Why is stick welding in A/C mode so dangerous?

By Lawrence (*****)

Date 11-04-2007 21:09

Welcome to the Forum Longshore!

Probably what is being referred to is the danger that occurs when two electrodes come together that are charged with different polarities... When they contact it will double the voltage..

AC will bring that situation about easily if it comes into contact with another electrode with DC+ DC- or another AC electrode.

See the American National Safety Standard
Z49.1 Safety in Welding, Cutting, and Allied Processes E11.3.6.3

Get if for free
http://www.aws.org/pr/jun17-2005.html

By DaveBoyer (*****)

Date 11-05-2007 06:28

I have heard an "old wive's tale" that a shock from AC will stop Your heart more readily than DC. I doubt their is any truth to it. I have allso heard that due to the way electric shock tends to make Your muscles contract, that DC is more harmfull, because it is always on [no change in polarity] and You have a harder time getting away from it. I am not sure this makes much difference. Both need to be treated with respect, as the actual power required to kill You isn't that great, if it gets conducted through You just right.

By CWI555

Date 11-05-2007 21:55

The way I understand it is, it doesn't have as much to do with DC or AC or voltage, but rather the amperage that is dangerous.

By DaveBoyer (*****)

Date 11-06-2007 04:11

Your body conducts the power more effectively at higher voltage. It is pretty hard to electrocute Yourself with 1 flashlight cell, but if You put 200 of them in series [300v] You probably could. Don't try this at home, kids.

By longshore weldr Date 11-07-2007 15:55

Thanks guys, for some reason I've run across a few articles saying to look out when welding in A/C mode.

I'll admit I'm an electrical chicken but I love welding so that just makes me be extra cautious about getting zapped. My brother told that one time he was welding some structural steel from an aluminum ladder and all was ok until he said he had gotten hot and sweaty so he took of one of his gloves. We'll he used that hand to hang on to the ladder and when he struck the arc he got bucked off the ladder.
So, I guess he wont be using aluminum ladders to weld w/anymore, hahahaha......

By DaveBoyer (*****)

Date 11-08-2007 05:17

Industrial welders often have 80-90+ volts open circut voltage, this is enough to readily conduct through sweaty clothing and wet gloves. My buz box farm welder is only 65 OCV and I have gotten mild "pokes" from it when soaked from sweat and in contact with the work while changing electrodes.

By Tommyjoking (****)

Date 11-08-2007 08:19

I can tell you from personal experience that A/C more readily will find a conductive path then D/C With high frequency superimposed over it it is much worse to look for alternate paths......I think it basically relates to the fact that it has a frequency of cycle imposed over it. Even straight household current has a low frequency of cycle....during the zero crossing during the cycle of + to - I can see the potential to find an alternate conductive path if one becomes available. Now all that was pre-qualified by the statement "I think". I also think it would not take much research to back that up with some hard science.

It takes less than 1/2 an amp to interrupt the cycle of the average human heart...it may start back up it may not. I have had way more current than that flowing from arm to arm and pulled every single muscle I had in my arms and chest and upper back...my heart did not stop beating...and that was nothing more then pure luck. If you would like to find out the voltage necessary to impose an amp of current "potentially" (pun intended) across your heart: Take a multimeter and set it on measuring resistance on the highest range, place the tip of each probe in between the index finger and thumb of each hand, take that reading and use this equation, Voltage = 1 X ohms , with 1 being equal to 1 ampere (.5 for 1/2 ampere and so on). Note that the ohms in this equation will vary a bit depending on your temperature, how much water you have in your body ect.