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Wiring A Motor Starter


hyu

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Hi,

 

I am currently in the process of building a saw table.

The saw table uses a basic run of the mill 1200W commercially available household circular saw (240V) which I have bolted to the bottom of the table.

I have locked the saw's switch to ON with a bunch of zip ties, so as soon as you plug it in the power outlet, it turns on.

 

Because a circular saw is extremely dangerous, I figured I could use one of those on/off switch boxes you commonly see on industrial equipment, etc. with one RECESSED ON button, and another EXTRUDING OFF button, so in the event you are accidentally in the middle of an accident, at least you can quickly turn the power off before it gets any worse.

 

I've tried talking to the local electrician. He suggested I use a DOL starter. Other than that, he wasn't very helpful.

 

Basically, I would also like to be able to run 2 power tools up to 2400W through the DOL starter. This would be the circular saw, and a router or a dust extraction unit (aka. household vacuum cleaner).

 

The circuit would start off with a power cable from the power outlet in to the DOL starter.

The DOL starter would then output to a ENCLOSURE, which has a normal double power outlet plate on it (the kind you'd see in your bedroom/kitchen/house wall/etc)

From there, I can plug in my power tools or whatever.

 

Now, I would rather not use the DOL starter because:

1. I REALLY don't think a circular saw needs any soft start or any overload protection, considering the switch of a circular saw is so basic

2. It costs over $100, which I think is stupid for something that is only going to turn my saw on and off

3. The buttons the DOL starter comes isn't what i'm looking for, and I don't think would fulfill the purpose of being the emergency stop button.

 

I was thinking of building a box out of wood or maybe get a double insulated enclosure, and attaching appropriate buttons too it. And whatever needs to go inside, goes inside.

 

Could anyone possibly suggest what I should do, what I should buy and any wiring diagrams/help would be apprieciated.

 

Thank you,

TL

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Hello hyu

 

Welcome to the forum.

 

The buttons on there own, will not do what you want. They are designed to control a contactor which has to be wired as an electrical latch for the buttons to perform.

A DOL starter is a set of buttons with a contactor wired as an electrical latch plus a thermal overload relay.

What you want is essentially a DOL starter without the thermal overload relay, but you would probably find that it is cheaper to buy a complete DOL starter than to buy the bits and get one made without the overload relay. - the overload relay will not interfere with the operation of the unit unless there is a continuous overload.

 

The wiring etc needs to be done by an electrician, this is usually law in most countries.

 

Best regards,

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A good reason to use a contactor in that circuit (Marke is correct, you don't want the Overload Relay part of it) is so that you can set up a "3-wire control circuit". This means you have a Stop button, a momentary Start button, and a "seal-in" auxiliary contact of the contactor. The Stop button has a Normally Closed (NC) contact, the Start has a Normally Open (NO) contact, and the Aux. is also NO. Control power for the contactor comes from your source, through the NC Stop to the NO Start, then out of the NO Start to the Contactor coil (the other side of the contactor coil goes to Neutral). Then the Aux. gets wired in parallel to the Start button. So when you press the Start, the coil pulls in, then the Aux. jumps around the Start so that when you let go, it stays on until someone hots the Stop button.

 

The reason for all this is that, should you have a power failure while running your equipment, the contactor drops out, the Aux. contact opens, and someone must push the Start button to re-start the saw. Without that, you might forget that the saw was on and when the power suddenly returns, the saw immediately re-starts, maybe cutting off your finger!

 

http://ecmweb.com/training/electrical_basics/704ecm-MFfig3.gif

"He's not dead, he's just pinin' for the fjords!"
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Thanks for the great input.

 

I am really inclined to do your method Jraef. The circuit looks simple enough. As for the power failure circumstance, I wouldn't have even thought of that, so thanks for mentioning that.

 

From what I can understand:

* When you press the START button it sends current through AUX M1, which "holds" the START button CLOSED, turning the saw ON.

* The STOP button breaks the circuit therefore releasing the "hold" on the START button and turning the saw off. Power outtage/failure would have the same effect.

* I have no idea what the BLUE M1 CIRCLE and OL capacitor-strike-through thing is.

 

If I could get your comments on that that'd be great,

hYu

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Thanks for the great input.

 

I am really inclined to do your method Jraef. The circuit looks simple enough. As for the power failure circumstance, I wouldn't have even thought of that, so thanks for mentioning that.

 

From what I can understand:

* When you press the START button it sends current through AUX M1, which "holds" the START button CLOSED, turning the saw ON.

* The STOP button breaks the circuit therefore releasing the "hold" on the START button and turning the saw off. Power outtage/failure would have the same effect.

* I have no idea what the BLUE M1 CIRCLE and OL capacitor-strike-through thing is.

 

If I could get your comments on that that'd be great,

hYu

 

The "M1" in the circle represents the coil of the starter (M is just a common designation for Motor starter). The OL represents an Overload Relay that would be part of the motor starter (that is a Normally Closed contact symbol, not a capacitor). You probably don't need one as most portable power tools have it built-in. The drawing I showed was cut and pasted from an industrial control diagram just to show the basic concept. So in your case, the M1 coil terminal on the right side would just connect to the neutral directly. The Aux. contact I mentioned is shown with a designation as M1 also, meaning it is physically attached to the Motor starter. The push buttons are all momentary; they do not stay in when released, so the Aux. contact M1 closes AFTER you push the Start button and the M1 contactor pulls in, keeping the circuit hot as it feeds the coil.

"He's not dead, he's just pinin' for the fjords!"
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