Question 1

In this motor control circuit, how would you ensure that there is no danger of electric shock prior to touching either of the motor terminals (shown as points A and B in the schematic diagram)? Describe both the action required to secure the power, and the means by which you would check for the presence of hazardous voltage at the motor:


Question 2

Linemen working on high-voltage conductors do not simply rely on open disconnect switches to isolate sections of power lines from sources of electricity during maintenance. They also attach “grounding” cables from line to line, and then to earth ground like this:

Explain why this decreases the risk of electric shock for the linemen, based on what you know about electrically common points in a circuit.


Question 3

Describe what the phrase zero energy state means for a system, in terms of safety for those performing maintenance work on it.


Question 4

When using a padlock to secure a disconnect device in the “open” (off) state, who should be able to open that lock? In other words, how many other people should share a key to the lock you use to secure a breaker or switch in the safe position, if you are the one working on the system?


Question 5

When securing equipment for safe maintenance, special tags are attached with the lock(s) used to keep circuit breakers and other disconnect devices in the open (off) state. A typical “lockout” tag looks something like this:

What is the purpose of attaching such a tag to an electrical disconnect device in addition to locking it in the open position? Why is a lock, by itself, not sufficient from a safety perspective?


Question 6

What step(s) must be taken after locking and tagging an electrical disconnect device for a circuit to be worked on, and prior to actually proceeding with the work? What step(s) come between the lock-out and the work itself?


Question 7

Suppose you are finishing a maintenance project where an electric motor was locked out and tagged, and now the work is complete. Your lock is the last one to be removed from the circuit breaker, everyone else already having taken their locks and tags off. What should you do before removing your lock and turning the circuit breaker back on?


Question 8

Large power distribution circuit breakers look nothing like the small breakers seen in residential and commercial electrical systems. They are large units, which “plug” into cubicles so as to facilitate removal and replacement for routine maintenance.

When securing an electrical system in a zero energy state prior to commencement of maintenance work, it is common practice to “rack out” any large circuit breakers feeding power to the system. What exactly does this term mean, and what is the procedure for “racking out” a circuit breaker?


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