Logic of using a large resistor on ground

Thread Starter

nickit88

Joined Apr 3, 2017
30
Came here hoping someone could clear up a question about a grounding pad that connects to the ground receptacle of a house outlet.
I was concerned it might be unsafe in a ground fault, so did a continuity test to determine if the pad and wire running from the outlet to it were conductive. Turned out it has a 100K resistor in the wire, apparently to reduce the possibility of electrocution in a fault.
Two questions:
Is it indeed safe?
And if the resistor prevents AC from flowing in a fault, doesn't it also impede its effectiveness as a ground to earth?
My brain tells me if I wanted to create a good ground I wouldn't want to build a ground wire with a lot of resistance in it.
 

Ylli

Joined Nov 13, 2015
851
You would need to be more specific as to what this is. For example, a sgereo receiver commonly has a 2.2 meg resistor from one leg of the input line connected to chassis ground. This provides a method to bleed any static accumulation off of the unit while not providing enough current to be harmful (or even noticeable) by the human operator.
 

ericgibbs

Joined Jan 29, 2010
9,117
hi,
Electroncis assembler workers who handle semiconductors are often grounded by wearing a anti-static wrist strap, connected to ground via a high value resistor.
This is to discharge static build up on the assembly operator.
E
 

Thread Starter

nickit88

Joined Apr 3, 2017
30
It's one of those new-age, alternative health devices some people who believe that walking barefoot on the earth either discharges harmful charges from you body into the earth or allows healing energy from the earth enter via your feet to cure ailments, destroy free radicals in the body, etc.
The idea is when you are in your house you are not grounded like you are standing barefoot on the ground so the mat provides that connection to earth.
The whole idea is questionable and looking into the science it appears to be woo-woo stuff, but my concern is if it is safe and beyond that, is there any reason to believe that this device is actually grounding you with any degree of effectiveness? Would seem to me if you wanted to normalize your body with earth, all you would have to do is touch the metal of a grounded appliance in the house and you are good to go.
If this pad device does indeed serve as a good/quality ground, doesn't is also make it more dangerous if somehow you were to come in contact with a live wire. It's not plugged into a GFI outlet and the company that makes it says it should not be used with a GFI outlet.
 

ericgibbs

Joined Jan 29, 2010
9,117
hi,
If you were grounded and you touched a 'live' wire, that could be bad news as the current thru your body would not be limited.:eek:
E
 

Ylli

Joined Nov 13, 2015
851
If this pad device does indeed serve as a good/quality ground, doesn't is also make it more dangerous if somehow you were to come in contact with a live wire.
And that is the purpose of the 100K resistor. That resistance is more than low enough to drain any static charge you may have accumulated, but is high enough that if you are standing on the mat and come in contact with a live wire there would not be enough current to be harmful. (I = 120/100K = 1.2 mA, a 'safe' level)
 

Thread Starter

nickit88

Joined Apr 3, 2017
30
And that is the purpose of the 100K resistor. That resistance is more than low enough to drain any static charge you may have accumulated, but is high enough that if you are standing on the mat and come in contact with a live wire there would not be enough current to be harmful. (I = 120/100K = 1.2 mA, a 'safe' level)
Ok, but if that's the case can you say you are truly well grounded by the device? Would seem if the pad is supposed to be the equal of standing barefooted on the ground, if you touched a live wire you would be lit up, not get just a 1.2mA tingle, no? The advertising and hype over these pads is that they provide the same effect of barefoot contact with the ground outside while you are inside your house.
Correct me if I'm wrong, but if the goal is simply to discharge static in your body, wouldn't that happen if you touch a door knob or metal that is grounded, like a stove? What would be the need to be constantly connected to ground via the pad, unless if you were of the belief some new-agers are that the earth feeds your body a continuous stream of healing energy as long as you are grounded to it?
Also, doesn't a static charge in the body dissipate all on its own eventually if you are just sitting in your easy chair and giving it some time?
 

Ylli

Joined Nov 13, 2015
851
A 100K resistor will quickly and effectively drain any static charge on your body. Barefoot contact with a good ground may take 0.001 second to fully drain the charge, and the mat, by adding that 100K resistor, may take 0.002 seconds. Does that millisecond make that much difference to you? Particularly since it makes the mat a safe ground.

BTW, it sounds like we are talking about a conventional anti-static mat.
 

Thread Starter

nickit88

Joined Apr 3, 2017
30
A 100K resistor will quickly and effectively drain any static charge on your body. Barefoot contact with a good ground may take 0.001 second to fully drain the charge, and the mat, by adding that 100K resistor, may take 0.002 seconds. Does that millisecond make that much difference to you? Particularly since it makes the mat a safe ground.

BTW, it sounds like we are talking about a conventional anti-static mat.
I get it, but $90 for a mat the manufacturer says you need to plug into a non-GFI outlet and keep your bare feet on it for several hours to receive the full health benefits of "earthing" yourself seems like something quite different - or at least they want you to think so - than a simple anti-static mat. Don't anti-static mats for electronics techs attach from the mat to your wrist, without the ground lug of a wall outlet involved?
Let me ask another way: is a wire with a 100k resistor in it just as effective as a ground as a piece of bare 14AWG shoved into the ground hole of an outlet and the other end wrapped around my big toe? If the answer is yes and it's safer, why don't grounds in all appliances and devices not include 100K resistors?
If just 1.2mA is all that can pass through a ground wire with a 100K resistor, how does that ground effectively deal with sending big amps to ground for your safety. If I'm barefoot on a concrete floor, am I not a way better path to ground than a wire that can only pass 1.2 mA?
 
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Ylli

Joined Nov 13, 2015
851
I get it, but $90 for a mat the manufacturer says you need to plug into a non-GFI outlet and keep your bare feet on it for several hours to receive the full health benefits of "earthing" yourself seems like something quite different - or at least they want you to think so - than a simple anti-static mat.
Typical advertising exagerations.
Don't anti-static mats for electronics techs attach from the mat to your wrist, without the ground lug of a wall outlet involved?
They are normally connected to an external ground such as the safety ground on an outlet.
Let me ask another way: is a wire with a 100k resistor in it just as effective as a ground as a piece of bare 14AWG shoved into the ground hole of an outlet and the other end wrapped around my big toe? If the answer is yes and it's safer, why don't grounds in all appliances and devices not include 100K resistors?
Yes to the first part, but note that in this case you are shunting away any static build up - very low current where the impedance in the ground wire will allow no significant voltage drop. In an appliance, you are dealing with the possibility of a high current short from the line to the case - in which case a low resistance ground is required to prevent any significant voltage from showing up on the case.
If just 1.2mA is all that can pass through a ground wire with a 100K resistor, how does that ground effectively deal with sending big amps to ground for your safety.
It doesn't. A mat like this is to discharge static build up, not bypass line current to ground.
If I'm barefoot on a concrete floor, as I not a way better path to ground that a wire that can only pass 1.2 mA?
Depends on how you define 'better'.
 

Thread Starter

nickit88

Joined Apr 3, 2017
30
Depends on how you define 'better'.
By better, I mean "preferred" or the path current chooses to take when trying to go to ground. Isn't the idea of a good ground to make it a better path to ground than your body would be?
Thought experiment: I'm standing barefooted a foot off the ground on a plastic stool and holding a live wire. I step off the stool and onto the grounding mat that's connected to the ground lug of a power outlet via a wire with a 100k resistor in it. What happens?
If I'm reading you right, the answer is essentially nothing - just 1.2 mA pass through my body due to the resistor impeding the flow.
If that's the case, doesn't it tell me that the pad is not a very good ground? Stepping off that pad and putting a bare foot on the ground would be a whole different story, would it not? That step onto bare ground would establish a good, much better ground, zapping me, correct?
That's what I mean by a device with a 100k resistor in it being a lousy ground, and lousy replacement for direct contact with the earth. Again, I accept that it can serve to discharge static, but that is not what this device is for according to the manufacturer. It is a device that is supposed to ground you just as well/effectively as standing barefooted on the ground.
 

Ylli

Joined Nov 13, 2015
851
The 100K makes it a *****SAFE****** ground. If you want the best ground just grab hold a grounded appliance with a metal case.
 

Thread Starter

nickit88

Joined Apr 3, 2017
30
The 100K makes it a *****SAFE****** ground. If you want the best ground just grab hold a grounded appliance with a metal case.
thanks. that's what I've been saying. By making it a "safe" ground, it isn't the best ground. It seemed to me from the beginning that it has to be one or the other - either very safe by including the resistor or less safe by excluding the resistor, which would put it more on par with touching a grounded metal appliance. I say more on par, as I doubt the surface of the rubberized mat with some carbon woven in is as conductive as my stainless steel stove.
For $90 I would expect something to be at least as effective at equalizing me with the earth as my stove.
 
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MrChips

Joined Oct 2, 2009
19,768
Really, you are overthinking this issue.

What makes a "safe" ground?

In your analysis, is a "safe" ground a connection to ground with:
(a) zero resistance
(b) moderate resistance, e.g. 100kΩ
(c) high resistance, e.g. 10MΩ

The purpose of any anti-static grounding pad is to remove any residual static charge buildup. For that purpose, any of the above will work.

The purpose of the resistor is to avoid electrical shock in the unlikely event that you come in contact with live power sources. In that case you want a high resistance to limit the current to "safe" levels. Option (b) or (c) makes it "safe".
 

Thread Starter

nickit88

Joined Apr 3, 2017
30
Not promoting whatever this is at all, but if I spent $90 on it I would expect it to be safe to use.
True, but pricey health and wellness devices that make a claim (in this case that standing on it is the same as standing barefooted on the earth) must deliver on the claim.

A sugar pill is safe, but if I pay $90 for a bottle of medicine it has to be more than safe: it has to work.

I know the device I've described is safer than wrapping a wire around your toe and connecting the other end to the ground on an outlet, but is it just as effective (not for discharging static, mind you) in terms of the integrity and absolute efficiency of the ground/connection to earth?

Remember, the claim is that it duplicates grounding that occurs when you stand barefooted on the grass. As I stated above, I suspect current will want to go through my bare foot on the ground rather than the other foot resting on one of these earthing/grounding mats, which to my mind means current decides this debate once and for all.

The notion that you can kill cancer cells or become more "naturally beautiful" (a couple of the many claims) by walking barefooted on the grass is a whole other can of worms, and as they say, extraordinary claims demand extraordinary evidence.

I came to the forum to find out whether the principal/science of duplicating standing barefooted on the grass via the device I've been describing is flawed. If it is, then I might convince my friend to send the pad back to Amazon for a refund. If he's dead set on the curative powers of earthing/grounding himself, I'd think he could just go out in the yard barefooted, touch a metal stove now and again. or do any one of a number of completely cost-free options available.
 
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