What is the difference between contactor and starter

A Contactor is a separate part of a motor starter which can be used as a power control device as well. It is used where frequent opening and closing ON — OFF operation needed in electrical equipment such as motors, light and heaters etc.

Because of this feature, manual starters are generally used on smaller loads where low voltage protection is not needed. The other main type of starter is the AC magnetic motor starter. Magnetic contactors are a form of electrical relay found on most electrically powered motors. They act as a go-between for direct power sources, and high-load electrical motors in order to homogenize or balance out changes in electrical frequency which may come from a power supply as well as to act as a safeguard.

Asked by: Haie Kuentz asked in category: General Last Updated: 19th June, What is the difference between a magnetic starter and a contactor?

The contactor applies voltage to a contactor coil to close the contacts and to supply and interrupt power to the circuit. The term ' motor starter ' usually refers to the complete assembly. How many types of starter motors are there? What are the two essential components of a magnetic motor starter? A 3-pole full-voltage magnetic motor starter is made up of the following components: a set of stationary contacts, a set of movable contacts, pressure springs, a solenoid coil, a stationary electromagnet, a set of magnetic shading coils, and the moving armature.

How do you set a motor overload? How do you check motor overload? To run the test perform the following steps: Turn the FLA dial back to its proper setting and let the motor run for at least 5 minutes.

Open the contact or while the motor is running and start a timer. Another way this can occur is if a rough edge of one con tact touches the other first and melts, causing an ionized path that allows current to flow.

In either case, the arc lasts until the contact surfaces are fully closed. Arc extinction Arc chute assembly. One major difference between AC and DC contactors is the electrical and mechanical requirements necessary for suppressing the arcs created in opening and closing contacts under load.

To combat prolonged arcing in DC circuits, the contactor switching mechanism is constructed so that the contacts will separate rapidly and with enough air gap to extinguish the arc as soon as possible on opening.

DC contactors are larger than equivalently rated AC types to allow for the additional air gap. For this reason, the operating speeds of DC contactors are designed to be faster than those of AC contactors. An arc chute or shield is a device designed to help confine, divide, and cool an arc, so that the arc is less likely to sustain itself.

There is one arc chute for each set of contacts that's fitted above the moving and fixed contact. Arc chutes split the arc established at contactor tips while breaking the current to quench the arc.

In addition, they also provide barriers between line voltages. The arc chutes used in AC contactors are similar in construction to those used in DC contactors.

However, in addition to arc chutes, most DC contactors employ magnetic blowout coils to assist with arc suppression. Blow out coils consist of heavy copper coils mounted above the contacts and connected in series with them. Current flow through the blowout coil sets up a magnetic field between the breaking contacts that "blows" out the arc. When an arc is formed, the arc sets up a magnetic field around itself. The magnetic field of the arc and the blowout coil repel each other.

The net result is an upward push that makes the arc become longer and longer until it breaks and is extinguished. Blowout coils seldom wear out or give trouble when operated within their voltage and current ratings. Arc chutes are constantly subjected to the intense heat of arcing and may eventually burn away, allowing the arc to short-circuit to the metal blowout pole pieces.

Therefore, arc chutes should be inspected regularly and replaced before they burn through. As part of a preventive maintenance program, large contactors should be checked periodically for contact wear, contact wipe, shunt terminal connections, free movement of the armature, blowout structure, blowout coil connections, coil structure, correct contact spring tension, and correct air gap.

Normally the slight rubbing action and burning that occur during normal operation keep the contact surfaces clean for proper operation. Copper contacts, still used on some contactors, should be cleaned to reduce contact resistance.

Worn contacts should always be replaced in pairs to ensure that complete and proper surface contact is maintained. High contact resistance produces overheating of contacts as well as a significant voltage drop across the contacts, resulting in less voltage being delivered to the load. A vacuum contactor switches power contacts inside a sealed vacuum bottle. The vacuum provides a better environment than free air for breaking the arc because without air to ionize, the arc extinguishes more quickly.

Housed in vacuum bottles, the arc is isolated and the contacts are protected from dust and corrosion. Com pared to conventional air contactors they offer a significantly higher electrical endurance and are the preferred switching devices in applications with a high switching frequency, for heavy-duty starting, and for line voltages above V. Two circuits are involved in the operation of a magnetic contactor. Identify these circuits and the part of the contactor each connects to.

A micro switch, when activated, is used to switch current to a solenoid valve coil by way of a magnetic contactor. To which circuits of the contactor would each device be wired? Which contactor coil rating refers to the amount of voltage below which the magnetic field becomes too weak to maintain the contacts in their closed position? Explain why the inrush current to an AC contactor coil is much higher than its normal operating current.

In what way can misalignment of the armature and core of an AC contactor cause a contactor coil to run hot? Does the severity of contact arcing increase or decrease with each of the following changes?

Why is it harder to extinguish an arc on contacts passing direct current than on contacts passing alternating current? List six things to check as part of routine preventive maintenance for large contactors. Home Articles Forum Glossary Books. GOALS : 1. Familiarize yourself with the basic uses for a contactor.

Explain how arc suppression is applied to contacts. Discuss the major factors in selecting the size of a contactor and type of enclosure. Explain the difference between a contactor and a motor starter. Explain the function and operation of motor overload relays. Understand the operation of a solid-state contactor and starter.

Main power contact; Auxiliary contact Magnetic Contactor The National Electrical Manufacturers Association NEMA defines a magnetic contactor as a magnetically actuated device for repeatedly establishing or interrupting an electric power circuit.

Switching Loads Contactors are used in conjunction with pilot devices to automatically control high-current loads. Two-wire control device; Three-wire control Ill. Auxiliary contact block; Main three-pole contacts; Fused disconnect switch The auxiliary contacts of a contactor have a much lower current rating than the main contacts and are used in control circuits for interlocking, holding, and status indication.

Electrically held contactor; Mechanically held contactor Ill. Contactor open; Air gap; Coil deenergized Ill. Suppression module; Contactor; Contactor coil; Suppression module Ill. Magnet coil current; Shading coil current Contactor coils operated from an AC power source experience changes in the magnetic field surrounding them. Arc chamber; Arc starts as contacts open; Current flows through ionized air; Arc is extinguished as distance between contacts increases Ill.

Arc Suppression One of the main reasons contacts wear is the electric arc that occurs when contacts are opened under load. Arc extinction Arc chute assembly One major difference between AC and DC contactors is the electrical and mechanical requirements necessary for suppressing the arcs created in opening and closing contacts under load.

QUIZ: 1. Give a brief description of how a magnetic contactor operates. What would most likely be used to lower the voltage level for the coil? Compare the operation of electrically and mechanically held magnetic contactors.

List three types of operating mechanisms for magnetic contactors. Why is the contactor coil molded into an epoxy resin? Explain how a shading coil prevents an AC contactor from chattering.

Why are AC contactor assemblies made of laminated steel? Why do manufacturers recommend that discolored silver contacts not be filed? Why do contactors require some form of arc suppression? A decrease in the voltage level b. Discuss different types of relays and contactors 2. Describe the difference between a contactor and a motor starter.

What is the main difference between a contactor and a magnetic motor starter? Draw the schematic for an across-the-line AC magnetic motor starter. With reference to this schematic, explain the function of each of the following parts: i. What is the major difference between a contactor and a relay? Draw a normally open and normally closed contact How many sets of double-acting contacts are contained on an 8 pin relay? Relays and contactors are single-input, multi-output devices.

What part of a relay or contactor is considered the input? Create an Account and Get the Solution. Log into your existing Transtutors account. Have an account already? Click here to Login. No Account Yet? Click here to Sign Up.