Ohm’s Law:
V = I x R I = V / R R = V / ILaw. These three equations are really the same; if you know two of the values,
you can find the third value.
In most settings, both at home and in manufacturing, voltage often remains
the same. Your outlets at home are around 120 volts, but in manufacturing, the
voltage is often much higher, from 480 volts up to several thousand volts.
The equations of Ohm’s Law are: voltage equals current times resistance, … current equals
voltage divided by resistance, … and resistance equals voltage divided by current.
Current is what kills workers when they are electrocuted. Lots of current is also what makes an
arc flash so powerful. These equations will help you understand why.
When someone is shocked, current is passing through their body. The second equation, then,
with current on the left, is what we will focus on.
I = V / R (highlight equation as it is discussed)
100 volts / 100 ohms = 1 amp
100 volts / 10 ohms = 10 amps
100 volts / 1 ohm = 100 amps
The level of current in someone’s body when they are shocked or electrocuted, or the amount of
energy released in an arc flash, is determined from the voltage supplied and the amount of
resistance that is holding back the flow of electricity.
Let’s go through some examples to see how this works.
100 volts divided by 100 ohms is 1 amp. 100 volts divided by 10 ohms is 10 amps, and 100 volts
divided by 1 ohm is one 100 amps.
As you can see, if the top number, the voltage, stays the same, the result, the current, goes up
as the bottom number, the resistance, goes down. If we take resistance down to 1/10th of an
ohm, the current would then go up to 1000 amps.
If the level of current depends on the resistance, a high resistance, similar to the top equation,
will lead to a low current.
If the resistance is small, similar to the bottom equation, the current will be dangerously high.
So the more insulated a person is, the more resistance they will have to the electricity. The more
resistance there is, the less current that will flow through the body, lessening the chance of
injury or death.
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