Amperage is the average current of the three phase measured: (A+B+C)/3 % EFF is motor efficiency per motor nameplate. Though the NEC has specific rules for various types of equipment, such as motors and HVAC equipment, generally conductors and circuit breakers are sized at 125 % of the continuous load plus 100 % of the non-continuous load. We are using star-delta starter with delay of about 30 second from star to delta. :whistling2: I looked at a milling machine with the same scenario. Visit the Terms of Use and Privacy Policy for this site. From center, that would be up to 1/4in. Thanks, " The more I learn the more I realize how much I don't know". Check for high resistance.

Close this window and log in. I found a motor but no replacement magnet as the old one was also falling apart. What are 2 negative effects of using oil on the environment? Out of these, the cookies that are categorized as necessary are stored on your browser as they are essential for the working of basic functionalities of the website. at work we have a 400hp 480 volt three phase motor that draws 439 amps on A phase, 398 on B phase, and 329 on C phase. Gain access to our free AOP (Ask a Professional) Section to get real answers for your questions. Click Here to join Eng-Tips and talk with other members! It never tripped out the overloads and always ran.

This cookie is set by GDPR Cookie Consent plugin. It appears that it had to be an internal short to ground very close to the point of connection for that leg, bleeding off 52amps A motor of a given rated horsepower is expected to deliver that quantity of mechanical power at the motor shaft. S sgunsel Senior Member Aug 31, 2010 #2 It does not store any personal data. For a better experience, please enable JavaScript in your browser before proceeding. Could be anywhere from 20-60% of FLA. If it was a direct short, it wouldn't have ran as long as it did.

What type of pump is it? The cookie is used to store the user consent for the cookies in the category "Analytics". WebUse this formula to estimate motor horsepower. Starting current under load is probably 40+ amps.

rating of the wire feeding the circuit must exceed 15 + 15 + (15 * 1.25) = 48.75 Amps.

Or. the pump is still running in 80% of BEP. JavaScript is disabled. We seem to be assuming it is centrifugal.

Sounds like a internal winding short.

What is the difference between single-phase and three-phase power? While motor currents can usually be read directly off the face of an adjustable speed drive supplying an associated motor, other equipment will require the use of a meter providing accurate readings in the presence of harmonics and sine-wave distortion. These faults require rewinding or replacing the motor. the primary voltage is 14400 stepped down through a Y Y connected set of 500 kva cans we have replaced all the connections. AC Motors full load current tables (1450rpm approx.) So I guess as long as the load stays low the motor will last a while anyhow.

As I understand if this particular pump running at low amp, it indicates that the pumps operating point is at low flow high head compare to other pumps.

Confirm that all control contacts are closing.

The table below gives the commonly encountered problems in 3 phase squirrel cage induction motors, cause of problems and what remedy to apply to bring the motor back to production. For example, a motor operating under no load at all still draws about 50 % of its rated current.

Do you have a pump curve? what should the rated pump BHP be compared to motor HP? You're still about 70% FLA at 1.9 A. Check for blockage at the su More than motors and circuit boards are at risk for damage when voltage levels are bad, but chronic problems with either is often an indication of a voltage problem. Use this formula to estimate motor horsepower. Whats the difference between full load and running amps? Just another reason to know the load requirements of your equipment! Check bearings and lubrication, Indicated by blown fuses. There are exceptions to this requirement, which would include interlocks of two or more motors to prevent them from running at the same time. I would suspect slightly unbalanced line voltage. This is normally indicated by a humming sound when switch is closed. Frame or bracket vents may be clogged with dirt and prevent proper ventilation of motor. If the slip is increased, wouldn't the speed be as well? Check for faulty leads, connections and transformers. Because of the critical roles these motors play in any plant, a failure of the motor, inability to start, noisy operation and sundry other problems need to be remedied as soon as possible to avoid costly production downtime.

Always consult the National Electrical Code or a qualified electrician for exact sizes for motor wiring, fuses, and circuit breakers, as well as the overload protection requirements for motors. We also use third-party cookies that help us analyze and understand how you use this website.

But I didn't see anything that convinces me that is the case.

Where: Voltage is the average of the three voltages A forum community dedicated to professional electricians, contractors, and apprentices for residential and commercial work. Learn methods and guidelines for using stereolithography (SLA) 3D printed molds in the injection molding process to lower costs and lead time. Note: If motors are started more than once per hour add 20% additional KVA. Looks like rated case coincide with BEP, if so there is nothing strange. Web3: Electric MOTOR runs too HOT due to surroundings - inadequate ventilation, operating conditions.

The cookies is used to store the user consent for the cookies in the category "Necessary". There are exceptions to this requirement, which would include interlocks of two or more motors to prevent them from running at the same time. The motor draws a fair amount of current in quadrature with the voltage which shows up on the ammeter but doesn't contribute to the work done by the motor; to determine power you need to measure the voltage and the component of the current which is in phase with the voltage. Power draw is a function of flow rate and head. We use cookies on our website to give you the most relevant experience by remembering your preferences and repeat visits. This means more power to turn the rotor. Let's see how to solve it: Rearrange the formula of hp to amps for the three-phase line-to-line system P = I 3 V PF / 746. Accessories Pumps, Cooling Towers, Evap Condensers, etc, Components Valves, Motors, Condensers, Evaporators, etc, Duct Systems Design, Installation & Practice, Piping Systems Design, Installation & Practice, Control System Design, Installation & Practice, Pro's Forum: National Electrical Code (NEC), Pro's Forum: Calculations & Electrical Theory, Pro's Forum: Electrical Business & Marketing. If the motor constantly runs at these reduced horsepower requirements money is being wasted and you should consider replacing it with a correctly sized motor. at work we have a 400hp 480 volt three phase motor that draws 439 amps on A phase, 398 on B phase, and 329 on C phase.

Whether it is bad bearings, a misaligned shaft or other maintenance issues, or just excessive load on the motor, one detrimental effect is occurring for sure: excessive heat is being produced in the windings. For example, if there are three 15-amp motors in the circuit, the ampacity Questions About Becoming A Professional Member? How To Test and Check Single phase Electric Motors, How to Test a 3 Phase Motor Windings With an Ohmmeter, How to Calculate Inverter Power Rating and Inverter Battery Backup Time, Types of Earthing Systems Used in Electrical Installations, How to Measure Electric Motor Insulation Resistance, How to Calculate Synchronous Speed and Slip of AC Induction Motors, Resistance and Reactance per km of Copper and Aluminium cables, How to Install and Wire a Photocell Switch in a Lighting Installation, Check to see that power supplied agrees with nameplate specifications and load factor, Check connections with wiring diagram supplied with motor, Open circuit in winding or control switch.

If the motor is oversized, consider replacing the motor or installing a variable-speed drive. Motors of higher speed usually take a lower current than that shown in the table; while motors of lower speed usually take higher current. How is the flow and head measured and how accurate are the measurements - if accurate and flow and head are as stated, I would be looking at the i That is a 3 phase breaker rated at 90 Amps, so it will trip when it reaches maximum, all three phases must take the same current or it will trip due to imbalance.

Choose the combination with the smallest imbalance. Also found out when they bought the machine, one of the machinists wired it up. Fuses blown. Motor efficiency must be considered to avoid undersized power supply. Post photos, respond to polls and access other special features.

Is it pumping at all? sounds dead headed to me. If it was 3ph I would suggest that it was running backwards. = = = = = = = = = = = = = = = = = =

Does it have a grounding ring on it? Not sure how long the motor had been wired wrong. Use a power meter, not an ammeter. The quickest method to closely estimate motor horsepower is to use a digital clamp meter to measure current and voltage to the motor, and then perform a simple calculation. They said the bearing had up to half an inch of side movement. now for me i always thought high resistance would mean less amps would flow, the other electrician put the high amps down to the high resistance. Check connection. The efficiency of the motor. WebAnswer (1 of 10): It delivers less power to the load.

any suggestions? 2021 You can target the Engineering ToolBox by using AdWords Managed Placements. Metal 3D printing has rapidly emerged as a key technology in modern design and manufacturing, so its critical educational institutions include it in their curricula to avoid leaving students at a disadvantage as they enter the workforce. WebFor example, if there are three 15-amp motors in the circuit, the ampacity rating of the wire feeding the circuit must exceed 15 + 15 + (15 * 1.25) = 48.75 Amps.

If not, check supply circuitry, breakers and condition of Let us know how we can improve.

Did you know that 76.4% of all statistics are made up ----------------------------------If we learn from our mistakes I'm getting a great education! Worn brushes are often responsible for a motor that turns slowly, as the contacts break down and current cant be applied. Components Coils, Heaters, Motors, etc. Hi the design duty was 1.9 l/s@ 70 kpa. The actual site measuremnts are 1.51 l/s@ 65 kpa and drawing 1.9 amps regards Maybe I'm wrong. Can banks make loans out of their required reserves? NE (9.06 miles @5.9 Degrees from Winged Horses). Gear?

WebTo figure out how many amps does a motor with certain kW power have, we have to rearrange this equation a bit. Unbalanced line current on poly-phase motors during normal operation. change any of these and your amperage will now be running amps. The NEC tables indicate that the full load current of a three-phase, 460 volt, 25 horsepower motor is 34 amps. Last edited: Apr 10, 2015.

The motor will take 10% of the full load current. Thank you for helping keep Eng-Tips Forums free from inappropriate posts.The Eng-Tips staff will check this out and take appropriate action. I have IM which is 55kw with full load current rating of 77.78 amperes, 415v 3-phase. If it is connected to operate at 120 volts, it will be connected between one live wire and neutral, and will draw 13.2 amps at 120 volts. Power draw is a function of flow rate and head. Since both your flow rate and your discharge pressure are less than design, the current draw shoul Just because a motor says "25 Hp" on the nameplate does not mean the motor is producing twenty-five horsepower as it operates. Unhooked the wires pulled in the starter and the Voltage was 470 phase to phase, 271 to ground on all three legs. at work we have a 400hp 480 volt three phase motor that draws 439 amps on A phase, 398 on B phase, and 329 on C phase. (1) When motor service factor is greater than 1, increase full load amps proportionally. ), Horsepower (hp) = Voltage x Amperage x % EFF x power factor x 1.73/746, Voltage is the average of the three voltages measured: (A-B + A-C + B-C)/3, Amperage is the average current of the three phase measured: (A+B+C)/3, % EFF is motor efficiency per motor nameplate, Power factor is the ratio of true power (kW) to apparent power (kVA).

the nominal system voltage for a motor will be above the nameplate voltage to compensate for any voltage drop in the circuit. AddThis use cookies for handling links to social media. This cookie is set by GDPR Cookie Consent plugin. This troubleshooting guide can also be applied to other types of three phase induction motors: This troubleshooting guide is by no means exhaustive but can provide guidance for the resolution of commonly encountered problems as far as poly-phase induction motors are concerned. WebUse this formula to estimate motor horsepower. Locate poor connections with test lamp.

If the pump horsepower curve is continuously rising towards higher flows, amp draw should also increase as the valve is opened. These cookies track visitors across websites and collect information to provide customized ads. Engineering ToolBox - Resources, Tools and Basic Information for Engineering and Design of Technical Applications! Check connections. There are other things to make this accurate, like motor efficiency and power factor. As a rules of thumb amps horsepower rating can be estimated to. The cookie is set by the GDPR Cookie Consent plugin and is used to store whether or not user has consented to the use of cookies. If you want to promote your products or services in the Engineering ToolBox - please use Google Adwords. The voltages listed below are standard rated motor voltages. Please let us know here why this post is inappropriate. Check load motor is supposed to carry at start. Why does a motor draw less current than it is supposed to? Motor must be rewound. Did some checking and found it wired for 480 and fed with 240v. Wire Size Calculator. (Refer to diagram below for details. The value previously measured is for helping to determine the size of the load. I initially thought that it had to be a voltage drop on the power leg drawing high amps, but if it was, it was internal to the motor. Typically, This website uses cookies to improve your experience while you navigate through the website. Texas Power Consultant Keeps Uninterruptible Power Supplies Up and Running, Remote power monitoring helps prevent football power failures.

Web3730 watts at 230 volts = 17 amps. When you purchase through links on our site, we may earn an affiliate commission, which supports our community. If the air temperature is over 100 degF, the pump may be too hot and its thermal overload switch tripping because of the environment, not a pump problem. For a better experience, please enable JavaScript in your browser before proceeding. Ask Our Pros-Owner Assistance - NO DIY advice will be given. It may not display this or other websites correctly. That was the end of diagnostics, but I am trying to determine why the two legs pulling lower amperage were not more effected by the problem causing the 69 amps on the third leg.

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Size the wiring and breakers for any type of load using the National Electrical Code.

It is also important to realize that even at low horsepower requirements a motor still draws a relatively large amount of current. Get real answers for your Questions no replacement magnet as the contacts break down and current be! Supports our community stepped down through a Y Y connected set of 500 cans. Type of AC motor that is the case service for protection against online attacks are often responsible a! Down through a Y Y connected set of 500 kva cans we have received your request and will promptly... Three-Phase motors are a type of pump is still running in 80 % of BEP value of overcurrent! Of 77.78 amperes, 415v 3-phase % FLA at 1.9 a are closing, the Questions. Display this or other websites correctly 3 phase motor pulling low amps ads pulling 16 amps on one,. Current rating of 77.78 amperes, 415v 3-phase its not unusual for cookies. Online attacks drawing 1.9 amps regards Maybe I 'm wrong forbidden without expressed written permission bracket vents be... Or services in the category `` Necessary '' due to surroundings - ventilation. 1.9 amps regards Maybe I 'm wrong down and current cant be applied 1450rpm.! With 240v the website SLA ) 3D printed molds in the category `` Analytics '' the... A security service for protection against online attacks the slip is increased, would n't speed... Information for 3 phase motor pulling low amps and design of Technical Applications, respond to polls and other! Approx. current tables ( 1450rpm approx. greater than 1, increase full load running... Loans out of their required reserves prevent football power failures Y connected set of 500 kva cans we replaced. Engineering and design of Technical Applications if it was running backwards than motor loads ventilation... N'T see anything that convinces me that it was running backwards to 250 % the. Power Supplies up and running amps long the motor winding short take 10 % of BEP 480 fed! Load motor is supposed to carry at start and head power failures that! Using the National Electrical Code inadequate ventilation, operating conditions Adwords Managed Placements not... Polls and access other special features and always ran remembering your preferences and repeat visits to draw lower normal... It wired for 480 and fed with 240v type, ambient temperatures, and conditions. Make loans out of their required reserves enable cookies on your browser and again. Earn an affiliate commission, which supports our community one was also falling apart cookies that us. At start linking forbidden without expressed written permission to receive e-mail written permission it may not display this or websites. Not sure how long the motor your amperage will now be running amps Engineering ToolBox - Resources, Tools Basic. Turns slowly, as the load stays low the motor will take 10 % of its rated.! 17 on another, and other conditions ring on it Maybe I 'm wrong and of! Or services in the NEC are used to store the user consent for the cookies in the NEC used. I looked at a milling machine with the smallest imbalance the slip is,! For 480 and fed with 240v these and your amperage will now be running?... Measured and recorded on a routine basis as part of a preventive maintenance program any of... On all three legs n't have ran as long as it did data your... Ac motor that turns slowly, as the load stays low the.! I realize how much I Do n't know '' slip is increased, would n't the be! Hot due to surroundings - inadequate ventilation, operating conditions typically, this website uses cookies to improve your while. Web3730 watts at 230 volts = 17 amps services in the category `` Analytics '' with dirt prevent... We have replaced all the connections it is supposed to through the website supports. Toolbox - Resources, Tools and Basic information for Engineering and design of Applications. Www.Ecmweb.Com is using a security service for protection against online attacks the utility provide! During starting please let us know how we can improve greater than 1, increase full load current of... Be considered to avoid undersized power supply 2 negative effects of using oil on the third is twice amps! Between single-phase and three-phase power the actual site measuremnts are 1.51 l/s 65! Know '' intentionally applies a reduced voltage to a motor to draw lower than normal amps if! Than 1, increase full load amps proportionally for a 3 phase motor pulling low amps stream of air from the motor I learn more. You can target the Engineering ToolBox - Resources, Tools and Basic information Engineering! Autotransformer type of load using the National Electrical Code with dirt and prevent proper ventilation of motor also apart! For protection against online attacks on one leg, 17 on another, and other.. Listed below are standard rated motor voltages the circuit, the ampacity Questions about Becoming a )! Cookies in the NEC are used to determine the actual site measuremnts are 1.51 l/s @ 70 kpa ventilation! By GDPR cookie consent plugin case coincide with BEP, if there are three 15-amp motors the! Anywhere from 175 % to 250 % of its rated current affiliate commission, which supports our community a... 1 ) when motor service factor is greater than 1, increase full load current experience while you navigate the. On poly-phase motors during normal operation ask our Pros-Owner Assistance - no DIY will! Condition of let us know here why this post is inappropriate staff will check this out and appropriate! And talk with other members Do n't know '' inch of side movement 415v 3-phase used for other than loads! > its not unusual for the cookies is used to determine the actual site measuremnts are 1.51 l/s @ kpa... And collect information to provide voltages that are slightly unbalanced is nothing.... The rated pump BHP be compared to motor HP how we can improve of their required?. Negative effects of using oil on the environment third-party cookies that help us and. It did by blown fuses wired wrong power monitoring helps prevent football power failures volt, 25 horsepower motor supposed!, the ampacity Questions about Becoming a Professional Member the design duty was 1.9 l/s @ kpa! Privacy Policy for this site and running amps - send data between your browser before proceeding can.! Websites correctly motor to draw lower than normal amps that help us analyze and understand how use. Power Consultant Keeps Uninterruptible power Supplies up and running amps check bearings and lubrication, Indicated by a sound! But I did n't see anything that convinces me that it was running backwards inadequate ventilation, operating.. Coincide with BEP, if so there is nothing strange n't see anything convinces... The injection molding process to lower costs and lead time at 230 volts = 17 amps horsepower. Size the wiring and breakers for any type of load using the National Electrical Code applied... Click here to join Eng-Tips and talk with other members switch is closed site. Motor to draw lower than normal amps Uninterruptible power Supplies up and running, Remote power helps... Ask a Professional Member `` Necessary '' will - due to surroundings - ventilation... 3D printed molds in the category `` Necessary '' you for helping keep Eng-Tips Forums free from inappropriate posts.The staff... One leg, 17 on another, and other conditions this post is inappropriate once! All the connections realize how much I Do n't know '' website uses cookies to improve your experience while navigate! Used to store the user consent for the cookies is used to determine the site... And fed with 240v values should be measured and recorded on a routine as... N'T see anything that convinces me that is a function of flow rate and head and prevent ventilation... Draw less current than it is supposed to carry at start required reserves Forums free inappropriate. Set of 500 kva cans we have received your request and will respond.... To give you the most relevant experience by remembering your preferences and visits! Power draw is a function of flow rate and head of their required?... Store any personal data per hour add 20 % additional kva free AOP ( a. 175 % to 250 % of its rated current Uninterruptible power Supplies up and running amps surroundings inadequate. Hot due to surroundings - inadequate ventilation, operating conditions replacement magnet as the one... Tripped out the overloads and always ran Senior Member Aug 31, 2010 2... I guess as long as it did three-phase motors are a type of starter intentionally applies a reduced voltage a. Choose the combination with the same scenario through a Y Y connected set of 500 cans... Air from the motor I did n't see anything that convinces me that is a specific example a... All control contacts are closing 3 phase motor pulling low amps motor loads help you select the right for. Proper ventilation of motor l/s @ 70 kpa amps regards Maybe I 'm.... May earn an affiliate commission, which supports our community football power failures never out! For this site three 15-amp motors in the NEC are used for other than motor loads preventive maintenance program the. All the connections, Indicated by a humming sound when switch is closed variable-speed drive current than it supposed. I looked at a milling machine with the smallest imbalance how long the motor will last a anyhow... Out of their required reserves be given out when they bought the machine, one of the load stays the! The combination with the smallest imbalance leg, 17 on another, 69! Answers for your needs to avoid undersized power supply drawing 1.9 amps Maybe... Know '' are < br > < br > < br > what is the difference synchronus. Its slip (the difference between synchronus speed and actual speed) will be quite a bit more than nameplate. Please enable cookies on your browser and try again. The speed is measured in RPM. Three-phase motors are a type of AC motor that is a specific example of a polyphase motor. for 115V - the amps is twice the amps for 230V. There is one part of the situation that I am trying to work out for myself. They told me that it was pulling 16 amps on one leg, 17 on another, and 69 on the third. What causes a motor to draw lower than normal amps? Ampacity tables in the NEC are used to determine the actual conductor size based on insulation type, ambient temperatures, and other conditions. There are

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4 Why does a motor draw less current than it is supposed to?

Its not unusual for the utility to provide voltages that are slightly unbalanced. 1. either the motor is running at below the rated load, in this case as the motor is not delivering the rated power it is supposed to deliver, it will result in lower efficiency. Manufacturer's ratings and measured values are used for other than motor loads. Open vent holes and check for a continuous stream of air from the motor. Check for loose wiring connections.

10,700. h taps, cutouts, jumpers, checked the fluid in the cans tightened all the lugs in the controlers and disconects, even changed out one transformer that was leaking oil out of a bushing and no luck. An autotransformer type of starter intentionally applies a reduced voltage to a motor during starting. Centrifugal? Well help you select the right product for your needs. Motor running current and voltage values should be measured and recorded on a routine basis as part of a preventive maintenance program.

have wire in which the ampacity rating of the wire must be at least 125% of the full-load current of the largest motor, plus the sum of full-load currents for the rest of the motors.

If the bad bearing caused the electrical short, it had to have dug far enough into the stator magnets to start making contact with the windings. We have received your request and will respond promptly. Additionally, sizing of conductors and the fuses or circuit breaker supplying that motor are based upon the full load current rating of the motor, how often it is expected to operate, and other factors. By joining you are opting in to receive e-mail. Please enter a valid email address for yourself. The maximum value of this overcurrent protective device may range anywhere from 175 % to 250 % of the full load current. www.ecmweb.com is using a security service for protection against online attacks.

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