Good afternoon!

I get a mild electric shock when I touch the metal part of my table saw (DWE7491). This only happens when I turn ON the saw i.e. when the blade is spinning. I confirmed by using a receptacle tester - it shows mild to high AC current.

There are no burnt smell when the machine is turned ON or when it's cutting lumber.

How do I troubleshoot this?

I would put a volt meter on the saw and see if you are getting a small amount of power from the neutral or the saw is getting a full 110v to the body of the saw. It may be you yourself are not grounded well enough to fully get zapped. If the voltage is low I would start with the switch. Open the switch and see if there is any wire touching the box. There should be no wire touching the box with the exception of the ground wire. It should be directly bonded to the box. You might also check the ground wire to see if it's still good. Use the ohm part of the volt meter and see if it conducts between the ground prong and the end of the wire in the box. This is suppose to be taking the electricity away from the saw in the event of a short. If everything is good in the switch there is probably a problem internally in the motor. You may need to take it to a motor repair shop and let them find the short.

 

The outlet could have hot and neutral wire reversed. Turn off the breaker and check the outlet. If the plug on the power cable to the saw has been replaced, the hot and neutral could be reversed there also.

 

Grounded?

 

How do I troubleshoot this?

1. Unplug the saw.
2. using a continuity meter with an audible "beep", check as follows:
A. clip the meter's black/ground to the cabinet and then see if any of the plug's prongs sound a beep.
B. If the center/ground prong beeps that's good.
C. If either of the other two beeps there's a problem.
3. Clip the ground/black wire to one of the prongs, and see if the motor housing gives a beep.
4. Test the other prong in the same manner. A beep is NOT good.
It means the motor housing is "hot" for some reason.
Inside the motor's wiring box there may be a wiring diagram show how to connect it for 120 or 240 volts.
Possibly, a white or black wire inside the motor's wiring box is touching the box.
There should be a bare wire or a green wire on a screw that secures the box to the motor.
Maybe a green screw.
The white wires should all be connected together with a "wire nut" on a simple, single pole ON/OFF switch.
The black wire should come from the ON/OFF switch.
Inside the ON/OFF switch box the white wires should be connected together OR depending on the type of switch,
be on the terminal opposite the incoming wire from the plug, for a double pole ON/OFF switch.
Same with the black wire, opposite the incoming wire from the plug.
On a simple ON/OFF switch ONLY the black wire gets switched.

Giving electrical advice on a woodworking forum is often regarded as dangerous.
Advice on how to check for a wiring issue should not result in any danger.
The danger is currently in place as is. It won't get better on it's own and the saw should NOT be in use!

 

I confirmed by using a receptacle tester - it shows mild to high AC current.

Confirmed what?
I suggest you seek the services of a qualified electrician.

 

Thanks for your tips.
I checked continuity using multimeter - no beeps. The electrical chord has no ground (3rd pin) - just neutral and live.
The outlet is equipped with GFCI.. and i checked. No issues there either. I couldn’t upload the video of how i checked with multimeter. Is it the motor?

 

Show photos of the ON/OFF switch box opened up and the motor wiring box opened up.
If the shock only occurs with "power on" then the issue is after the switch is ON.
It may be time to call the electrician because you may now need to check voltages with power ON.
OR unplug the saw and turn the switch ON.
Then start checking for for continuity from the HOT prong to the motor housing and cabinet.
Report back.
If it were a "direct short" the voltage would knock you "speechless".....
It would also trip the breaker.
It's a weird issue. I doubt it's static shock, but might be?

 

Take the advice in post #6.

 

Thank you! I have reached out to my electrician. Will report back what he finds.

 

Good choice, much of the advice given here, though well intentioned, is not from qualified electricians.

 

Step #1, replace un-grounded cord with a grounded cord and go from there.

There were some recommendations to measure voltage, but you need to measure current. If that sounds confusing, seek professional assistance for sure.

 

According to AI the saw is a double insulated tool so it would not require a grounded cord, let your electrician diagnose the problem.

 

We had an edge bender that the ground onmtye machine was just laying there unconnected. Seems each time you used it , it would shock.over a period of time it damage tye breakers in the machine. I opened up the panel one day and finally noticed the ground

 

I looked up that saw and I got shocked. $650.00 for that little saw, gees.

 

To add to what woodkiller said about testing your power supply, you can get an inexpensive tester at any hardware store. It looks like the male end of an extension cord, but has three LED light instead of a cord. The lights will show whether the receptacle is correctly wired for polarity and whether it has a good ground. For a couple of dollars more, you can get one with a push-button GFCI tester.
Someone should probably have already asked where you are, but we tend to forget we have members from outside the USA and Canada. If you're in Europe, the UK, or somewhere else, you can get into trouble following a lot of our advice on electrical matters.
Assuming you're in North America, does the circuit you're using have a ground fault circuit interrupter (GFCI)? If so, it should be tripping if you're getting enough of a shock to feel. If not, consider putting one in. It's no harder than replacing a receptacle, and it's cheap insurance against such mishaps. Just be sure to get one rated for 20 amps.
What Steve Nuel said about looking for bare wires touching inside the switch box is good advice. I'd also check the spot where the power cord enters the machine. If someone has jerked on that, it's possible that a sharp edge there might have cut through the insulation. There should be a strain relief or grommet there to prevent that, but things happen. Look inside the machine, too, for any spots the cord might have rubbed or chafed. If you don't see any sign of that, I'd suspect an internal short in the motor. The field windings that surround the armature (the spinning part of the motor) aren't really all that well insulated, because they're completely surrounded by the motor housing and not exposed to much damage, but a badly assembled motor can vibrate and wear through the insulation, which is usually just a couple of coats of shellac. If that's the case, you'll need to take it to a electric motor shop for a rebuild.

 

o add to what woodkiller said about testing your power supply, you can get an inexpensive tester at any hardware store. It looks like the male end of an extension cord, but has three LED light instead of a cord. The lights will show whether the receptacle is correctly wired for polarity and whether it has a good ground

This would be a great "first step" in this case:

EOHELGRO Outlet Tester, Socket Tester for Standard North American AC Electrical Outlets, Receptacle Tester for Plug Security Test: Amazon.com: Tools & Home Improvement

EOHELGRO Outlet Tester, Socket Tester for Standard North American AC Electrical Outlets, Receptacle Tester for Plug Security Test: Amazon.com: Tools & Home Improvement

www.amazon.com

 

Good Morning!
My electrician is ghosting me.. and hasn't yet turned up. Didn't want to let the weekend slip away doing nothing.

Just to recap: American electrical system; the outlet has GFCI - tested it using receptacle tester, like the one jgrickett51 (comment #18) mentioned. Line and neutral are properly wired; tested the overload button on the outlet, and the socket tester. Both tripped the line - as expected.

Disassembled the switch board on table saw. Tested the terminals. Here's the interesting part.. the continuity tester shows a reading of 294 when I place the tester leads on the Motor's White (MW) and Black (MB) terminals on the switch - meaning there's a mild short. There was no sound, just a non-1 reading.

(MB - Motor Black, MW - Motor White, LB - Line Black, LW - Line White)

All other tests on the terminals shows 1 i.e. open ckt with the switch OFF.. and loud beep between MB to LB & MW to LW when the switch is turned ON.

Photo 1 is the reference diagram on the switch.
Photo 2 & 3 shows the continuity test reading with the leads placed on MW and MB on the switch turned OFF.

Does this show there's a mild leak between line and neutral? Is this the smoking gun? Is this why there's mild shock only when I turn the line on.. because that's when current flows from the line to the motor leads?

Again, thanks for patiently engaging me.. much appreciated.

 

Just to recap: American electrical system; the outlet has GFCI - tested it using receptacle tester, like the one jgrickett51 (comment #18) mentioned. Line and neutral are properly wired; tested the overload button on the outlet, and the socket tester. Both tripped the line - as expected.

GFCI are deigned to prevent injury and death, so they won't trigger for small currents that can cause a tingling sensation but are not dangerous currents. There is a current threshold that needs to be exceeded for a GFCI outlet to trip. This is why I mentioned that you need to measure the current from the metal parts to ground. This is step 1 to figuring out what you are dealing with. It's like taking a temperature of someone who appears sick and complaining of having a fever.

 

@Karthik

Question has the saw been exposed to rain or extreme humidity conditions for extended period of time this is what they call a double insulated motor assembly therefore there is no need for a ground because there should be no way for power to potentially get to the frame. But water is still a good conductor.


power cord is a two wire only.

DWE7491 Start + Stop Switch Wiring (Non A/V Content)

from the video

what is the model you have DWE7491 what is after like RS or type 2 or X for type3 or RS type 10

some use a 4 wire switch. coast to stop VS 6 wire switch with braking.

you need to check the wire Pathways one of the wires may be pinched in the metal framework where should not be and maybe leaking voltage through due to being crushed but not a direct connection.

If your electrician says the house wiring is correct no reverse wiring at the GFI .
then you're strictly looking at the wiring Pathways inside of the saw. I have seen with tools of various kinds of having wire insulation breakdown causing them to become slightly positive voltage which will feel like an electrical shock.

I would not recommend using this until this has been resolved.

 

Good afternoon!

I get a mild electric shock when I touch the metal part of my table saw (DWE7491). This only happens when I turn ON the saw i.e. when the blade is spinning. I confirmed by using a receptacle tester - it shows mild to high AC current.

There are no burnt smell when the machine is turned ON or when it's cutting lumber.

How do I troubleshoot this?

Is the building where you use this separate from the house/main building where the electrical service enters and the breaker panel is located? Also, does the saw connect to a sub-panel? If a sub-panel is in a separate building, it's required that a bonding wire be run with the other power wires, with its own grounding stakes.

If the tester is just a light, it's testing for voltage- use a meter that can measure up to 600VAC (a typical limit).

The fact that the shock only happens after turning the sa won tells me that it has a magnetic switch- can you post a photo of the saw and power switch? I looked at a photo of this model and it shows a magnetic switch- if the neutral was open, you wouldn't be able to use the saw- do you have 120VAC in the same area, fed from the same service?

Extremely dry soil can cause the grounding rod(s) to lose good electrical contact and that can cause many types of problems.

Do you know any electricians who might do a low-cost quick check of the service and grounding?

It's possible that the motor's field is shorting to the frame- turn the saw on and measure voltage from the metal to a known good ground on a different junction box or even better, the breaker panel.

 

Another remote possibilty that happened to me a few years ago. Squirrels chewed through the neutral cable coming from the pole and caused current through any available ground source. It was going through the cable ground and was melting the connections. Never got any shocks from anything luckily. Power company came out and had it spliced pretty quickly.

 

What is your meter reading? 294 what? Ohms? Volts? Especially with the 2 leads where they are on the switch.

 

BW and MB. Probably reading ohms of the motor windings

 

I didn't see this mentioned... are you using a dust collector with the saw? Dust collection units, depending on the conditions and the piping, can cause static electricity to build up in the saw.

We had some pvc pipe as part of our dust collection system at work. Occasionally you'd touch the saw and it'd light you up, I mean it felt like 220. The saw was sitting on linolium. I don't remember what I did to ground it out, but we grounded it and the problem was solved.

 

Post 8 above:

It's a weird issue. I doubt it's static shock, but might be?

I didn't see this mentioned... are you using a dust collector with the saw? Dust collection units, depending on the conditions and the piping, can cause static electricity to build up in the saw.

It could be that simple, but it should be checked out to make certain.
I used a bare copper wire on my DC from the separator to the motor. No more shocks!

 

Post 8 above:


It could be that simple, but it should be checked out to make certain.
I used a bare copper wire on my DC from the separator to the motor. No more shocks!

I am using a shopvac based dust collector (the dust cyclone w/ 5 gallon bucket) connected to the table saw via ... PVC pipes! This could be it!

 

Thank you all.
Here's the latest, and hopefully the last update. To recap, I ruled out the damaged cable by doing continuity tests on the power chord.

Since the weekend, I did further investigation (aka ChatGPT) - and narrowed down it to three possible root causes.
(a) The Switch (to be specific, the Noise/EM filter capacitor inside it)
(b) Motor
(c) It was just a static shock. Non Contact testers can dish out false positives, and I didn't trust my multimeter or my skills enough to measure the voltage between the metal cabinet and ground. I couldn't get a 120 V reading on my multimeter when I tested it against the socket. (More on this later).

With the help of ChatGPT, I ruled out (b) - did continuity tests for line (black) & neutral (white) wires of the motor with the metal cabinet. I replaced the switch.. but I still got 2 bars on the non-contact tester. Unwilling to touch the cabinet for safety reasons, I got hold of another electrician to diagnose and confirm things were okay. He performed all the diagnostics and declared that the machine was safe to operate.

At this point, it could be (a) or (c). And, he verified it by measuring the voltage between the metal cabinet and the motor housing.. and touched the metal cabinet while I was cutting a piece of lumber. Also, he told me that they don't use multimeter to measure voltage out of the sockets because the contact points are not uniform.. and he uses a plug-in type meter to measure voltage.

So, in summary, it could either be a static zap or a faulty switch. And, the switch replacement should resolve it if it was the latter.

I sincerely appreciate all of you chipping in with your thoughts & troubleshooting steps to guide me - despite being very new to the site!
For those interested in the ChatGPT troubleshooting - here are the chat threads.
ChatGPT - Table saw shock diagnosis
ChatGPT - Test DWE7491 capacitor

 

Yep. Left and right hands were both on the table.

 

The table is a solid piece though. It can't have a difference of potential across the table. If you were touching the power button with one hand, and the table with the other hand, and only then getting shocked, that would make more sense.

 

A ground fault circuit interrupter, called a GFCI or GFI,

from the above link
A ground fault circuit interrupter, called a GFCI or GFI, is an inexpensive electrical device that can either be installed in your electrical system or built into a power cord to protect you from severe electrical shocks. GFCls have played a key role in reducing electrocutions. Greater use of GFCls could further reduce electrocutions and mitigate thousands of electrical burn and shock injuries still occurring in and around the home each year. Ground fault protection is integrated into GFCI receptacles and GFCI circuit breakers for installation into your electrical system, especially for circuit outlets in particularly vulnerable areas such as where electrical equipment is near water. Portable GFCls are also available to provide on-the-spot ground fault protection even if a GFCI is not installed on the circuit. The GFCI is designed to protect people from severe or fatal electric shocks but because a GFCI detects ground faults, it can also prevent some electrical fires and reduce the severity of other fires by interrupting the flow of electric current.

This saw does not use a three wire plug that is not frame grounded to Earth in any way.

If I were testing this saw myself I would go to the outlet where the ground of the GFI is located having the saw nearby where my meter can reach between the ground Earth pin and the table top of the saw should be zero voltage or near there since it is a floating surface there could be some static electricity build up from the spinning saw blade but you should not notice it.

If the original poster had a qualified electrician to come out and check the gfci and it tested correctly then you're down to either a pinch cable touching the table top or static electricity.

 

This saw does not use a three wire plug that is not frame grounded to Earth in any way.

If I were testing this saw myself I would go to the outlet where the ground of the GFI is located having the saw nearby where my meter can reach between the ground Earth pin and the table top of the saw should be zero voltage or near there since it is a floating surface there could be some static electricity build up from the spinning saw blade but you should not notice it.

If the original poster had a qualified electrician to come out and check the gfci and it tested correctly then you're down to either a pinch cable touching the table top or static electricity.

A qualified electrician would say that a three wire plug is not necessary at all for GFC interrupter to work.

 

Basically it comes down to the fact that it is nearly impossible to diagnose the problem without a qualified electrician there in person.

 

I think he could have told if it was static electricity or actual power by putting a volt meter to the body of the saw. It would have started very small and gone to nothing.

 

@Karthik

also when testing from the cord and through to the motor it will only test correctly testing
With the motor switch being held in constantly as it is a magnetic latch switch. Which means when it loses power it automatically opens and disconnects to prevent the soft and restarting unexpectedly when being plugged in and or with a power Interruption of any sort.

I said or indicated how long you've had this saw is this a new acquisition or you've had it for a long time and this just a sudden new problem?

Did not say what part of the country you're in and therefore not knowing if you have extreme low humidity problems occurring helping with the shocks I eat static electricity.
These are problems I've seen people complain about more so during the dry winter then during the summer.

Have you tested your saw with no dust collection no connection other than the two power with saw blade all the way down do you notice a static electrical charge? A small shock?

Have you completely clean the saw of all dust especially around in around the motor area and the wiring pathways?

The original saw version of the DeWalt dwe 7491 came out about 20 years ago. On the tag in the upper right corner on the face will be the model number and a date code it could be like this 2021-37-49 means made in the 37th week of 2021 in a chinese plant. 41 USA, 49 and 69 Mexico two different plants, 47, China, 59 Czech Republic and many others

The reason I bring up the date of manufacture is due to there was a spell of wire being made over in the Far East made out of soybean oil and is known to cause bugs and critters and just flat-out wire breakdown over time.

note I added a picture to post #20.

 

With the motor switch being held in constantly as it is a magnetic latch switch.

Are you suggesting this "el cheapo" saw has a magnetic type switch?
That type of switch would cost 1/2 as much as the saw!