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tiptop
03-08-2009, 09:01 PM
Hi All,
I have been trying to finish up my wiring job of the shop and came to the conclusion, I should have motor disconnect switches for my lathe, compressor and lineshaft motor. The lathe has a 3 ph. 5 hp. 13 amp motor, the compressor has a 1 ph. 5 hp. 15 amp motor and the lineshaft has a 1 ph. 3 hp. 13.5 amp motor. I would like to have a switch that fits in a 4 X 4 box instead of the large knife switch boxes. I have been looking at these two switches (see links) and would like to know what your thoughts are on them.

this;

http://www.grainger.com/Grainger/items/6A614

or this;

http://www.fruitridgetools.com/storefrontprofiles/DeluxeSFItemDetail.aspx?sfid=136763&i=233160593&c=0

Thanks, Jay

Roy Andrews
03-08-2009, 09:51 PM
the current rating or the hp rating of your two single phase motors is way out of whack. a true 5hp single phase motor will draw 50 amps on 115 and 25 amps on 230. depending on efficiency that can change a little but not much. if the motors only draw what you state then either switch will work but the overload protection of the one switch will not function as advertised and will offer no protection.

wierdscience
03-08-2009, 10:14 PM
Does it have to fit in a 4x4? If it could be bigger these are a good bit cheaper-

http://web1.automationdirect.com/adc/Shopping/Catalog/Circuit_Protection_-z-_Fuses_-z-_Disconnects/UL_508_Rated_Non-Fusible_Load_Disconnect_Switches/SD1_Series_Disconnects_(16-40_Amps)/SD1-040-BR

tiptop
03-08-2009, 11:14 PM
Roy,
That is the information on the motor tag. Neither stated if it referred to start up or full load. They are all on separate breakers at main panel for load protection but the switch does need to be able to handle the loads. I am not up on what they are or should be.

Wierd, They look good to me, especially the price. But as I am not sure what I need exactly, I will have to wait for more replies.

Thanks for the help and direction so far, Jay

J Tiers
03-08-2009, 11:53 PM
A "disconnect" does NOT break load current.

It ONLY has to be rated for "carry current", and is ONLY used to isolate the machine from the mains in cases where there is no plug on the cord.

If you have a cord and plug, that already functions as an acceptable disconnect.

If you are hardwired, then you need a disconnect, but it need only be rated to CARRY the current.

That manual motor starter is rated to turn the motor on and off up to its HP rating. In IEC areas, I believe that would be its "AC-3" rating.

You don't need a motor starter if you have control switches on the machine already. A "disconnect" is different and distinct from a "motor starter", and generally cheaper.

For single phase, a simple "knife switch in a box", or the "pull-out-block" type will do the job. Those disconnects, complete with conduit-ready box are cheap. Lowes reports a 30A cutler-hammer single-phase fused disconnect at $10. I didn't see a price for the 60A version, possibly $15 or $20.

The 3 phase is harder to find, Lowes etc won't have it, but an electrical supply place will have it.

tiptop
03-09-2009, 12:14 AM
J Tiers,

The air compressor and lineshaft motor have no on / off switches. What got me going on this was, since I am updating my wiring, I thought I would try to be closer to code. I have never in the 20 years I have been running this compressor had an on / off switch, I have always used the breaker. So far so good, haven't had to replace a breaker yet. But I know this isn't proper and so the change. I was hoping to have a smaller unit than most knife switch boxes I have seen as I want to mount them on a 6" X 6" post near the middle of the shop.

Jay

J Tiers
03-09-2009, 12:23 AM
OK, then you need a HP rated switch like your manual motor starter.

Don't sweat the current, the HP rating is what you need. Only IEC starters rate in amps...... You just need a starter rated for at least the HP of your motor, AT THE VOLTAGE YOU USE. Never mind what is marked on the motor for current.*

The compressor, though, should already have a pressure switch, and those commonly have a lever or other means on them to turn them on/off manually. So you WOULD have an on-off switch for it, and could use a real "disconnect" for it.

* The "locked rotor" current of motors runs by HP, and by a subtype rating letter giving the KVA per HP. That is the current drawn if the motor is stalled.

A starter rated for 7.5 HP, for instance can safely close or open the locked rotor current of any motor up to the maximum HP of 7.5 as marked on the starter.

crrmeyer
03-09-2009, 12:26 AM
Ebay is great for finding things like this at a fraction of the retail price.

Charles

tiptop
03-09-2009, 12:56 AM
J Tiers,

My compressor is in the loft so as to not use up valuable floor space. I believe it does have a switch as you mentioned but I have not used it and will check. So if I understand you correctly I need a switch like the Leviton MS603-FW manual motor starting switch without overload protection, as in my second link. Is the switch that wierdscience posted a link to similar, it is a lot cheaper. It is rated for 10 hp, 3 ph, or should I get the SD2-080-BR as this;

http://web1.automationdirect.com/adc/Shopping/Catalog/Circuit_Protection_-z-_Fuses_-z-_Disconnects/UL_508_Rated_Non-Fusible_Load_Disconnect_Switches/SD2_Series_Disconnects_(63-125_Amps)/SD2-080-BR

that is rated for 7.5 hp, 1 ph,? I believe those would take care of my single phase motors and I can use a drum switch on the lathe.

Am I following this correctly?

Thanks for the time, Jay

tiptop
03-09-2009, 12:58 AM
crrmeyer,

I have been watching the bay, but have not found anything that caught my interest that was cheaper yet.

Jay

JoeFin
03-09-2009, 01:36 AM
Jay

The first one you showed from Grainger will work fine. That is what I use on my rotary converter.

Stay tuned until 7pm tomorrow night, I'll look around the shop in the morning and see if we still have a few of them around. They had them in used but nice Stainless 8 x 4 x 4 hinged cover NEMA 14 cans and were tossing them out.

Me and FREE get along just fine

hardtail
03-09-2009, 03:49 AM
Firstly since we are mixing industrial and residence there are some differences to observe.........a local disconnect is intended as a safety device for maintenance personnel to perform work with a lockout device, a disconnect is not intended to be used as a switch as most are not really built to deal with the current inrush on a daily basis, that said I've used them as such too many times, the real function of isolating your power source would be your MCC or load center. Being these are all exisiting tools that you've used they are likely to function fine in the future with the addition of properly rated switches installed in your place of choice just be wary that conductor runs don't get too lengthy for the given size.

Your amp ratings for the motors are likely correct for 230V service, many 5hp compressor motors are 3450 rpm and draw more like what a true 3hp would.

Sparky_NY
03-09-2009, 06:51 AM
Just a couple comments:

The current rating for the 5hp motor seems out of wack because it is a "compressor duty rated" motor. This is the way they get away with calling a 3hp motor a 5hp. It can produce 5hp for short periods only. Larger air compressors use a true 5hp motor and thus rated about 25A at 230volts. I remember the first time I seen one of these, a huge 5HP decal on the air tank along with a 15amp cord and plug. Recently I seen one at home depot that is now claimed as 6.5HP yet still has a 15amp cord/plug. Calling it "stretching the truth" is a understatement!!

The NEC code allows the use of a circuit breaker as the disconnect device so long as the equipment being disconnected is within sight of the breaker panel. A cord/plug/receptacle setup can also serve as the disconnect.

Someone already mentioned the cheap pull-out type disconnects. They are commonly used for air conditioners and available in 30 and 50 amp flavors in 240 single phase and quite cheap ($10-$15).

J Tiers
03-09-2009, 08:55 AM
The use of the CB is fine for many applications, but in the loft is maybe an issue for the visibility requirement (I am always thinking OSHA/NEC, you may ignore in your own place, at your own risk).

The manual motor starter is clearly the best choice, although for strict compliance, you should have an overload etc for motors over 1 HP.....

I do NOT like the Automation direct one, it is an IEC-rated switch, seems to have its UL rating as an afterthought, and the ones I have used just like it I was not impressed by. They ARE rated, though, and can be used within their UL ratings, so yes, if your load is under 7.5 HP you can use it.

if you can use a regular disconnect, that will be far cheaper, but I understand for a remote load.

tiptop
03-09-2009, 01:51 PM
Joe,
That sounds good. I am not in a hurry as I have been using the breaker for twenty years.
hardtail,
This is a shop, not a residence. I do not want to use the breakers to shut off the air compressor or the lineshaft when not in use. This is why I am looking for switches. The air compressor motor does indeed run at 3450 rpm. As I said it is an older two stage style compressor, not one of the newer ones.
Sparky_NY,
I can not comment on 3 or 5 hp. just what the motor tag indicates. It is not a Home Depot type model though. I guess my post title is misleading folks. I want an on / off switch. My compressor and lineshaft motor can be seen from just about anywhere in the shop, but I do not want to use the breaker to shut them off at night or to run them when needed. The breaker box is at one end of the shop and most of the lineshaft machines are at the other end, to much walking. The compressor was not an issue as it is on most of the day.
J Tiers,
I believe the CB is fine for a service/repair type disconnect as visually it is within the code parameters. As noted above, my title was misleading. I am looking for an on / off switch that smaller than a "bread box", knife type switch.

I want to thank you all for helping and I think I am getting the idea, but more is good. I am sure I can be taught, just not easily.

Jay

hardtail
03-09-2009, 04:51 PM
For the single phase stuff I would just go with a good quality switch, Allen Bradley, Cutler Hammer, Siemens etc as each load is less than 15 amps, much the same as any residential.......my AC has both the pressure switch and an additional. I'm not saying this is a HD compressor but years ago they started building these things and choose to advertise a 5hp, they are but they aren't, they build a light duty motor and spin the crap out of em to get their rating, lift a 230V real 5hp and you'll see the difference likely by close to 80 lbs.....

For the 3ph I would choose a motor starter as you get a switch and true current protection for your device via heaters........

If your set on disconnects they do make them fairly narrow and they would mount on a 6" post........

Roy Andrews
03-09-2009, 10:47 PM
i know i will be flamed for this but if you just want to turn them on and off just put a decent 20 amp house type wall switch in a regular box. just switching one phase. i would also post a sign stating that this was not a disconnect and did not remove all power from the device. anyone who thinks this is a bad or unacceptable arrangement should look at a number of 230 v appliances. i can remember a welder and an electric dryer that both had 115 to one side of a motor that was hot whenever the unit was plugged in and the start button or an internal control switched the other leg on to power the motor. both of these devices were UL approved. they also make these switches for 230v at 30 amps so that you could switch both legs. they are a little hard to find but i have a few that i use for large outside lights. i purchased them years ago at a industrial electronics place.

J Tiers
03-09-2009, 10:49 PM
This isn't flaming...... But the OP evidently wants something better than that.

Otherwise he could keep doing what he is doing now.

wierdscience
03-09-2009, 10:54 PM
Also not flaming,but disconnect means completely so there is no chance of an accidental start or potential of voltage across the legs or to ground.

tiptop
03-09-2009, 11:30 PM
Roy,
When I first started thinking about this, I had come up with a similar idea, although I thought I might use two of them on my single phase circuit and pin the toggles together. Then I came to the conclusion if I was going to do anything, I might as well head towards where the code was pushing me.

I checked my compressor today and it does not have the small handle toggle by the pressure switch that some do. It was evidently set up to have a switch in the service line.

My dust collector in the wood shop has a magnetic motor starter with a 110V circuit I wired into a switched plug. That made that easy.

So far I think I like the SD2-080-RR, the best, that way if I change out a motor or machine it will handle something larger.

I appreciate the thoughts and will continue my search. Jay

JoeFin
03-10-2009, 12:00 AM
Jay

I bailed out on work today and didn't get a chance to look. I stayed up late finishing up my taxes and then tossed and turned the rest of the night. I don't think I slept more then 1 hour the whole night.

By the time I got to work I was pretty trashed so I just called the boss from outside the gate and went home.

Gemmie a shopping list of your electrical needs and I'll see what I can fish out. We are cleaning house right now

Joe

hardtail
03-10-2009, 01:11 AM
I think Joe will hook you up with something but if it falls through this is probably what you need.........I'd look for something small (surface mount) for the single phase stuff........

http://www2.sea.siemens.com/Products/Controls/Product/Manual+Motor+Starters.htm

Paul Alciatore
03-10-2009, 02:20 AM
For the single phase stuff I would just go with a good quality switch, Allen Bradley, Cutler Hammer, Siemens etc as each load is less than 15 amps, much the same as any residential.......my AC has both the pressure switch and an additional. I'm not saying this is a HD compressor but years ago they started building these things and choose to advertise a 5hp, they are but they aren't, they build a light duty motor and spin the crap out of em to get their rating, lift a 230V real 5hp and you'll see the difference likely by close to 80 lbs.....

For the 3ph I would choose a motor starter as you get a switch and true current protection for your device via heaters........

If your set on disconnects they do make them fairly narrow and they would mount on a 6" post........

I would not use a standard light switch (15 Amp) for any motor over 1/10 HP. I tried that once on a table saw and it burned out in a few starts due to the heavy startup current. There are 20 Amp switches and they are a lot better quality. One of them lasted till I sold the saw decades later. I think it was a 1/2 or 1/3 HP motor. Expect to pay $8 to $15 or more.