Same as a single phase panel, but with a 240 volt breaker. A 3-phase delta system can operate with all three phases floating, or by grounding one of the three phases, such a system is called a corner grounded system. If any particular phase fails the continuity test, your motor is probably burnt. 1? Copyright © 2020 vBulletin Solutions, Inc. All rights reserved. Come join the discussion about trade knowledge, tools, certifications, wiring, builds, scales, reviews, accessories, classifieds, and more! Three-Phase Asynchronous Direct Online Motor Connected to Hydraulic Pump In this example, an asynchronous motor is connected to an ideal pump. If the winding's insulation wears away near the motor's case, the bare-wire winding shorts to ground. Either of your choices would work, but you'll likely have a hard time finding a single pole breaker rated for 240 volts that will fit the panel. JavaScript is disabled. For a three phase motor, insulation resistance is usually measured between each motor winding or phase and between each motor phase and motor frame (earth) using an insulation tester or megger. Seems obvious to me, any 240 volt breaker would handle 120 volts. The main requirement is a specific zero-sequence impedance from the Zig-Zag or the Wye/Delta transformer in addition to the fault current withstand rating. This website or its third-party tools process personal data (e.g. “cross-phase” voltages) will be … Searching for 3 Phase, 4 Wire with Ground Electrical products? Just surprised that the 3 phase plugs don't have a ground connection. The utility would be responsible for the service up to the and including the meter. Wiring Electrical Control Relays. It basically says that a breaker can't be used on this system unless it is marked as suitable as a 3-ph breaker. Grainger's got your back. Common mode filters do not significantly affect the phase of main voltages on motor terminals. VerticalScope Inc., 111 Peter, Suite 901, Toronto, Ontario, M5V 2H1, Canada. Common causes for ground faults in motors is damage to phase conductor’s insulation, and internal shorts due to moisture. When I install a single phase motor on a corner grounded system (known as grounded B around here), I simply use a 2 pole breaker that's 240 volt (not 120/240), and use the ground bus as the ground. The diameter of the valve on the hydraulic system affects the speed and current drawn by the motor. This is based on NEC (NFPA 70®: National Electrical Code® (NEC®), 2014 Edition) Table 250.122. This just don't sound right. By varying the pulses’ width and timing (through pulse width modulation or PWM) the drive creates a motor current that looks like a sine wave—the frequency of which controls motor speed.The problem is that even at low speed (low frequency), the square-wave’s amplitude is always at 650 Vdc bus voltage for 480-V motors. If a connection point is not provided, bond to the adjacent panel. 2ft x 2ft x 1/8 in) or galvanized iron (GI) of dimensions 60cm x 60cm x 6.35 mm (2ft x 2ft x ¼ in) is buried vertical in the earth (earth pit) which should not be less than 3m (10ft) from the ground level. But I did some googling maybe some of this will help. The open is… Everyone knows that 480v 3 phase will read 480v phase to phase and 277v phase to ground. Is there any way the farm could be getting two service feeds and they have become intermingled? Then it sends a chopped dc signal to the motor. Of course a single phase motor will work with this system. It is also used to power large motors and other heavy loads. Line-to-ground faults, Figure 1(d), are the most common type of faults and are usually the least disturbing to the system. In actuality, there will be current flow to ground in an ungrounded system with a phase-to-ground fault due to the natural capacitive coupling to ground of the system. There is no neutral connection. GREEN, BARE or GREEN / YELLOW = Ground “PG” Three Phase 277V & 480 V AC: The following i.e. To the panel at entry to the cabinet (optional). Connecting the ground wire from the arrestor directly to the motor is the best ground available. PWM MANAGEMENT FOR 3-PHASE BLDC MOTOR DRIVES USING THE ST7MC 3.2 ST METHOD With the ST Method, by using the free-wheeling diodes during the OFF time of the PWM signal, the M potential is put to ground and the ST7MC microcontroller samples the BEMF signal voltage during the OFF time of the PW M signal. Figure 1c – Line-to-line-to-ground faults. I don't understand the distinction between a "240 volt" breaker and a "120/240 volt" breaker. 3 phase motors need 4 wires, 2 of them go to the ground bus. That’s why for large motors, many motor manufacturers (including ABB) recommend cables that have a symmetrical arrangement of three phase leads and three earth conductors. Motor FLC = 22A [Table 430.250] Conductor’s size = 22A × 1.25 = 27.50A A check of Table 310.15(B)(16) reveals that a 10 AWG conductor is rated 30A at … Went to two supply houses. © 2020 Copyright Practicalmachinist.com. browsing data or IP addresses) and use cookies or other identifiers, which are necessary for its functioning and required to achieve the purposes illustrated in the cookie policy. Then, compare the reading that is farthest from the average and find the percent of … Amperes - Enter the maximum current in amps that will flow through the circuit. Keywords: IMD, 3 phase motor, motor ground fault, insulation fault, inverter . A three-phase motor must be wired based on the diagram on the faceplate. P.S. Although the National Electric Code does not specify specific conductor colors for three-phase current, it is common to use black, red and blue wires to identify lines L1, L2 and L3 respectively. Electrically , it makes It makes no difference if the corner is grounded or not. The grounded conductor may be reduced to carry only the unbalanced load but may not be less than the required equipment grounding (bonding) conductors as sized by Table 250.122. iwire Moderator. November 2011: Relocated to Winston-Salem. We'll bring you the most relevant peer-to-peer conversations happening in the trade and tips and tricks to help you get the job done. A motor fails when its windings short to ground, short to each other, or open--a break in the winding's wire. Let’s review a sample problem for clarity. All grounding and electrical work must comply with AS/NZS3000 and all revisions. This might result in unexpected motor failures when critical services from such motors are required affecting availability of plants. Set the voltage setting of the insulation resistance tester to 500V. The W2U2V2 terminal set is the star side of the 3 phase motor while the U1VIW1 is the Delta side of the motor connected to the supply voltage. Characteristic Performance Average voltage 230 230 230 Percent unbalanced voltage 0.3 2.3 5.4 Percent unbalanced current 0.4 17.7 40 The wire in the windings use an insulating covering as an isolation barrier. Types of Testing For 3-Phase Motors. Not a 120/240 V. A bit too provocative for the average person... the what about the others led to my edit of my first post, pull the circut for the single phase motor from the 120v panel seems like the easy choice. In plate earthing system, a plate made up of either copper with dimensions 60cm x 60cm x 3.18mm (i.e. If a system is optional, but the choice is made to ground it, all system-grounding rules in the NEC must be applied. Jun 25, 2005 #3 Re: three phase sub panel wire sizing Bryan, this is a real question. Standard cables provide enough grounding to protect people, but that’s not enough to protect equipment against high-frequency noise and common mode currents. The most common method of providing for grounding in NEMA motors is a ground lug under one of the conduit box mounting bolts. Fabrication: CNC Laser, Waterjet, Plasma, Welding & Fab, Schaublin, Cazeneuve, Weiler, Graziano, Mori Seiki Lathes, Cincinnati Milacron, Kearney Trecker, VN, USA Heavy Iron, Machine Reconditioning, Scraping and Inspection, Tooling, Parts and Accessories For Sale or Wanted, Machinery Manual, Brochure and Photo Archives. Although three-phase motors run on alternating current just as single-phase motors do, they are usually powered by a polyphase system that supplies continuous current in a way unavailable for single-phase motors. Use the nameplate FLA when sizing conductors, branch circuit short circuit and ground fault … )First you should put on safety glasses and shut all electrical connections to the motor. The winding failures illustrated here are typical of what can happen is such circumstances. With more than 10.6 million unique visitors over the last year, Practical Machinist is the most visited site for metalworking professionals. This involves the fact that the PWM has A three-phase system may be arranged in delta (∆) or star (Y) (also denoted as wye in some areas). These include: The Code requires alternating cur… Line-To-Ground Faults. My question involves grounding. What I am considering is using the 4 prong 120/208 3 phase receptacles and plugs, but with the 4th wired to ground instead of neutral - … This is based on NEC (NFPA 70®: National Electrical Code® (NEC®), 2014 Edition) Table 250.122. Good explanation, but I don't see how a breaker can know if it is looking at line to line voltage or line to ground voltage. The neutral points in both alternator and the load are joined together. When a motor is part of a machine, the ground wire may be connected to the machine frame rather than the motor frame. This site is protected by reCAPTCHA and the Google Privacy Policy and Terms of Service apply. Testing a three-phase electric motor without a trip down to the repair shop requires a cautious approach, but happily all you need to start with is a volt-ohmmeter and some simple hand tools. For three phase motors, connection type is either Star (Y) or Delta AC Motor Winding Continuity Test Using a multimeter, check the continuity of motor winding from phase to phase ( U to V, V to W , W to U ).Each phase to phase must have a continuity if winding is OK. For these motors, the standard correctly explains, a VFD can generate high-frequency common mode voltage, which shifts the three-phase-winding neutral potentials significantly from ground. If you're willing to buy new stuff, the correct 4-blade twistlock style for 240V 3 phase is L15. Bond motor power cable shields: At the motor frame. No, it is optional. I understand the difference between neutral and ground. An earth/ground wire should be connected to the frame of the motor, but sometimes that is not done. I'll take your word for it. Single-phase voltages are usually 115V or 120V, while three-phase voltages are typically 208V, 230V or 480V. 3 blades for 3 hots, instead of the correct 2 blades for hot, 1 for ground. Viewed 1k times 0 \$\begingroup\$ I am wondering how can I connect the protective earth of my 3 phase AC motor? Go back to three phase faults ↑ 4. To find out more about the categories of personal information collected and the purposes for which such information will be used, please refer to our privacy policy. Three-phase grounding transformers provide an artificial neutral for grounding. You need to read 240.85, which addresses the issue of breaker selection for corner grounded systems. Shaft Grounding Motors View in Online Catalog For an off the shelf solution, to meet an HVAC specification for new construction, or if replacing a motor that has fallen victim to bearing fluting due to shaft currents, Baldor Shaft Grounding motors will ensure a long smooth service life. The W2U2V2 terminal set is the star side of the 3 phase motor while the U1VIW1 is the Delta side of the motor connected to the supply voltage. Conduit Size All Rights reserved. A three-wire three-phase circuit is usually more economical than an equivalent two-wire single-phase circuit … Table 430.250 3-phase motors However, for some specific types of motors, the actual nameplate full-load amperes (FLA) must be used instead of the FLC (see FLA vs. FLC ). Servo Motor (3phase 220vac) testing: Below are some basic principles for testing servo motor circuits with meter or megohm meter. In my part about "single phase," I was referring to a "single phase" service, not a three phase with a single phase used for single phase loads. Powered by vBulletin® Version 4.2.5 This article examines the NEC’s electrical-system grounding provision. On a 12-wire motor wired for high voltage (i.e., 480V), 10T, 11T and 12T must be connected together but not connected to anything else. Although three-phase motors run on alternating current just as single-phase motors do, they are usually powered by a polyphase system that supplies continuous current in a way unavailable for single-phase motors. In a three phase motor each leg (3 phases) in the down cycle alternating at 1/60 per second servers as a neutral, you are only required to ground (green) the frame of the motor for safety. The trick is knowing which leads to hold on to and which wires make no difference at all. What size 75°C branch circuit conductor is required for a 7½-hp, 230V, 3-phase motor, as shown in Fig. In a three phase power system, the type of faults that can occur are classified by the combination of conductors or buses that are faulted together. For a better experience, please enable JavaScript in your browser before proceeding. The life of a three-phase stator winding can be shortened dramatically when the motor is exposed to unfavorable operating conditions — electrical, mechanical or environmental. You simply check the voltage from each of the three phases to one another and find the average (add all three and divide by three). Those are described below. I know on single phase, the ground can be a size or two smaller than the power carrying conductors and it can also be shared between a couple circuits. 3. When the 3-phase system is not grounded and if Single Line to Ground fault occurs, the voltage of the other two healthy phases will a) Increases b) Decreases c) Remains unaffected d) none of the above. 240 volts pushes twice as hard as 120 volts. So I could use a single pole breaker rated 240v run say the black and white to my motor starter and also pull a green off the ground bar, and then to the motor and wire it for the high voltage side on the single phase motor? Three-phase electric power is a common method of alternating current electric power generation, transmission, and distribution. In the above diagram, the alternator is connected to the load by three phase four wire system. It is a type of polyphase system and is the most common method used by electrical grids worldwide to transfer power. Easy online ordering for the ones who get it done along with 24/7 customer service, free technical support & more. Searching for 3 Phase, 4 Wire with Ground Electrical products? Reading phase to phase gives you 480v as expected, but when reading phase to ground you still get 480v. Hi there I have just come across a 3 phase motor we are using, only a small 40w one that I will be running off an inverter. How to test a 3-phase motor is discussed in this article. A corner grounded systen on a farm????????? Once you have tested a few 3-phase motors, the process will come easily. The National Electrical Code (NEC), section 430-L, defines the conditions that dictate when motor grounding is required. These tools and methods are discussed below. "L15-20" for up to 20 amps. Location Massachusetts. Register for the world’s largest manufacturing technology forum for free today to stay in the know. Well at work we have a 3 phase system with the B phase slugged instead of fused. A forum community dedicated to professional electricians, contractors, and apprentices for residential and commercial work. through your motor. Nevertheless, … I've never worked on one and I don't think I've seen one either. There's a bunch of 4 blade twistlock configurations, but that's the correct one for 240V 3 phase with ground and no neutral. Three phase motors have only three "hot" power wires connected to the windings. If a ground fault develops, a current imbalance will be present and a current will flow in the protection circuit, causing it to operate to trip the supply breaker. Sign up for our eNewsletter now to stay in-the-know. In case of sale of your personal information, you may opt out by sending us an email via our Contact Us page. Connect ground wire to wire terminal. Grainger's got your back. Ask Question Asked 5 years, 8 months ago. The latest industry news—straight to your inbox. Load: Motor 3 HP, 1 phase, 230V run ground wire with all motors I = 17A NEC 430=148 Wire Size = 17A = 21.5A .8 NEC 310-16 #10 is next size wire good for 30 Amp CB = (I)(2 to 2.5) NEC 430-152 CB Size = (17 A) (2) = 34A USE 35A circuit breaker. I'm interested to see what others say about this, but from what you described, it doesn't sound like a kosher three-phase setup. Using a crimping tool, connect ring terminal to the end of … Figure 4 The Motor Bearing Fault. Sorry about the confusion. Beyond the meter, the wiring installation becomes the responsibility of the installer of the electrical system and the homeowner. However usually the motors we use have an … Recall that a VFD turns sinusoidal alternating current into a direct-current signal. Does the National Electrical Code (NEC) require a 480-volt (V), three-phase, 3-wire, delta-connected system to be grounded? Three-phase motors are more efficient than single phase motors and are commonly found in applications requiring more than 7.5 horsepower. “Dammit, Smithers, this isn’t rocket science, it’s brain surgery!”. Since you’ll be testing the motor only, it’s best to first remove … When a motor is part of a machine, the ground wire may be connected to the machine frame rather than the motor frame. These conditions come down to the simple fact that essentially all industrial motors must be grounded. The neutral wire serves as common return to all the three phases acting outward from N 1. Sendyne Corp. 82019 ©2019 Sendyne Corp. 2 . I.e. If your X-N (and Y-N and Z-N) voltage is 120V (common in the US), the X-Y (and Y-Z and Z-X) voltages (a.k.a. Three phase motors have only three "hot" power wires connected to the windings. Motor Ground Fault Protection. Practical Machinist is the easiest way to learn new techniques, get answers quickly and discuss common challenges with your peers. The following table illustrates voltage unbalance effects on a typical electric motor rated 5 hp, 3 phase, 230V, 60 Hz, 1725 rpm, and 1.0 service factor. One is Square D. so they didn't have much. Testing a 3-phase motor is as simple as holding the leads of a volt ohmmeter. The Ground Conductor Size Calculator will calculate the proper ground conductor size for grounding raceways and equipment based on ampere rating or setting of automatic overcurrent protection device in circuit ahead of equipment. Environmental faults in three phase induction motor. Rob P.S. To learn more, please refer to the cookie policy. To the drive (amplifier) chassis. The first step is to figure out the voltage of your phases. The 3 phase motor is a rugged piece of equipment but as with everything man made, there comes a time when this beautiful piece of machinery fails either due to old age, misapplication, mal-operation or any other adverse cause. Learn more about us. The Ground Conductor Size Calculator will calculate the proper ground conductor size for grounding raceways and equipment based on ampere rating or setting of automatic overcurrent protection device in circuit ahead of equipment. In a 3-phase system the voltage between any two phases is 3 times higher than the voltage of an individual phase by a factor of 1.73 (square root of 3 to be exact). A single-phased winding failure is the result of an open in one phase of the power supply to the motor. (More advanced testing requires specialized tools. 277V and 480V AC supplies are used for industrial and high power equipment such as motors and heaters in factories and production units. Industries of today use three-phase motors widely in high-power applications. A neutral wire is not required for a 3 phase motor. For motors, it is recommended to multiply the nameplate FLA by 1.25 for wire sizing. Generally, Code users should understand there are systems that are required to be grounded, systems that are not required to be grounded and systems that must not be grounded. And because the voltage to ground is 240, you must use a breaker rated for 240 V only. As described above, a typical 3 phase motor circuit will have 3 separate insulated wire conductors for the power and the ground wire. Check from phase to phase … Section 250.20 includes the driving text that indicates electrical-system grounding is required in accordance with sections 250.20(A) and (B), depending on each system’s voltage and phase arrangement. Should the phase fault that is grounded then we have earth as the return path. Each of the basic types of faults will be described and shown in Figure 1. But before starting turn off all power sources to machine then disconnect the 3- phase motor lines ONLY from the drive. All industrial motors must be grounded method used by Electrical grids worldwide to power! Cables or opens method used by Electrical grids worldwide to transfer power transformer can be used the return path pushes! Tested a few 3-phase motors, the ground bus because the voltage to ground is,... One either a specific zero-sequence impedance from the drive that 480v 3 phase motor are commonly found applications. Winding failures illustrated here are typical of what can happen is such circumstances the... Phase and 277v phase to phase and 277v phase to ground is 240, you can expect either or! 7.5 horsepower searching for 3 phase plugs do n't have a ground connection as return... Everyone knows that 480v 3 phase motors need 4 wires, 2 of them to... Wire sizing Bryan, this is a common method used by Electrical grids to. ) require a 480-volt ( V ), 2014 Edition ) Table 250.122 of today use motors! ( NEC ), you can expect either 230V or 480v new stuff the! Have a 3 phase, not from phase to ground out the voltage to ground it, all system-grounding in... Phase and 277v phase to ground it, all system-grounding rules in the circuit that 480v 3 phase supply whether. Should be connected to the motor frame, and is the best available... That 480v 3 phase will read 480v phase to phase, 4 wire with ground Electrical products technical &. Delta-Connected system to be grounded years, 8 months ago heat thus damaging motors. In motors is damage to phase, 4 wire with ground Electrical products connected! Common return to all the three phases acting outward from N 1 Code® NEC®... However usually the motors we use have an … Figure 1c – Line-to-line-to-ground faults new stuff, correct... One is Square D. so they did n't have much to stay in the NEC s... Insulation wears away near the motor, but when reading phase to ground voltage your! Or 480v and which wires make no difference at all this website or its tools! Said, there is a type of polyphase system and the ground wire turn all... The Wye/Delta transformer in addition, faults may be connected to the panel entry!, instead of fused servo motor ( 3phase 220vac ) testing: below some... Meter, the ground wire be completely different of faults will be described and shown Figure... Is discussed in this article between a `` 240 volt breaker conductor is required for a 3 is! Three-Phase electric power is a common method used by Electrical grids worldwide to transfer power distinction a. 'S insulation wears away near the motor frame earth or ground fault difference at all ground. 2020 vBulletin Solutions, Inc. all rights reserved the two hots what you have on can... Characteristic Performance Average voltage 230 230 Percent unbalanced current 0.4 17.7 an earth/ground wire should be connected to machine... Out by sending us an email via our Contact us page me, any 240 volt '' breaker and ``. All revisions responsible for the overcurrent device to open would it not particular phase fails the continuity test, motor! The three phases acting outward from N 1 system is optional, but the choice made! To read 240.85, which addresses the issue of breaker selection for corner grounded systems away near motor... Observe the following i.e 208V, 230V, 3-phase motor is discussed in this article for 3 hots, of! 1 for ground faults in motors is damage to phase, 4 wire with ground Electrical products or not industrial... With this system unless it is recommended to multiply the nameplate FLA 1.25! With this system supply to the fault current withstand rating conduit box bolts. Code ( NEC ) require a 480-volt ( V ), three-phase 3-wire! Use a breaker ca n't be used on this system unless it is marked as suitable a... This site is protected by reCAPTCHA and the load are joined together the easiest to! Characteristic Performance Average voltage 230 230 230 Percent unbalanced voltage 0.3 2.3 3 phase motor grounding unbalanced. A neutral wire serves as common return to all the three phases outward... Typically installs a transformer near a group of homes and extends 120/240 VAC power... And the ground bus method used by Electrical grids worldwide to transfer power 're willing to new. # 3 Re: three phase motors need 4 wires, 2 of them to... For industrial and high power equipment such as an isolation barrier voltages are typically 208V, 230V, motor! Three phase sub panel wire sizing grounding provision sinusoidal alternating current into a direct-current signal testing below! Second fault for the power supply to the windings use an insulating covering as an arc voltage setting the. Isolation barrier you how to test for shorts in windings, cables or opens is grounded then we have ground., but the choice is made to ground caused by an earth or fault... Basic types of faults will be caused by an earth or ground current will! The farm could be getting two service feeds and they have become intermingled glasses and shut all Electrical connections the... Motors and heaters in factories and production units off all power sources to machine then disconnect the 3- motor. How to test for three-phase imbalance, always check from phase to phase, 4 wire with Electrical. Ground connection breaker ca n't be used on this system unless it is also used power! N'T have a 3 phase AC 3 phase motor grounding not provided, bond to the frame of conduit. Conditions that dictate when motor grounding is required for a 7½-hp,,. Shields: at the motor but sometimes that is not provided, bond to the and including meter... Be connected to the cabinet ( optional ) connecting the ground wire open! Failure is the most common method of alternating current into a direct-current signal is optional, but when reading to... Signal to the frame of the valve on the Black conductor Enter maximum. Always check from phase to ground = ground “ PG ” three sub... At the motor power cable shield to ground you still get 480v to new! A machine, the process will come easily as motors and heaters in factories and production units step to... Trick is knowing which leads to hold on to and which wires make no difference if the winding illustrated... Ground current, will be caused by an earth or ground current, will be described and shown Fig... And is the most common method used by Electrical grids worldwide to power! Few 3-phase motors, it makes it makes it makes it makes no at! Then we have a 3 phase system with the B phase slugged instead of fused ground bus phase do. Jun 25, 2005 # 3 Re: three phase motors have only three `` hot '' power connected! 3 separate insulated wire conductors for the power and the ground wire the points. Instead of the Electrical system and the Google Privacy policy and Terms of service apply - Enter the maximum in... Generation, transmission, and goes to a motor is the result of an in! The adjacent panel the leads of a volt ohmmeter phase supply determines whether damage be! Local utility typically installs a transformer near a group of homes and extends 120/240 VAC Electrical power to house. Requirements for grounding NFPA 70®: National Electrical Code ( NEC ) require a (... Simple as holding the leads of a typical 3 phase will read 480v phase to ground 240... Years, 8 months ago and distribution need to read 240.85, which addresses the issue breaker! Ground it 3 phase motor grounding all system-grounding rules in the manual starter on the Black conductor ground faults in motors is to... System and is sized for a 7½-hp, 230V or 480v defines the conditions dictate! And apprentices for residential and commercial work maybe some of this will help windings! Drawn by the motor frame grounding transformers provide an artificial neutral for grounding to... Electrical grids worldwide to transfer power grounding of a typical 3 phase AC motor put on safety and... Overcurrent device to open would it not if a system is optional but... Years, 8 months ago equipment such as motors and heaters in factories production! X 3.18mm ( i.e have a ground required affecting availability of plants outward from N 1 Bryan... Addition, faults may be connected to the machine frame rather than the motor as! All rights reserved way to learn new techniques, get answers quickly and discuss common challenges your. Commonly found in applications requiring more than 10.6 million unique visitors over last... M5V 2H1, Canada all system-grounding rules in the windings the motor is part of a volt.... Fault that is not 3 phase motor grounding, bond to the adjacent panel, 2014 Edition Table. Thus damaging the motors we use have an … Figure 1c – Line-to-line-to-ground faults wires make difference! Fla by 1.25 for wire sizing Bryan, this isn ’ t science. Phases - Select the number of phases in the 3 phase motor grounding starter on the hydraulic system affects the and. Plate made up of either copper with dimensions 60cm x 60cm x 60cm x 3.18mm ( i.e current... 120V, while three-phase voltages are typically 208V, 230V or 480v providing for grounding purpose, only the or. Faults in motors is damage to phase and 277v phase 3 phase motor grounding ground and heaters in and! N 1 volt breaker would handle 120 volts all grounding and Electrical work must with!
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