Does being connected to a battery's ground prevent ESD? - Page 1
Forum section: electronics / beginners

author: Jay112
author_rank: Regular Contributor
timestamp: April 11, 2016, 10:05:07 pm
content: If a battery is not connected to the Earth's ground, and a person is connected to the ground of the battery, would that offer any level of ESD protection when he's working with disconnected electronic devices? Is that protection worse than if he was connected to the Earth's ground?

author: danadak
author_rank: Super Contributor
timestamp: April 11, 2016, 10:22:44 pm
content: Ques 1 : Yes, partial protection, as person is at same potential as equipment heis working on. But unknown is potential difference between earth and person/equipment.Ques 2 : Yes, worse. Ideal is person, equipment, earth all at same potential.Regards, Dana.

author: BobsURuncle
author_rank: Regular Contributor
timestamp: April 11, 2016, 11:22:55 pm
content: Quote from: Jay112 on April 11, 2016, 10:05:07 pmIf a battery " is not connected to Earth's ground" then there is no battery ground connection that can be connected to by a person. Your question makes no sense.

author: Jay112
author_rank: Regular Contributor
timestamp: April 12, 2016, 02:52:02 pm
content: Quote from: BobsURuncle on April 11, 2016, 11:22:55 pmI don't understand what you're saying. Are you suggesting that the negative terminal on a battery can't be called "ground"? According to wikipedia a ground connection is any reference point that electricity can return to:"In electrical engineering, ground or earth is the reference point in an electrical circuit from which voltages are measured, a common return path for electric current, or a direct physical connection to the Earth."

author: mongo
author_rank: Contributor
timestamp: April 12, 2016, 03:12:09 pm
content: I think the point is that a negative terminal on a battery can be called "ground", it cannot be called an "earth ground"."Ground" is a reference point to measurement. "Earth" is the most common ground reference. If a battery's ground is not at the same potential as the "Earth" ground, and provide a path for that energy differential it is not an effective protection against ESD.As an practical example which will be technically wrong for many reasons, an Altocumulus cloud effectively is a battery but that does not stop lighting.

author: BobsURuncle
author_rank: Regular Contributor
timestamp: April 12, 2016, 05:29:36 pm
content: Quote from: Jay112 on April 11, 2016, 10:05:07 pmWhat I mean is that clause contradicts itself. Batteries have no inherent ground so if it is not connected to ground you can't call a terminal ground, the terminals are either + or - with respect to each other and they will float with respect to ground unless one or the other is tied to ground. Also ground is rather sloppily referred to in casual conversation in the industry, so for example when earth ground and a common bus in a circuit are both called ground, but the bus could be at a different potential - even dangerously different. So when it matters, it is best to be clear and specify to which you are referring and whether they are common or not , i.e. chassis common/ground, earth ground, signal ground??? There are standardized symbols for indicating these in a schematics but unfortunately the standards are often ignored and might even have regional differences. Perhaps you understand these finer points, but your statement left me guessing as to what you meant.

author: Kilrah
author_rank: Unknown
timestamp: April 12, 2016, 05:54:16 pm
content: As a corollary, in any mobile device without a tie to actual earth ground any "ground" will only be such a thing in the scope of the device itself.

author: Jay112
author_rank: Regular Contributor
timestamp: April 12, 2016, 06:11:55 pm
content: Is there really an error in my original question? Please point out to me where I misused the term "ground". I'm just interested in learning.

author: Kilrah
author_rank: Unknown
timestamp: April 12, 2016, 06:30:06 pm
content: The whole point is that this term can refer to 2 things, and it's not always obvious which is used.On a generic schematic "ground" is the power supply's negative point. Depending on that supply it may or may not be "earth ground". If it is you may get ESD protection, if it isn't you don't.In the case of a battery powered device, you pretty much certainly don't. You only would if there was also a grounding strap that was connecting battery minus to earth ground, which pretty much doesn't exist since the whole purpose of the battery powered device is typically to be tether-free and that wouldn't be the case anymore.

author: ade
author_rank: Unknown
timestamp: April 12, 2016, 07:26:23 pm
content: We control ESD by bringing "everything" (persons, equipment, devices, chips) to the same potential.This is often done by connecting everything to earth ground (since most equipment will already be grounded). But strictly speaking, it is not necessary to tie to earth ground. Any common ground should suffice.Connecting a person to a battery terminal just means that person and that terminal will be at the same potential. That's all. The person + battery terminal might still be at a very different potential compared to lab equipment, to the floor, to sensitive devices, etc., because they are notalltied together.So simply connecting a person to a battery terminal cannot eliminate ESD.

author: IanB
author_rank: Super Contributor
timestamp: April 12, 2016, 08:21:22 pm
content: Quote from: Jay112 on April 11, 2016, 10:05:07 pmQuote from: Jay112 on April 12, 2016, 06:11:55 pmIt's because you said "the ground of the battery". If a battery is not connected to Earth's ground then the battery is floating, and therefore it doesn't have a ground terminal.Now the equipment you are working on may have a metal chassis that acts as a common reference, and maybe this metal chassis is tied to one of the battery terminals, and therefore this metal chassis could be considered a circuit ground. If you connect yourself to this metal chassis then your body should be at no dangerous potentials relative to the circuit under investigation, and therefore that circuit will be somewhat protected against hazardous discharges from your body.But, this doesn't mean that any static accumulated on your body will be discharged to safety. You can still damage other equipment if you touch it while charged up.Furthermore, you may be safely tied to earth ground through a protective earthing strap, but that doesn't mean you cannot damage anything by static discharge. If the other equipment happens to be floating and holding a static charge (maybe it is battery powered and in a plastic enclosure) then you can still damage it by touching it. Protection from damage depends on everything being at equal potential.

author: BobsURuncle
author_rank: Regular Contributor
timestamp: April 13, 2016, 02:35:59 am
content: In modern electrical equipment....There is earth ground, which I think is self explanatory.There is (unfortunately IMO) chassis ground, which may or may not be earth groundedThere is the common return path for the signal - which incorrectly is often called ground.Ground does not carry current under normal operating conditions.IEEE has standardized symbols, attached, for showing these in schematics, but again these standards are often violated. Likewise in discussion the terms are often incorrectly used but correctly interpreted because of the mutually understood context in which they are used.