Manual switch vs. Magnetic motor starter
locash
| Posted in Power Tools and Machinery on
Hi, this is my first post and I hope that it is not asking too much.
Some time ago I purchased a used Unisaw at what I thought was a good price. Since that day I have been educated in the differences between single phase and 3 phase power. I decided to go with a new motor rather than a phase converter and purchased a Baldor WWL3515 (2 hp|115V/230V|24A/12A). My question is do I need a magnetic motor starter like the Delta 52-704 or can I get away with a manual switch like the Delta 52-346?
Replies
3 hp uses a magnetic starter. 2 hp can use a regular switch. One of the things about a mag starter is if the power shut it won't restart by itself when power is returned. You can get an inexpensive mag switch through Woodworkers Supply or Grizzly. You can figure these things out yourself by comparing catalog specs. Also don't be afraid of using your local motor repair shop.
Hi locash -
I agree with Rick - on a table saw a mag starter is prefered for the very reason he menitons. Plus, if you've had the saw unplugged to change blades or otherwise have your hands inside the machine, if for some reason the switch got turned on in the interim, it would start the saw when you plugged it back in without the mag switch.
That said, I purchased what I thought was a mag starter switch for my bandsaw when I made a new table/stand for it. Got it from Grizzley. Now, on a band saw it's not quite as important, I just thought it would be a nice feature. None the less, I never was able to get it wired correctly. So, I's suggest, as Rick pointed out, work with a local shop that can help guide you through it.
Incidentally to the topic, I bought a small concrete mixer recently that had a mag switch similar to the one I had purchased at Grizzley. Couldn't get the motor to keep running unless I held the ON button in. Fussed around with the wires and found that the leads had been connected backwards on the switch. So ....
It ain't pure and simple. They seemed to screw it up at the factory!
From Beautiful Skagit Co. Wa.
Dennis
You can certainly use the manual switch for 2 hp. As I said before 3 hp always has a mag starter. I would opt for a more generic brand as you will pay a lot more for the Delta switches. You can still have the safety features of a mag starter by using a JDS safestart plug. http://www.saf-start.com/
And always unlpug your saw when changing blades. Even a mag starter won't guarantee the saw can't start unexpectedly. I've seen hair trigger mag starters that would turn on if the saw was slightly tapped by a shop cart.
Rick,
Unless they have added to their product line, the maximum rating for the JDS 120v is 18 amps. That is borderline on inadequate for a 2hp motor. The 240 unit is only rated for 15 amps but that should be marginally sufficient for a 3hp motor.
I don't know what these cord cost but they could be a more cost effective alternative to mag switches.
Doug
The safe starts are good up to 2 hp only. I was recommending them for 2 hp and under as an alternative to replacing the switch. It's a good retrofit for schools and the cautious home shop folks. 3 hp should be using mag starter as I stated before.
Been dealing with these issues for many years, especially servicing machines in schools and OSHA requirements.
Edited 10/27/2004 12:05 pm ET by rick3ddd
So, to summarize what I think I have learned:
For the 2 Hp/230V/12A motor I plan on using the switch and cord combination I linked to in my earlier posting would satisfy the electric code and would protect against accidental restart.
A magnetic switch, if one could be found at a reasonable price, would additionally offer protection against overheating.
If these points are correct, I think I have found a suitable magnetic switch on EBay and I will contact the seller. Here's a link if you are interested: Siemens Mag Switch. Thanks again for your insight.
Edited 10/27/2004 11:44 am ET by locash
Can't pull up the site you are referring to from work...blocks. But looking back at your first post I'm assuming it came with a three phase mag starter. If so then get new heaters and an electrician can put a jumper on it so it works on single phase. Again I stress, have you checked with your local motor shop??? A good one will have some generic priced switches and the free technical advice will more than offset a few dollars savings buying from E-bay. This will be the guy you go to down the road when you have problems so get to know him now. This is how you educated yourself in the days before the web and it's still a great way to validate some of the web knowledge. At least you know he's a professional...advice on the web should be taken with a grain of salt, especially on electricity. I'm not an electrician but I pretend to be one at work.
The magnetic switch is a much better approach, since it will prevent accidental restarts and also protect the motor from damage.
Note that the switch you are looking at on E-bay does not have a start and stop button in the housing, so you will need to purchase a separate start/stop button assembly or reuse the one with the old switch if possible, but that is unlikely. The single blue button on the unit is a reset if the switch trips from an overload.
Before you bid on a more expensive switch, you should know that you can purchase a 220 volt, single phase, 2 HP, magnetic switch from Grizzly with self contained on/off buttons for $49.95, their part number G4572. It is an Asian made unit, probably not as well made as the Siemens switch, but the Grizzly switch should be adequate for your needs.
Just to add to everyone's knowledge, I noticed on the same page that they also sell simple magnetic switches, to prevent accidental restarts but with no overload protection for under $10, max capacity is 10 amp, 110 volt only.
John W.
Edited 10/27/2004 12:36 pm ET by JohnW
Rick - thanks for the embelishments, but I got the point the first time you made it. Part of the reason that I was happy to find this listing on EBay is that the seller is a local shop. I just wanted a second opinion if someone was willing to give it.
John - thanks for pointing out the missing buttons, that's something I'll ask about. I saw the Grizzly switch, but didn't think it would work. It's a 220V and the motor is 230V.
The voltage difference is unimportant, for all practical purposes 220 volt and 230 volt both refer to the same nominal voltage, which may not, in reality, be either at the socket depending on what kind of day your power company is having.
John W.
Edited 10/27/2004 2:05 pm ET by JohnW
Nominal (mean that's what it's named) household voltage in the US is 120V and 240V. Actual voltage in your house will vary, depending on the load on the system, and on what the utility strives to maintain. Most houses I've had hovered around 117V, but the house I'm in now stays very close to 120V, sometimes a little higher.
Devices are usually rated 125V and/or 250V (look at the rating on a plug or receptacle, for instance).
Induction motors that comform to the NEMA MG-1 standard are designed to operate precisely at 115V and/or 230V, and will operate satisfactorily at higher or lower voltages (but things like temperature rise, efficiency, power factor, service factor, and so on will no longer be at the design values).
There is no such thing (not officially, anyway) as 110V or 220V in the US, though some imported things may be marked as such.
Just thought you'd find that interesting.
Edit: JohnW is right; that 220V starter is fine to use to control your 230V motor running on 234V power from a 240V power system via a 250V plug on the end of a 300V (or even 600V) cord.
Be seeing you...
Edited 10/27/2004 3:07 pm ET by Tom Kanzler
Edited 10/27/2004 3:35 pm ET by Tom Kanzler
Funny how those ratings don't work out cleanly. I've always wondered how we got 200A and 225A panelboards but only 200A meter cans? At least 225A corresponds to a standard breaker frame size. A standard panel board is limited to 80% so that means 160A or 180A. But a UL listed 100% panelboard can run at 200A or 225A but you only have a 200A meter can and the code doesn't limit meter cans to 80%. Another one is that the code requires a service entrance ground to neutral bond be made at the first oportunity. So why do you always have to order the neutral ground kit for meter cans? And my favorite is on a service entrance the disconnect and overcurrent protection have to be combined or adjacent per code. But there's no limit on the distance between the service entrance disconnect and the meter. So you can run 500' of unprotected conductor from the meter to the disconnect and meet code.
Anyway back to the thread topic. I have a couple of the Grizzley marketed (Titan mfr. I think) starters and they're great and very attractively priced. Also the NEMA motor standards mentioned require the motor to operate at +/- 10% on voltage at rated horsepower. Fortunately woodworking machines rarely reach nameplate current unless you stall them so there's plenty of safety factor. For instance when I set up my planer/molder I put a 5 hp 1 ph motor on it per the mfr. recommendation if I intended to do moldings. I put my Fluke on it and ran some very hard old salvaged oak through it taking a 3/16" pass on a 10" plank - 16-17A was all it pulled and anymore load would choke it. So I can't see how it would ever pull 28A/5HP.John O'Connell - JKO Handcrafted Woodworking
The more things change ...
We trained hard, but it seemed that every time we were beginning to form up into teams, we would be reorganized. I was to learn later in life that we tend to meet any new situation by reorganizing; and a wonderful method it can be for creating the illusion of progress while producing confusion, inefficiency, and demoralization.
Petronious Arbiter, 210 BC
So what did you do with the 3 phase motor and electrics you removed? I may be interested in a purchase. I only have 9 Unisaw motors sitting on the shelf, could use more. Email me if your interested in selling the other motor.
If your saw has the LVC 3 phase electrics, it can be wired single phase and with a heater change can be used with the new motor.
Dave Koury
Thank you all for your advice. Given your comments, its my plan to get this switch and cord combination. I am planning on running this saw at 230V/12A so I am pretty sure this will suffice.
In addition to preventing accidental starts, an equally important function of a magnetic starter is to protect the motor from overheating. The electrical code allows you to skip this on smaller motors, up to 2 HP, I think, but it is still a worthwhile investment on motors over 1 HP. The panel mounted circuit breakers do not offer this protection.
For the protection to work, the switch will need to be matched to the size of the motor, and this is done in two different ways. Some switches can be adjusted to the motor's size with a knob inside of the housing, other brands use a component called a heater that is bought separately from the switch. You will need to purchase a heater that matches you motor's size.
As someone else has mentioned, the three phase switch you already have can possibly be rewired to work on single phase, but you may have to replace the heater in it.
If you purchase a replacement switch from Delta it may not come with the proper size heater, you are better off purchasing an after market switch and it will almost certainly be less expensive.
Often the wiring instructions that come with the switch can be extremely difficult to follow, I've seen electricians wire them wrong more than once.
It's a tough choice to make either way, but it is easier, and often no more expensive, to use a three phase converter than to replace the motor, wiring, and switches on a machine.
John W.
Edited 10/27/2004 10:36 am ET by JohnW
Matching magnetic motor starter switch to motor's amp rating
I have been reading this forum because I need to replace the broken, old magnetic switch on my Powermatic PM66 table saw. When I purchased it,itcame with a Dayton 5K470D 2 HP, 115/230v, 22/11A motor. Now I am considering two different switches, one is a 3hp 18-26A magnetic switch, the other is a 2hp 8.5-12A? I am concerned with limiting feature of the “heater” alluded to by JohnW.
If I ere to install the 2 HP switch, should I set the internal heater dial to 11 to match with my motor’s 22/11A rating?
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