Contactor Questions

Liquid Force

ok, I primarily do residential so I don't know much about contactors and relays etc., but right now I'm looking for one with at least 1 NO contact and 1 NC contact, and both change when the coil is energized. 120v coil... Obviously I don't want to get or spend anymore than I need. It will only be carrying 1-2 amps, at 120v. Inductive loads. What kind of contactor should I be looking for? Any brand or model suggestions?

A couple other questions though... Is an auxilary contact something you can just add on to any contactor? Also, what is a reversing contactor? It basically looks like 2 contactors side by side with some wires ran between... what are they used for?

CE1

Here you go:
http://www.grainger.com/Grainger/wwg...BaseItem=4FE16

and

http://www.grainger.com/Grainger/wwg...mId=1611792630

Plus you can order it online and get delivered tomorrow before noon.

mdshunk

For an amp or two, I'd use an ice cube relay for that.

RobertWilber

I vote for the ice cube.
.. and the reversing contactor is used to swap two legs on a three-phase application, which will cause a motor to rotate the other way.

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MSSI

Also switches leads 5 & 8 from motor on single phase apps..

Aux contact screws/bolts onto a contactor and has an open and closed contact. They are not rated to carry or switch the same load as the contactor..They are usually a microswitch used on the control side for a holding circuit...

mdshunk

Some AUX contacts can stack on the sides of a contactor and can carry full rated current, such as with a lighting contactor. Some stack on top and carry full rated current, such as a control type contactor. Generally, MSSI is right, aux contacts are mostly only pilot duty.

MSSI

I was being a little "general" in my description... I have seen some pretty beefy aux. contacts, but in the full load configuration I call em expansion blocks..

Sparky Joe

What you're looking for is a 'relay' not a 'contactor'
A contactor uses one switch to control several circuits and a relay uses one control circuit to operate around 4 seperate switching actions.
And "Ice Cube Relay" is what you want and I hear they are around 60 bucks.

You'll have to read the diagram on the relay for the coil/control inputs and the NO and NC contacts.

Auxiliary contacts are what you find on a motor starter hence the name auxiliary and are used to control NO or NC when the motor is operating/non-operating.
Aux contacts are not on contactors because every contact on there is for the same purpose

Magnettica

A relay and contactor are basically the same thing. Generally, a relay is used in applications where the load is less than 15 amps, like in a control box for a hot water heater, A.K.A. a boiler. A contactor is used to for much larger applications where the load exceeds 15 amps. For instance, parking lot lights at a large shopping mall would most likely be controlled by a contactor that had several poles so that all the lights would come on at the same time. This type contactor would be normally open, and would become closed when the coil within the contactor became energized by way of say, a photocell.

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Sparky Joe

Thanks for lesson Mag, and your example is right in the sense that a contactor has several poles(or sets of contacts). And a relay is something that relays a control function into a work function.

There is no difference between the two, they are all just sets of contacts NO or NC and actuated by a solenoid, even a motor starter falls in this category.
The difference is what they are called. A motor runs from a motor starter, lights run from a contactor, and every other odd thing uses a relay(commonly known as an ice cube relay, due to the way it looks)

Magnettica

I've never worked on a motor controller, or a start/ stop station for that matter. They are contactors with OL protection, to protect the motor windings from excessive heat due to single-phasing, correct? Just like the OP, most of my experience is in residential service and installation.

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frenchsparky

Mag:

The motor O/L system do have either thermal [ heater ] or electronic sensing to read the current when it get cerentin [ sp ] level it will trip the O/L relay to the contractor.

yes just about all the O/L will trip on single phasing [ when you loose one of the 3 ph leg ] when the motor is pretty well loaded but when the motor is freewhelling it will make funny noise like koncking noise.

and the other thing that with 3 Ph motors if single phased it will NOT start from standstill and it will draw current more than twice than normal running amps .

but with new electronic O/L relay if they sense single phaseing they will trip very fast before the motor get a chance to become a cooker or smoker.

the other thing Mag,, if you work on the HVAC system you will get the idea with protection as well on the unit[s]

Merci , Marc

drlightman

Liquid Force, your relays and sockets can be found on pages 862-863 of McMaster-Carr's catalog. (www+mcmaster+com). I have used these components extensively, very reliable and wide variety of wiring/ mounting methods. I recomend the DPDT flange mount relays at the bottom of pg 863. They are small enough to mount in a 4" box. Like Grainger, McMaster consistently gave me next day delivery.

Recyclist

"There's always time to fix it later. Why not just use that time to do it right in the beginning?" (Shut up, Murphy!)

hanapaa

Liquid Force,
What are you trying to contol with that paticular relay?

drlightman

As stated in other posts auxilliary contacts are usually used for light loads (pilot duty). Most contactors and starters can accomodate one or two. They are available in NO, NC and dual versions. They're specific to each manufacturer and series. There are also contact renewal sets and replacement coils (you can change to a different coil voltage).

Starters are simply contactors specifically set up and rated for motor starting. They usually include overload protection as mentioned but not always. The overload relays can be discrete modules, could be mounted externally in series with the load.

A reversing contactor is composed of two (usually identical) contactors electrically and mechanically interlocked to prevent both sets of contacts from being energized at the same time. As stated they're most often used to reverse motors. An overload relay is usually included in series with the load. I have also seen them employed as motor starters (wye-delta), voltage and load selectors.

Recyclist

"There's always time to fix it later. Why not just use that time to do it right in the beginning?" (Shut up, Murphy!)

Magnettica

Yes, I know about the internal OL protection for the compressor coil on an A/C condensor unit. Let either the start coil or the run coil cool down so the OL can automatically reset before condemning the compressor and charging a customer for something he ir she does not need. *Every electrician knows that! (*sarcasm)

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hcecalaska

the ice cube is a good choice and very versitle and come in configurations from 1 contact to 4 contacts. when purchasing an ice cube you typicaly need a base and an enclosure. one of the very popular choices that we use here most of the time are RIB's (relay in a box) these are made by functional devices. the price is very good and super easy to install, mosgt instals are as easy as throught a 1/2"ko on a 4s box

CE1

17 posts to answer a simple question. You guys are great entertainment. Keep up the good work.