Explain how grounding the frame of a motor can prevent someone from receiving an

Question

Explain how grounding the frame of a motor can prevent someone from receiving an electric shock. Compare the terms grounding and bonding. What is the minimum amount of leakage ground current required to trip a ground-fault circuit interrupter? List the seven steps involved in a lockout/tagout procedure. A disconnect switch is to be pulled open as part of a lockout procedure. Explain the safe way to proceed. What is the prime objective of the National Electrical Code? How are the standards contained in the NEC enforced? Explain the difference between a Code Article and a Section. What do the icons found on most fire extinguishers indicate? What does a UL-labeled or -listed electrical device signify? List three motor control devices that are rated by NEMA. Compare NEMA and IEC motor standards.

Explanation / Answer

1. On grounding the frame of a motor grounding will represent a very less resistive path and current will pass to the ground path rather ffrom the person touching it hence it is safe from the electric shock.

2. Grounding is the connecting the metal body of the machine or equipment to the earth for safety purpose in case there is a leakage or wing touch to metal part of the machine which can cause an electric shock to the operator.

Bonding: Bonding is simply the act of joining two electrical conductors together. These may be two wires, a wire and a pipe, or these may be two Equipments. Bonding has to be done by connecting of all the metal parts that are not supposed to be carrying current during normal operations to bringing them to the same electrical potential.

3. 6m A min current : GFCIs, as they are designed to interrupt the circuit when a ground fault current exceeds 6 mA.

4.

Step 1: Detailed procedures for equipment
Begin by making sure you’ve identified the equipment correctly and accurately, including its specific location. Next, determine the correct procedure for shutting down and restarting the equipment. Detail that procedure, step by step, in writing. Consider all of the energy sources that may be connected to the equipment. Be very specific, because ambiguous language could lead to an incorrect or even dangerous action.

Step 2: Notify affected employees
When maintenance is going to be performed, all of the employees that may be affected should be notified. Let them know the timing of the work, and how long the equipment may be unavailable. If the unavailability of the equipment requires a change in work processes, be sure they are familiar with the steps to be taken.

Step 3: Shut down equipment properly
Explain the shutdown process in detail. It’s not enough to say something like “disconnect the machine.” To ensure everyone’s safety and reduce the potential for damage, the shutdown instructions should be detailed. Spell out the exact actions to be taken and the correct sequence for performing those actions.

Step 4: Disconnect all primary energy sources
Although this may seem fairly self-explanatory, once again, it’s important to be very detailed. Whether the primary energy sources include electricity, steam, water, gas, compressed air, or others, don’t assume that the person performing maintenance will know the correct procedure to follow. Again, explain exactly what needs to be done.

Step 5: Address all secondary sources
While disconnecting the primary energy sources may remove much of the potential danger, it’s possible that there sources of residual energy, such as trapped heat in a thermal system, fumes that may need to be vented, or even tension in a spring assembly. Identify the process that will relieve any remaining pressure or other energy. Also consider other hazards, such as moving equipment that must be secured before work begins.

Step 6: Verify the lockout
Once you’ve disconnected all primary and secondary sources of energy, attempt to start the equipment to verify that the lockout has been successful. Before you try to start it, verify that nobody is in a position where they could be hurt. Assuming that the procedures have been successful, return all switches and other equipment back to their “off” positions so the machine won’t start unexpectedly when the energy sources are reconnected. Once you’ve verified the lockout, attach a lockout or tagout device to the equipment to ensure that it cannot be started without removing the device.

Step 7: Keep it in force during shift changes
The equipment must remain in lockout/tagout condition across shift changes, so that workers arriving at the site are aware that the equipment is out of service. If individual locks or tags are used, the individual responsible for designating the lockout/tagout and the individual responsible for it during the next shift must both be present as the locks or tags are switched.

5. Electrical disconnect switches should never be pulled while under load, because of the possibility of arcing or even explosion. so on no lad they ust be pulled open.

6.The NEC’s purpose is clearly evident in the introduction of the text. Section 90.1, the very first rule, indicates that the purpose of the Code is the practical safeguarding of persons and property from hazards arising from the use of electricity. This long-standing requirement serves as a simple and straightforward reminder of the basics of electrical safety. Compliance with the NEC rules results in electrical installations and systems that are essentially free from hazards. The NEC is the minimum set of electrical rules that must be followed for compliance and assurances that occupancies are safe from potential electrical hazards. Without question, consumers expect electrical safety, even when they are not aware of the rules that make residences and businesses safe.

12.

Smaller size and more precise ratings are just two reasons for switching to IEC motor controls. IEC devices are an average of 30 to 70 percent smaller than their NEMA counterparts. The size difference is most dramatic at or below 50 horsepower (HP), where 80 percent of the world’s motors are rated.

There are two main factors responsible for this radical size difference. First, IEC devices use sophisticated arc quenching techniques to reduce excess heat on the contacts. NEMA devices rely on a greater mass to dissipate the heat, resulting in a larger physical size.

Second, IEC devices are more precisely rated than NEMA controls.

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