A multimeter can measure the AC/ DC voltage, AC/ DC current and ...

Digital Multimeter: (Sample- Wavetek Meterman 5XP)A multimeter can measure the AC/ DC voltage, AC/ DC current andresistance, which means it will perform the functions of voltmeter,ammeter & ohmmeter. It can have various test functions like checkingthe diodes, electrostatic field and continuity.Always make sure you set the selector switch in right mode/ function.An OL / –OL will be displayed if an over load condition exists. To clear thiscondition, move the selector switch to the next higher range. The OL is commonfor functions like resistance, diode and continuity. Don’t take the readings untilyou clear the OL.1. Test Leads:• Connect the red test lead in V/ resistance/ diode/ Battery 9V and blackto COM to measure the AC/ DC voltage, resistance and to check thediode, 9V battery and electrical continuity.• Connect the red test lead in mA/ uA / Battery 1.5Vmode and black toCOM to measure the AC/ DC amperage and to check the battery.2. Continuity Test:• Checking continuity means checking two things electrically connected.• This test will determine if a wire is broken in the middle of the run.• Continuity test is non-directional.Always Remember:• To be performed only when the devices you are testing are not powered.• Always make sure the meter you are using is working by brushing the twotips together. You will hear a beep sound. If not you might need to checkwhether you are in the right mode or the battery went bad.3. Diode Test:• Connect the red test lead in V mode and black to the com mode andconnect the probes across the diode.• A good diode has a forward voltage drop of about 0.6V. An open orreverse biased diode will read OL.Always Remember:• This test is to be performed only when the devices you are testing are notpowered.• To free at least one end of the diode from the circuit.

4. Measuring Voltage: (Volts)• Select the desired range.• Always connect the test probes across the device to measure thevoltage.Always Remember:• To measure the right voltage (AC/ DC)• Do not exceed the rated voltage of the meter.5. Measuring Current: (Amps)• Select the desired range.• Turn OFF the power and open the circuit to make the measurementpoints.• Connect the test probes in series with the load and turn ON the power.• Use current clamps to measure current >10A (not for the shown model)Always Remember:• Turn OFF the power before connecting the test probes• Make sure the open circuit voltage is < 1000V.• Always measure current in series with the load and never measure acurrent across the voltage source.• To avoid injury, do not attempt to measure the current of an open circuitif the voltage is greater than the rated voltage of the meter.6. Measuring Resistance: (Ohms)• Select the desired range.Always Remember:• To wait until you discharge the capacitance that affects the reading.• To connect the test probes across the resistance.• Never measure a resistance across a Voltage source or powered circuit.7. Testing the Battery:• Connect the red test lead depending on the battery voltage (9V or 1.5V)• Connecting the proper test probe across the battery will apply anappropriate load to the battery.• For 1.5V Battery if the reading is >1.2V GOODFor 9.0V Battery if the reading is >7.2V GOOD

8. Additional Features:• HOLD button will capture and display the measured readingcontinuously.Pressing the HOLD button again will release the locked reading.• MIN MAX button is used to measure the minimum and maximum valuesof the reading. To be in this mode you need to press the MIN MAXbutton for < 1sec. To change the modes from max to min and min tomax you need to press the MIN MAX button. To disable this mode, youneed to press the MIN MAX button for >1sec.• NON CONTACT VOLTAGE (NCV) Senses the steady state electrostaticfield produced by AC voltage (70-600VAC) through insulation withoutrequiring contact to the bare conductor. A red glow at the tip and abeeping noise (if not switched OFF) indicates the presence of voltage.Troubleshooting:If the meter is not operating normally, here are the main 3 things to test:• Check the continuity of test probes.• Ensure the battery is in good operational condition (Replace the batteryas soon as you see the low battery icon to get accurate readings)• Check the fuse (0.315A) if you are having problems with current ranges.Category Levels:The Category levels determine the safety of the meter to withstand voltagespikes when used in different circuits.• CAT I – Protected Electronic Circuits• CAT II – Receptacle outlet circuits, Plug in loads• CAT III – Distribution Wiring (Main Bus, Feeders, Branch Circuits,Permanent installed Loads)• CAT IV – Utility Level and Outside Cable Runs.

Standard Organizations:• UL (Underwriters Laboratories)• NEMA (National Electrical Manufacturers Association)NEMA Enclosure Types: The classification is based on the degree ofProtection in different environmental conditions.• Check the handout for different types of NEMA Ratings• NFPA (National Fire Protection Association)• IEC ( International Electrotechnical Commission)IEC writes international standards for electrical and electronictechnologies and practices.Industrial Controls:• Electrical Symbols: All electrical contact symbols are shown in theirDe-Energized state and are used to indicate the path of current flow.Check the handout for wiring symbols. The Schematic diagrams arearranged for simplicity and ease of understanding circuits without regardfor the actual physical location of any components.• General Motor Control (Most Basic Control):This is the most generallayout of a motor &control circuit.Always connect thecontrol loads parallel.

• I/O Devices: These are the devices used to control the logic/ currentflow in the circuit.Push Buttons & Selector Switches:Two Types(a) Momentary and (b) MaintainedN.O (Normally Open): When the contacts arein Normally Open state (De-energized), thecontacts are normally opened. As soon as youpush the switch, the contacts close and it willallow the current to pass through the circuit.N.C (Normally Close): The contacts remainin the closed state (de-energized) allow thecurrent to pass through until the switch isenergized. This is mainly used for e-stopcircuits.Pilot Lights:These are used toindicate the statusof operation of thecircuit they areused in to theoperator.Different colors indicate different states:Red- Danger/ Emergency/ FaultyGreen- Safe/ RunningAmber- Warning/Caution/ AbnormalBlue- Mandatory ActionClear, White, Gray and Black- No specific meaning assigned

Transformers: The power source to the motor is frequently higher than thecontrol circuit. So we use the single phase transformers to step down to therequired control voltage. Provide proper fusing on both the line side (Primary)and the load side (Secondary) of the transformer.Control Relays: Unlike contactors, this device is used to switch multiplecontrol circuits / loads. The contacts in the control relay are small becausethey are used to handle the control circuits.Poles describe the number of isolated circuits that can pass thru the relay atone time.Throw describes the number of different closed-contact positions per pole.This is the number of different circuits that each pole controls.Break describes the number of separate contact points used to open or closeeach circuit.Time Delay Relays:Time delays have 2 functions.(i) On-delay indicates that a timer will turn on and its contacts will changestate at a predetermined time after the timer receives a signal to turn on.(ii) Off delay indicates that a timer will turn off at a predetermined time afterthe timer receives a signal to turn off.

Circuit Breaker & SCCR Ratings:Circuit breakers provide a manual means of energizing and deenergizinga circuit. This can be re-activated quickly after a short circuit /overload is cleared.The voltage rating of a circuit breaker shows the ability to suppress theinternal arc that occurs when the circuit breaker's contacts open.The continuous current rating of a circuit breaker is the maximumcontinuous current a circuit breaker is designed to carry without tripping.The Interrupt current rating of a circuit breaker is the maximum current acircuit breaker is designed to handle at rated voltage.The Short Circuit Current Rating (SCCR) on components is themaximum amount of short circuit current the component can handle.Advantages:Senses and measures over current and trip when a fault occurs.Shunt Trip is an accessory on circuit breaker used to remotely trip theCircuit Breaker.Contactors: There are 2 circuits involved in the operation of a contactor.(a) The control circuit is connected to the coil of an electromagnet and(b) The power circuit is connected to the stationary contacts.

Coils: These are used in electromagnetic circuits to open or close itsrespective contacts when energized.When the control circuit supplies the power to the coil, it generates themagnetic field, which in turn closes the contacts to make the current flowfrom line to load side. This will de-energize when there is no power tothe coil.When the motor contactor is combined with an overload, then it is calleda Motor Starter. There are 2 basic types: 1. NEMA and 2. IECWhen the motor starter is incorporated with a short- circuit protectionand a disconnecting device, then it is called a Combination Starter.2. Overloads: (N.C) these are used to protect the motors from overheating.Reasons- Low Line Voltage; Open phase in a 3-Phase system; overloading the motor => Higher Current draw => Overheating.When the motor generates high temperatures, the thermal relay opens(trips) to protect the motor from damage.We can reset the overload relay after the overload condition is cleared.

Test Button on the overload is used to test the electronic functions.Overload Relay Class determines the time it takes to trip the overload.(E.g. Class-10 OL relay allows up to 600% of FLA for up to 10 seconds)Manual Motor Starter Protector: This consists of a manual contactor and anoverload protection device.Soft Starters:• What is a Soft Starter and why do we use it?A soft starter is an electronic device that controls thevoltage of the motor by giving smooth transition fromstart to stop. The soft starter is designed so that itcan adjust the initial voltage to the motor by userdefined acceleration (soft start) and decelerationperiod (soft stop).Advantages:• We can limit/ reduce the starting currents &torques.• We can have a better control of acceleration &deceleration.• Less mechanical stress by avoiding the wear &tear of belts, chains, gears and bearings.Cable Wiring- Current & Temperature Carrying Capacity:Before selecting the wire/cable, youalways need to check that it is rated toproper voltage, temperature andampacity. Check the wire gauge quickreference for proper wire selection.

AC Motors:The basic concept of an AC motor is to take the electrical energy; generateelectromagnetic fields and convert it to mechanical energy.The motor has mainly the parts shown in the picture below.Stator is the stationary part ofthe electromagnetic circuit.This is made of many thinmetal laminations, whichreduce the energy lossescompared to solid core.Coils of insulated wire areinserted in the slots of thestator and ends of the coilsare connected directly to thepower source to generate therequired electromagnetic field.Rotor is the rotary part of theelectro-magnetic circuit. This is made of thin laminations of steel. The conductorbars are inserted in the slots instead of conductor wires and are electrically &mechanically connected to the end rings. The steel shaft is then inserted to formthe rotor assembly.The Enclosure consists of the frame and end brackets. The stator is mountedinside the frame and then the rotor is inserted inside the stator with a slight airgap. The enclosure protects the parts inside from environmental elements.Bearings are mounted on the shaft to support rotor rotation. The Fan is alsomounted on the rotor, which is used to cool the motor.Reasons for Motor Failure:• Bearing Failure, Vibration, Harsh Environment, Improper motorselection, Inadequate Installation, Inadequate Maintenance, ElectricalProblems, Unbalanced Voltage, Mechanical Failure and MotorRepair.

Three Phase System:• This is the most commonform of transportation ofcurrent.• The phase shift betweenthe voltages is 120degrees.• Look at the picture belowhow to measure the linelinevoltage and voltageswith respect to ground forWye (480VAC) & Delta (240VAC) type of connections.• The picture shown above is the motor connections inside the motor j.box forhigh & low voltages

Motor Name Plate Details:The nameplate information on the motor gives us the detailed informationlike the Model #, Enclosure type, Insulation Class, Duty type, HP, Voltage,full load amps (FLA), Frequency (Hz), phase(PH), Service Factor (SF),RPM, power factor (PF), wiring details, efficiency and temperaturenecessary for proper application.Service Factor: This is the number that can be multiplied by the rated HPof the motor to determine the maximum operating HP.Always remember that any motor operating continuously will have areduced service life.Insulation Class: This describes the motor insulation to handle heat. Theclass determines the maximum allowable temperature raise from ambienttemperature (40°C). For every 10°C rise in temperature, the motorinsulation expectancy life is cut by half.Voltage Variation: A small variation involtage can have a dramatic impact on themotor performance.If there is a voltage drop of 10%, the motorperformance is reduced by 20%. This maycause the motor not to start or keep up tothe rated speed.If there is a voltage hike of 10%, the motorstarting torque will increase by 20% and willresult in the damage to the motor duringstart-up by increasing currents and temperature.• Things to be keep in mind while wiring:An electrical connection that is over tightened can cause several problems.Over tightening can flatten the conductor to a point that it breaks. Overtightening the connection can also cause the connection to heat up. Theconductor will push away from the stud area causing the conductor to cupwhich reduces the amount of contact with the lug. This smaller contact areacauses overheating just as a loose connection will. Over tightening candamage the lug by causing small hairline cracks in the lug.

Connections can be over-torque as well as under-torque. The inch-poundsof torque required by the manufacturer is the ideal value that must beachieved as closely as possible to get the most effective electricalconnection, minimizing creep and cold flow of the conductor metal andprevent overheating due to increased contact resistance.Electrical Safety:There are mainly 3 steps that need to be taken to be safe while workingwith electricity.• Recognize Hazards:To recognize this, you need to know which situations can place you indanger. Listed below are some possibilities of danger:1. Inadequate sizing of wire like wire gauge, ampacity & overload.2. Exposed Electric parts- Incorrect wiring practice.3. Overhead power rails.4. Wires with bad insulation can give shocks.5. Improper grounding- Electrical systems & tools that are not properlyinsulated are dangerous.6. Overloading the circuits- Draws too much current and can lead to fire.7. Use ladders that are non conductive to electricity.8. Working in wet environmental conditions is dangerous.9. Using wrong PPE (Proper protective equipment), tools and somechemicals.10. Make sure you are working on De-energized circuits.11. Circuits with over/under sizing are a good chance for danger.• Evaluate Hazards:Always think that you are working in a hazardous environment and youmust constantly evaluate your risk. You can see clues that there is anexistence of electrical Hazard.1. Tripped circuit breakers and blown fuses show that too much currentis flowing in a circuit. This condition might be due to several factorssuch as malfunctioning of equipment or a short. You need todetermine the cause in order to control the hazard.

2. Any wire or connection that feels warm indicates that there is toomuch current flowing in that circuit. You need to evaluate and preventthe risk.3. A burning odor may indicate overheated insulation.4. A GFCI that trips often indicates that there is a current leakage fromthe circuit.5. Check for the worn out or damaged insulation around a wire toprevent the hazards ahead.You need to evaluate the seriousness of any damage and decide whatactions need to be performed to eliminate these hazards.• Control Hazards:The best way to control hazards is to follow the NEC and OSHAregulations. Here are some of the tips:1. Always treat the conductors (Energized / De-energized) as energizedunless they are locked out and tagged.2. Lock out and tag out the circuits and machines when you want toservice.3. Prevent overloading of the wire by selecting the right size.4. Prevent exposure to live wire and parts by providing insulation.5. Prevent shocking currents by proper grounding and by using GFCI.Always lock out and tag out circuits for service.