shocking table saw

[Troy Hall]

Where did I say my fence was bad??????? It wouldn't work with a sheet of ply 6' x 36" deep. WELL DUH!!! the table is barely more then that!! I was making a cut 30½" in from the end to cut the board into two pieces so I could laminate into a 1" top for a router table. Is my fence the easiest thing in the world to use... nope. Is it the most accurate? NOPE! Is it functional? YEP! Measure 3x cut once. PERSONALLY I can handle a 120v shock without much more then a blink. But I ain't gonna sit there and do it!! SHEESH. I realize it needs to be fixed. Thats why I asked the question in the first place! There has been a lot of useful information given on exactly how to do that and why I should NOT recitify the missing ground before doing these tests. Having a shop is a dangerous place. There are a million things that could go wrong and it is not wise to INTENTIONALLY bybass these safetys. HOWEVER, How many still have the blade guard on their saws? How many have a GOOD RF grade ground in their dust collection network? You do realise that is can instaneously combust don't you? Happens every day. How many have a FLASH proof rag container? Have a FLASH PROOF paint locker? Or even Flash proof ventilator? Lets stop the flaming and understand that we all probalby have things in our shop that we have/do that we shouldn't, and when it is obvisous to you that the OP doesn't realize that this may be dangerous, point out the reasons, and alternatives and then allow the OP to make the decision. It IS his/her life after all isn't it?

GOD BLESS and lets get back to woodworking

[Bob Peterson]

You may have a short circuit to the frame. Might need to replace the motor with a new one that has a three wire plug on it. This problem will not get better on its own. This is a dangerous situation. Adding a ground wire to the frame will probably stop the problem by tripping the breaker its plugged in to, but of course that won't solve your problem.

[Dave W]

The motor is probably shot! Replacing a motor on an old saw is no problem at all. Do not chuck the saw, it is probably better than any modern equivalent replacement. Dave

[LRod]

You were doing fine until you got to that. Happens every day? Cite ONE verifiable instance where this has occured in a home workshop...ever.

- - LRod

Master Woodbutcher and seasoned termite

Shamelessly whoring my website since 1999

[toller]

Sorry, I thought you were saying the fence was no good and you had to clamp a piece of wood to the table. I have cut plywood like that many times with no problems at all; so I guess you are just clumsy.

Go add a ground. Do any stupid thing you want.

[toller]

True, but they serve entirely different purposes. Oh why bother, when you don't really care.

[Lawrence Wasserman]

Are you talking about North American wiring here?

[Wes Stewart]

On Mon, 13 Sep 2004 20:58:31 -0500, "Todd Fatheree" criticized thus:

|Next to listen "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:

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

[Troy Hall]

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.

[TeamCasa]

Flame on!

[bob peterson]

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.

[U-CDK_CHARLES\Charles]

Wiring isn't magic or voodoo, despite what some seem to imply. All it takes is a methodical approach and attention to detail. Most anyone who posts here should be able to look at a wiring job and decide whether or not it's within his or her comfort/ability zone. If you're wondering whether or not is IS, then it isn't. Simple.

1. Check the cord. Replace if necessary. See if it's feasible to add an equipment ground. If the motor neutral is isolated from the frame, you're good to go. If not, consider replacing the motor--old equipment that's neither doubly insulated nor grounded isn't worth the danger.
2. Cord okay? Take the motor to a motor shop.

1. Consider replacing the motor with a modern frame-grounded unit. If the saw is otherwise sound, it might be worth it.

2. If the saw is NOT otherwise sound, buy a new one.

[John McCoy]

"Troy Hall" wrote in news:Tfp1d.575$ [e-mail]:

Well, you've gotten a load of conflicting answers here. My guess is you have bad shop wiring, and the neutral is developing a voltage (which it shouldn't). Connecting a ground wire will probably remove the shock by providing an alternate path for the current (which will result in less voltage being developed across the combined return path of the neutral and the ground). In general running a significant current down the ground wire is a bad idea.

The frame of the saw should not be connected to the neutral, especially if it has a non-polarized plug, but 1940 vintage equipment wasn't particularly strict about that (not to mention it might have been rewired by someone unknowledgable somewhere along the line). So you should probably trace down why that is happening, as well as whether you've got a problem with the shop wiring.

You would be wise to have someone experienced with electricity help troubleshoot this.

John

[Secret Squirrel]

[e-mail] (bob peterson) wrote in news: [e-mail]:

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.

[Wes Stewart]

|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.

[Andy Dingley]

No, US practice for wiring electric motors _is_ voodoo.

Europe is scared of your machinery wiring.

[Wilson]

[Wilson]

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.

[U-CDK_CHARLES\Charles]

Been there, done that.

I was building power test systems for HP TMO (now part of Agilent). The units sent to Europe had some requirements that were universally regarded with a shrug, but they weren't especially difficult to implement.

The most obvious change was that they required a the neutral to be run through a breaker, which in US practice would be thought dangerous.

[sr_wood]

Sounds like you have a Van de Graaff generator. Electrons from the belts are released and stored in the metal of your table saw. Probably the best thing to do would be looking for a way to isolate this charge dispersal.