ESD shock recieved from metal cased resistor in plastic box? - Page 1
Forum section: electronics / beginners

author: Faringdon
author_rank: Super Contributor
timestamp: March 13, 2023, 08:23:59 pm
content: Hi,In our lab , we have a plastic transparent box full of metal case chassis mount resistors.I picked a resistor out of this box and it gave me an ESD shock when I touched it.Was this due to tribo-electric effect of the metal case resistors rubbing against the plastic box material?Did it mean I was thereafter charged up and thus a danger to electronics components?Chassis mount resistorhttps://uk.rs-online.com/web/p/chassis-mount-resistors/0159736p?cm_mmc=UK-PLA-DS3A-_-google-_-CSS_UK_EN_Passive_Components_Whoop-_-Chassis+Mount+Resistors_Whoop-_-159736P&matchtype=&pla-809231884452&cq_src=google_ads&cq_cmp=9771206638&cq_term=&cq_plac=&cq_net=g&cq_plt=gp&gclid=Cj0KCQjwk7ugBhDIARIsAGuvgParoZhBh1C5meCspPx4xU4IfPmRjifyBFmtTkK7Eje0XwYTRSF3Hi8aAoA2EALw_wcB&gclsrc=aw.dsplastic box:https://www.viking-direct.co.uk/en/p/EURO-C?sgt=GB-R21&customerType=consumer&utm_source=google&utm_medium=organic&utm_campaign=surface_google&cm_mmc=Google-_--_--_-EURO-C&gclsrc=aw.ds&gclid=Cj0KCQjwk7ugBhDIARIsAGuvgPYdHYfckZgj3hKdbCZGE4L6_8G7E8g8oncMWLXH83KQ5Sl8XA4jk7oaAoGnEALw_wcBOn a side note, do you know how to insert the above links as clickable "words"? "insert hyperlink" doesnt work

author: sparkydog
author_rank: Regular Contributor
timestamp: March 13, 2023, 09:58:18 pm
content: No idea on the ESD. For URLs,[​url=http://example.com]linkproduceslink. (Beware the zero-width space after the first[that's preventing the sample from being treated as markup.) Note: don't quote the url (i.e. don't write[​url="http://example.com"]).

author: Stray Electron
author_rank: Super Contributor
timestamp: March 13, 2023, 11:10:47 pm
content: Quote from: Faringdon on March 13, 2023, 08:23:59 pmYes, it's very possible but are you sure that there wasn't a capacitor somewhere in the circuit that was charged up? What kind of voltages are in the circuit?I used to work in a TV shop and would take brand new CRTs from their shipping boxes and they usually had a significant charge! No capacitors involved, that was just the charge between the inside anode and the outer metal frame work and through the heavy glass (insulating) CRT wall. Most of the CRTs had been in storagein our shopfor over a year! After a time or two of getting shocked we learned to use a wire jumper to short the anode to the outer framebeforewe tried to take the tube from the box.

author: Kim Christensen
author_rank: Super Contributor
timestamp: March 14, 2023, 12:39:51 am
content: Quote from: Faringdon on March 13, 2023, 08:23:59 pmCould be, but more likely your action of walking across the floor could have built up a charge on your body.They don't say what type of plastic those boxes are made of, but I doubt its an anti static type. Though it's OK for your resistors since they won't be damaged by it.If you are worried about being "charged up" after such an incident, go touch some grounded object like a metal water tap (assuming copper plumbing) or some piece of metal electric equipment whose chassis is earthed via the power plug. But walking around again can build up a charge once more, especially during the winter indoors when the humidity is low.If you're handling static sensitive electronic components you should do it at a proper antistatic workstation and wear a grounding (via 1Mohm for safety) wrist strap. (Not expensive to setup)

author: amyk
author_rank: Super Contributor
timestamp: March 14, 2023, 03:15:03 am
content: Quote from: Stray Electron on March 13, 2023, 11:10:47 pmThe CRTisa capacitor, and was probably charged up (along with some dielectric absorption) during factory testing.

author: Faringdon
author_rank: Super Contributor
timestamp: March 14, 2023, 08:11:26 pm
content: QuoteThanks, that would be bad news, as this was a floor in an electronics lab...and so it would mean its not an anti-static floor....So you mean, since the resistors were in an insulating box, then they have just charged up to the voltage on my hand?...and the act of that occurring, gave me a buzz?...but usually when you get a static buzz from your body being charged up, it happens when you touch something thats earthed...or a low resistance to earth?....the resistors in the insulating box were not earthed.

author: floobydust
author_rank: Super Contributor
timestamp: March 14, 2023, 09:00:16 pm
content: You developed a static charge walking in the lab/getting out of the office chair etc.The discharge is to the parts bin, its plastic is likely a tiny bit dissipative, has dirt/dirt on it etc. Somewhere you need the capacitor's second plate.If you do some math, the metal resistor and shuffling the parts bin cannot make enough charge that you can feel.Unless you have a pinched nerve, or apparently antidepressants can also cause a mental "zap" and it was not actually ESD you felt.Floor in an electronics lab means nothing because cheap bastard management will put in the lowest cost flooring material. Anti-static anything is super expensive, floor wax included. Laminate flooring to total garbage unless you want to make a Van de Graaff generator as you walk across the floor.Cold winter weather gives lower indoor humidity. I spray anti-static fabric softener like Downy on floor/carpet to tame ESD as a last resort.One thing I figured out as a tech and continue to this day -ALWAYS TOUCH GROUND before picking up a pc board, component etc.ALWAYS! Even if someone hands me a board, I tap their hand first to ensure equipotential.People that don't do this end up killing boards, lab test equipment, have weird hardware failures many a week or two afterwards due to damaged junctions and ion migration.It's a simple habit to cut down ESD problems because I've never seen manufacturing/engineering lab do it that well.

author: Kim Christensen
author_rank: Super Contributor
timestamp: March 14, 2023, 09:47:43 pm
content: Quote from: Faringdon on March 14, 2023, 08:11:26 pmNeither object needs to be earthed to get a static discharge between them. A good example is getting a zap from your car outside. The car is sitting on rubber tires and you are wearing rubber/insulating shoes, but you still get zapped when you touch it. So all that's needed is for one of the objects to have different charge from the other.

author: coppercone2
author_rank: Super Contributor
timestamp: March 14, 2023, 11:29:26 pm
content: I would like to say I found a big hole in my shoe when I stepped into a puddle and I do not trust shoes for being strongly isolated unless their like profesionally cleaned rubber boots. IDK how insulated the tire is to HV also, it drives in tons of metal dust from other car breaks and spark plugs engine dust and stuff on the street..Just for the experimenter, if you are trying to test this, put a nice clean rubber mat infront of the car to ensure you are insulated rather then trust shoes.What I am saying is I want to know the insulation resistance of a parked car from a tesla coil

author: Jwillis
author_rank: Super Contributor
timestamp: March 15, 2023, 10:45:39 am
content: It's in the plastic box. Your discharging it through the conductive metal case of the resistor. Look up Triboelectric effect or triboelectric charging. Common household plastic products are not produced to be anti static. Electronic storage boxes and bags are. The ABS enclosures for electronic don't build up static.

author: Stray Electron
author_rank: Super Contributor
timestamp: March 15, 2023, 01:54:18 pm
content: Quote from: amyk on March 14, 2023, 03:15:03 amI realize that but the point is that the CRT was still charged OVER a year later. So it's possible that the metal frame inside of the OP's insulated box is also holding a charge long after the circuit was turned off / disconnected. That's one reason why I asked what kind of voltages were present in his circuit. Is there enough voltage in the circuit to account for static shock? If not, then the static is coming from another source. That's also why I asked if there were any capacitors in his circuit.

author: Stray Electron
author_rank: Super Contributor
timestamp: March 15, 2023, 02:20:59 pm
content: Quote from: Kim Christensen on March 14, 2023, 09:47:43 pmExactly. One of my first great learning experiences with static electricity was at a remote computer site in an old wooden house (in a rock quarry!) in Virginia in the 1970s. When the weather was cold, the owner repeatedly complained that their printer would randomly go off line and mess up their print jobs. We ran test after test on the computer and the printer but couldn't duplicate the problem. Finally I went out there on a bitterly cold day and just experimented around. I found that I could simply walk across the floor and just touch the door knob on the door going into the computer room and I would always get an electric shock AND it would consistently knock the printer off line! Everyone working there knew that the brass door knob would shock them so they tried to avoid touching it. If they did avoid it then everything was fine but if anyone touched the knob, they would get shocked and the printer went off-line, absolutely 100% of the time when the weather was cold (and dry).The knob was made of brass and was set in a wood door in a wooden wall in an all wood house and there was no electrical connection what so ever to the knob or from it to the computer. But I ordered an anti-static mat to lay on the floor just outside of the door and that fixed the problem. Strangely, the mat wasn't grounded or anything, it just laid on top of the normal carpet. The mat costs a lot of money, over $400 in 1976 dollars and was only about 28" wide and 36" long but I was sold on them after that and I convinced a lot of other computer site owners to install them in their sites as well.Since then I've learned a lot more about the effects of static electricity on electronics and I will tell you right now, if your lab isn't employing anti-static mats and personal ground straps and other static control measures then they're going to have a lot of equipment trouble. Static will outright destroy some electronic devices but more often it will only damage them. Often they will continue to functionfor a time, but ESD will leave internal damage and will frequently cause them to fail prematurely.