Shop electrical safety designs

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All,
Spent some time trolling the archives and Google, and couldn't really find what I was looking for. I suspect in part it's because I'm suffering from a Language Gap - there's a specific term for what I'm looking for, and I don't know what it is.
So, I apologize in advance if this has been talked to death before, but I can't find it, if it is.
First of all, my knee has recovered enough from surgery in the past week that I've been spending my free time in the new shop (18' 6" x 19' fully detached garage) emptying all the boxes that don't belong there, emptying the boxes that do belong there into the hideous cabinetry out there, running boxes to recycling, giving things to Goodwill, etc. Very exciting! I expect to be able to set the tablesaw back up by this weekend! February of last year was the last time I made sawdust.
The walls and ceiling in the shop are exposed studs (16" centers) right now. I'm planning on putting drywall up on the ceiling and plywood on the walls. But that's not what I want to talk about (THAT is easy to find in the archives) - before I can do that, I have to get some wiring done. To get the wiring done, I have to make some key decisions.
I'm a bit of a safety freak, and I have two small children (4 & 2). Short term I want to keep them out of the shop entirely without supervision, and the lock on the garage door will do well with that. Long term, I want to let them in the shop, but not let them do anything really dangerous without supervision (i.e., anything involving power tools). I'm also interested in emergency power cutoffs, mostly for my own use. Right now the garage is fed by a 240v 40 amp circuit that terminates in a sub panel in the garage. I recognize I may need more in the future, but it's enough for now.
Without any thought whatsoever to the practicality or cost, the two big things I want are:
A lockout box. I want to be able to leave lights and battery chargers on, but throw a switch, put a lock on it, and have no power tools operate.
Several Big Red Buttons. I want to be able to hit a quick disconnect from one of several places in the shop, and have it kill the power to all the power tools (but not the lights or the battery chargers). Part of my problem is that I do not know what the industry Term of Art is for these buttons.
Of course, we don't live in a world where practicality and cost aren't concerns, so if any requirement I list above is too much work or too much expense, I'm willing to rethink. If it's gonna cost me $2000, I can lose the emergency cutoffs and just put a lock on the subpanel I have and be done with it.
So, here are my questions, and thanks in advance for anyone with the knowledge to answer, the inclination to help and the patience to read through my long-winded explanation:
1) What are Big Red Buttons called?
2) How do they work? Can I wire three circuits through one without needing a second subpanel?
3) What are the lockout box things called? Googling for "lockout box" gives me a bunch of storage boxes to store my lockout/tagout keys in. I think maybe a "safety switch" is what I want, something like this: http://www.builderdepot.com/browse.ihtml?pid 5815&step=5&prodstoreid"45
4) How do *they* work? Can I wire three circuits through one without needing a second subpanel?
5) If you held a gun to my head and said "Do it right now with what you know," I'd drop the emergency cutoff switches for now, install a new subpanel on a 30A breaker, and put a "safety switch" between the two of them. Is this, in fact, the best plan, or am I artificially limiting myself by my lack of knowledge?
6) Stupid question - I have this kooky idea to hook up a 50 ampish inline AC ammeter prior to the first subpanel. Is this stupid, or just geeky? I think it'd be pretty cool to always know how much juice I'm pulling.
Thanks in advance...
-BAT
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Just so you know, the word "trolling" in Usenet terms has a pretty specific meaning, something along the lines of "posting controversial messages to stir up people and prolong a useless discussion", which I don't think is what you're really doing.

The easiest way to do this would be to have the big power tools on a sub-panel, and the outlets on the main panel. Master-switch the whole sub-panel on and off.

Yup.
"Emergency Stop" is what most/all of them seem to be marked with.

I can't see the e-stop switches adding much cost, even if you run conduit from them back to the contactor (we call 'em relays). It's easy but time-consuming work, so it's worth considering doing yourself if you can get an Electrician to do the design and advise you.

See above.

Put 'em before the subpanel with all the switched stuff, and let them control the relay for the whole subpanel.

No, you're doing it right, the big red buttons juust control that subpanel.

It's geeky. I'd do it, and wish I had thought of it. Let us know how that goes, I may just retrofit my shop.
Dave Hinz
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Dave Hinz wrote:

Dave,
Thanks for the info so far, this has helped a lot.
I'm planning on doing it myself, which is part of why I'm really trying to understand the components.
So, it sounds like what I want is an "emergency stop" button, but the key thing I needed to know is that it's connected to a "contactor." I get a big red button, say, one of these beauties:
http://www.recycledgoods.com/ProductDetails.aspx?productID 196
And hook it to a "contact block," which then runs (24 V?) back to a relay at the subpanel which causes the shutoff. Is that correct, and, are there any other special terms that would be helpful in searching for suppliers?
Thanks again. Oh, and for those searching Usenet archives in the future:
Big Red Button = Emergency Stop button hooked to a contact block or contactor. You might also be looking for a relay, emergency switch or a switch.
If someone had done that ten years ago I wouldn't be bugging you folks, now. :)
-BAT
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Sorry to follow up to my own follow up, but I think I've figured out more.
It looks like I hook up a button/contact block. I like the look of this one:
http://web4.automationdirect.com/adc/Shopping/Catalog/Pushbuttons_-z-_Switches_-z-_Indicators/Eaton_Cutler-Hammer_22mm_ (E22_Series)/Emergency_Stop_-z-_Mushroom_Pushbuttons_-a-_Stations/E22JLB2N8B
That's an "N.C." which I presume stands for "Normally closed." So, when you push it, it opens a circuit (briefly? Until it's pulled back out or released some other way?)
That circuit is then hooked up to - what? A relay, I guess, but is there a special name for it? Or do I just get a 30A relay someplace? And what voltage (and AC or DC) do I run the contact blocks at?
If I figure it out on my own, I'll followup here...
-BAT
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OK!
As long as you hold it, which is long enough to trip the relay and/or breaker your 24v is controlling.

The control circuit is usually 24v (AC - it'd be spelled 24V if it was DC).
I'd switch the whole subpanel rather than a bunch of individual breakers, it's cheaper that way. Current capacity of the contacter (relay) should be more than the total current of the breakers it's feeding.
Many buttons to control one relay, which switches off many breakers in the entire subpanel all at once. Simplest, most cost-effective way to do what you want to do, I think.
Dave Hinz
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Ok, almost got it then, I think. Thank you, you've saved me many hours!
So, I get three or four button and contactor blocks, like this one:
http://web4.automationdirect.com/adc/Shopping/Catalog/Pushbuttons_-z-_Switches_-z-_Indicators/Eaton_Cutler-Hammer_22mm_ (E22_Series)/Emergency_Stop_-z-_Mushroom_Pushbuttons_-a-_Stations/E22JLB2N8B
I then connect them to a 40 amp, 24 volt contactor, such as this 2 pole model:
http://store.yahoo.com/waterheater/c2con40amp2p.html
I also connect one side of the contactor to a 30 amp/220 volt circuit on my existing subpanel, and the other side to the input of the new subpanel.
Assuming all this is correct, I only have one question - does the contactor step the 220 down to 24v for the buttons? Or do I need a seperate transformer to do that? Something like this, maybe?
http://www.surpluscenter.com/item.asp?UID 04120915272670&item-1164&catname=electric
Thanks again!
-BAT
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Brett A. Thomas wrote:

You might want to consider some start buttons to turn it all back on. They make pushbutton stations that have large "panic" buttons for the stop button and also include a start. Also, check your codes as to what gauge wire is going to need to feed your subpanel. See if they will allow your particular setup.
I have some of those definite purpose contactors and didn't really know a use for them. Now you have me thinking. I'm not plannning what you're planning. But, the noggin is smoking. As I've never used one and don't know their proper wiring, I do have this question. Can several pushbutton stations operate the same contactor or would there need to be a series of contactors? I've only wired magnetic starters and one per machine. I haven't tried to feed a subpanel with them.
I look forward to seeing how this thread progresses when some of the electrician types get home from work. Eric T. in MN
ps. Brett, where are you located?
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robdingnagian1 wrote:

Yes, that's actually one of my questions - exactly how do I turn this back on? And, obviously, I'll need to include my building inspector in all this. But I need to be able to talk vaguely intelligently about what I'm going to do, first.
As to the question, I think of two basic possibilities:
Either, as you suggest, there needs to be a "turn it all back on" switch that resets the relay somehow, or, the way this is *supposed* to be wired is so that, when the relay closes, it causes a dead short and trips the breaker on the original subpanel, and when the power cuts the relay opens automatically. I have no opinion about whether that's a good idea, or if it works, but, if it's not, I'm expecting to get flamed right about now. :)
All the threads I've seen previously on this subject have tended to the "tell an electrician you want emergency stops" type of answers, but it doesn't seem to me this should really be rocket science, and I hope we can figure it out and document it for everyone else.

I'm in San Carlos, CA.
-BAT
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I work for a large temperature controls company and we use the contactors you are discussing all of the time. What you are trying to do is set up an electrical circuit where you have multiple switches wired all in series. The voltage used to power the contactor is supplied by a transformer. It steps the voltage down from 120 VAC to 24 VAC. One side of the transformer (the common) is wired to the common side of the transformer, the other is wired through the normally closed switches, one after another, to the other side of the contactor coil. If any one switch is hit, the circuit will open preventing the contractor from being powered, killing the power to your power tools.
Depending on your local codes, you can mount a 24VAC transformer at the circuit breaker panel and route the wires through the wall to the switches, without conduit. The 24VAC transformer should be sized to handle the contactor while not exceeding a rating of 100VA (about 4 amps). That will meet the requirements for class 2 wiring, and can normally be run with thermostat wire. A 40VA, 24 VAC transformer will more than do the job for you assuming a typical 30 or 40 amp contactor.

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Brett A. Thomas wrote:

You might want to consider some start buttons to turn it all back on. They make pushbutton stations that have large "panic" buttons for the stop button and also include a start. Also, check your codes as to what gauge wire is going to need to feed your subpanel. See if they will allow your particular setup.
I have some of those definite purpose contactors and didn't really know a use for them. Now you have me thinking. I'm not plannning what you're planning. But, the noggin is smoking. As I've never used one and don't know their proper wiring, I do have this question. Can several pushbutton stations operate the same contactor or would there need to be a series of contactors? I've only wired magnetic starters and one per machine. I haven't tried to feed a subpanel with them.
I look forward to seeing how this thread progresses when some of the electrician types get home from work. Eric T. in MN
ps. Brett, where are you located?
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robdingnagian1 wrote:

contactor and the start ones in parallel to start it.

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A contactor is just a big relay and steps down nothing. You will need a 24V source You will also need a N.O. momentary contact switch (probably a key type) and a 24V relay to complete your system. Now I know that this sounds confusing but let me explain where I'm coming from. With what you seem to be describing, you are going to connect your contactor between the existing sub panel and a new one that will be switched by it. This is cool and is something I am considering as well. To control the contactor, it looks like you are going to hook up its field coil to a 24V source with 3 or 4 push button shut down switches in a loop configuration so that if any of the buttons are pressed, the contactor will open and kill the power. While this sounds good, there are a couple of problems. These push button switches are momentary action type which means that they only work when held in position. IOW, they will open (turn off) only for as long as you hold the switch. Now this is where problem comes in. If your 24V source is getting power from something that is not controlled by the contactor, the contactor will only open (cut power) when one of the switches is being pressed and as soon as you let it go, the power will be restored to the contactor and it will close again and re-power the new box. This will not be of much help. If you supply power to the 24V source comes from the contactor supplied side, you will never have power to turn the contactor on. So what do you need to do?? You need to build a self energizing relay to control the contactor and that is where the 24V relay comes in and you will need a momentary contact N.O. switch to activate it.. I can email you a schematic if you need it
--
If at first you don't succeed, you're not cut out for skydiving



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Just get a good contactor ( about nema #2) and you can put an aux N.O. contact block on it to perform the "latch" function
William....

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Dave, if he switched the whole subpanel then how would he still have lights? He'd have to have a separate sub panel for the lights and batteries and whatever else he didn't want switched. I think that was an original requirement....not sure if it changed.

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Ron Short wrote:

One of my original questions was "do I need a second subpanel?" and it seems like the answer is "yes."
-BAT
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One option is to put Solid State Relays in the feeds to your machines. These take a very low current to activate (3 - 30vdc at several milliamps each) A small wall wart can run a bunch of them. You can even run these off of CMOS chips. Then you can selectively turn on machines as your kids get old enough to use them. My grandfather did that with me (just with verbal warning) and I still have 10 fingers.
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That's why it's a sub-panel. The smaller outlets and the lights would be on the main panel for the shop.

Nope, no change.
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Hi, This is not something I know much about, so there could be any number of flaws in my reasoning, but how about switching (pun intended) things around: a normally open relay with normally closed stop switches? That way any tools on the subpanel after the relay will get power only if there is 24v on the relay. As soon as you hit a stop switch, you open the 24v circuit and the relay opens. Restore 24v and the relay closes again. Note that I'm assuming you can get stop switches that are N.C., and that will stay open after you push them (as opposed to closing again as soon as you let go). Lewis
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snipped-for-privacy@mchsi.com writes:
[... something similar to oridinary practise ]

ANY safety switch is N.C. and will stay in once it's pressed, some can be released by pulling it out, others need a key for rearming them. You can also have a rope attached to special emergency switches, so that when you pull the rope the power goes away, they are used for example along converor belts or other large machinery that's hard to secure with ordinary switches.
--
Dr. Juergen Hannappel http://lisa2.physik.uni-bonn.de/~hannappe
mailto: snipped-for-privacy@physik.uni-bonn.de Phone: +49 228 73 2447 FAX ... 7869
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On Fri, 10 Dec 2004 19:42:50 +0100, Juergen Hannappel

Our experience differs; I have seen some that are momentary contact, but they were connected to systems which dropped a relay based on that momentary opening of the contacts.
I don't know how old that system was, however. But momentary-contact e-stop mechanisms _do_ exist, and on medical equipment even.
Dave Hinz
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