This article was posted 07/18/2006 and is most likely outdated.

The Hazards of Electricity – Do You Know What They Are?
 

 
Topic - Safety
Subject - The Hazards of Electricity – Do You Know What They Are?

July 18, 2006  

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The Hazards of Electricity – Do You Know What They Are?

 

The three main hazards of electricity are electric shock, electrical arc-flash, and electrical arc-blast. OSHA statistics show that several hundred deaths occur annually as a result of electric shock. This number has come way down since the introduction of GFCIs but is still a tragedy on an enormous scale. Studies also show that 10-15 employees are hospitalized every day with arc-flash burns. It is for these reasons that it is important that everyone understands the hazards of electricity.

 

Electric Shock

Electric shock occurs when a person’s body completes the current path between two energized conductors of an electrical circuit or between an energized conductor and a grounded surface or object.

 

Electrical Arc-Flash

There seems to be a serious misconception in the industry that electrical arcs are a product of only high voltage. Actually,  electrical arc-flash is not voltage sensitive but is more a product of short-circuit current and clearing time or arc duration. In some cases, it is possible to generate higher arc energy from a low-voltage source than from a high-voltage source. The amount of energy will in turn determine the temperature of the arc, which can reach  20,000°K (Kelvin) or about 35,540°F.

 

Electrical Arc-Blast

According to studies on the subject, the pressures from an arc are developed from two sources, the expansion of metal in boiling and vaporizing, and the heating of air by passage of the arc through it. Copper expands by a factor of 67,000 times when it vaporizes. This accounts for the expulsion of near-vaporized droplets of molten metal from an arc. These droplets can be propelled for distances of up to 10 feet (3 m). Plasma (ionized vapor) is also generated outward from the arc for a distance proportional to the arc power. One inch³ (16.39 cm³) of copper vaporizes into 1.44 yards³ (1.098 m³) of vapor. The air in the arc stream expands in warming up from its ambient temperature to that of the arc, or about 20,000°K (35,540°F). The arc-blast created by the heating of the air is similar in nature to the generation of thunder by the passage of lightning through it.

 

Go to the following link to read the full report presented at the 2006 IEEE IAS Electrical Safety Workshop, February 7-10, 2006, Philadelphia, Pennsylvania.

http://www.ewh.ieee.org/cmte/ias-esw/pdfs/Hazards_of_Electricity.pdf 

 

 

Edited By

David Herres

Wildernesslight1@aol.com

http://www.electriciansparadise.com.

Herres Construction Co.

Balsams Grand Resort Hotel

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Comments
  • Hi Mike -

    It is still true that bedrooms can be on the same AFCI circuit? We just remodeled our basement and I wasn't sure if it was ok to put all the plugs in the two bedrooms on the same 20 AMP circuit (8 plugs total).

    Thanks!

    Lani de la Motte
    Reply to this comment
  • Reply from: Mike Holt   
    Please post your questions on the Questions Forum at www.MikeHolt.com.
    Reply to Mike Holt


  • Great E-mail That"s Why I Think The !-7 is so important. To get some Understanding. www.WireNutts.com

    Steven Hardin
    Reply to this comment

  • I just investigated the death of a Home Depot delivery man electricuted by installing the dryer cord incorrectly and energizing the insulated stack dryer from the washing machine. When he pluged the dryer in he was behind the dryer touching the washing machine and became a conductor to ground and had no where to go. He leaves a wife and 3 children. How many people must die before people understand electricity kills and professional people must install electrical work!! Please pray for the family

    Ned Freeman
    Reply to this comment
  • Reply from: Duncan   
    Sad though this incident is (I cannot call it an accident) ! Home Depot should only enploy qualified persons to do electrical work. This employer should be taken to task for requiring an unqualified person to do work which clearly requires a degree of knowledge and at least an appliance Repairman/installers qualification.

    Duncan S.
    Reply to Duncan

    Reply from: Mike Holt   
    The death was related to a drywall screw into romex. It was not the fault of Home Depot...
    Reply to Mike Holt

    Reply from: Ned Freeman   
    This was not a new outlet. Old working appliances were working the day they were removed to install new ones. No drywall screw in romex!!!
    Reply to Ned Freeman

    Reply from: Ned Freeman   
    There was not even any romex in this house, it was all EMT.
    Reply to Ned Freeman

    Reply from: Mike Holt   
    Oh, this is a different case. Sorry.
    Reply to Mike Holt


  • On the Arc Flash, the danger zones depend heavily on the often ill-defined bolted fault current. Is there a better way to nail this down? The utility can give me a number, but is it right?

    Regarding the incident, Home Depot should have put the cord on for him. We usually see a 30A or a 50A outlet for electric dryers. It would be really nice if some genius would make a 50A rated cable and offer a safe plug adapter so you wouldn't have the homeowner hooking this up himself.

    I've been doing this for a while, but being senile, I still have to go look up which prong is Neutral on a 115V plug, and if I get some European cord, whether it's brown or blue that's hot, and on the 240V or 3-phase, I still read the instructions twice.

    Take your time. It takes longer than 10 minutes to get to the emergency room, or to have to go back to the store for more hardware when you screw it up.

    Matt

    Matt
    Reply to this comment

  • I understand that the code requires each bedroom circuits to be supplied by separate AFCI. If 2 or more bedrooms are back to back, can we still power a receptacle from one bedroom to an adjacent bedroom like we used to before the AFCI rule came out?

    Jesse
    Reply to this comment
  • Reply from: Mike Holt   
    There is no requirement that there be a separate AFCI circuit for each bedroom. Just wire the bedrooms like you have in the past, just be sure that all bedroom outlets are AFCI protected.
    Reply to Mike Holt


  • In Telcom Power room I saw an non-insulated steel wrench fall onto -52VDC and Ground 10,000A Buss Bars. The Arc Blast blew copper and steel vapor over 55 feet one way and 30 feet the other. This hurt 11 people missing me by inches. The 12in*12in*10ft bars had to be replaced and the kid that dropped the wrench whas taking to the hospital for mental shock from the self generated fear.

    Kid
    Reply to this comment

  • I also encountered an instance in 1987 where 3-wire electric dryer and stove outlets had 240 volts corner grounded in them and the system was C-phase grounded rather than B-phase grounded. This created a sparking surprise when a tenant for a temporary factory got some 3 and 5 KW protable electric heaters and used the center wire of dryer and range cords as the equipment "ground". That is, the "neutral-ground" of the receptacle was 240 volts to ground. I had to change the wiring of these receptacles to put the neutral on the center terminal.

    I tell people that electrical equipment contains surprises. Thanks to snakes and yellow jackets electrical equipment does not need to even be energized. There are some photos over at www,themeterguy.com where snakes have popped the cover off of meter sockets and wrapped themselves around the 240 volts or 480 volts. Since snakes do not have perspiration glands they can do this to warm themselves up without geting electrocuted. There is even a picture of 2 snakes using a meter socket as the Rock Em Sock Em Motel!

    Akron, Ohio has 240 volts corner ground systems, both utility supplied and separately derived, where sometimes the B-phase is grounded or the C-phase is grounded. How we get C-phase grounded is that the neutral bar of some fusible switches is on the right and the color code is black red blue. Since blue is neutral in a number of European countries it does make sense. In the beginning of 1995 I told somebody from IBEW to think of it as a British corner ground.

    How fusible fusible switches should be wired on corner ground is to put the grounded phase in the center switch and fuseholder of a genuine 3-phase switch. This give you the option of installing a dummy fuse or providing overload protection for the grounded phase. Article 430 used to require a fuse of circuit breaker pole in the grounded conductor of a corner grounded motor circuit. Perhaps this was taken out because corner grounded is obsolete but I know that it was still in there in 1993.

    When installing circuit breaker panelboards on 240 volts corner grounded I have always insisted on using a panel with 3 phase busbars so that there is a circuit breaker pole in the grounded conductor of a branch circuit. The grounded conductor of a corner grounded system is NOT a neutral and is subject to overloading from unbalanced single phase loading. Also, a genuine 3 phase panelboard makes it possible to hook up a 3-wire T primary 4-wire T secondary transformer that supplies 120/240 4-wire delta. A better way to get 4-wire delta is to use 2 single phase transformer in the T primary T secondary configuration. A 3-wire floating neutral wye primary 4-wire delta secondary transformer like in utility practice needs 5 supplementary overload relays, one in each primary hot wire and one for each half of the center tapped secondary winding. T primary T secondary can use convenbtional primary and secondary protection and the impedance imbalance is a lot less than open delta vee. Also, this configuration avoids currents that might circulate in a delta winding.

    Maybe that was off the subject, but opening a fuse or circuit breaker pole in the grounded conductor of a corner grounded system only causes single phasing, not the overvoltages that occur when a 120/240 volt neutral opens.

    Corner grounding of 240 volts is better than ungrounded operation opartially since ungrounded systems can build up static electricity during rainstorms if a ground detector is somehow disconnected or never installed. Sure, 240 volts corner grounded puts as much stress on circuit breakers as 240Y416 or 277Y480. Some manufactures are actually pushing the use of 277Y480 volt circuit breakers on 240 volts corner grounded so as to avoid misapplication of 120/240 volt circuit breakers and to get improved short corcuit ratings.

    Mike Cole, mc5w at earthlink dot net

    Michael R. Cole
    Reply to this comment


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