shocking table saw

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Yes. Go out and buy a length of 16ga cord with three conductors - usually Black, White and Green. Wire the black and white wires into your motor the way that it is currently wired and secure the green to the metal chassis of the motor. You can usually find a screw to slip the ground wire under and then tighten the screw back down. Wire a three prong plug to the other end and you're off. Maybe cheaper and easier is to buy a 25 foot extension cord and cut it down to the length you want. Wire the cut end to your saw and your plug end will be already wired in a nice factory molded plug.
You can also run a separate ground from the motor to a ground in the building, but that tends to get pulled loose or otherwise damaged. I like the first way better.
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On Mon, 13 Sep 2004 23:20:02 GMT, "Mike Marlow"
|
| |> I have an old Craftsman table saw that has an external motor. It runs the |> blade via two belts. it only has a 2 wire non-polarized plug. If I |> remember right its circa 1942. Anyway, frequently when we lean against it |> with a sensitive part of the body, ( face, belly, leg ) we'll get a slight |> zap. Can a ground wire be added to this to stop it? Where would one |place |> it? |> |> signature Troy & Michelle Hall Cogy Farm Clay Center, Kansas 67432 |> | |Yes. Go out and buy a length of 16ga cord with three conductors - usually |Black, White and Green. Wire the black and white wires into your motor the |way that it is currently wired and secure the green to the metal chassis of |the motor. You can usually find a screw to slip the ground wire under and |then tighten the screw back down. Wire a three prong plug to the other end |and you're off. Maybe cheaper and easier is to buy a 25 foot extension cord |and cut it down to the length you want. Wire the cut end to your saw and |your plug end will be already wired in a nice factory molded plug. | |You can also run a separate ground from the motor to a ground in the |building, but that tends to get pulled loose or otherwise damaged. I like |the first way better.
Mike is right on, especially about buying an extension cord and cutting it to length. You buy a "pigtail" and it costs big bucks. Buy a 10' extension cord on sale for a few bucks.
As to the others bunching up their panties about *danger*, it's very possible the shock is from nothing more than static build up. If it's actually leakage in the motor, then the ground will at best make it safe and at worst will pop a breaker, in which case the OP can take the motor to a shop for troubleshooting.
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Next to listening to Dan Rather, this is just about the stupidest thing I've heard all week. I'm guessing the OP has been shocked by static electricity in the past, so I think he knows the difference between that and an AC current. The only reason it's not that bad right now is that the hot isn't making a very good connection to the frame of the saw. Maybe one of these days, it will make a good connection. At that point, I don't want to have to rely on ground or a circuit breaker to protect me. If you think I'm getting my undies in a bunch, let's do a test. I'll hand you a steel bar connected to ground. You hold onto it and I'll connect it to 120. Sound like a good idea, genius? Here's a better idea. Find what's wrong with the motor now instead of trying to half-assed work around the symptoms.
todd
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For the record, let me say that I agree that if the motor is defective internally then it should be repaired or replaced. I jumped past that in my original reply. However, adding a ground in no way presents a danger or a stupid move to the OP. What do you suppose we use grounds for if not for the type of situation being discussed here? If you don't want to rely on a ground or a circuit breaker to help protect you from leakage from hot, then perhaps you should stay away from electrical appliances since that is the very reason for grounds.
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To provide a margin of safety when accidents occur. If it's intentional, it's not an accident, it's stupidity.

Grounds protect you from accidental leaks, not intentional ones.
Plus, if your saw is in a basement or garage, it should have a GFI anyway, and using a ground that way would trip the GFI.

No, a ground is not appropriate for bypassing a KNOWN wiring fault to obviate the need for repairs. Grounds are a safety net, not a band aid.
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writes:

Your points are well taken and I posted a different reply in which I indicated that I had jumped right past the matter of having the motor looked at. It remains however that the comments I replied to were flat out wrong in that they completely ignored the purpose of ground. Ground, according to the comments I replied to, has no real purpose.
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Electricity does not "leak" to ground under any normal US electrical system. if you have current flow to ground it is a FAULT and represents a serious hazard. Current in a 120V circuit flow only in the hot and neutral legs.
The ground is there to provide a low impedance path for any fault that might happen so the branch circuit protection (usually a CB - but maybe a fuse if its old enough) will trip and clear the fault.
Sometimes a little trickle of electricicty will escape because of wet insulation or other reasons that is not enough to trip the CB. A ground fault circuit interrupter (GFCI) will detect that there is a difference between the current flow in the neutral and hot legs and trip to prevent you from being killed.
My suspicion is that the motor has insulation that has failed and allowed an electrical path to the frame. The impedence of the fault may be high enough that the little bit of current flow is low enough that it does not trip the CB, but this does not make it safe.
Installing a ground to the frame of the motor will not fix this problem, but may well hasten the point at which the fault gets bad enough that it will trip the CB.
I suspect a motor replacement is in order. When you install the new motor make sure you do it with a three wire plug. The old style 2 wire plugs, especially the unpolarized ones can be deadly - its why they are no longer used.
Another poster mentioned something about having 56 volts from neutral to ground. This is absurd. Ground and neutral are bonded together electrically at your service panel (thats how a neutral is created), so there should be virtually no voltage there under no load conditions, and only whatever voltage drop is generated in the wiring from the service panel out to the device under load. If you are exhibiting this kind of voltage between neutral and ground in the US, you have an extremely unsafe condition that should be corrected immediately by someone competent.
The exception to this would be someone living in Australia who have a different electrical scheme.
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snipped-for-privacy@aol.com (bob peterson) wrote in

Of course it does. It's called leakage current. While it would be ideal that leakage current is zero, in many cases it is not. It's not even that uncommon to see labels on equipment to notify operators of high leakage current. The solution? Ground the equipment properly. Grounding is not a solution to a fault, but it IS an appropriate solution to leakage current.

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So answer me this. If he adds this ground, and the motor frame is also connected to the neutral (not at all uncommon in older motors), what will be the effect of this connection on the stove, dryer, and other metal appliances in the home which are grounded?
scott

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On Tue, 14 Sep 2004 20:49:27 GMT, snipped-for-privacy@slp53.sl.home (Scott Lurndal) wrote:
| |>For the record, let me say that I agree that if the motor is defective |>internally then it should be repaired or replaced. I jumped past that in my |>original reply. However, adding a ground in no way presents a danger or a | |So answer me this. If he adds this ground, and the motor frame is also connected |to the neutral (not at all uncommon in older motors), what will be the |effect of this connection on the stove, dryer, and other metal appliances |in the home which are grounded?
We should ask you for the answer since it is your hypothetical. But I'll take the bait and reel *you* in.
Let's assume for a moment that the neutral is indeed connected to the motor frame. I'm not sure this is as prevalent as you and others suggest, but I'll play along.
First the two-wire case:
If Murphy's Law is on holiday and the extraordinary happens and the non-polarized plug is actually plugged in correctly, then the motor frame is connected to Earth via the neutral (grounded conductor). The neutral is a current-carrying conductor; therefore there will be a voltage drop along its length.
Assume for example that this is a 20 A circuit wired with 12 AWG and it is 100 feet to the service panel. (We'll ignore the few feet of flex pigtail from the saw to receptacle) To keep the numbers easy, let's also assume that the motor draws 10A @ 120VAC. (1.2KW or ~ 1.6 hp)
From the copper wire tables in any edition of "Reference Data For Radio Engineers" we find that 100' of 12 AWG at 20 deg C has a resistance of 0.1588 Ohm. Dusting off Ohm's law, we calculate that the voltage drop along this length of wire is 10(A) * .1588(ohm) 1.588 VAC.
Now if this is a hazardous voltage then I better go attach a ground rod to my Tony Stewart model Mag-Lite flashlight, because it has not one, but three, 1.5 V cells in it and it's orange besides.
When the motor isn't running, there is zero current in the wire, the voltage drop is zero and the frame is effectively grounded via the neutral. Does this meet current code, no. Is this a good thing, no; but with the givens, it is *not* a shock hazard.
Now to your question. With everything as before, let's hook up the three wire cord with "grounding conductor" (a terrible term as it is too easily confused with "grounded conductor", hence my personal penchant for calling it a "safety ground.")
Circuit wise, we now have two 12 AWG wires in parallel connected from the motor frame back to the service panel. The resistance is half, as is the voltage drop. And there is the benefit of redundancy in case the neutral wire should open, which is one reason the safety ground is now a code requirement. BTW, use of a GFI will expose this connection in less than a heartbeat.
Now (absent a GFI) you want to know what happens to all of the other appliances connected to this circuit branch. Note: I said *this* branch; nothing happens to anything not connected to this branch. Other loads don't give a rat's ass what is going on in the three wires running to the table saw any more than they care what is going on in your neighbor's house.
Other loads on *this* branch with metal frames or enclosures that are grounded via the third conductor will be elevated above ground by some factor. If they are downstream (further away from the service panel) from the table saw, and don't have any fault currents of their own they will be at the same potential as the saw, ~0.8 VAC in this example. If they are upstream then they will be proportionally closer to ground potential as they get closer to the panel.
BTW, do you realize that in recent memory, stoves and dryers had the neutral tied to the frame and were "grounded" that way. And they typically had unbalanced currents in the two hot legs since lights, motors, etc were operated line-to-neutral. Thus, the chassis was elevated above ground by the voltage drop in the neutral, miniscule as it was. Did this worry you?
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writes:

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Nada. IF the ground carries current, it will not affect other grounded equipment on the "line", as it will carry the current directly back to the service panel, where, as I said before, the neutral & ground are bonded together, so any ground current that makes it that far will rejoin the neutral, which is also connected to the water pipes, building ground, and in the case of the code here, where I am about to have a 200A 240V service installed, will also be connected to a 6 or 8' 1/2" copper(coated) rod driven into the ground.
I'll back up a *little* bit here. When I recommended rewiring with a 3 wire, I did say that if it popped the breaker, to have the motor checked out. This should only occur if there is some shorting from the hot to the frame somewhere. Otherwise, the ground will protect from any slight leakage in the motor windings(which has been suggested by others) causing the OP to be shocked.
Codes went from 2 wire non-polarized to 2 wire polarized to prevent "hot" chassis problems, then when people would replace polarized plugs with non-polarized, or otherwise destroy this integrity, went to 3 wire grounded, all to maintain safety.
IIRC, when I was working on computer installations & spec-ing them, EVERYTHING had to have "hot", neutral(if needed, such as a 240V plus neutral for 120 legs), and a ground wire. The reason given @ that time was that an electrical system could have unbalanced load on the "legs" and end up with slight current in the ground. Thus they insisted on a good ground wire, not depending on metal conduit, to eliminate any "ground loop" interference.
That's my story, and I'm stickin' to it.
--
Nahmie
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Probably little effect, but the point is valid. Any other items on the same branch would have some portion of their neutral return current shunted to the ground path. You might not notice it, although a GFI would. Items on other branches should not be effected.
Perhaps I just haven't worked with old enough equipment, but would find it odd if the motor frame itself was connected to the neutral, unless somebody removed a polarized plug (which is, of course, possible).
I still suspect, instead, that he's dealing with a leakage current. While grounding the frame is not the proper solution (not by itself), it at least keeps him alive long enough to post his results. GerryG
On Tue, 14 Sep 2004 20:49:27 GMT, snipped-for-privacy@slp53.sl.home (Scott Lurndal) wrote:

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criticized thus:
|Next to listening to Dan Rather, this is just about the stupidest thing I've |heard all week. I'm guessing the OP has been shocked by static electricity |in the past, so I think he knows the difference between that and an AC |current. The only reason it's not that bad right now is that the hot isn't |making a very good connection to the frame of the saw. Maybe one of these |days, it will make a good connection. At that point, I don't want to have |to rely on ground or a circuit breaker to protect me. If you think I'm |getting my undies in a bunch, let's do a test. I'll hand you a steel bar |connected to ground. You hold onto it and I'll connect it to 120. Sound |like a good idea, genius? Here's a better idea. Find what's wrong with the |motor now instead of trying to half-assed work around the symptoms.
My response was based on the facts in evidence. In a follow-up post the OP said:
"I think its only when it is on and not always. It is VERY mild. Not a 110 shock. Which is whats (sic) weird."
So if you guess that the op has been shocked by static discharge and knows the difference between that and an AC current shock then we are on the same page.
As to your dismissing the static discharge idea, here is what a belt manufacturer says about it:
http://www.gates.com/facts/documents/Gf000046.pdf
Certainly it's possible that there is a fault from one or both sides of the line to the frame of the motor, although a hard fault would be delivering results much different from what the OP reports, particularly when his face is in contact with the saw. (In this case: face in contact with a running table saw, electrical shock would seem to be the least of his worries)
It is equally possible that a build-up of conductive material (saw dust) has been introduced into the cooling slots of the motor and this explains leakage that comes and goes. No amount of motor rebuilding will eliminate this eventuality; a safety ground will---well, make it safe.
Even with motor rebuilding or replacement, a three-wire system is a must, so why not convert to a three-wire system first, particularly when the act of doing so will automatically repair of many of the potential (no pun intended) sources of leakage.
I suppose the error in my previous post it was that it was based on what *I* would do in this case, based on *my* experience. I had a Craftsman saw, albeit not as old, and I remember the configuration: rubber feet, open cooling slots in the motor, motor in the path of saw dust discharge, loose motor mounting with gravity belt tensioning.
When I opened the motor to rewire, *I* would blow out the accumulated debris, look for carbon tracks, make sure the motor frame and the saw body were bonded together, etc. I can see that someone less experienced might not understand the nuances of this. For this I apologize.
Wes Stewart, retired EE
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Wes, thank you for this.. You've given me even more information to use. My saw has a gravity dual belt system also. I think the stand is a universal one even though it matches the color. Kinda a cream color. I was totally unaware that the saw dust could get into the motor and cause problems. I'll bet theres plenty after all these years. I'm going to go over this saw well before I make any more cuts and see what I can find. I discovered the other day that the blade was off plumb by a 1/16" and that that was what was causing crooked rips. Thats been fixed but it wasn't easy. not much adjustment that I could find. the one thing I don't like about this saw is that I don't see and easy way to accurately adjust the bevel cut. Nor to assure its plumb again once you've moved it. The face comment came from my son when night before last we moved the saw 6" to give better placement for the future router table and as he was leaning his face against the metal frame to level the legs he said "its giving me tiny shocks". He described it like a 9v dc battery does to your tongue. The motor frame sits on a pivoting rod that then attaches to the saw framework. I'm not at all sure how I would bond this short of doing an RF braid type bond. Is that acceptable? Again thanks for addditional clarification. Once I find out what exactly it is, I'll be sure to report back.
signature Troy & Michelle Hall Cogy Farm Clay Center, Kansas 67432

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On Tue, 14 Sep 2004 15:22:45 GMT, "Troy Hall"
|Wes, thank you for this..
You're welcome.
|You've given me even more information to use. My |saw has a gravity dual belt system also. I think the stand is a universal |one even though it matches the color. Kinda a cream color. I was totally |unaware that the saw dust could get into the motor and cause problems. I'll |bet theres plenty after all these years.
Saw dust can be a source of leakage curent since it does contain moisture. I'm only suggesting it as a *possible* cause, however.
[little snip]
|The face comment came from my son when night before last we moved the saw 6" |to give better placement for the future router table and as he was leaning |his face against the metal frame to level the legs he said "its giving me |tiny shocks". He described it like a 9v dc battery does to your tongue.
Okay, this does raise the threat level. I had the impression that the problem was only while the motor was running, and surely that isn't the case here.
| The motor frame sits on a pivoting rod that then attaches to the saw |framework. I'm not at all sure how I would bond this short of doing an RF |braid type bond. Is that acceptable?
Yes.
Whatever you decide to do about the motor, you need to go to the three-wire connection and I would *strongly* recommend that you add a GFI receptacle to the circuit that feeds the saw as a second level of protection.
|Again thanks for addditional clarification. |Once I find out what exactly it is, I'll be sure to report back.
Okay.
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Take the three wire cord through the switch and to the motor. You don't need to rely on the friction connection at the pivot, even though it would almost certainly blow the breaker if necessary.
BTW, I'd be surprised if your floor is conductive enough to deliver a fatal shock, but who knows...if the concrete has a lot of calcium added, it might be higher conductivity than normal.. We've about killed this, so I'm looking forward to hearing the outcome. Meanwhile, keep faces away! Their thin skin is more conductive than hands.
Unbelievably, no one has mentioned the most dangerous scenario with this thing. On a floor of low conductivity, like wood or dry concrete, you could hook the hot wire right to the frame and not get much of a shock, BUT if you touched ANYTHING properly wired you'd get blasted. Current would flow through you to the grounded frame of whatever you touched, like a light fixture, metal circular saw, metal water pipe, frame of your drillpress, etc. In a small shop, this could happen without much effort.
I once was working in a new building and when I tried to connect a coax cable from one piece of electronice to another I got a nice 40A 120V arc right at my fingertips! It was plain luck I wasn't didn't take hold of the second piece of equipment and the coax connector at the same time! The fools who wired the building switched hot and neutral on SOME plugs and never checked their work, so I had gear at 120VAC above ground. Even so, I didn't get shocked when standing on the concrete floor and touching the hot gear.
The surprise of that arc in my fingers won't be forgotten, although I was not shocked or burned at all.
Wilson

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After more than 40 years of working with that stuff, I have an old habit that I don't even think about: I always assume everything and anything is hot, and ground it before grabbing, even if I've already checked with a meter sometime earlier. It only takes a second and will pop a breaker or at least show a spark. Come to think of it, an experience similar to what you described started that habit. GerryG
<snip>>

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|After more than 40 years of working with that stuff, I have an old habit that |I don't even think about: I always assume everything and anything is hot, and |ground it before grabbing, even if I've already checked with a meter sometime |earlier. It only takes a second and will pop a breaker or at least show a |spark. Come to think of it, an experience similar to what you described |started that habit.
Heh heh. There's always at least one "experience." In electronics (vacuum tube stuff) the adage was keep one hand in your pocket. This was to prevent that killing current path through the chest.
I went to a short course on corona testing for insulation systems and my employer bought a corona ("partial discharge") tester that had 10KV DC stacked on 40KV AC capability. When you ran that thing you kept *both* hands and maybe your feet too in your pocket [g].
The lab in the company that offered the course and made the equipment would have made Tesla jealous. I think they could have made lightning in there.
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wrote:

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Well, we're getting even further off the topic here, but in my previous non-IT life I did a fair amount of high voltage testing. I was involved in the design and manufacture of transmission insulators. Part of my job was supervising corona and RIV (radio-influence voltage) tests on insulators and insulator sets. The lab I frequented had a 1000kV AC generator and about a 2500kV impulse generator (which really was used to test for lightning surges). The wire that connected the voltage divider to the unit to be tested was just regular thin wire (in the neighborhood of piano wire). When doing corona testing, we would black out the lab, bring the set we were testing up to voltage, and observe for any visible signs of corona. In order to do that, a couple of people had to be inside the test area. This lucky day I was a spotter. The first disconcerting feeling is that even at 30 feet away, the electrical field coming off the divider made the hair on your arms stand up. During this particular test, someone had left a wire hanging down from the divider that was about 3 feet off the ground. I was sitting in the darkened lab waiting for the voltage to come up when at probably 350-400kV the electricity found ground by flashing over from the wire, which was on my end of the lab. I just about peed my pants trying to get the hell back to the control room.
todd
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I don't think anybody directly responded on your question. Yes, a flexible braid strap is fine, as long as it's properly attached and capable of carrying the max current, which is probably not an issue for anything other than a very thin braid. GerryG
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