what is a motor starter

7/31/2019 What is a Motor Starter

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What is a Motor Starter?

Motor Starters are switches specially designed for starting motors. These switches are designed to withstand the largerloads required by motors. There are basically two types of motor starters, Manual Starters and Magnetic Starters.

Motor Starters serve two main purposes:

1. The relay contacts are heavy duty and are rated for the motor starting current.2. Service Panel circuit breakers are designed to protect building wiring, not motors plugged into wall receptacles. If yourelectrical box circuit breaker trips before your motor burns up, it is incidental, not on purpose. However, motor starters are

designed to trip on heater overload before the motor they start burns up.

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Manual Motor Starters

Manual motor starters are simply manual switches designed to control larger current loads typical of motor control. Theymay be small and similar to the light switches in your home, or they may be much larger dedicated switches designed forcontrol of high amperage circuits. These motor starters may be either Single Pole (switch one line only) orDouble/TriplePole devices (switch 2/3 lines). When a Double/Triple Pole manual motor starter is turned off, the powerfrom the power cable is completely disconnected from the motor. Manual motor starters may also be equipped withmatched heaters, which are overload protectors designed to open when the current load is too high. These heaters mustbe properly sized to the motor they are protecting or else they will either open too soon, or will not protect the motor. Thedisadvantage to manual motor controls is that they cannot have remotely located On and Off controls.

DO NOT USE LIGHT SWITCHES TO START MOTORS
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Manual Starter? Follow the wiring sequence as below and merely ignore the control wiring in RED.

There are single pole starters that should only be used for 120 volt motors. L1 is Line 1 in and should be the "hot" blackwire. T1 is Motor 1 out and goes from the starter to the motor. In this case, Neutral "White" is carried through to themotor bypassing the starter altogether. This wiring should not be used on 240 volt circuits.

240 volt, 1 phase motors should use a 2 pole starter. L1 is Line 1 in and should be connected to one of the "hot" wires, L2is Line 2 in and should be connected to the other "hot" wire. T1 and T2 are the corresponding motor out connections andshould be carried through to the motor.

Three Phase motors require 3 pole starters and each of the "hot" lines must be switched through the starter.

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Magnetic Motor Starters

Magnetic Motor starters are essentially heavy duty relays, often equipped with heater/thermal overloads matched to themotor they start. They are then controlled using a lighter duty (low or high voltage) circuit, auxillary relay contacts and acontrol station (or several stations) utilizing lighter duty switches (usually momentary sometimes latching). These switcheswould not be capable of switching the large loads required by the motors. Because the control circuitry is separate fromthe Load circuit, the On/Offcontrols can be mounted remotely and can even be duplicated if desired.

This type of motor starter will usually have an auxiliary contact switch: a smaller set of contacts that opens or closes alongwith the motion of the main contactors. These contacts will be used to latch the system in an on condition (contacts shownin the picture below as 2-||-3). Latching means that the auxiliary contact bypasses the ON button so the solenoid remainsenergized, until a separate OFF button cuts the power. Additional contacts (NO & NC) may also be provided and may beused for auxiliary circuits or to provide feedback to the rest of the system that the starter is engaged and the motor haspower.
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Some older style motor starters have built-in latching. These starters have four terminals labeled 3, P, E, and C (historicalleftovers from older models). The E and C terminals are for the hot and neutral wires, respectively, and remain powered.When power is applied to 3 and P at the same time, the starter will engage until power is removed from P. Power can beremoved from 3 at any time without affecting operation. The wiring for these starters is not addressed below............

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TYPICAL WIRING

Connector numbers will vary among manufacturers - typical numbers in brackets().

L1 (1) - first line in from power source (phase 1 for 3ph / Neutral for 1ph) L2 (3) - second line in from power source (phase 2 for 3ph / Hot for 1ph* see below for alternate wiring using L2 & L3) L3 (5) - third line in from power source (phase 3 for 3ph / NC for for 1ph) T1 (2) - first line out to motor (phase 1 for 3ph / Hot for 1ph) T2 (4) - second line out to motor (phase 2 for 3ph / NC for 1ph* see below for alternate wiring) T3 (6) - third line out to motor (phase 3 for 3ph / Neutral for 1ph) -||- (1-2, 13-14, 53-54)is a normally Open NO contact (closes when the relay energizes) -|/|- (95-96) is a normally closed NC contact (opens when the thermal overloads trip if associated with the overload block

- as shown in all three diagrams)

-|/|- is a normally closed NC contact (opens when the relay energizes if associated with the relay coil as auxiliary circuit -as shown in the motor reversing diagram as coil isolation contacts)

M - Relay CoilDuplicating Controls

START Button must be wired in Parallel to one another STOP Buttons must be wired in Series with each other

NOTES:

Low Voltage Control with transformer - The transformer output must be rated at the appropriate value for the relay coil(typically 12 or 24 VAC) in your particular starter. This should not be an issue with a manufactured magnetic motor starteras the transformer will have been chosen by the manufacturer to match the coil. Input power for the transformer comesfrom two legs of the primary input power, chosen to match the input voltage requirements of the transformer.

Line Voltage Control without transformer - Magnetic Motor Starters which have relay coils at line power levels do not usetransformers. Power for the starter relay is taken from two legs of the primary input power, chosen to match the inputvoltage requirements of the relay coil.

In either case, power should be taken from below the manual disconnect (if used). This will ensure that there is no powerin the box once the manual disconnect has been thrown.

All diagrams are intended to illustrate the logic of a latching contol circuit. Your motor starter may use wiring which isinternal to the starter, wiring which is different than the diagrams, etc. Please refer to the manufacturer's literature if indoubt.

If you are not sure of how to make the connections on your equipment, hire an electrician. Improper wiringcan Kill, Injure, Start Fires, Burn Out Motors or any/all of the above.

Edit3ph Starter/3ph Motor
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Line Voltage Control three phase (3ph) motor starter controlling a three phase motor (rev 08 Aug 2006)

Manual Starter? Merely ignore the control wiring in RED


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3ph Starter/1ph Motor

Line Voltage Control three phase (3ph) motor starter controlling a single phase motor (rev 08 Aug 2006) Some 3 phaseMagnetic Motor Starters require current to be seen across each of the three overloads. This may be accomplished bydirecting the output of second circuit back into the input of the third (previously unused) circuit and feeding the motor offof the output of the third circuit (rather than the second). Wiring then becomes: Line 1 L1 T1 Motor 1 (L1-hot240vor neutral120v) Line 2 L2 T2 L3 T3 Motor 2 (L2-hot120v or 240v)

Manual Starter? Merely ignore the control wiring in RED
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3ph Starter/3ph Motor/Reversible

Line Voltage Control - double contactor three phase motor starter controlling a reversible three phase motor (rev 08 Aug2006) (Note: L1 becomes T3 and L3 becomes T1 when the reverse relay is actuated.) The motor must be STOPPED beforeREVERSING unless the contactor allows for on-the-fly reversing. The coils are locked out via the NC contacts (M1, M2)usually contained within the mechanical interlock. When Coil #M1 is engaged, Coil #M2 is locked out and vice-versa.

Magnetic Starter - Control Stations

One of the advantages of magnetic starters is the ability to add control stations. These stations may be located at anyconvenient location and duplicated as required. The maximum number of stations and their location is unlimited for allpractical purposes. Stations are built using Normally Closed (STOP) and Normally Open (START) momentary contact

switches. These switches must be rated for the control circuit voltage at a minimum. Over-rated switches will work fine.Many manufacturers incorporate both Normally Open (NO) and Normally Closed (NC) contacts in a single switch body. Byrewiring the switch you can change it from one to the other. Many manufacturers also provide interchangeable buttons inat least red and green.
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The last station must always be provided to complete the circuit. The intermediate stations may be repeated as manytimes as required. Suitable 3 conductor control wiring is required from the starter to each of the control stations in turn(daisy chained).


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NEMA Starter Size Charts

what is a motor starter

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