How does the grounding work if the table saw itself is on a wooden stand ? - Woodworking Talk - Woodworkers Forum
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post #1 of 21 Old 02-28-2019, 05:14 PM Thread Starter
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How does the grounding work if the table saw itself is on a wooden stand ?

Apparently I am not good with the science stuff. So I thought about asking you smart guys here.

I am wondering how would the grounding work if my table saw itself does not touch the floor, but sits on a wooden stand? There is a ground wire in the motor that screws on to the metal body of the motor. But if the metal part of the body of the machine itself is not in contact with the ground/floor how is it going to work?

Thanks
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post #2 of 21 Old 02-28-2019, 05:21 PM
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It grounds back to the electrical panel. My PM66 table saw is sitting on concrete and that doesn't provide ground, either. It grounds back to the panel.

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post #3 of 21 Old 02-28-2019, 05:28 PM Thread Starter
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It grounds back to the electrical panel. My PM66 table saw is sitting on concrete and that doesn't provide ground, either. It grounds back to the panel.

David
Thanks David 🙏
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post #4 of 21 Old 02-28-2019, 05:40 PM
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"green" is ground .....

Quote:
Originally Posted by Rency View Post
Apparently I am not good with the science stuff. So I thought about asking you smart guys here.

I am wondering how would the grounding work if my table saw itself does not touch the floor, but sits on a wooden stand? There is a ground wire in the motor that screws on to the metal body of the motor. But if the metal part of the body of the machine itself is not in contact with the ground/floor how is it going to work?

Thanks
Rency

There is a green wire that is part of the supply cord or line which connects to a ground terminal in the panel. That green wire must also be connected to the saw cabinet and motor even though the cabinet sits on a wooden stand. Just run a separate wire if it's not there. Use a star washer under the "crimp on" terminal to insure a good ground connection, on both ends. If you use a sheet metal screw, no crimp on terminals, then wrap the wire fully around the screw and cut off the excess. Good to go.

White wires never go to switches, only black ones. FYI

The answer to your question will only be as detailed and specific as the question is detailed and specific. Good questions also include a sketch or a photo that illustrates your issue. (:< D)
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post #5 of 21 Old 02-28-2019, 06:00 PM Thread Starter
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Quote:
Originally Posted by woodnthings View Post
Quote:
Originally Posted by Rency View Post
Apparently I am not good with the science stuff. So I thought about asking you smart guys here.

I am wondering how would the grounding work if my table saw itself does not touch the floor, but sits on a wooden stand? There is a ground wire in the motor that screws on to the metal body of the motor. But if the metal part of the body of the machine itself is not in contact with the ground/floor how is it going to work?

Thanks
Rency

There is a green wire that is part of the supply cord or line which connects to a ground terminal in the panel. That green wire must also be connected to the saw cabinet and motor even though the cabinet sits on a wooden stand. Just run a separate wire if it's not there. Use a star washer under the "crimp on" terminal to insure a good ground connection, on both ends. If you use a sheet metal screw, no crimp on terminals, then wrap the wire fully around the screw and cut off the excess. Good to go. <img src="http://www.woodworkingtalk.com/images/smilies/vs_cool.gif" border="0" alt="" title="Vs Cool" class="inlineimg" />

White wires never go to switches, only black ones. FYI
Yes
I have wired it already and it is running.
Just was wondering about how it would work without the saw cabinet or stand not touching the ground.

Thanks
Much appreciated
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post #6 of 21 Old 02-28-2019, 06:27 PM
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Quote:
Originally Posted by Rency View Post
Apparently I am not good with the science stuff. So I thought about asking you smart guys here.

I am wondering how would the grounding work if my table saw itself does not touch the floor, but sits on a wooden stand? There is a ground wire in the motor that screws on to the metal body of the motor. But if the metal part of the body of the machine itself is not in contact with the ground/floor how is it going to work?

Thanks
Rency
Electricity will follow the best route to ground. The base of the saw doesn't matter. It's the motor where the electricity is that the body of it needs to be connected to a wire which goes to ground. In your houses electrical wiring there is a copper rod which is about 8' long and driven into the ground where the breaker box is connected to. By having the motor's body wired to the ground bar at the breaker box you have the motor wired to the ground which would protect you. Now, if your saw has the ground prong broken off the plug then your saw isn't grounded. Still it doesn't happen very often when the body of a saw becomes energized but it can happen. The worst time I've ever been shocked is using a old circular saw that had a metal body on it which became energized. Working for hours bent over I reached over to a table saw to stand up with the saw in my hand and found out the table saw was energized too. I managed to get 120v in each hand. I had to tell myself over and over to let go to get away from it.
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post #7 of 21 Old 02-28-2019, 06:57 PM
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Is the ground the ground?

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Yes
I have wired it already and it is running.
Just was wondering about how it would work without the saw cabinet or stand not touching the ground.

Thanks
Much appreciated

There's two types of ground, the dirt and the electrical/earth ground.
When a part of a machine becomes "energized" that is a hot wire touches the metal parts, and you are holding or touching it YOU become an electrical conductor, not a train conductor.


The "juice" passes through your hands and the rest of your body to your feet or your other hand which may be touching something that is electrically grounded. It is a "shocking" experience.



Other shocks come when you become a conductor between the white or green wire and the black/hot wire accidentally. Usually nothing really bad happens, but under certain circumstances it can be fatal. Unlike the movie, it is a "Fatal Distraction"


Electricity is hard to understand because we can't watch it, unless the voltage is up around 1,000,00 volts.

The answer to your question will only be as detailed and specific as the question is detailed and specific. Good questions also include a sketch or a photo that illustrates your issue. (:< D)
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post #8 of 21 Old 03-01-2019, 12:34 AM
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Guys,
The green wire is connected to an earthen ground. Fancy words for a rod driven into the ground and by code connected to the cold water pipes of a building.

What most of us fail to recognize is that the green wire is connected to a bus in the breaker panel. AND oh HORRORS, the ground bus is connected to the (white) neutral bus in the circuit breaker panel. This may be confusing but exceptionally important, the connection between the green bus and the white bus IS ONLY DONE ONCE IN A BUILDING. This ground neutral connection is only done in the circuit closest to the building entrance of electricity. If you do the connection more than once it will cause all kinds of problems with such obtuse things like cable TV. In technical terms, you are creating a ground loop. In not so technical terms, a ground loop in an analog system is Excedrin Headache number 17. :)

Electrical machinery (e.g. Table Saw) have a green wire connected to the chassis. Contrary to various myths, the frame of the motor is connected to the chassis and therefore both motor frame and chassis are grounded. In theory this is ground is unnecessary. Well theory is theory. Code requires the ground for safety reasons. In the old days, bearings in motors were poor and the commutator could touch the chassis (i.e. Short out) and possibly injure the user.

IIRC back in the mid 1960s, Phoenix, Arizona, a body shop technician was electrocuted by a faulty disk sander. It seems that the tech was standing on a very wet floor wearing wet athletic shoes while using the disk sander. The disk sander faulted and the tech just fell to the floor. A heart attack was the initial report. The coroner arrived to investigate and discovered that the grounding prong of the plug had been cut off due to problems with the disk sander. The cause of death was changed to homicide.

BTW - The "L" have it. if the grounding Lug is in the Lower position of an outlet the Large spade of the plug is on the Left.

Rich
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post #9 of 21 Old 03-01-2019, 01:52 AM
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Just to be totally accurate and for any readers of this from europe and many other countries, black white and green are USA standard colours. In Europe the wires do exactly the same job but are coloured thus;
Live is brown (or red in very old machines)
Neutral is blue (just to be really confusing, neutral on old machines is black!)
Ground is green /yellow spiral stripes.
So always check your local (national) standards if you have no experience of wiring or if you have an imported machine.
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post #10 of 21 Old 03-01-2019, 02:42 AM
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SunnyBob,
Thank you for that bit of international info.

There is another thing that I don't know the answer to also.
In North America we use both the positive phase and the negative phase of our electricity. We connect the phase to our equipment on the black wire and for most internal home electrics the white wire is connected to ground or the CENTER between the two phases. This gives us our nominal 120 volt AC. When we need 240 volts we use the two phases (Typically Black and Red) as the electrical supply. The ground is still ground and the white may not be used at all.

Many international electric suppliers provide 240 volts to neutral or ground. While this may not be a problem is a US machine is used on an international system. The reverse using an international electrical device may be problematic on our electrical system. One of the hot leads may be connected to the chassis.

In the US our 240 volt system has the device connecting to 120 volt plus and 120 volt negative for an operational voltage of 240. An international device expects to be connected 240 plus and zero, neutral or ground for an operational voltage of 240. If the manufacturer assumes that the device could be used in the US there shouldn't be a problem. However if the manufacturer assumes non US operation and the device is used in the US there could be a problem.

The SCREAMING message is "I don't know."

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post #11 of 21 Old 03-01-2019, 06:36 AM
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I think your system is 110 volt per line, I'm not sure quite how you use the other line to get 110 volts as well, I havent ever worked on your system. i suspect a phase inverter somewhere, but hey?

The UK system is now 220 volts. When I was a lad 50 years ago the UK had 240 volts and Europe had 220 volts. Once international travel became common there were many instances of european equipment being bought into the UK and soon after exploding all over the place. So to bring the UK into line with europe (and of course to save quite a bit of money) the UK dropped its standard voltage to 220. This is why you hear older english people referring to 240v.

To confuse matters a bit, all construction site tools in the UK MUST be 110 volt for safety reasons, so every contractor has to haul around really heavy transformers unless the site is big enough to have 110 volt distribution boards available

If you need more power than a trailing lead can supply, then you have to go to three phase, which gives you 410 volts through 3 live wires to the machine. But this is not allowed on construction site mobile tools.
In Europe, 3 phase is quite common in domestic premises as the power per phase available is fairly small. In the UK, 3 phase in a house is very rare.

It gets worse... USA uses 60 Hz power, europe and uk use 50Hz. This means that imported equipment (motors especially) run at different speeds than they are meant to, causing all sorts of reliability issues
Just to add a final spanner in the works, where I live now, in Cyprus, we still have 240 as standard, although if you use a test meter its usually 236v.

About 30 years ago in the UK I started work with a company that was importing American catering equipment (fast food stuff) and the first time I looked inside and found just a mass of black and white wires I thought someone was winding me up. It took quite a while and a lot of schematics study before I worked out how to install and repair them safely.
So, as I said at the start, It depends WHERE in the world you are, on what kind of electrical advice you can give and receive.

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post #12 of 21 Old 03-01-2019, 08:38 AM
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AND, to confuse things further, "good ground" from the actual soil depends upon where in the country/world you live.


Here where I live in the Panhandle of Florida, we do not get a good ground by just driving a copper rod 8' into the soil. At Eglin AFB, when we needed a good ground it was found that it was necessary to bury a copper place 110" underground in a salt bed.


In the private setting it is not possible to go for the ultimate grounds found on our Air Force Base. We have to settle for something else. My house was hit b e lightening 6 weeks after I moved in. I decided to improve on the existing ground rod. I jetted a 20 foot piece copper pipe 20' into the soil. While not perfect, it was as improvement.


George
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post #13 of 21 Old 03-01-2019, 09:15 AM
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Where in the world are you located?

Quote:
Originally Posted by Rency View Post
Apparently I am not good with the science stuff. So I thought about asking you smart guys here.

I am wondering how would the grounding work if my table saw itself does not touch the floor, but sits on a wooden stand? There is a ground wire in the motor that screws on to the metal body of the motor. But if the metal part of the body of the machine itself is not in contact with the ground/floor how is it going to work?

Thanks
Rency

Sounds like you may be in UK?
Different rules and codes apply than in USA. We need to know, since 98% of members here are in USA.
You can't/should come here asking an electrical question without letting us know your location.... bad things could happen if you wire stuff up the "wrong" way.... just sayin'.

The answer to your question will only be as detailed and specific as the question is detailed and specific. Good questions also include a sketch or a photo that illustrates your issue. (:< D)

Last edited by woodnthings; 03-01-2019 at 11:16 AM.
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post #14 of 21 Old 03-01-2019, 11:13 AM
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a few things:
- a sheet metal screw is not approved by the NEC for grounding connection, s.b machine screw threads
- alternating current is + and - with reference to grounded neutral, which is produced by the transformer feeding your residence. read up on center-tap transformers to understand electrical service theory
- residential electrical power is called single phase, with Line A and Line B. both being 120v with respect to neutral, 240 vac with respect to each other.
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post #15 of 21 Old 03-01-2019, 01:32 PM Thread Starter
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Quote:
Originally Posted by woodnthings View Post
Quote:
Originally Posted by Rency View Post
Apparently I am not good with the science stuff. So I thought about asking you smart guys here.

I am wondering how would the grounding work if my table saw itself does not touch the floor, but sits on a wooden stand? There is a ground wire in the motor that screws on to the metal body of the motor. But if the metal part of the body of the machine itself is not in contact with the ground/floor how is it going to work?

Thanks
Rency

Sounds like you may be in UK?
Different rules and codes apply than in USA. We need to know, since 98% of members here are in USA.
You can't/should come here asking an electrical question without letting us know your location.... bad things could happen if you wire stuff up the "wrong" way.... just sayin'. <img src="http://www.woodworkingtalk.com/images/smilies/vs_cool.gif" border="0" alt="" title="Vs Cool" class="inlineimg" />
I am in USA.
I wired everything according to the diagram. The ground is connected properly to the motor body and to the body of the saw from the switch boxes.
I was just trying to understand how this ground thing works. And this thread have brought some information. Thanks to everyone. &#x1f64f;&#x1f600;
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post #16 of 21 Old 03-01-2019, 02:33 PM
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Quote:
Originally Posted by Rency View Post
I am in USA.
I wired everything according to the diagram. The ground is connected properly to the motor body and to the body of the saw from the switch boxes.
I was just trying to understand how this ground thing works. And this thread have brought some information. Thanks to everyone. &#x1f64f;&#x1f600;
Something else you might want to know is if you are working around machinery in a place where the floor is wet. Under those circumstances you might want to install a GFCI outlet. With a machine wired correctly if you are standing in water you can still provide a path to ground for electricity. Under normal circumstances a circuit breaker is just used in the event something goes wrong however the breaker is designed to run enough power through it until it heats up enough to maybe melt the wire. By this time a person would be dead before the breaker would trip. The GFCI is sensitive to anything in the circuit that goes to ground too easily and would trip before it would kill you. This is why you see these type outlets in a bath in case someone has a hair drier or radio that might drop in water as it's turned on.
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post #17 of 21 Old 03-01-2019, 08:02 PM
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I sure wish we had 3 phase in homes in the US. Now some home appliances convert single phase to 3 phase internally. My washing machine does that. I keep seeing people refer to 240/230/220V as two phase. It is not! Where I live the power co. will no longer provide 220/230/240V. You get 208V center tapped for 120V. It helps the power company balance their load. BTW voltage can vary by 10% and still work fine for most things. When there is high demand the line voltage typically drops a few volts. A 50 cycle motor is perfectly happy running on 60 cycle. It just spins 20% faster. The reverse is not true for most motors. A 60 cycle motor is likely to over heat if run on 50 cycles and under full load.

I've got a bunch of transformers in my shop to convert my line 208 three phase to 380/400V for the European tools and to 460/480 for my US tools. I always avoid single phase tools if at all possible. If you get Canadian 3 phase tools they are commonly 575V.
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post #18 of 21 Old 03-01-2019, 08:18 PM
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I sure wish we had 3 phase in homes in the US. Now some home appliances convert single phase to 3 phase internally. My washing machine does that. I keep seeing people refer to 240/230/220V as two phase. It is not! Where I live the power co. will no longer provide 220/230/240V. You get 208V center tapped for 120V. It helps the power company balance their load. BTW voltage can vary by 10% and still work fine for most things. When there is high demand the line voltage typically drops a few volts. A 50 cycle motor is perfectly happy running on 60 cycle. It just spins 20% faster. The reverse is not true for most motors. A 60 cycle motor is likely to over heat if run on 50 cycles and under full load.

I've got a bunch of transformers in my shop to convert my line 208 three phase to 380/400V for the European tools and to 460/480 for my US tools. I always avoid single phase tools if at all possible. If you get Canadian 3 phase tools they are commonly 575V.
Most people don't understand that single phase and three phase has little to do with voltage, it's the timing when the line is hot.

I think two phase is pretty much a dinosaur. I believe there is only a couple places in the U.S. that still has it.
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post #19 of 21 Old 03-01-2019, 11:44 PM
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Rency I just wanted to simplify the answer because everyone gave very detailed info but that could be hard to understand.
If there was for any reason voltage energizing your metal components, that green wire gives it the quickest path back to ground. If the machine was not grounded properly and voltage was energizing the unit, then your body is likely to become that path when you touch it while running.

Not trying to be a wise guy but just trying to explain in a different way.

Maybe that helps maybe it doesn’t.
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post #20 of 21 Old 03-02-2019, 03:28 AM Thread Starter
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Rency I just wanted to simplify the answer because everyone gave very detailed info but that could be hard to understand.
If there was for any reason voltage energizing your metal components, that green wire gives it the quickest path back to ground. If the machine was not grounded properly and voltage was energizing the unit, then your body is likely to become that path when you touch it while running.

Not trying to be a wise guy but just trying to explain in a different way.

Maybe that helps maybe it doesn’t.
Yes. I understood that part from all the explanations here. And you just made it simple. I appreciate that and all the other. Thanks. &#x1f600;
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