OPERATING INSTRUCTIONS for AMPROBE MEGOHMMETER MODEL AMB-2 (Battery Powered) See Precautions for Personal and Instrument Protection on Page 4 See Limited Warranty on Page 2 A AMPROBE INSTRUMENT* i, DIVISION OF CORE INDUSTRIES INC . LYNBROOK. NEW YORK 11563LIMITED WARRANTY Congratulations! You are now the owner of an AMPROBE instrument. It has been quality crafted according to quality Standards and contains quality components and workman- ship. This instrument has been inspected for proper opera- tion of all of its functions. It has been tested by qualified fac- tory technicians according to the long-established standards of AMPROBE INSTRUMENT. Your AMPROBE instrument has a limited warranty against defective materials and/or workmanship for one year from the date of purchase provided that, in the opinion of the factory, the instrument has not been tampered with or taken apart. Should your instrument fail due to defective materials, and/or workmanship during the one-year warranty period, return it along with a copy of your dated bill of sale which must iden- tify instrument by model number and serial number. For your protection, please use the instrument as soon as possible. lf damaged, or should the need arise to return your instrument, it must be securely wrapped (to prevent damage in transit) and sent prepaid via Air Parcel Post insured or UPS where available to: Service Division AMPROBE INSTRUMENT 630 Merrick Road (For U.P.S.) P.O. Box 329 (For P.P.) Lynbrook, NY 11563-0329 Outside the U.S.A. the local Amprobe representative will assist you. Above limited warranty covers repair and replace- ment of instrument only and no other obligation is stated or implied. MODEL: emia: le Megohm Range Switch Function SwitchPRECAUTIONS FOR PERSONAL AND INSTRUMENT PROTECTION Although there is high voltage at the tips of the test leads when the AMB-2 is used as a megohmmeter, low current flow reduces any danger to relatively safe levels. However, contact with the probe tips while the instrument is energized should be avoided. DO NOT USE IN AN EXPLOSIVE ATMOSPHERE. if the equipment to be tested was in use up to the time of testing, it will most likely have a capacitive charge built up. This capacitance must be discharged before making any resistance measurements. Equipment under test with the megohmmeter may build up a capacitive charge from the testing. This charge is automatically discharged by the Model AMB-2 when the Press-to-Read button is released. When the AMB-2 will not be used for a period of time, remove the batteries to avoid possible instrument damage due to a leaking battery. Before connecting the AMB-2 to any circuit as either an ohmmeter or megohmmeter check for any voltage. The AMB-2 has a 0-600VAC Test Band for this purpose. Do not connect the AMB-2 ohmmeter or megohmmeter to a live circuit. Always store the instrument in its carrying case. Ra SPECIFICATIONS Model AMB-2 nges: 0-100 Megohms (2.5 Megohms midscale) Test Voltage 500 VDC 0-50 Megohms (1.5 Megohms midscale) Test Voltage 250 VDC 0-100 ohms (4 ohms midscaie) Test Voltage 300mV 0-600 VAC Test Band (May also be used for DC) Battery OK Test Band Accuracy: Megohm range 0.1 to 10 Megohms: +5% of reading Over 10 Megohms: + 10% of reading Ohmmeter range: + 3% of arc Power: 8 AA Batteries (not supplied) Fuse: 8AG-361 1 Amp Fast Blow (1 spare supplied) Size: 4.09 x 6.25" x 2.81" Weight: (104mm x 158.8mm x 71.4mm) 1 Ib. 3 oz. (.54Kg) without batteries OPERATING INSTRUCTIONS IMPORTANT: See Precautions for Personal and instrument Pro- tection before proceeding. Note that lid of the AMB-2 Carrying Case can be detached from the case and snapped in position on the back of the car- ryi 1. ng case. Remove panel on back of instrument by removing large black screw on bottom and install 8 type AA batteries (two Cat. No. 915, Pkg. of 4) observing proper polarity. Note that the instrument is fused and that one spare fuse (Cat. No. 8AG-361 1 Amp Fast Blow) is in battery compartment. Set function switch to ACV/MQ position. Use zero adjust screw located just below window to ad- just pointer to oo on MQ scale. Do not press red button. Move function switch to BATT (Battery) position. Press the red button. If pointer does not indicate within BATT. OK box, replace batteries. Move function switch to ACV/MQ position. Press red button. Pointer should indicate at the oo scale division on the MQ scale. Plug test leads into instrument and short the probe tips together. Press red button. The pointer should indicate at the 0" division on the MQ scale. If not, replace fuse. 5A\ WARNING! Do not exceed 600 volts AC. 5a.To use as a megohmmeter or an ohmmeter, disconnect the device or circuit to be tested from the line. b. Move function switch to the ACV/MQ position. Plug test leads into instrument and apply test probes to circuit or device to be tested. Do not press red button. If pointer moves up the red ACV band, there is voltage present in circuit or device. Disconnect device or circuit from any voltage supply before proceeding. c.Move function switch to appropriate position ACV/IMQ for megohms, Q for low ohms. if ACVIMQ is chosen, set range switch to either 50 MQ or 100 MQ. d.Connect test leads to device or circuit to be tested. e. Press red button. f. Take reading on scale corresponding to range switch position. Why Insulation Resistance Testing? The primary purpose of insulation is to keep electricity fiow- ing in the desired path. The perfect insulation would have infinite resistance which would prevent the flow of any cur- rent through the insulation to ground. However, there isnt any perfect insulation material so there is always some current flow. Good insulation is one that has and keeps a high resistance value in order to minimize the current flow. Unless there is accidental damage of some sort, insulation failure is generally gradual rather than sudden. This is because failure is generally a wearing down process due to repeated heating and cooling, the related expansion and contraction, dirt, physical abrasion, vibration, moisture and chemicals. When insulation starts to fail, its resistance decreases allow- ing more current to flow through the insulation. If the resistance continues to decrease, the condition of the insula- tion may reach a point where it may permit a lacge enough current flow through the insulation to cause 1) a simple blow- ing of a fuse, 2) equipment damage, or 3) even fatal shock. That's why, if you're responsible for the servicing, maintenance or installation of electrical equipment, you must be concerned about insulation resistance! An Insulation Resistance Testing Program helps reveal fail- ing insulation before it becomes a serious probiem. Such a testing program consists of periodic insulation resistance tests on critical equipment and systems. The results are recorded on a control card or file for each piece of equipment 6 or each test point in a system. Any trend that indicates a decreasing insulation resistance value is an indication that the insulation is failing and that corrective maintenance should be scheduled. MEASURING INSULATION RESISTANCE Without going into a great deal of technical explanation, let us State that insulation resistance measurements are af- fcted by a number of factors. Temperature and the dura- tion of the measurement are two primary ones. Humidity may also affect readings so it is a good idea to make a note as to whether the air is dry or humid at the time of the measurement. You may find that insulation resistance readings are lower on humid days and higher on dry days. Wet or flooded equipment should be dried and cleaned as much as possible before measurements are taken. Lastly, dirt or other contaminents (corrosion, chemicals, etc.) can also affect readings, either raising or lowering them. Therefore, steps should be taken to make certain that the contact points at which measurements are to be taken are reasonably clean. TEMPERATURE Insulation resistance can vary significantly with temper- ature. If your periodic insulation resistance measurements can not be taken at the same temperature, it is important that resistance measurements be adjusted to a base temperature. From IEEE Std 43-1961 for Rotating Machin- ery. Raoc = Ktaoc x Rt where Race = insulation resistance (in megohms) corrected to 40C R= measured insulation resistance (in megohms) att Ktaoc = temperature coefficient of insulation resis- tance as observed for temperature tC see ig. Example: An insulation has a resistance of 100 megohms at 30C. From Fig. 3, Ktsoc is 0.5 oc = 0.5 x 100 = 50 megohms For temperature correction factors for cable insulation, refer to specifications of the Insulated Power Cable Engineers Assn.. and the Assn. of Edison Ifluminating Companies. 7TIME The duration of the resistance measurement also affects the reading. If the insulation is good, the reading will continually increase as long as the megohmmeter is connected to the in- sulation. See Fig. 2. The most common megohmmeter measurement is taken at the end of a 60 second interval as this time period generally gives a satisfactory measurement of the insulation resistance. A second type of test involves taking a reading after 30 seconds and 60 seconds. The 60-second reading divided by the 30-second reading is known as the Dielectric Absorption Ratio. Comparing periodic Dielectric Absorption Ratios may prove more useful than comparing one-minute readings. Generally speaking a ratio of 1.25 is the bottom limit for borderline insulation. An extension of this test is one that in- volves readings taken after 60 seconds and 10 minutes. The ratio of the 10 minute reading to the 60 second reading is referred to as the Polarization Index. The resistance measurement taken at the end of 10 minutes should be con- siderably higher than at 60 seconds. The measured insula- tion resistance of a dry winding in good condition should reach a relatively steady value in 10 minutes. If the winding is wet or dirty the steady value will usually be reached in one or two minutes. The Polarization Index is helpful in evaluating the winding dryness and fitness for over-potential testing. For a fuller expianation of these ratios and safe values see IEEE Std 43-1961 IEEE Standard Guide for Testing insula- tion Resistance of Rotating Machinery and IEEE Std 62-1958 Recommended Guide for Making Dielec- tric Measurements in the Field *May be ordered from: {EEE 445 Hoes Lane Piscataway, New Jersey 08854 As a guide, the recommended minimum value of the Polariza- tion Index for alternating current and direct-current rotatin machines is 1.5 for 105C (Class A) insulation systems and 2. for 130C (Class B) insulation systems. 8 INSULATION RESISTANCE TEMPERATURE COEFFICIENT. Ki 40. oO ne AOA, Approximate Temperature Coefficient insulation Resistance Rotating Machine Armature Windings Figure 1 THIS VALUE MEGOHMS: Q TIME 60 SEC Typical curve of insulation resistance (in megohms) versus time Figure 2 : 9WHAT THE READINGS MEAN As we have already pointed out, insulation resistance measurements are affected by temperature, humidity and the time duration of the measurement. They are also affected by such things as type of insulation, its thickness, cleanliness and even the design of the equipment. Therefore, to try and give specific values for each and every situation would repre- sent an impossible job for this manual. However, there are some basic guide lines that are usable. From the IEEE Std 43-1961 Standard Guide for Testing Insula- tion Resistance of Rotating Machinery: Rm=Kv + 1 where Rm=recommended minimum insulation resistance in megohms at 40C of the entire machine winding Kv = rated machine potential, in kilovoits If winding is not at temperature of 40C, temperature correc- tion should be made. See page 7. This essentially follows an old rule of thumb which set a minimum value of 1 megohm for every thousand volts of equipment rating. For specific information about individual products, contact the manufacturer for specifications on insulation resistance values and test procedures. The important thing to remember is that periodic testing is the primary method of picking up sudden decreases in in- sulation resistance and this is the key to detecting insulation that is failing. Because it is possible for insulation to fail bet- ween tests, testing should be scheduled based on the type of equipment. Generally speaking, equipment that involves movement (e.g. motors) should be checked more frequently than stationary equipment (e.g. cables). In addition, the more critical the equipment is to a companys operation, the more frequently it should be checked. 10 WHAT TO RECORD So that your periodic insulation resistance measurements can be compared meaningfully, you must have certain infor- mation recorded. Each piece of equipment should have its own record card on file. Typical information that should be included: 1) Equipment description including rating and serial number. 2) Equipment location (department, floor, etc.) 3) Date of installation. 4) Dates of repairs and description. 5) Specific test points (e.g. motor frame and motor lead disconnected at motor junction box). In some cases a sketch might help another person performing the test at a later time. 6) Equipment temperature at time of reading. 7) Room (ambient) temperature at time of reading. 8) Relative Humidity measurement. 9) Correction factor used to adjust reading to base temperature. 10) The adjusted insulation resistance. With this information, you can make meaningful compari- sons between readings. See page 16 for a typical record card. CONNECTING THE MEGOHMMETER The basic purpose of an insulation resistance measure- ment is to test the insulation. Connections, therefore, must be made so that the test voltage is applied across or through the insulation. Within any system or piece of equip- ment, there may be more than one set of points that should be tested. The illustrations and related descriptions that follow will serve as a guide for testing the specific equip- ment shown. The approaches shown can also be used as guides for other similar equipment. Note: Disconnect equipment or circuits to be tested from the power supply. Verify that equipment or circuit is de-energized by checking with a volt-meter (the AMB-2 has a 0-600VAC Test Band for this purpose). See Precautions for Personal and Instrument Protec- tion on page 4. 11POWER TOOLS AND SMALL APPLIANCES This test would also apply to other similar equipment that has a line cord. For double-insulated power tools, the megohmmeter lead shown connected to the housing would be connected to some metal part of the tool (e..g chuck, blade). See Fig. 3 Note: The switch of the device must be in the ON position. Megohm- meter Figure 3 MOTORS ACDisconnect the motor from the line by disconnecting the wires at the motor terminals or by opening the main switch. If the main switch is used and the motor also has a starter then the starter must be held, by some means, in the ON position. In the latter case, the measured resistance will include the resistances of the motor, wire and all other components between the motor and the main switch. if a weakness is indicated, the motor and other components should be checked individually. If the motor is disconnected at the motor terminals, connect one megohmmeter lead to the grounded motor housing and the other lead to one of the motor leads. 12 O0CDisconnect the motor from the line. To test the brush rigging, field coils and armature connect one megohmmeter lead to the grounded motor housing and the other lead to the brush on the commutator. If the resistance measurement in- dicates a weakness, raise the brushes off the commutator and separately test the armature, field coils and brush rigg- ing by connecting one megohmmeter lead to each of them in- dividually, leaving the other connected to the grounded motor housing. The above also applies to DC Generators. Figure 4 _ GROUND = @ STARTER (Must be in ON Position) CONNECT TO MOTOR HOUSING (Ground) i es wa + MAIN - oe SWITCH CONNECT TO wor v MEGOHMMETER MOTOR SIDE 7 OF SWITCH ) LINE CABLES Disconnect the cable from the line. Also disconnect opposite end to avoid errors due to leakage from other equipment. Check each conductor to ground and/or lead sheath by con- necting one megohmmeter lead to a ground and/or lead sheath and the other megohmmeter lead to each of the con- ductors in turn. Check insulation resistance between con- ductors by connecting megohmmeter leads to conductors in pairs. 13a- MEGOHMMETER Figure HERMETIC COMPRESSOR SYSTEMS The following table may be used as a guide to determine the extent to which a system may have been contaminated by moisture. MEGOHM- SUGGESTED METER COMPRESSOR PREVENTIVE READING CONDITION MAINTENANCE 100 Megohms to Good None necessary Infinity 50 to 100 Megohms 20 to 50 Megohms 0 to 20 Megohms Moisture Present Severe moisture and possible con- taminated oii Severe contamination 14 Change drier Change numerous driers, change oil Dump oil and entire refriger- ant charge, evacuate system, install liquid and suction line driers, re-charge system with new oil and refrigerant CIRCUIT BREAKERS AND SWITCHES Disconnect from line. To test each terminal to ground, con- nect one megohmmeter lead to the frame or ground and con- nect the megohmmeter lead to each terminal, one after the other. To test between terminals, connect megohmmeter leads to pairs of terminals. RELAYS AND COILS Disconnect from line. To test coil, connect one megohm- meter lead to one of the coil leads and the other megohm- meter lead to ground. Then connect megohmmeter between one coil lead and core. For relay, connect one megohmmeter lead to the relay con- tact and the other megohmmeter lead to the coil and core, one after the other. SERVICE Serial number is located on the label on the back of the instrument. For Factory service, package instrument and packing stip with sufficient cushioning material in a shipping carton; make cer- tain your name and address also appear on box as well as packing slip; ship prepaid via U.P.S. (where available) or Air Parcel Post insured to: Service Division AMPROBE INSTRUMENT 630 Merrick Road (Use for U.P.S.) P.O. Box 329 (Use for Parcel Post) Lynbrook, NY 11563-0329 Outside the U.S.A. the local Amprobe representative will assist you. 15TEST RECORD - INSULATION RESISTANCE SERIAL NO. EQUIPMENT DESCRIPTION VOLTAGE TYPE & MODEL MFGR. DATE INSTALLED LOCATION. SWHODIW UENP Vo suypnes ig ANVHO ONIGWaN U3 2RNHOD I 16 ADJUST READINGS TO T RELATIVE EMPERATURE BASE TEMPERATURE DATE READING | auMoITY | amen | a Corsection Adusted mobien pparatus Factor tasul. Res. 17TEST RECORD INSULATION RESISTANCE SERIAL NO. EQUIPMENT DESCRIPTION HP VOLTAGE TYPE & MODEL MFGR. DATE INSTALLED LOCATION REMARKS 18 SWHOODIW WeNs UO Murpees 2014 LUVHD ONIOV3Y H3LNHOOIN ADJUST READINGS TO DATE READING RELATIVE TEMPERATURE BASE TEMPERATURE i Correcti Adjusted men Ambient Apparatus Factor . Inout. Ras. 19AX AmpRoBE INSTRUMENT DIVISION OF CORE INOUSTRIES INC , LYNBROOK, NEW YORK 11563