Reference no: EM132879979
Isolate the electrical installation and determine it is safe by:
a) Positive identification of the electrical installation, all of its energy sources and their isolation points.
b) Isolate and discharge where necessary the electrical installation from all sources of supply e.g. substation, main switchboard, distribution board, and isolation switches.
c) Secure the isolation by locking off, where possible, switches used for isolation by using a device for securing the switch in the open position (e.g. by clip, screw, bolt, pin, padlock, that will prevent the switch from being operated. Also apply a personal danger tag to each isolation point.
d) Prove that the electrical installation and conductors have been adequately de-energized.
e) Identify the safe area of work.
Note: Work on de-energized equipment shall proceed if the equipment is isolated and any other exposed conductors in the work area are either: a) De-energized and isolated; or
b) Separated by barriers or by distance
If the above requirements are not satisfied, then work shall be done in accordance with the energized Section below.
2. Energized Working Procedure
It is to be expected that a Category 1 competent person will occasionally need to consider undertaking electrical work on or near the energized electrical installation. Such work should only be considered when all means of de-energizing the installation are deemed inappropriate, and then only after the hazard assessment below has been completed.
The hazard assessment below documents the practices used to eliminate the risk of inadvertent contact with energized conductors.
If the risk of working on the energised installation cannot be effectively controlled (ie, the risk of inadvertent contact cannot be eliminated) the work shall NOT be undertaken on the energized electrical installation.
When performing work on or near exposed energized conductors there is a risk of electric shock, arc, blast, flash burn injury. To control this risk, the following precautions shall be taken before work commences on or near exposed energized conductors.
a) The above hazard assessment (Hazard Identification and hazard Assessment for Electrical Hazard) has been completed
YES. / NO (If NO, work does not proceed until hazard assessment completed) Confirm Complete with hazards identified:
b) A safety observer shall be used as an essential risk control element when working on any exposed energized conductors.
Indicate name, and electrical license No of observer:
c) The electrician who plans to undertake electrical work on or near exposed energized conductors shall be competent in the work to be carried out. The work to be undertaken shall be authorised by Facilities and Services management, as relevant.
d) Precautions have been put in place to prevent the possibility of simultaneous contact with conductors at different voltages, while work is being carried out on or near exposed energized conductors?
e) The following safety equipment, safety tools and personal protective equipment (see Notes) is to be supplied and used for the task, as relevant?
f) Where work on the exposed energized conductors is carried out on a work platform, the work platform must be stable. Has the structure been checked? YES /NO
g) Do temporary protective earthing conductors need to be installed? For protection when removing electrical equipment from earthed metal? YES / NO
If YES the temporary earthing conductors used, shall be appropriately rated to withstand and remove any charge from the prospective short-circuit/fault current of the primary protection without failure.
Low voltage Exam
1 A circuit is shown in Figure 1. In this figure,
(a) Label all the nodes (1, 2, 3, ...) in the circuit excluding the ground node which is already labeled as 0.
(b) How many nodes are there?
(c) How many simple nodes are there?
(d) How many essential nodes are there?
(e) How many branches are there?
(f) How many meshes are there? List all meshes.
(g) How many loops (including meshes) are there?
(h) List all loops that are not meshes.
2. In the circuit shown below, find the currents I1, I2, and I3. Also, find the powers on R1, R2, R3, and Vs and state whether power is absorbed or released by each element.
2.2 The current through resistor R6 in the circuit shown below is 2 mA, that is, I6 = 2 mA.
(a) Use Ohm's law to find the voltage V4 across R6.
(b) Use Ohm's law to find the current I5 through R5.
(c) Use KCL to find the current I4 through R4.
(d) Use Ohm's law to find the voltage V3 across R4. (e) Use KVL to find the voltage V2 across R3.
(f) Use Ohm's law to find the current I3 through R3.
(g) Use Ohm's law to find the current I2 through R2.
(h) Use KCL to find the current I1 through R1.
(i) Use Ohm's law to find the voltage V1 across R1.
(j) Use KVL to find the voltage Vs.
Find the equivalent resistance between terminals a and b of the circuit shown below.
Find the equivalent resistance between terminals a and b of the circuit shown below.
Find the equivalent resistance between terminals a and b of the circuit shown below.
In the circuit shown below,
(a) Find Ra = R7 || R8.
(b) Find Rb = R6 + Ra.
(c) Find Rc = R5 || Rb.
(d) Find Rd = R2 || R3.
(e) Redraw the circuit consisting of Vs, R1, Rd, R4, and Rc. Find the equivalent resistance Req seen from the voltage source.
(f) Find the current I1 through R1, Rd, R4, and Rc.
(g) Find the voltage across R1, voltage across Rd, voltage across R4, and voltage across Rc. (h) Find the voltage V1, voltage V2, and voltage V3.
(i) Find the currents I5 and I6.
(j) Find the voltage V4, and currents I7 and I8.
In the circuit shown below,
(a) Find the equivalent resistances Ra = R3 || R4, Rb = R5 || R6, and Rc = Ra + Rb.
(b) Redraw the circuit consisting of Is, R1, R2, Rc.
(c) Use the current divider rule to find the currents I1, I2, Ic.
(d) Use the current divider rule to find the currents I3, I4, I5, I6. (e) Find the voltages V1, V2.
In the circuit shown below,
(a) Find Ra = R5 || R6 and Rb = R3 || R4.
(b) Redraw the circuit consisting of Vs, R1, Rb, R4, and Ra. Find the equivalent resistance Req seen from the voltage source.
(c) Find the current I1 through R1, Rb, R4, and Ra.
(d) Find the voltage across R1, voltage across Rb, voltage across R4, and voltage across Ra. (e) Find the voltage V1, voltage V2, and voltage V3. (f) Find the currents I2, I3, I5 and I6.
Find V1, V2, and V3 in the circuit shown below.
Practice Questions
The following resource is associated with the next question.
If the frequency of the source is 1 kHz, what is the value of the capacitive reactance (XC) of the circuit if the capacitor value is changed to 0.01 µfd?
A. XC = 63.6 k
B. XC = 31.8 k
C.XC = 15.9 k
D. XC = 5.0 k
The frequency of the second harmonic of 60 Hz is:
A. 30 Hz
B. 60 Hz
C. 120 Hz D. 180 Hz Answer:
What is the approximate peak-to-peak voltage of a 2 VRMS sine wave?
A. 2.0 Vp-p
B. 2.8 Vp-p
C. 4.0 Vp-p
D. 5.6 Vp-p
DC Circuits
The formula for electrical current is:
A. Voltage / Resistance.
B. Resistance * Voltage.
C. Voltage + Resistance.
D. Resistance / Voltage.
Electric current is the flow of which of the following?
A. Neutrons
B. Photons
C. Electrons
D. Quarks
Which of the following is a unit of electrical resistance?
A. Volt
B. Amp
C. Ohm
D. Coulomb
In a simple DC circuit with a constant voltage, where the resistance increases current will:
A. decrease.
B. stop.
C. increase.
D. remain constant.
The following resource is associated with the next question.
What type of circuit is shown in the diagram?
A. Parallel Circuit
B. Series-Parallel
C. Wye-series Circuit
D. Series Circuit
Discrete Components
Zener diodes are most commonly used in:
A. voltage amplifier circuits.
B. oscillator circuits.
C. power supply circuits.
D. current limiting circuits.
Compared to bipolar transistors, field effect transistors are NOT normally characterized by:
A. high input impedance.
B. a reverse-biased PN junction.
C. low input impedance.
D. low power consumption.
The following resource is associated with the next question.
This figure is a schematic representation of a/an:
A. differential amplifier.
B. inverting amplifier.
C. noninverting amplifier.
D. voltage follower.
Digital Circuits
The following resource is associated with the next question.
For the signal shown, which of the following represents its inverted waveform?
What are the characteristics of a coaxial cable?
A. It has twisted pairs with a shield.
B. It has a center conductor covered with an insulator, then braided or solid outer conductor and then insulation. C. It has heavier insulation than most cables.
D. It is vulnerable to high frequency interference.
Attachment:- Hazard Identification.rar