Simply memorize that 30 volts is the minimum voltage that constitutes a shock hazard for people.

A simple mnemonic is "Thirty can hurty!"

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Tags: electromotive force (voltage) safety

Your nervous system functions using electrical signals. Further, your body acts as a resistor. These two factors are the basis for electricity causing a health hazard. Because your nervous system uses electrical impulses, electricity can disrupt the cells' normal functions, cause muscles to contract or even disrupt the electrical signals to your heart causing it to beat irregularly or stop. Since your body acts as a resistor, an electrical current through the body will dissipate heat. As the current increases, the heat dissipated also increases and may transfer enough heat energy to damage tissue.

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Tags: electrical current safety

Standard electrical cable contains three wires. The black wire is the 'hot' wire or source. The white wire is the return. The third wire is the safety ground and may be either bare (no sheath) or green. If there is a green wire, it's the safety ground. Normally, current does not flow in the safety ground. It's there to prevent accidental shocks. If you need a last second reminder, just remember that green usually means ground.

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Tags: safety grounding

A "ripple" would be an up and down type of effect, which is not what a fuse necessarily prevents.

A fuse doesn't prevent a person from getting shocked or even mortally harmed depending on the circuit.

When a circuit draws too much current, it is described as 'overloaded. This condition may damage the equipment or pose a shock hazard. The method to respond to an overload condition is to use a fuse. The fuse is designed to vaporize a small wire if the current becomes too large, thereby creating an open circuit. The fuse is always placed in series with the source, or 'hot,' wire.

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Tags: electrical components electronics safety

This would completely eliminate the purpose of having a fuse in the first place. Clearly with the intended 5-amp fuse for the circuit, that would be the maximum current that would be safe. A 20 amp fuse would not stop the circuit from overheating in the scenario.

Fuses are selected based on the capability of the circuit they protect to handle a specific amount of current. If the current exceeds the current rating of the circuit, it can cause it to dissipate too much heat and start things on fire. A rather vivid demonstration of this is sometimes used in college physics classes where a 12 gauge copper wire is directly connected across the terminals to a 12 v car battery. Because the wire is unprotected and the car battery can supply hundreds of amps, so much heat will be generated in the copper wire that it glows bright white and melts. (This is NOT recommended to try, because it splatters very hot, molten copper.)

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Tags: safety electrical components

The key to avoiding electrical shock is to use properly connected electrical wires and good safety grounds. A three wire ground includes the safety ground and should be used for all equipment. Two wire cords should be avoided because they lack the ground wire. The use of a common ground ensures proper grounding of the equipment and avoids 'ground loops,' which may circulate currents and pose a shock hazard.

A mechanical interlock, more specifically a mechanical safety interlock, turns off power when an equipment access door is opened or a cover is removed.

Finally, a GFI (ground-fault interrupter) will sense cases where current is flowing in the safety ground wire and disconnect the power.

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Tags: safety grounding

Installing switches is a way to bypass the ground system, which defeats the purpose of having a ground system in the first place. Connecting the antenna ground to station ground will cause nothing but problems for your station equipment. The correct answer is to connect the protectors to a common plate, giving them a heavy duty connection point that channels the current to an external ground wire. Be sure to observe local building codes for correct grounding. Also note that any ground wires should be large, short and follow a direct path. Avoid sharp turns and wires longer than necessary.

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Tags: grounding safety feedline

A 12 volt lead-acid battery is nothing more than a car battery. Even if it's a marine or other deep cycle battery, the charging voltages will be the same, so they can be charged using your car in the same way you would 'jump' another car if it's battery was low. (Although, you might also consider a small solar panel for this kind of emergency.)

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Tags: mobile operation batteries dc power

12 volt storage batteries use lead and sulfuric acid. When the battery is charged, Hydrogen gas is generated. Hydrogen is extremely flammable and in the right combination of oxygen will burn so fast that it explodes. Obviously, the 12 volt battery is not high voltage and it won't generate ozone.

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See answer A09 for more details on hydrogen. Fast charging or discharging generates hydrogen faster which makes it easier to create concentrations capable of exploding. Also, the chemical processes that occur when charging or discharging are exothermic (heat generating), so it is possible to overheat and damage the battery. Note that the battery terminal voltage will not be reversed and there is no 'memory effect' for lead acid batteries like there is for the nickel-cadmium batteries used in some consumer electronics.

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Tags: batteries safety

Use large wires over short distances on a direct path to the grounding rods - Lightning is high voltage, high current electricity, short and direct paths will lessen the chance of electricity to jump to nearby conductors.

The answers of using loops and right angles are the opposite of using short and direct connections. Lightning is high voltage, high current electricity.

Bends in the wire may allow the electricity to 'jump' from the wire to nearby conductors, thereby defeating the grounding system.

The longer the wires are, the more resistance there is and the hotter the wire will get.

Once again: Use large wires over short distances on a direct path to the grounding rods - short and direct.

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Tags: grounding safety

Power supplies may use large capacitors to help provide smooth output voltages. These capacitors can store a significant amount of energy and may store it at large enough voltages (more than 30 volts) to pose a shock hazard. The charge could last quite a few minutes, depending on the power supply capacitors. If there is a charge on the capacitor, you may inadvertently become the low resistance drain, so it's a good idea to check the circuit with a voltmeter before you expose yourself to a potential shock hazard. Even without the shock hazard (lower voltage), it's a good idea to drain the capacitors to prevent damage to sensitive circuits. A resistor between 1 and 10 Megaohms generally works well for something like this.

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Tags: dc power capacitance safety

Refer to question A04 for a discussion on fuses. As noted there, the fuse should always be in series with the source, or 'hot' conductor.

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Tags: ac power safety