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Electrocution of the Human Body

Charles Dalziel, GFI Inventor (UC Berkeley) - RF CafeMan being electrocuted: funny picture - RF CafePhysiological effects of current density on the human body are shown in the table below. Contrary to popular belief, it is the current - not the voltage - level which is responsible for effects. According to Ohm's Law, of course, a certain voltage is required to cause the necessary currents to flow. Values show vary depending on the body.

Personally, I have been hit with 480 V while working on a 3-phase industrial motor connection. It didn't feel good.

See article on shock level versus pain level from Discover magazine.

The following table of quantity of electrical current and its effect on men and women is from work done by the inventor of the Ground Fault Interrupter circuit, Charles Dalziel.

Other RF Cafe resources on electrocution: Mac's Service Shop: Electric Shock | Eliminate Risk of Fatal Electric Shock with the GFI | Mac's Service Shop: Electric Shock | Potential Neutral Conductor Hazards | Electrocution of the Human Body | Biological Effects of Electrical Shock | Resuscitation for Electric Shock | Electrical Shock: Fact and Fiction | Look Out! It's Hot!

Effect

Direct Current

(mA)

Alternating Current (mA)
60-Cycles 10,000 Cycles
Men (mA) Women

(mA)

Men (mA) Women

(mA)

Men (mA) Women

(mA)

Slight sensation on hand 1 0.6 0.4 0.3 7 5
Perception threshold, median 5.2 3.5 1.1 0.7 12 8
Shock - not painful and muscular control not lost 9 6 1.8 1.2 17 11
Painful shock - muscular control lost by ½% 62 41 9 6 55 37
Painful shock - let-go threshold, median 76 51 16 10.5 75 50
Painful and severe shock - breathing difficult, muscular control lost by 99½% 90 60 23 15 94 63
Possible ventricular fibrillation

Three-second shocks

Short shocks (T in seconds)

High voltage surges

* Energy in watt-seconds

500

50

500

50

100

165√T

13.6*

100

165√T

13.6*

   

Table retrieved from the "Deleterious Effects of Electric Shock," by Professor Charles Dalziel, 1961.

Current Level (mA) Effect
1 Threshold of sensation
8 Mild sensation
10 Painful
13 Cannot let go
21 Muscular paralysis
20 Severe shock
38 Breathing labored
42 Breathing upset
70 Extreme breathing difficulties
90 Ventricular fibrillation
100 Death

Above is the original table for this page.

Regarding how to properly handle the ground (aka earth ground) and neutral wire connections.

Per the National Electric Code, the neutral wire is bonded (physically connected) to the ground at only one point, which is where the service originates (referred to as "service equipment"). IAs with nearly all residential installations, the neutral and ground are bonded at the main circuit breaker panel; i.e., service equipment, aka service entrance panel. Without going into gory detail, the purpose is to ensure that the current being supplied by the two phases (120 V each) has a return path only through the system neutral.. If some other point in the system (e.g., a remote secondary breaker panel or in your case an inverter) has the neutral bonded (connected) to a separate ground (connected to a different ground rod), then some of the current that would normally return to the source via the neutral wire will instead go to ground. The division ratio of how much current goes to the alternate ground and how much goes through the system neutral depends on their relative resistances. Two problems are caused by that scenario. One is that there is an unbalanced condition at the service entrance point. The other is that the alternate ground wire will have current running through it which, since the wire going from the panel to the ground rod is usually uninsulated, an electrical shock hazard is present. Simply put, there must only be a single point in an electrical distribution system where the neutral wire and the earth ground are physically connected, and that is where the electrical service originates (in your circuit breaker panel). The separate ground wire in Romex cable is present as a "safety ground" whose purpose is to provide an alternate path for return current if the neutral is inadvertently opened, in order to prevent an electrical shock (a scheme which only works under certain conditions). Regarding the unbalanced condition, that is the principle on which GFI circuit breakers and receptacles work. A circuit inside the GFI device measures the difference between the current in the "hot" wire and the current in the neutral wire, and if there is a difference of just a couple thousandths of an amp, it shuts off. A tenth of an amp of AC current passing through the heart (e.g., from one hand to the other) is enough to cause defibrillation and kill you. - Kirt Blattenberger

 

 

Posted April 26, 2004

Holzsworth
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