Sunday, September 21, 2014


Effects of an AC or DC Currents on the Human Body

The three basic factors that determine what kind of shock you experience are the amplitude of the current, the duration of the current passing through the body, and the frequency.
Direct Currents actually have zero frequency, as the current is constant. However, there are physiological effects during electrocution no matter what type of current.
The factor deciding the effects of the AC and DC current is the path the current takes through the body. If it is from the hand to the foot, it does not pass through the heart, and then the effects are not so lethal.
However DC current will make a single continuous contraction of the muscles compared to AC current, which will make a series of contractions depending on the frequency it is supplied at. In terms of fatalities, both kill but more milliamps are required of DC current than AC current at the same voltage.

If the current takes the path from hand to hand thus passing through the heart it can result in fibrillation of the heart. Fibrillation is a condition when all the heart muscles start moving independently in a disorganized manner rather than in a state of coordination. It affects the ability of the heart to pump blood, resulting in brain damage and eventual cardiac arrest.
Either AC or DC currents can cause fibrillation of the heart at high enough levels. This typically takes place at 30 mA of AC (rms, 60 Hz) or 300 – 500 mA of DC.
Though both AC and DC currents and shock are lethal, more DC current is required to have the same effect as AC current. For example, if you are being electrocuted or shocked 0.5 to 1.5 milliamps of AC 60 Hz current is required and up to 4 mA of DC current is required. For the let-go threshold in AC a current of 3 to 22 mA is required against 15 to 88 of DC current.

Portable Units

If you are setting up a temporary pasture, a battery-powered unit is a great choice. The units are small, lightweight, and simple to install. Clamp them onto the dual purpose mounting/grounding post, attach the fence wire and you're done. While the units may look small, they're still capable of delivering a strong shock. All of them rely on D cell batteries for power, and their obvious disadvantage is that the batteries frequently need to be replaced. Zareba and Dare Products both manufacture energizers of this type

Larger Battery Units

For larger pastures, larger battery-powered fence chargers are also available. They are powered by either six- or 12-volt deep cycle batteries. Because of their greater weight, they require mounting on a fence post or other sturdy support. Like their D cell counterparts, the batteries in these units require periodic replacement; though less frequently. Deep cycle batteries can be recharged, but while this is taking place, a fresh battery must be installed. As their power supply is both finite and constantly being depleted, when using any battery-powered charger it is very important to keep weeds from making contact with your fence wire. Weeds "bleed off" power and shorten the time interval between replacement and recharging.

Battery-Solar Units

Your choices for DC-powered fence chargers are quite varied, as are the prices of these units. Your decision will be governed by your budget and specific fencing requirements.

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