Motor Starting & Running Current

What's a DOL? When you say (paraphrased) "help in designing starting, running current and help with sizing cables," are you asking for someone to give you a list of starting and running currents for all kinds of motors, or are you designing motors? Given a specific motor, and the distance it is from the power source, the wire size can be determined. The National Electric Code (used in the US) specifies wire size and circuit interrupter size for motor circuits, as well as voltage drop considerations for motors, for example.

Direct On Line(Starter), I am asking help in Designing procedure/ Typical calculation for designing starting, running current and help with sizing cables for different kinds of motors. The list of starting and running currents for all kinds of motors will be easier for my further references.

I was being facetious when I asked, " . . .are you asking for someone to give you a list of starting and running currents for all kinds of motors . . .?" There are such things as motor handbooks, which have general data in them concerning starting and running current for a given horsepower and voltage, but such data won't be typed into a message and sent to you in the near future by me or anyone else, I'd bet. Sorry I mislead you . . . I just searched Amazon.com for "electric motor handbook" and got hundreds of titles. One search engine for information on motors is globalspec.com, which will give you a long list of motor manufacturers, some of whom will send you a hard copy of their motor data, although a lot of such information can be found on line.

You have to give us your specification if you want to calculate the current and sizing for the cable for 1 KW motor or 10 KW motor and so on..... Without these data's no body can do the calculation and sizing of the power cable either for DOL, Stat Delta, or Auto Trans starter.

For the typical calculation purposes for starting, running current and sizing cables for different kinds of motors (DOL, Stat Delta, or Auto Trans starter) u can assume any specification & its distance from the power source (some 10kw and 35 meters like that).

Starting an Induction motor on a fixed voltage and fixed frequency source is dependent on various factors, among them some are pertaining to the system parameters and some pertain to the driven load. Among the system parameters the major issue pertain to restricting the voltage dips during the starting process and with regards to the driven load the torque produced by the motor shall be higher than the load torque such that the motor accelerates the load with out the motor getting unduly heated. The common method of starting induction motors include Direct On Line (DOL), Star - Delta (Open transition type and Close transistion type) and finally Auto transformer starting. It is an established fact that the starting power factor of an Induction motor is low (typically 0.25 for smaller motors and down to 0.1 for very large motors). This low powerfactor results in the motor drawing a very high starting current typically (450 to 720% of the rated current). This high current results in excessive voltage drop upstream of the motor and may lead to various problems, which includes even normally running motor to "Pull Out" of the system. Thus all the above means ultimate involve some means of reducing the applied voltage to the motor during starting. While doing so the following issues shall be specfically observed. a) The total voltage drop from the source bus to the motor terminal shall not be >15% .Thus the cable IZ drop shall be calculated considering the full starting current during DOL operation. b) The torque produced by the motor shall be higher than the acceleration torque required by the load (The torque speed characteristics of the load shall be matched with that of the motor). Another important issue to be checked if the motor thermal with stand capability is not exceeded. While DOL starting ensures the highest torque, Star delta and Auto transformer produces a lower torque (torque is dependent on the square of the voltage, thus with star delta starting, when the applied voltage is reduced to 58% the starting torque is reduced to 33% of the rated starting torque). c) While using open transistion type of star Delta starter, care shall be taken to ensure that the spike in current during the transistion time from star to Delta,such that the the spike duration is minimum

Ugly's Electrical References Guide will have all your answers. Its pocket sized. I don't leave home without it.

u can consider 7 times starting current of normal runing curent