Magnetic switch - Woodworking Talk - Woodworkers Forum
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post #1 of 33 Old 10-22-2019, 12:05 AM Thread Starter
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Magnetic switch

I have a 240v, 1.5 hp Unisaw.
It has an awkwardly mounted Square D magnetic switch with small buttons. Iíd like to have something like this photo but Iím not sure of the reason for the magnetic switch.
Can someone enlighten me please?


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post #2 of 33 Old 10-22-2019, 12:30 AM
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A magnetic switch has many benefits, not the least of which is that if power goes out your machine doesn't automatically restart when power comes back on. There are other benefits but this is one big one.

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post #3 of 33 Old 10-22-2019, 02:43 AM
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To help you in your search, they are most often referred to as a Non Voltage Release switch
so searching for an "NVR switch" will give you many hits.

The simplest safety device you can install.
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post #4 of 33 Old 10-22-2019, 05:53 AM
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David hit it on the nose, biggest advantage to a mag switch is if the switch loses power it automatically opens the circuit, so once power comes back the saw doesnt start up again. Handy safety feature, but personally i prefer the big paddle switched

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post #5 of 33 Old 10-22-2019, 07:05 AM
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The one in the above pic is an NVR, with a paddle emergency cover. If you want a bigger paddle, its easy to make one.

The give away on an NVR switch are there are 2 separate buttons, one green, one red.

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post #6 of 33 Old 10-22-2019, 10:39 AM
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Not all switches with separate green and red buttons are magnetic. The green/red switch that came on my used bandsaw was not magnetic. I tested it.

Not all paddle-style switches are magnetic, and some are limited to 15 amps. I looked for a paddle style magnetic switch suitable for my bandsaw, but didn't find one. (I didn't know to search for "NVR.")

For the bandsaw, I bought a non-magnetic switch. I can live with that on a bandsaw. It was the large paddle OFF switch that I wanted. The original red OFF switch was hard to hit (small target), and hard to press (too firm for safety).
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post #7 of 33 Old 10-22-2019, 08:33 PM
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magnetic switches are used in commercial locations...

Liability insurance and OSHA requires that a machine may not come back on when power is lost unless the switch is manually turned on. This is where magnetic switches are most often used.


I have about six of the large paddle safety switches all over my shop:
https://www.grizzly.com/products/Woo...120-230V/D4151


They are dual voltage, but NOT magnetic. I don't need or want that feature.

The answer to your question will only be as detailed and specific as the question is detailed and specific. Good questions also include a sketch or a photo that illustrates your issue. (:< D)

Last edited by woodnthings; 10-22-2019 at 08:35 PM.
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post #8 of 33 Old 10-22-2019, 11:07 PM
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Quote:
Originally Posted by woodnthings View Post
Liability insurance and OSHA requires that a machine may not come back on when power is lost unless the switch is manually turned on. This is where magnetic switches are most often used.


I have about six of the large paddle safety switches all over my shop:
https://www.grizzly.com/products/Woo...120-230V/D4151


They are dual voltage, but NOT magnetic. I don't need or want that feature.
Can you explain more about why you did not want the magnetic feature?
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post #9 of 33 Old 10-22-2019, 11:35 PM
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Yes, one man shop, no employees, no children, no visitors

If the power goes out at night, I'll have no lights or operational power tools. I'll have to shut down the machine "blind" using my knee to bump it off. Usually the lights flicker a bit before a complete shut down giving me some warning to shut down any machines.



I'm OK, with all that. I would like to think that I would instinctively shut the machine down during any variation in power supply, but I donno if that's the case?

The answer to your question will only be as detailed and specific as the question is detailed and specific. Good questions also include a sketch or a photo that illustrates your issue. (:< D)
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post #10 of 33 Old 10-23-2019, 07:10 AM
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Quote:
Originally Posted by Tool Agnostic View Post
Can you explain more about why you did not want the magnetic feature?
Not the one with the original dislike, but if i can hop in i dont like them for the cost and complexity. Mag switches are pricey, especially compared to a paddle switch, and theres a lot more that can go wrong. Standard switch youve got a couple metal contacts and some form of mechanical hinge, any more than that and youre inviting Murphy in in my opinion

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post #11 of 33 Old 10-23-2019, 07:17 AM
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Here is the homemade paddle switch on my bandsaw. I glued a block on the hinged part to push on the stop button of the factory switch.
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post #12 of 33 Old 10-23-2019, 11:05 AM
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you can cut a hole in your paddle for the start switch, and reach through to start the saw, and the paddle remains in place..

a magnetic switch is also used on saws which have motors that draw over a certain number of amps (typically 20a) because standard switch contacts usually aren't rated for more than that. a magnetic switch (contactor) can handle higher amp ratings.
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post #13 of 33 Old 10-23-2019, 11:58 AM Thread Starter
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Quote:
Originally Posted by TimPa View Post
you can cut a hole in your paddle for the start switch, and reach through to start the saw, and the paddle remains in place..



a magnetic switch is also used on saws which have motors that draw over a certain number of amps (typically 20a) because standard switch contacts usually aren't rated for more than that. a magnetic switch (contactor) can handle higher amp ratings.


I suspect in my case itís a safety matter as my saw came from a commercial facility. The motor draw is 17.8A at 120v or 8.8A at 240v.

Now that I understand I do like the safety aspect of a magnetic switch. Just need to find a better way to mount it in an accessible spot.


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post #14 of 33 Old 10-23-2019, 02:27 PM
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if your saw already has a magnetic start you can wire any number of momentary on/off switches into the circuit and place any one of them in a more convenient location. amazon has this stop/start switch box for $13




the above would wire in similar to this, though it would need slight modification if you keep the original switches too. this diagram is 3 phase, just eliminate L3/T3

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post #15 of 33 Old 10-23-2019, 02:32 PM
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with a magnet starter you can also wire in an on/off toggle switch
though this method would start after power failure
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post #16 of 33 Old 10-23-2019, 02:33 PM Thread Starter
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Quote:
Originally Posted by _Ogre View Post
if your saw already has a magnetic start you can wire any number of momentary on/off switches into the circuit and place any one of them in a more convenient location. amazon has this stop/start switch box for $13









the above would wire in similar to this, though it would need slight modification if you keep the original switches too. this diagram is 3 phase, just eliminate L3/T3




Thanks,
I canít see the wiring diagram. Are you able to provide a link or repost the diagram?


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post #17 of 33 Old 10-23-2019, 03:06 PM
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google "magnetic starter wiring diagram" and you'll see hundreds of them

if you choose to go this route...
post up a picture of your magnetic starter: outside, inside and any wiring diagram there is
that way i can recommend a method of wiring in an auxiliary switch
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post #18 of 33 Old 10-23-2019, 03:08 PM
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there is typically a hold contact on any starter
when the momentary 'start' button is pushed, the magnet is energized and the hold contact keeps it energized
the stop button is wired into the hold contact circuit, when the momentary 'stop' button is pushed, it cuts the power, opening the starter

to add a 2nd set of switches
the start is wired in parallel, so that any switch has power
the stop is wired in series, so that any switch kills power

screen grab of the diagram posted
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Last edited by _Ogre; 10-23-2019 at 03:16 PM.
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post #19 of 33 Old 10-23-2019, 03:55 PM
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fyi... that switch i posted is sort of small, i've used them before
there are many bigger and more expensive
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post #20 of 33 Old 10-23-2019, 05:46 PM
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Hang on, that circuit bypasses the safety circuit.
Surely youre not advising someone to remove a safety feature?

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