My UPS saved me from shock? - Page 1
Forum section: electronics / beginners

author: sam1275
author_rank: Frequent Contributor
timestamp: February 01, 2016, 12:26:08 am
content: Hi everyone, I touched the 220v AC line a few times by accident these days, but I only few a strong shake and move away with no more hazard, my another hand is touching the ground line and pain, but I neither lose conscious nor "stick finger to the line and cannot move" like other describes. Is this because I'm using a line-interactive UPS and the auto-transformer isolated the current from the real city-elecronics? Thank you.

author: Len
author_rank: Frequent Contributor
timestamp: February 01, 2016, 12:38:13 am
content: No. An autotransformer does NOT isolate the output from the input. They are directly connected.

author: wraper
author_rank: Unknown
timestamp: February 01, 2016, 12:52:54 am
content: Quote from: Len on February 01, 2016, 12:38:13 amUPS does not isolate either. I have received electric shocks many times, even with a little of burned meat but never passed out, was blown away, or had any serious consequences. The trick is that current flows within one hand so never stick both of your hands where the high voltage is present. If the current flows between the hands or from the hand to the leg past your heart, then you will be in serious danger.Some people just have a high skin resistance and can just touch the mains voltage without much effect. Also US voltage is just 110V AC, so that is nothing near compared with 220V AC here (I have "enjoyed" 380V AC too)

author: Brumby
author_rank: Unknown
timestamp: February 01, 2016, 02:14:20 am
content: Quote from: sam1275 on February 01, 2016, 12:26:08 amThat is concerning.... VERY concerning.It indicates a lack of care, negligence, not paying attention, complacency or whatever you want to call it. When working on equipment at these sorts of potentials, your attitude should not be anything less than respectful of the fact that youcan be electrocuted!Isolated, floating or whatever other safety mechanisms in place mayreduce the chancesof this - but if the volts are there with any sort of current behind them, then you can die.In all my years, I have only been bitten twice. The first was when I was young - and that made a lasting impression. The second was years later from a hidden danger that I should have thought about.The idea of doing it 'a few times' really worries me.

author: MarkS
author_rank: Unknown
timestamp: February 01, 2016, 04:09:39 am
content: 220 in the US isn't the same as 220 in Europe. In the US, a residential/commercial 220 outlet has two live 110 volt wires, each out of phase with the other. If you touched a single wire, you were only exposed to 110-120 volts.Still, SEVERAL times? What the...

author: MarkS
author_rank: Unknown
timestamp: February 01, 2016, 04:23:09 am
content: The point I was trying to make is that he was only exposed to one leg of the outlet. In the UK, 220 - 240 (whatever) is supplied from a single hot wire. In the US three phase power is supplied to the pole, with typically two phases brought out to the installation, each 60 degrees out of phase with each other. For a standard 120 outlet, one hot and one neutral wire is supplied along with ground. A 240 outlet has two hot, o e neutral and a ground. If he doesn't know this, he has no business messing with mains power.

author: Brumby
author_rank: Unknown
timestamp: February 01, 2016, 04:29:24 am
content: How do you get 240v from two 120v that have only 60º phase difference?

author: miguelvp
author_rank: Super Contributor
timestamp: February 01, 2016, 04:34:34 am
content: Quote from: Brumby on February 01, 2016, 04:29:24 amLike this?https://en.wikipedia.org/wiki/High-leg_deltaWe have three phase installations in the US.

author: vk6zgo
author_rank: Super Contributor
timestamp: February 01, 2016, 04:47:30 am
content: Quote from: Brumby on February 01, 2016, 04:29:24 amBecause that isn't what happens.I also though it was phase to phase,which would yield only 208V,until I had occasion to deal with some US stuff.240v in the USA is supplied by using one phase of the supply via a pole transformer ("pole pig") with a centre tapped 240v secondary ---"240 volts a side" in the old Oz terminology.Several 120v circuits may be connected off each side of the secondary,with the centre tap as Neutral,or the whole secondary may be used to supply 240v (commonly for things like Washing Machines,Dryers,etc,but sometimes made available as standalone power sockets).

author: vk6zgo
author_rank: Super Contributor
timestamp: February 01, 2016, 04:57:10 am
content: https://en.wikipedia.org/wiki/Split-phase_electric_power

author: Mechatrommer
author_rank: Super Contributor
timestamp: February 01, 2016, 05:02:55 am
content: Quote from: sam1275 on February 01, 2016, 12:26:08 amusually we hit the mains with tip of our finger, when electrons hit, we tend to contract muscles, if the vector of our finger+arm contraction tends to move away from the current source, then thats luck, we call that untrimmable or unstable condition in avionics where subject tend to move away from stable condition in time. furthermore, contact with tip of finger produce higher resistance at contact point, means less electrons hence less contraction. but if we hit with palm a great length of copper, enough electrons to contract your finger to grip the cable, and thats said to be in trimmed or stable condition aka toasted. any significant energy content 220Vac source is capable to put a subject in cardiac arrest even though it is isolated go figure V = IR, P = VI, E = Pt...

author: pickle9000
author_rank: Super Contributor
timestamp: February 01, 2016, 05:53:02 am
content: Sounds like a lucky guy. Do be careful.

author: rs20
author_rank: Super Contributor
timestamp: February 01, 2016, 06:09:24 am
content: Quote from: sam1275 on February 01, 2016, 12:26:08 amThe lethality of an electric shock is acomplexfunction of untold many variables: skin condition, position of body, footwear, voltage, frequency, presence of earthed objects, etc. I'm not going to give example of subtle changes to your circumstances that would transform these jolts into lethal shocks, because evidently you'd just consider the list complete and assume that it's otherwise safe. The fact that you're so nonchalantly getting electric shocks so frequently indicates that you A) have absolutely no understanding of how dangerous this is, and B) that there is a high probability of you being KILLED if you continue doing so.What you're doing is tantamount to looking down the barrel of a loaded weapon, except the danger is far more subtle and complex. If you couldn't help looking down the barrel of your gun, I'd tell you to get rid of the gun.So stop touching live wires. It's not that hard. If you find you can't stop, find a different hobby.

author: Brumby
author_rank: Unknown
timestamp: February 01, 2016, 06:42:00 am
content: Quote from: blueskull on February 01, 2016, 04:55:56 amYep.QuoteYep.Quote... Ah, I don't believe so.My read on this is any 2 phases (L1,L2) (L2,L3) (L3,L1) in a US residential 3 phase system have 240v. 208v being the neutral to high leg phase voltage (L3,N).Or am I missing something?

author: miguelvp
author_rank: Super Contributor
timestamp: February 01, 2016, 06:56:11 am
content: Yes you are right, from the wiki page I linked before (https://en.wikipedia.org/wiki/High-leg_delta) you can also find this:Maybe it's more clear. If you tap from the High leg to say L2 you get 240V.

author: Brumby
author_rank: Unknown
timestamp: February 01, 2016, 07:04:07 am
content: That's fine. It's just putting all the numbers down.It makes this statement even more mysterious...Quote from: MarkS on February 01, 2016, 04:23:09 am

author: miguelvp
author_rank: Super Contributor
timestamp: February 01, 2016, 07:11:23 am
content: We have many plugs:Source:https://en.wikipedia.org/wiki/NEMA_connector

author: Brumby
author_rank: Unknown
timestamp: February 01, 2016, 07:13:16 am
content: Oy vey!

author: miguelvp
author_rank: Super Contributor
timestamp: February 01, 2016, 07:24:28 am
content: I have a NEMA 6-20 (240V 20Amps) in my living room which I never used, it probably was here from before for maybe air conditioner or a pretty heavy duty heater?I'm glad its in there in case I ever need it

author: sam1275
author_rank: Frequent Contributor
timestamp: February 01, 2016, 08:02:41 am
content: Thank you very much everyone!!!Sorry I cannot reply one by one, so I'll say things in one post.The current do flow between by hands because another hand is touching a ground line and feel pain.My hand was a little wet because of working, so I think the resistance won't be too high.I'm currently living in China, so it's 220v AC.I did not feel stick to it, nor bounce away, nor burn, I can even remember that second clearly and I move away my hand using my mind, not muscle reflect. I feel so strange...I usually very careful, but these days I was working on a computer power supply without the metal case, I first thought it's a 110v line inside, but I'm sure it's 220v later because I feel the same touching the plug directly, but without touching the ground line this time.I don't know if there should be a "electronic leaking protect" switch that should cut off the power somewhere in the house, however it never react.Thank you everyone again, I will be careful next time.

author: Srbel
author_rank: Frequent Contributor
timestamp: February 01, 2016, 08:03:54 am
content: Quote from: sam1275 on February 01, 2016, 08:02:41 amSame thing happened to me.Quote from: rs20 on February 01, 2016, 06:09:24 amxD

author: vk6zgo
author_rank: Super Contributor
timestamp: February 01, 2016, 08:19:51 am
content: Quote from: sam1275 on February 01, 2016, 08:02:41 amIf you are in China,it's the real thing---220v ac between Active & Neutral,& hence also to Earth.Do nottouch it again---that is what meters are for!

author: station240
author_rank: Unknown
timestamp: February 01, 2016, 09:43:11 am
content: As for the original post, you actually have two auto transformers, as a Line Interactive UPS has an auto transformer internally.I'd assume one of them is limiting the current flow.However as it only takes 20mA to stop the heart, even low currents can be lethal.To be honest a full isolation transformer would be better, as far as limiting the smoke output of whatever failed device you have connected to the output.

author: MarkS
author_rank: Unknown
timestamp: February 01, 2016, 11:58:01 am
content: Yes, 120 degrees out of phase. It was a typo. I was typing on a tiny phone keyboard in a hurry in the middle of a store. Geez....

author: Brumby
author_rank: Unknown
timestamp: February 01, 2016, 12:02:42 pm
content: It's an EE forum. If you're going to throw a typo - don't pick a phase angle!Murphy will get you every time.

author: MarkS
author_rank: Unknown
timestamp: February 01, 2016, 12:11:00 pm
content: Quote from: Brumby on February 01, 2016, 12:02:42 pmYeah... Make a simple mistake in a forum populated by engineers and you'll never hear the end of it!

author: Mechatrommer
author_rank: Super Contributor
timestamp: February 01, 2016, 12:51:41 pm
content: Quote from: MarkS on February 01, 2016, 11:58:01 ami'm more concern of this than touching mains with a finger...http://www.theguardian.com/technology/shortcuts/2013/jun/18/smartphones-and-rise-of-child-accidents

author: sam1275
author_rank: Frequent Contributor
timestamp: February 02, 2016, 12:31:31 am
content: Quote from: station240 on February 01, 2016, 09:43:11 amSorry, I only have one that inside the UPS, I don't have another one..