If a circuit board is connected to a long wire say 10 feet long and they are isolated with no connection to ground/earth. The circuit board and wire are in equipotential. If your hands have super high static and you touch the 10 feet wire at the end, would the static travel the 10 feet wire and flow to the circuit board and damage the ESD sensitive pin? If not, what if the wire is just 2 inches long?

If answer is no to both, then it means if my equipment is not connected to ground/earth and I'm touching the pins/chip/ etc. The million of volts of static in my finger won't fry the circuit? But then when the static fly into the circuit, won't the part that gets hit be damaged?

 

Both scenarios can potentially destroy the ESD sensitive pin, regardless if the system is fully isolated.

There are probably deeper and more rigorous explanations around the web, but a shorter explanation is that a static discharge can always potentially happen if there is charge buildup anywhere in the system. In other words, an inert body (the board) has balanced charges but, when put in contact to another body that has a buildup of charges, an inrush of electrons/electric charge will flow between the two (a current). If the current is too high, the pin may be damaged. The ability to damage the pin depends on the circuit connected to the pin itself and the current that flows between the two bodies.

For example, if the charged body has a potential of 1MV but it is exceedingly small (i.e., just a handful of charges waiting to be discharged), then the chances of damaging the part are minimal, since the inrush current will be very quick and thus will not build enough energy to heat up the circuit connected to the pin and damage it.

The charge buildup does not happen in conductors, since the high mobility of electrons/charges on such materials levels things out. On the other hand, insulators and poor conductors can buildup charges and therefore need to have procedures to prevent this buildup from happening - discharging your own body, hands, other insulators such as boxes, adhesive tapes, labels, etc are critical to reduce the chances of damage to happen.

The only thing that the longer wire may do is add resistance between the two pins. If this wire has enough resistance (MΩ), it will limit the current inrush by dissipating the heat on itself.

 

Both scenarios can potentially destroy the ESD sensitive pin, regardless if the system is fully isolated.

There are probably deeper and more rigorous explanations around the web, but a shorter explanation is that a static discharge can always potentially happen if there is charge buildup anywhere in the system. In other words, an inert body (the board) has balanced charges but, when put in contact to another body that has a buildup of charges, an inrush of electrons/electric charge will flow between the two (a current). If the current is too high, the pin may be damaged. The ability to damage the pin depends on the circuit connected to the pin itself and the current that flows between the two bodies.

For example, if the charged body has a potential of 1MV but it is exceedingly small (i.e., just a handful of charges waiting to be discharged), then the chances of damaging the part are minimal, since the inrush current will be very quick and thus will not build enough energy to heat up the circuit connected to the pin and damage it.

The charge buildup does not happen in conductors, since the high mobility of electrons/charges on such materials levels things out. On the other hand, insulators and poor conductors can buildup charges and therefore need to have procedures to prevent this buildup from happening - discharging your own body, hands, other insulators such as boxes, adhesive tapes, labels, etc are critical to reduce the chances of damage to happen.

The only thing that the longer wire may do is add resistance between the two pins. If this wire has enough resistance (MΩ), it will limit the current inrush by dissipating the heat on itself.

Someone told me if a system is isolated. No static can harm it. Do others believe this?

 

I don't. If there is a closed circuit created within an isolated system then current can flow.
I'm sure astronauts on the ISS have to take anti-static precautions with sensitive equipment.

 

Someone told me if a system is isolated. No static can harm it. Do others believe this?

No. Once the wires are touched, the system is no longer isolated.

What are the qualifications of this person?

 

Someone told me if a system is isolated. No static can harm it. Do others believe this?

hi
I belive this might have come from one of your other posts , where you were amongst many other things discussing your house wiring, circuit breakers, current in your wires having momentum so it flowed after voltage was removed , and about ecg .

your understanding is right
and wrong ,
primarily in that your extrapolating .

an analogy , would be if some one asked us what PI is.

we could answer,
Just over 3
around 22/7
3.141592654....
the ratio of parts of a circle

etc.

all. are right , in the right circumstances.
which number would you use if you were working out planetary intercepts, might not be the one you use to guess how much ribbon you need to wrap around the old oak tree !

so, lets take step back.

if no current can flow, then no damage can be done to a circuit.
the classic example is in anti static protection, where every thing is at the same potential due to extensive bonding between all parts .

there is zero need for an earth connection,
the classic example is a space ship, they equie bond every thing, there is no wire going back to the earth, and all is well.

btw: you've mentioned Faraday shielding before,
this is similar , but different, so lets not go there...

now you mention about having millions of volts on your finger, what happens when you touch the esd se sensitive part.
ok then current will flow , and probably damage the electrical part

which is why we dont do that .
anything thats bought onto the equi potential bench new , needs to become equipotential,
the classic way of doing this is a wrist strap, with a resistance in it. you might be at millions of volts, but your capacitance is low, so low charge,

you would typically connect into equi potential are at a point that the current flow is not crossing a sensitive part and is at low current , uA , due to the resistor .

then once your at equipotential all, is well.

when working on electronic parts , its normal to connect the equipotential zone to a big earth spike / system,
obviously in a space ship this is not possible, but on the earth its normal, but as you see, not needed.

your question above is about medical.

medical is a very special , and regulated area.

in general , in medical , the equipotential zone is not connected to earth , and strict procedures are in place if mains equipment is used.

its imperative I medical that there are multiple levels of isolation between the patient and the mains ,
and that these are approved, tested and re tested.

the idea is the patient is basically a equi potential area,
so if their is say a earth fault , no way can the fault currentbflow through them, think if there was a lighting strike, and they had electrodes on their heart or head, and the local earth potential jumped up , you dont want that anywhere near the patient.

I hope this answers your question , and please mark this as closed,

 

Did you watch the video of the lineman and helicopter approaching the HV transmission line?

The helicopter is isolated. The lineman took the time to stabilize the voltage before clamping to the HV wire. If he had not done that, he would be toast as soon as he approached the wire.

How are sensitive electronic devices destroyed by ESD?
In the structure of semiconductor devices there are very small features that are closely separated. The separation is the weak spot. A large electric field across the gap can cause ionization and breakdown of the insulation material.

The lineman is like that weak spot. High electric field can cause a breakdown before equipotential is reached.

Answer: isolation does not prevent ESD damage.

 

Long or short wire does not matter.
The goal is to eliminate charge build up before coming into contact with sensitive semiconductor components and devices.

Whether isolated or non-isolated, make sure charge build up is reduced before connecting two things.

 

Did you watch the video of the lineman and helicopter approaching the HV transmission line?

The helicopter is isolated. The lineman took the time to stabilize the voltage before clamping to the HV wire. If he had not done that, he would be toast as soon as he approached the wire.

Why are sensitive electronic devices destroyed by ESD?
In the structure of semiconductor devices there are very small features that are closely separated. The separation is the weak spot. A large electric field across the gap can cause ionization and breakdown of the insulation material.

The lineman is like that weak spot. High electric field can cause a breakdown before equipotential is reached.

Answer: isolation does not prevent ESD damage.

How does the lineman stabilize the voltage in the high voltage line?

 

Long or short wire does not matter.
The goal is to eliminate charge build up before coming into contact with sensitive semiconductor components and devices.

Whether isolated or non-isolated, make sure charge build up is reduced before connect two things.

Yes thats the thing i missed. I thought when objects were in potential equalization, it is immune to any static damage. So one still have to eliminate the buildups.

But then in helicoper is huge buildup. What examples of other setting in high buildup? How do you raise your potential so you can join it? Opposite of the above case.

 

How does the lineman stabilize the voltage in the high voltage line?

They connect to the line using a long pole with a resistance between them and the pole , and a good route for the current to flow safely

How does the lineman stabilize the voltage in the high voltage line?

https://en.m.wikipedia.org/wiki/Live-line_working

 

Yes thats the thing i missed. I thought when objects were in potential equalization, it is immune to any static damage. So one still have to eliminate the buildups.

But then in helicoper is huge buildup. What examples of other setting in high buildup? How do you raise your potential so you can join it? Opposite of the above case.

you
a. ensure the current that flows to equalise is directed along a route where no sensitive equipment / parts are

b. control the current flow with resistance .

 

How does the lineman stabilize the voltage in the high voltage line?

You did not watch the video?

The lineman did not stabilize the voltage in the high voltage line.
He brought the helicopter to the same voltage as the HV line.
He used a rod approaching the line, followed by a clamp, rather than using his finger and hand.

 

hi
I belive this might have come from one of your other posts , where you were amongst many other things discussing your house wiring, circuit breakers, current in your wires having momentum so it flowed after voltage was removed , and about ecg .

your understanding is right
and wrong ,
primarily in that your extrapolating .

an analogy , would be if some one asked us what PI is.

we could answer,
Just over 3
around 22/7
3.141592654....
the ratio of parts of a circle

etc.

all. are right , in the right circumstances.
which number would you use if you were working out planetary intercepts, might not be the one you use to guess how much ribbon you need to wrap around the old oak tree !

so, lets take step back.

if no current can flow, then no damage can be done to a circuit.
the classic example is in anti static protection, where every thing is at the same potential due to extensive bonding between all parts .

there is zero need for an earth connection,
the classic example is a space ship, they equie bond every thing, there is no wire going back to the earth, and all is well.

btw: you've mentioned Faraday shielding before,
this is similar , but different, so lets not go there...

now you mention about having millions of volts on your finger, what happens when you touch the esd se sensitive part.
ok then current will flow , and probably damage the electrical part

which is why we dont do that .
anything thats bought onto the equi potential bench new , needs to become equipotential,
the classic way of doing this is a wrist strap, with a resistance in it. you might be at millions of volts, but your capacitance is low, so low charge,

you would typically connect into equi potential are at a point that the current flow is not crossing a sensitive part and is at low current , uA , due to the resistor .

then once your at equipotential all, is well.

when working on electronic parts , its normal to connect the equipotential zone to a big earth spike / system,
obviously in a space ship this is not possible, but on the earth its normal, but as you see, not needed.

your question above is about medical.

medical is a very special , and regulated area.

in general , in medical , the equipotential zone is not connected to earth , and strict procedures are in place if mains equipment is used.

its imperative I medical that there are multiple levels of isolation between the patient and the mains ,
and that these are approved, tested and re tested.

the idea is the patient is basically a equi potential area,
so if their is say a earth fault , no way can the fault currentbflow through them, think if there was a lighting strike, and they had electrodes on their heart or head, and the local earth potential jumped up , you dont want that anywhere near the patient.

I hope this answers your question , and please mark this as closed,

Here is a very important question that is in the back of my mind the past weeks but couldn't put my fingers on it. It may be trivial for those very familiar with ESD, but not to ordinary people.

You don't connect earth to the potential equalization conductor to avoid earth fault. Ok.

But is there any concern another reason not to connect to earth ground to the potential equalization conductor of ECG,EEG,EMG is because when there is path to ground, and you hold the electrodes and leads and there is static in your hands, it can damage the differential inputs pins by the mere fact there is path to ground in the equipment? If there is no path to ground, the damage to the inputs is none or less?

 

Yes thats the thing i missed. I thought when objects were in potential equalization, it is immune to any static damage. So one still have to eliminate the buildups.

But then in helicoper is huge buildup. What examples of other setting in high buildup? How do you raise your potential so you can join it? Opposite of the above case.

Equipotential bonding and charge buildup are two separate things.

The driver of a car can be at equipotential with the body of the car.
The car itself can acquire charge build up, whether moving or not moving. Some vehicles have anti-static straps at the back of the car.

 

Here is a very important question that is in the back of my mind the past weeks but couldn't put my fingers on it. It may be trivial for those very familiar with ESD, but not to ordinary people.

You don't connect earth to the potential equalization conductor to avoid earth fault. Ok.

But is there any concern another reason not to connect to earth ground to the potential equalization conductor of ECG,EEG,EMG is because when there is path to ground, and you hold the electrodes and leads and there is static in your hands, it can damage the differential inputs pins by the mere fact there is path to ground in the equipment? If there is no path to ground, the damage to the inputs is none or less?

you make statement
"You don't connect earth to the potential equalization conductor to avoid earth fault."

be cerefull in your mixing up of different cases .

medical is very different to mains.

in medical you dont connect the patient to ground, and all mains equipment is isolated via medical grade isolation .

 

On the subject of isolation and its importance, here's a little LTspice simulation of the effect of a lightning strike (which could also apply to static discharge) :-

The human body is modelled as a 1.5k resistance in series with 100pF capacitance.
Two people hold hands to maintain equi-potential. Lightning hits them. Person1 is grounded. Person 2 is isolated from ground. The potential of both rises instantly to the lightning strike potential. Poor person 1 gets zapped with a 7A current pulse, but lucky person 2 gets a mere 1nanoAmp pulse (which is actually a sim minimum conductance artifact).

 

But is there any concern another reason not to connect to earth ground to the potential equalization conductor of ECG,EEG,EMG is because when there is path to ground, and you hold the electrodes and leads and there is static in your hands, it can damage the differential inputs pins by the mere fact there is path to ground in the equipment? If there is no path to ground, the damage to the inputs is none or less?

You are missing something when you keep referring to damage to differential input pins.
There are many weak spots in electronic equipment and not only input pins.

As I mentioned before, the primary weak spots are in the microscopic spacing in the semiconductor features. ESD will always find the weakest spot in the system.

We can safeguard against ESD by removing charge build up in both object-A and object-B before the two come into contact.

Every object has capacitance. Before you can attain equipotential across a sensitive gap, you need to allow time for charge to flow, When a high electric field occurs before equipotential is reached, the insulation breaks down resulting in damage.

Having static on your hands is one part of the problem. Remove the static on your hands before proceeding.

 

you make statement
"You don't connect earth to the potential equalization conductor to avoid earth fault."

be cerefull in your mixing up of different cases .

medical is very different to mains.

in medical you dont connect the patient to ground, and all mains equipment is isolated via medical grade isolation .

In my unique all battery usages, all equipment are battery operated, so even if I connect the equipment to ground, no mains danger. But my concern is if the unit is connected to ground, and my hands have statics and I touched the input leads of the differential amplifier or the ADCs, then it has more chance of causing ESD damage than if the device is not connected to earth?

 

In my unique all battery usages, all equipment are battery operated, so even if I connect the equipment to ground, no mains danger. But my concern is if the unit is connected to ground, and my hands have statics and I touched the input leads of the differential amplifier or the ADCs, then it has more chance of causing ESD damage than if the device is not connected to earth?

As a first step, remove the electrostatics on your hands.

"Officer, I was only speeding when I drove through the red light!".