Unisaw Switch Help

[Sam Chambers]

I made the trip over to Redmond & Sons this afternoon for their big open house, and nearly came home with a good gloat to report. As Maurce mentioned in another thread, Redmond has several bare-bones Unisaws for sale, as-is. I was looking at a stripped-down X5 Unisaw, 3hp, 1 phase, left tilt model that appeared to still have the shipping grease on the table. It was missing several things:

1. Fence & rails - No big deal, since I have a Jointech Saw Train.

2. Blade guard/splitter assembly - I hate Delta's design, and I'm thinking about switching to the MicroJig splitter and a Grrrripper, so this wasn't a big deal either.

3. Miter gauge - I have a Jointech Smart Miter, but I'd also pick up a cheap aftermarket miter gauge.

4. Dust connector - No big deal here either.

5. Extension wings - I'd like them, but I'd add tables on both sides anyway, so this wasn't a big problem either.

5. Switch and electrical cord to motor - This was the reason I didn't bring it home. Redmond told me that the Delta switch would be around $175 - $200!

When I got home and looked up the switch assembly on Delta's web site, they were about right on their estimate of the cost for the switch. But I looked at Grizzly's site and found a switch (http://www.grizzly.com/products/item.cfm?itemnumber=G4573) that looks like it would work.

Can any of you electrical geniuses tell me if I'm on the right track? I could be way off base thinking that switch would work. Is a switch and related wire all I would need to add to fire that saw up?

[Alan Schaffter]

Should work fine. I believe the 3 HP Uni motor draws only 12 Amps.

[mike malone]

hi sam
a simple push button on/off switch ($25) will work fine AND
the grizzly mag starter at $59 is hard to beat too
go get the saw
regards
mike

[Steve Rowe]

Sam,

You may also want to check out automationdirect.com for switches and magnetic starters. Also, they are located in your area. Good products, good prices, and good service.
Steve

[Jamie Buxton]

McMaster-Carr (www.mcmaster) has a toggle switch rated for 3 hp. It is what is controlling my cyclone. With a NEMA electrical box to enclose it, it costs $26. Part number is 7657K31.

[Dev Emch]

Hi Sam...

Couple of things.

First, does Redmond still have a vintage, fully restored Dewalt RAS on the main lobby show room floor? This is one which appears to have chrome handles and a solid wood top. Dont know the disposition of this unit however.

Second. Your on the right track. There are lots of options you can look into. Are you missing the mag starter? If you go with a mag starter or contactor, you need to keep a couple of things in mind. First, the switch used on a mag starter is actually two switches linked together. They often come in a neat little package with one green and one red switch. The green one is push to close. The red one is push to open. Lots of folks makes these including Dayton, Square D, Furnas, Cuttler Hammer, General Electric, Allen Bradley, etc. etc. etc. They have been a mainstay of everything from metal lathes to woodworking machines to car wash machines. Nothing sepecial here.

The mag starter is also nothing unique. The one from grizz has a price that is hard to beat. But also note that you can use a three phase contactor here as well. In many cases, one will use a three phase device in a single phase application because its cheaper to do so. Its a supply and demand thing. Also note that certain online auctions whose name cannot be said also have these items in mass. I often go shopping for all sorts of goodies. In fact, right now I am looking for an allan bradley differential air compressor cutout switch for my compressor.

Should you decide to go top drawer then you need to use the following. You will need a green and red allen bradley bulletin 800 push to start 35 mm switches. The bodies are the same regardless of application. In otherwoods they have dual sets of contacts allowing them to be used as either a push to close or push to open switch. The button hardware for the red button sticks up a bit for safety reasons and the green button hardware sits flush. You will also need a square D or hoffman box with two 35 mm holes. You could use the allan bradley box but these are way too expensive.

So bottom line is you have options. I go shopping the used and surplus electrical supply chains all the time for this stuff and never buy the parts from the dealers. Delta's price for that switch is way overboard. I could just about go with top of the line brand new allan bradley for that price.


And if you have questions about wiring, just post a request here or on the OWWM forum. There are plenty of folks including myself who can tell you which wire goes where.

[Sam Chambers]

First, does Redmond still have a vintage, fully restored Dewalt RAS on the main lobby show room floor? This is one which appears to have chrome handles and a solid wood top. Dont know the disposition of this unit however.Dev, that's probably the same one I saw in there yesterday, so, yes it's still there. There's something about the older stuff - it looks more like art than the modern stuff does.

Thanks to all of you for the advice on the Unisaw switch. I just wanted to be sure that I was thinking on the right track. I'll call Redmond in the morning to see if the saw is still there.

Assuming it all works out, I'll definitely need some help with the wiring. While I've run my share of phone lines and computer cable, and have soldered too many audio cables over the years, I don't usually mess with AC power.

Thanks again, guys!

[Dominic Greco]

I was also shocked to see the prices of the Delta switches. All I wanted was a magnetic switch that would not turn back on again in case of lost power. Grizzly had one that was rated for use with a 3HP motor and was very inexpensive. I think I paid $45 and I got a nifly little anvil as a gift (don't know if they're still giving them away).

Anyway, that's the switch I have installed on my Unisaw. It's been working perfectly for the past 5 years.

[Charlie Knauer]

One thing to check is thermal overload protection. If it is not in the motor it needs to be in the switch. Some magnetic starters have thermal overloads in them. Thermal overloads add to the cost of the switch but its cheaper than buying a motor. Also the overloads should be set to the amperage of the motor.


Charlie

[Sam Chambers]

Charlie:

Thanks for the info. I hadn't thought to look into thermal overload protection. Thanks for pointing that out to this electrically challenged woodworker!

According to Grizzly's web site, the switch I'm looking at does "protect against thermal overload". So, It looks like I'd be OK with that one.

[Sam Chambers]

Dominic:

Thanks for the info on the switch. It's nice to hear from someone who is using the same setup that I'm considering, and was just as shocked as I was over Delta's price.

[Dev Emch]

You hear the terms "Contactor", "Starter" and "Magnetic Starter" thrown around all the time. These are all relays in function. The most common are three phase which makes them also cheaper than single phase applications.

A motor "Starter" or "Magnetic Starter" are one and the same and these differ from say a "Contactor" by the use of "Heaters" or other overload protection devices. Often you see "Contactors" used in lighting applications.

On the output side of the starter is an overload protection device and this needs to be sized to the size you need to use. It does not hurt to use a slightly oversize Starter for you application as long as you size the overload protection.

The older style of protection are three bi-metallic switches called "Heaters". There are pages of these and you need to select the ones that you will need based on voltage and current loads. For three phase you need three heaters. For single phase, you can live with one or two depending on if you wish to protect both legs of the circuit.

More modern overload protection involves the use of overload relay modules in place of the heater block. Some of these can work on either single phase or three phase. ABB overload relays can do either. Some of the initial AB stuff cannot. It assumes the loss of a leg in a three phase system and automaticly trips out. So if your using a three phase overload relay on a single phase application, make sure you can tolerate the absence of one leg.

Some motors have overload protection built in. Often this is a very cheap and cheesy way of doing this and more often than not, these are cheap, low power, single phase motors. Its done this way because the application assumes from the get go that no standard motor "Starter" will be used. I personally would not rely on this method.

So as you can see, a mag starter or motor starter is a darn nice device to have. It offers a number of advantages and in three phase systems is actually needed because your switching in three power legs at the same time. In 220 single phase applications, you should have both legs protected in which case your switching in two legs at once. Both are examples where standard switches are not a good idea.

[Sam Chambers]

Dev...

Thanks for the info...but now my brain hurts. This makes me realize that: 1.) You know what you're talking about, and 2.) I know less about electricity than I thought!

[Dev Emch]

Hi Sam...

Hope I did not scare you you off. Its really pretty simple. The magic box is self contained and often you only need to wire in at most a few wires to the front end of the box. Its all straight forward.

The functionality and techo-rant capability of these boxes are all in the box. For many of us who refurb old woodworking machines, its just adding the box. Once closed, you rarely need to go int there. Its nice to be able to purchase a hunk of functionality to get you from the machines power cord to the motor with as little brain work as possible.

Honestly, its really pretty straight forward. I just got my 1933 yates bandsaw running using a modern Allan Bradley starter box which I got second hand from an old ice cream machine what was being thrown out. I really love how that old saw cuts!

[Jamie Buxton]

So, Dev, a "thermal overload switch" is exactly the same as a "circuit breaker": too much current trips the device. In fact, both operate by the current heating some little bit of something inside the device. Saying that the device provides thermal overload protection would make more sense if it were actually mounted on the motor, so it could sense the temperature of the motor.

[Jamie Buxton]

Putting a circuit breaker on a machine in a big factory makes sense to me. The electrical supply may be able to deliver hundreds of amps, so each machine takes care of protecting itself. However, in a small shop, the argument for individual circuit breakers is weaker. Say you put a "thermal overload switch" (that is, a breaker) on a 3 HP saw, and set it at 15 amps because the motor plate says it can draw 12 amps. Then you plug the saw into the circuit on the wall, which is protected by a breaker in the breaker box. Often the circuits in a home shop are wired with 12 gauge wire, and the breaker is a 20 amp one. Or maybe somebody put in #10 wire and a 30 amp breaker. For the machine's breaker to trip, you have to suppose a fault which is just over the the machine's breaker size, but less than the circuit's breaker. That's a very well-controlled fault, and not very likely.

[Dev Emch]

Hi Jamie...

Not quite sure about what you mean in your last message so bear with me. I dont think I would be willing to compare a breaker to a heater. There is more involved here than this.

A breaker's function is to protect the downstream circuit from amperage overloads. In fact, there are cases in which the starting current of a motor actually trips the breaker. You need to slow down the trip window and that is why some machines use slow blow fuses in lieu of breakers.

A motor thermal overload protection device has one purpose in life. To shut the motor down before permanent damange to your stator windings occur. Not all motors are created equal so you cannot say that any motor overheats at a particular temperature. Depending on the make and model, each motor has its own ability to transfer heat energy away from the stator windings. Usually, if a stator gets to a certain temperature capable of activating a protection device such as an embedded thermistor, its to late. Also just because you have overheated a motor does not mean it will not work. In fact, the rule of thumb is that you have shortened the available operation time in hours left on the motor by 50 percent for *EACH* overheat event that does not itself smoke the windings.

Also during start and instantaneous torque draws, the current in the windings can exceed the continous current load rating for the stator windings. Under normal conditions, it will take a certain amount of time for this overload condition to become destructive. By time, I mean a matter of miliseconds to no more than 2 or 3 seconds. This is considered normal. Now you can use devices such as VFDs to implement a soft start on the motor which calms down that startup current spike but whats the point if you have not reached an overheat condition.

When I size heaters, I can look up in the allen bradley engineering book and select just the right heater. Single phase versus three phase. What is the size of my starter? What is my line voltage? 208 versus 220 versus 240 versus 440 versus 480 etc. etc. And heaters are pretty cheap. So I can mix and match to obtain just the right amount of protection for that particular motor in that particular application.

The point is this. I already know ahead of schedule what it will take for me to overload my motor. Instead of waiting for my motor to heat up and shorten its life so that I can trip an oboard sensor, I can use the heaters to head this one off at the pass. To stop the destruction *before* it happens.

Note that this approach is not new. I have seen motor starter/heater combos going back to machines built during the 1920s. And three phase motors are nortorious for leaving out everything that is not needed to run that motor. If it costs money and does not produce, its not included! Period.

Also consider dual voltage motors. These come in both single phase and three phase flavors but the principle is the same. By boosting voltage, I reduce current flow in the stator windings. You dont save anything because power is power and that is what you ultimately get billed for. But your stator runs cooler because the amp load is lower. And its amps that will cause you to overheat... not voltage... well, at least not directly. Look at standard THHN wire. A 10 gage THHN conductor can take up to 600 volts but its limited to 20 amps. It does not matter if I get that 20 amps on 55 volts or 110 volts or 220 volts. This all confuses the onboard motor protection. With a stand alone heater block, I can ajust my selection of heaters to compensate for this within minutes.

Hope this round about diatribe gives everyone who is interested a bit more feel for what heaters are and how they can help.