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#151280 - 08/23/06 08:46 PM got shocked &question  
scott2828  Offline
New Member
Joined: Aug 2006
Posts: 10
east wenatchee
I got locked up for 3 sec. by the pos side of a 9000v 30ma ac transformer (?rectifier) and grounded by a 120v ac ground metal wall of a commercial building (safeway).
I got a lot of problems my doc is looking into but my question is will the amps be increased above the 30ma because i was grounded to the 120v ac plain? and how do I figure out the amps tha went through my arm/torso to help my doctor out.


Arc Flash PPE Clothing, LOTO & Insulated Tools

#151281 - 08/23/06 09:10 PM Re: got shocked &question  
HotLine1  Offline


Member
Joined: Apr 2002
Posts: 6,872
Brick, NJ USA
Scott2828:
Welcome to ECN, first

As to your question, the "AC" ground should not have any potential, if the installation is NEC compliant.

As to the neon transformer that 'bit' you, IMHO should not exceed the rated 30Ma. One of the other guys here (Scott35) may have better info.

That all said, your profile says you are a 'sign apprentice'......why did your foreman or boss allow you to get your body into a 'live' neon enclosure???

Neon signage deserves a LOT of respect; hence the required enclosures, conduit, etc on the high voltage GTO.

BTW: Good luck & a speedy recovery

John


John

#151282 - 08/23/06 09:31 PM Re: got shocked &question  
Larry Fine  Offline
Member
Joined: Feb 2005
Posts: 693
Richmond, VA
Most neon transformers have a grounded center-tapped secondary, so the shock voltage should have been 4.5 Kv. In theory, that alone would halve the current to a max of 15 ma.

Unless you are caught between points of opposing voltage (such as two transformers), there's no way you could conduct more current than the source can supply; simple Ohm's Law.

The resistance of your body also reduces the current. That you are alive and kicking indicates that the current you were subject to was probably below 5 ma, but it's a guess.


Larry Fine
Fine Electric Co.
fineelectricco.com

#151283 - 08/23/06 09:41 PM Re: got shocked &question  
scott2828  Offline
New Member
Joined: Aug 2006
Posts: 10
east wenatchee
I was working with another apprentace of 1 1/2 years, we(unlawfully) had no journyman/admin. or any other supervisor on the job nor have we for the two weeks I have been working for the company(just got hired). the boss had been pushing us to get the job done due to his due date, i stepped into the center of the sign, dropped my strippers, bent over to pick them up and my butt was pushed onto the neon electroded on the glass housing as my hand was holding the angle iron on the opisite wall. The trainee that was with me desided that he needed to hurry and started to take the switch off the sign and accedently turnrd it on, followed by a very long scream, (doc thinks i blacked out for a breaf time) and finially my rear came off the electrode. Thankfully I had a set of dickes in my rear pocket with a thick wallet. it also destroyed my watch that was on my wrist. I could feel the pulsing of the current, that was weared! I just thought there has to be a reason for the extent of the injury.
OH OH, after the shock, my partner went to the base of the sign and tryed to unhook the 120v feed for the sign, there was a arc bettween the nutral and ground as he unhooked the wires, why would it do that? i thought nutrals only carred 2v or so?


#151284 - 08/23/06 09:45 PM Re: got shocked &question  
scott2828  Offline
New Member
Joined: Aug 2006
Posts: 10
east wenatchee
the transformers in the sign,,, if this helps there were 3 9000v and two 12000v, and they were all old and showed signs of heat discoloration, i did notice that they had a ground strap in the middel, one of them did have a black tar like stuff at the corner of the housing.


#151285 - 08/23/06 09:50 PM Re: got shocked &question  
scott2828  Offline
New Member
Joined: Aug 2006
Posts: 10
east wenatchee
thanks guys for your help, doc said i have nerve damage, and is worried about my spinal coum, weakness, dizzyness and felling lightheaded is anoying but the twitching in my hand and arm is driving me crazy! surpizingly I only had two small exit wounds in my hand and a small red mark on my but, I think thats because it didnt have to arc to get me.
thanks agian and any other info wound be great.

the one hand typing man!


#151286 - 08/23/06 11:30 PM Re: got shocked &question  
Scott35  Offline

Broom Pusher and
Member
Joined: Oct 2000
Posts: 2,708
Anaheim, CA. USA
scott2828,

Welcome to ECN!!!

You are among some very knowledgeable People here!

As to the shock:

Like "Hotline1" mentioned, the maximum output of the Transformer's Secondary side would be 30 mA (30 milli-Amps, or 0.03 Amp).
This is what would be available if the Secondary side was Short-Circuited, and an Ammeter was placed in Series with the Secondary's Current (like placed in series with whatever is used to short-circuit the secondary circuit).

Also, as mentioned by "Larry Fine", the Secondaries of Gas Tube Discharge type Transformers are Center Tap Grounded (or "Mid-Point" Grounded).
So if the output of this Transformer was 9 KV (9,000 Volts), the Voltage-To-Ground on the Secondary side will be 4.5 KV (4,500 Volts).
However, the available Short-Circuit Amperes (SCA) will still be 30 mA.

Some Transformers will have "Split Coil" Secondaries - which are two separate Secondary Windings, connected together in Series Additive fashion (the jumper between the two coil ends is tapped; thus creating the Mid-Point tap to Ground), while others will have a physical tap made to a "Full-Length" single Secondary Winding, at a point which is 50% of the entire Coil's Winds (or turns).
Example: 120V Primary x 12,000V Secondary (100:1 winding ratio).
Primary Winding has 500 turns of # 22 AWG Copper wire wound around the Core, and the Secondary has 50,000 turns of # 40 AWG Copper wire wound around the core.
At the 25,000th turn, a Copper wire lead is terminated to the Coil - thus creating a Mid-Point Tap.

OK, enough of that!

The Transformer you were involved with, should have the following ratings:

Primary (Input): 120VAC, 2.25 Amps (270 VA)
Secondary: 9,000VAC, 0.030 Amps (Mid-Point Grounded).
Voltage To Ground - Secondary: 4,500VAC

Since you were connected to the Secondary of this Transformer only, and to only one of the Secondary side's Termination (off one Secondary Bushing), the potential _SHOULD_ only have been 4,500 Volts - plenty high enough to kill!

Anything above 50 Volts may be considered lethal (as the Voltage may be high enough to push a high level of Current)

If the skin is very wet, plus conductive materials are present - like Salt, Chlorine, Iron, etc., Voltages lower than 50 Volts may allow lethal levels of Current to flow through a Person's body.

If your skin was very dry at the time of the shock, and there was very little to no conductive material on your skin, the _Contact Resistance_ of your skin may have been as high as 5M Ohms (5,000,000 Ohms) - which would allow 900 µA (0.0009 Amp) to flow.
This is less than a lethal level, but will still do some harm.

If the _Contact Resistance_ of your skin was 100K Ohms, this would allow 45 mA (0.045 Amps) to flow.
This is a lethal level!

Since the maximum Short-Circuit Amperes of the Transformer is 30 mA (0.03 Amps), a shock with a _Contact Resistance_ of anything at 150K Ohms and below, will result in 30 mA flowing through the body, for a Ground-Fault type of shock (4.5 KV L-G)

Quote

doc thinks I blacked out for a brief time


This is most likely what saved your life!!!

Quote

OH OH, after the shock, my partner went to the base of the sign and tried to unhook the 120v feed for the sign, there was a arc between the neutral and ground as he unhooked the wires, why would it do that? I thought neutrals only carried 2v or so?


Well, this could have been from a number of things, but the most likely reason for the Arc is the Grounded Conductor (AKA "Neutral") is open between the Panelboard, where the Circuit(s) are derived, and some point outside of the Panelboard (like a junction box) - and there is some load on the Grounded Conductor.

Another likely reason may be from something connected mistakenly to the Grounded Equipment, instead of a Grounded Conductor for the Circuit feeding that Equipment.

A lot depends on the actual size of the Arc seen.
If the Arc was a small little "snap", this may be from normal Voltage Drop on the Branch Circuitry, and is a result of the Neutral Current dividing and flowing through both the Equipment Grounding Conductor ("Ground Wire", Conduit, etc.) and the Grounded Conductor.
If the Arc was large and loud, it may from an open Neutral scenario.

Good luck with you!

Hope this is helpful.

Scott35


Scott " 35 " Thompson
Just Say NO To Green Eggs And Ham!

#151287 - 08/24/06 01:33 AM Re: got shocked &question  
scott2828  Offline
New Member
Joined: Aug 2006
Posts: 10
east wenatchee
Oh thank you so much.

That's what I needed is somebody to spell it all out, and you did beatifully. It really makes sence now. I was very, very sweaty from working, you really put it together.
Thanks all of you guys for your postings!
I think this will help the doc greatly! And you are right, you guys really know your stuff.

From a greenhorn trainee I just can't say thank you enough.
your a great bunch of profesionals!
Thanks


#151288 - 08/24/06 07:23 AM Re: got shocked &question  
resqcapt19  Offline
Member
Joined: Nov 2000
Posts: 2,148
IL
Scott2828,
Have your doctor get in touch with one of the electrical trauma centers. I think that there are 3 or 4 in the country. This is a very special area and if the doc doesn't work with it every day, he won't know all of the ins and outs of dealing with your problem. One such center is at the Univerisity of Chicago. http://etrp.bsd.uchicago.edu/mission.html

Don


Don(resqcapt19)

#151289 - 08/24/06 12:19 PM Re: got shocked &question  
Trumpy  Offline


Member
Joined: Jul 2002
Posts: 8,223
SI,New Zealand
Gidday there Scott,
Welcome to ECN, mate!. [Linked Image]

Well, I can honestly say that that is no way to enter any trade.
From a legal stand-point, your employer is grossly negligent for allowing one apprentice to supervise another, in the first place, without even considering that High Voltages were involved as well.

I'm not sure what OSHA would say about this, but in my books, there was a real risk of serious harm here and adequate supervision was not provided.

The supply to this installation should have been locked and tagged before the work even started (ie: covers removed, etc).

This guys attitude to safety is at best seriously lacking, I don't care if he has a deadline or whatever, one injured or dead apprentice is one too many in my mind.

Scott,
I hope you make a good recovery from this accident and I have to agree with Don's (resqcapt19) advice, a lot of the damage caused by a serious electric shock is never seen on the outside, but it can have far-reaching effects in terms of internal injuries.
Sorry, I'm not trying to scare you at all, but the human body is controlled by minute electrical signals from nerves, anything foreign of (comparatively) huge magnitude would have some effect.

I hate to say it, but if I were in your situation, I would find another employer, however, that is entirely up to you.
I would also stick with the electrical trade as well, sure having a bad start like that is not good at all, but it wouldn't keep me away from a career like this one.

Stick around here Scott,
You'll learn heaps, I know I have.
Cheers,
Mike. [Linked Image]
[Linked Image]


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