A,C. If the phase line was solidly grounded you would be reading 0 volts. Agreed, corner grounded delta, but strange that they have two separate conductors for 'grounded phase conductor' and 'neutral conductor'. Proper grounding reduces overvoltages, improves uptime, and isolates faults. A second fault, on a different phase, however, presents a problem. Our PoCo will not supply it, but many factories install it currently. Since one phase is already grounded this 4th wire is somewhat redundant. 2 requires a grounded conductor in all premises wiring. Claim this business (250) 884-1942. Location Kentucky Occupation Electrician Jan 21, 2021 #1 Our system had 490 phase to phase. Corner-grounded delta. Corner grounded delta. This normally would not be to big of an issue however the Haas machine VFDs and servo amplifiers probably require the 277 for surge overload and if a storm hits or we get a fault. 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”. 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. A grounded wye system has each phase at line voltage divided by the square root of three above ground. There are multi-tap ballast units, which can be 480V, 240V, or 208V, in addition to 277V, all of which are Line-to-Line connections. Google a pic for corner grounded delta transformer. 480V. The other solution would have been to corner ground the 480 Delta, but I've posted before why I don't like that setup. 430. A 3-phase disconnect or overcurrent device shall not be connected to the bus of any panelboard that has less than 3-phase buses. When the bond is made from B phase to ground, you are simply creating a reference point. PowerPacT B-Frame Let-Through Energy Curve.