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3: Electrical Safety
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- 3.01: The Importance of Electrical Safety
- 3.02: Physiological Effects of Electricity
- Most of us have experienced some form of electric “shock,” where electricity causes our body to experience pain or trauma. If we are fortunate, the extent of that experience is limited to tingles or jolts of pain from static electricity buildup discharging through our bodies. When we are working around electric circuits capable of delivering high power to loads, electric shock becomes a much more serious issue, and pain is the least significant result of shock.
- 3.03: Shock Current Path
- As we’ve already learned, electricity requires a complete path (circuit) to continuously flow. This is why the shock received from static electricity is only a momentary jolt: the flow of electrons is necessarily brief when static charges are equalized between two objects. Shocks of self-limited duration like this are rarely hazardous.
- 3.04: Ohm’s Law (again!)
- A common phrase heard in reference to electrical safety goes something like this: “It’s not voltage that kills, its current!” While there is an element of truth to this, there’s more to understand about shock hazard than this simple adage. If voltage presented no danger, no one would ever print and display signs saying: DANGER—HIGH VOLTAGE!
- 3.05: Safe Practices
- If at all possible, shut off the power to a circuit before performing any work on it. You must secure all sources of harmful energy before a system may be considered safe to work on. In industry, securing a circuit, device, or system in this condition is commonly known as placing it in a Zero Energy State. The focus of this lesson is, of course, electrical safety. However, many of these principles apply to non-electrical systems as well.
- 3.06: Emergency Response
- Despite lock-out/tag-out procedures and multiple repetitions of electrical safety rules in industry, accidents still do occur. The vast majority of the time, these accidents are the result of not following proper safety procedures. But however they may occur, they still do happen, and anyone working around electrical systems should be aware of what needs to be done for a victim of electrical shock.
- 3.07: Common Sources of Hazard
- Of course there is danger of electrical shock when directly performing manual work on an electrical power system. However, electric shock hazards exist in many other places, thanks to the widespread use of electric power in our lives. As we saw earlier, skin and body resistance has a lot to do with the relative hazard of electric circuits. The higher the body’s resistance, the less likely harmful current will result from any given amount of voltage. Conversely, the lower the body’s resistance,
- 3.08: Safe Circuit Design
- As we saw earlier, a power system with no secure connection to earth ground is unpredictable from a safety perspective: there’s no way to guarantee how much or how little voltage will exist between any point in the circuit and earth ground. By grounding one side of the power system’s voltage source, at least one point in the circuit can be assured to be electrically common with the earth and therefore present no shock hazard. In a simple two-wire electrical power system, the conductor connected
- 3.09: Safe Meter Usage
- Using an electrical meter safely and efficiently is perhaps the most valuable skill an electronics technician can master, both for the sake of their own personal safety and for proficiency at their trade. It can be daunting at first to use a meter, knowing that you are connecting it to live circuits which may harbor life-threatening levels of voltage and current. This concern is not unfounded, and it is always best to proceed cautiously when using meters. Carelessness more than any other factor
- 3.10: Electric Shock Data
- The table of electric currents and their various bodily effects was obtained from online (Internet) sources: the safety page of Massachusetts Institute of Technology (website: [*]), and a safety handbook published by Cooper Bussmann, Inc (website: [*]). In the Bussmann handbook, the table is appropriately entitled Deleterious Effects of Electric Shock, and credited to a Mr. Charles F. Dalziel. Further research revealed Dalziel to be both a scientific pioneer and an authority on the effects of el