Static electricity, cell phone in a rubber case

[chilli42]

Please be kind - have probably a silly question about static electricity, the type when you walk across a carpet and touch something and you get a spark/shock on your finger.

Hoping someone here can answer as I’m getting confused.

If I’m holding say a cell phone in a rubber case and I have built up static charge on me, could I experience that spark/shock if a finger touched an exposed metal button on the phone (not covered by the case), or because I’m already holding the phone, would that not happen. Would I only get the shock if I were to touch something separate, like a door handle?

Hope that make sense.

 

[phinds]

You, the cell phone, and the rug are a closed system. Unless you build up enough charge to spark over to something nearby (unlikely) OR you touch something that will take the charge off of you by including it into your closed system and distributing the charge between you and it, you're good.

The phone should be good in any case unless you discharge the static electricity THROUGH the phone by hold it and touching IT to something. That would be particularly bad if you touched something that was grounded since ALL of the charge would leave you and go through the phone. Not sure just what that might cause to happen to the phone but I don't recommend trying it. Also, If the phone has a metal case, the charge should just go through the case and not through the internal electronics.

EDIT: Oh, and by the way, it's not a silly question at all. Seems like quite a reasonable one to me.

 

[chilli42]

Thank you for your answer. I got a shock from the dog (coming from him to me I think. So before I picked up the phone I touched a faucet, and door handle and no zap, then picked up the phone. While holding the phone I opened another door and still didn’t experience and discharge that I could feel.

What made me ask what I touched near the open metal charge port on the phone and it got me wondering if anything would have discharged via that opening. But, I’m assuming all I would have been fully discharged at that point.

I’m also assuming that phone are designed to handle static or thousands would be dying daily.

 

[chilli42]

You, the cell phone, and the rug are a closed system. Unless you build up enough charge to spark over to something nearby (unlikely) OR you touch something that will take the charge off of you by including it into your closed system and distributing the charge between you and it, you're good.

The phone should be good in any case unless you discharge the static electricity THROUGH the phone by hold it and touching IT to something. That would be particularly bad if you touched something that was grounded since ALL of the charge would leave you and go through the phone. Not sure just what that might cause to happen to the phone but I don't recommend trying it. Also, If the phone has a metal case, the charge should just go through the case and not through the internal electronics.

EDIT: Oh, and by the way, it's not a silly question at all. Seems like quite a reasonable one to me.

Also, if I move off the rug and stand on the wooden floor with the phone, do me the phone and floor become a closed circuit? Where does the closed circuit end? As in the floor is attached to walls and the door and door handle.

 

[phinds]

I’m also assuming that phone are designed to handle static or thousands would be dying daily.

I have no idea whether that's true or not but I'm doubtful about it. First, I'm not so sure about the phones and second, I mean how many people build up static electricity and then discharge it through their phone?

 

[Borek]

how many people build up static electricity and then discharge it through their phone?

In winter, when the air is dry, I am sparking like crazy, touching everything that has any capacity or is in any way grounded (often just by lying on something else). I can easily believe this is a potentially serious problem.

 

[phinds]

In winter, when the air is dry, I am sparking like crazy, touching everything that has any capacity or is in any way grounded (often just by lying on something else). I can easily believe this is a potentially serious problem.

I'll take your word for it. I'm a dinosaur and do not HAVE a smart-phone, just a brick and I rarely use it, so no personal experience.

 

[berkeman]

I got a shock from the dog

Bad Dog!!

I’m also assuming that phone are designed to handle static or thousands would be dying daily.

Oh the Humanity!!

Oh wait, you mean thousands of phones, not thousands of people. C'mon man, please be more clear.

Anyway, sure, smart phones as well as all electronic devices need to pass certain levels of immunity testing in order to be sold under the CE Mark (which mainly applies to the EU, but also has been adopted in much of the Rest of the World). After all, if thousands of people phones were dying each day, from ESD shocks, that would lead to a lot of complaints and warranty replacements.

The standard test used for ESD immunity is EN 61000-4-2 (look it up). There are a number of design techniques used to ensure that whichever pathway an ESD voltage transient is applied to a device, the device can guard itself against damage.