# What is this electrical box?



## AR1911 (May 12, 2013)

I got this with some miscellaneous tooling, trying to decide if it's something I can use or just sell.
Near as I can figure it's a  relay to control a 3-phase circuit from single phase.  

I'd like to know the correct name for it.

The left side of the photo is the cover, the right side is the inside.

Rex


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## Old Iron (May 12, 2013)

It is a contractor can be used on single phase, It only has 2 heaters. It could be used to start a RFC.

Paul


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## AR1911 (May 12, 2013)

That's helpful, thanks.  What do the heaters do?
Is it normally used to control a 3-ph circuit from a single-phase switch?


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## Ulma Doctor (May 13, 2013)

the heaters are used to control amperage to the intended circuit.
think of them as fuses that reset themselves. in this case there is a reset button to be reset by the operator in case of overload.
there is a heating element inside the heater that changes length as the heater element changes temperature.
when a circuit is overloaded ,the heater is heated beyond it's rated capacity and no longer conducts electricity to the intended circuit.

no, sorry it is for controlling a single phase circuit. you could utilize it's design for a RPC.
 keep in mind the contactor only switches 2 poles, unless the picture is hiding the 3rd pole somewhere...


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## AR1911 (May 13, 2013)

Thanks both of you. That let me refine my search terms and I found a lot of information online. 

This was particularly helpful

http://www.allaboutcircuits.com/vol_4/chpt_5/2.html


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## Tonym47 (May 13, 2013)

AR1911 said:


> I got this with some miscellaneous tooling, trying to decide if it's something I can use or just sell.
> Near as I can figure it's a  relay to control a 3-phase circuit from single phase.
> 
> I'd like to know the correct name for it.
> ...


The proper term would be MOTOR STARTER W/ OVERLOAD


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## WDG (Nov 17, 2013)

As stated it is called a magnetic starter.   The red coil with the two  wires will become energized and pull in the silver part with the four  screws on the front.  The heaters are like a little coil and the fit  over the little point sticking up.  You can see it on the left side.   The two screws, one at the top and one is offset on the bottom is how  the heaters are held in place.  Most heaters have a dual range with  means you can put them in upside down.  If you take the heaters out of  the box, usually one end will be kind of pointed and the other flat.  On  the door should be a label that will tell you what the amperage is that  they will protect depending which way you install them.  The way they  work is the heaters get hot and heat up the little point that sticks up  thru the middle.  That little point (for want of a better description)  is filled with an eutectic alloy which will melt at a very distinct  temperature.  If the amperage gets too high the  alloy will melt.  The  back of this point has a round ring with notches on it and a little  lever rests on it and is held in place by a spring.  When the alloy  melts the little wheel will release the lever which move and lets the  aux contact that is holding the coil in drop out thereby protecting the  motor or what ever you are using it for.   As stated below, the heater  gets hot and will no longer conduct electricity, is not correct.  You  can put a meter across it and see that you still have continuity.  The  little post can be removed and you can look at the back and see what I'm  talking about.  When you push on the rest button you are moving the  lever back into place resting on the wheel with the notches on it.  If  you do not wait for the heaters to cool off a little it may not hold so  you will usually wait for awhile, couple minutes, to reset the motor and  at the same time try to figure out why it tripped.  This happens to be a  Cutler Hammer but all motor controls work basically the same way.  This  is a very old model but should work very good.  Just make sure you size  the heaters to the motor.  They do not have to be over sized like the  fuses do.


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