# BPHgravity

Senior Members

142

10 Neutral

• Rank
Baryon

• Website URL
http://

## Profile Information

• Location
Florida
• Favorite Area of Science
Electricity
• Occupation
Electrical Contractor / Instructor
1. ## Question about electrical shock.

Static discharge or better described as charge separation can be very dangerous. Tall light poles that do not have effective bonding to the earth can build up a lethal amount of charge. Electrical installers prevenmt this occurance by addding equipment bonding conductors with the circuit conductors to assist in "bleeding" off this separaion charge. Ground rods bonded to the pole can also be effective.
2. ## Question about electrical shock.

Imagine a simple circuit consisting of resistors in a series/parallel configuration. Current will flow thorugh each resistor. The amount of current depends on the connected voltage and the value of resistance of the resistor. Each person can be assumed to be a resistor that is in series with each other and possibly in parallel with the circuit. The typical resistace of a human person can range from 1,000 ohm to 100,000 ohm. In all likely-hood, the last person would receive the least amount of shock potential from the series of voltage drops that would occur across each person. If the voltage reduces to under 40-volts, it would no longer be lethal.
3. ## Capacitor

I deal with capacitors on a very frequent basis, so i am well aware of the dangers involved. My first post stated this concern very clearly. The fact that I was trying to point out is that the origin and circumstance of the cap in question is known. It is being removed from a monitor that has been de-energized. Knowing this, per the requirements of NEMA/ANSI specifications and listing by UL, the cap is required to have a discharge circuit that reduces the voltage potential of the cap to under 50 volts in under one minute. When a cap is pulled from a shelf or has an unknown orgin, OSHA recommends discharge through a 1 K ohm, 10-watt resistor for all caps up to 1,000V, 500uF. My other point is that discharge through an insulated conductor will not "melt" the wire. Caps discharge in five time constants (TC). A TC=R*C. So if R = 0 then theoretically the cap discharges instantly. So it is important there be some resistance. How much resistance depends on how long a discharge time you want verse the size of the cap. For example a 300 micro farad cap discharged with a 100 ohm resistor would discharge in 5 * .0003 * 100 = .15 seconds. An insulated copper conductor can withstand 1A for every circular mil for 5 seconds. Common #12 awg wire has 6,530 circular mils. So trust me when I say the wire will be fine.
4. ## Question about electrical shock.

Current doesn't just take the path of least resistance, it takes all paths of resistance to its source, not to the ground. If a person or in this case a series of persons come in contact with an energized component of an electrical system and are insulated from a conductive path to the source, no potential will exist, and in effect no current will flow and no shock will occur. Most systems in the US have significant system grounding to Earth and in some cases to the buiding foundation and structural supports. There is a possibility that a very high resistance path could be created through one if not all the persons in contact with ground in the case of standing on a concrete floor or the Earth itself. A scenior that would certainly cause for all persons to receive shock is by having the last person in line in contact with a object that is bonded to the electrical grounding system, like an appliance. This way a return path for current exists and current will use the persons as a conductor.
5. ## Capacitor

Your all nuts! Short the leads with a short peice of any small gauge wire or a few quick taps with a screwdriver is all you need to do. If the unit was denergized for any period over a few minutes, the internal circuitry has already dischraged most of the eneregy from the cap. All that will be left is some residual charge. 4,000 or 40,000 amperes at 1/100 of a second isn't going to melt a copper conductor anyway.
6. ## SPDT Switches

This is usually for interference suppression. Your circuit looks good. I personally would install an interlock that holds the paired switches from being operated independently and add a stop switch in series with each motor for an off fuction. This allows single function control and prevents two off postions from existing.
7. ## Capacitor

If the capacitor has a full charge on it, you could receive a pretty severe shock from contact with the two terminals. Equipment with capacitors are required by Underwriter Laboratories to have permanent and automatic means to discharge capacitors to a residual voltage of under 50-volts nominal within one minute after disconnecton from the power source. Still, it only requires 15-mA to kill a person, so don't take any chances. All you need to do to completely discharge the capacitor is to short the two leads. A simple loop of insulated wire is all that is needed.

Try using two plastic cups and some string
9. ## Are Cures The Cause?

It seems to me that when a virus or illness is eradicated from Earth, another much worse one follows. For example, measels, plague, polio, small pox; all these horrible diseases have been removed by large from human civilization, yet cancer, HIV, and others have followed. My question is; is it possible that nature and evolution has automatic population control? Meaning, AIDS has a purpose. It is meant to limit the over-population of the Earth. With the finding of a cure, what will nature retaliate with? This also extends to the possible origins of homosexuality. Is it possible that nature and evolution is forcing population control by changing our sexual tendencies and thus reducing births? Mathematically speaking, the larger the homosexual population, the lower the birth rate. Makes sense to me. Has nature and evolution figured out that if viruses and disease doesn't slow our growth, changing human sexuality will?

11. ## Earth's Magentic Field

Is it possible for the Earth's magnetic field reverse in polarity? I have recently read an article that suggested the Nothern Aurora is getting weaker due to a change in the flow of molten magnetic material in the center of the Earth. This in effect will flip the magnetic poles. It also suggested the Earth's magnetic field may have reversed several times in its history. I've never heard of this.
12. ## Screen Savers

http://setiathome.ssl.berkeley.edu/
13. ## Can Oxygen freaze?

-218.79 degrees C.
14. ## Mental Fatigue

I have recently been studying for a very important professional exam that I will be taking later this summer. I have been reading and working problems in 3 or 4 hours sessions. On occasion, I get to a point that I can't concentrate, focus, or even keep my thoughts straight. I feel as if my brain is about to explode. However, I can simply turn on the TV, go on my computer or do some other activity and the fatigue instantly goes away. What chemical and physiological cahnges take place at the moment mental fatigue sets in and how does the brain know the difference between reading for the sake of work verses reading for the sake of pleasure? With physical fatigue, simply changing physical activity doesnt make the fatigue go away. Only rest will. However with mental fatigue, simply changing the focus of mental activity does. Why?

27/m/USA Birthday on Turkey Day every few years.
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