- Pt. No. 947750 OPERATING INSTRUCTIONS AMPROBE Hand-Cranked MEGOHMMETER Model AMC-2 Model AMC-3 Model AMC-4 See Precautions for Personal and Instrument Protection on Page 4 See Limited Warranty on Page 2 A AMPROBE INSTRUMENT? WG, LYNBROOK, NEW YOR 19563LIMITED 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 a- 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. f damaged, or should the need arise to retumm your instrument, it must be securely wrapped (to prevent damage in transit) and sent prepaid via Alr Parcel Post Insured or U! where available to: Service Division AMPROBE INSTRUMENT 630 Merrick Road {For ULP.S.) P.O. Box 329 (For P.P. Lynbrook, NY *oe3 dad9 . Outside the U.S.A. the local Amprobe rpresentative will assist you. Above limited warranty covers repair and replace- ment of Instrument only and no other obligation is stated or implied.MEG-OHMSPRECAUTIONS FOR PERSONAL AND INSTRUMENT PROTECTION Although there is high voltage at the tips of the test leads when the AMC-2/3/4 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. This can be accomplished as follows: . 4. Plug test leads Into instrument. 2. Connect LINE test lead to equipment to be tested. 3. Touch the EARTH test lead to the same point on the equipment that the LINE test lead is connected to. 4. If the equipment has multiple windings, this should be done with each winding individually. Equi int under test with the megohmmeter may bulid up a capacitive charge from the testing. With the AMC-2/3/4, you can (1) walt a few minutes for the charge to dissipate or (2) remove the test lead from the EAI ack on the tester and touch to the equipment terminal that the other test lead (LINE) is connected to. See Figure 1. Before connecting the AMC-2/3/4 to any circuit as either an ohmmeter or megohmmeter check for any voltage. Do not connect the AMC-2/3/4 ohmmeter or megohmmeter to a live circuit. Always store the Instrument in Its carrying case.SPECIFICATIONS Model AMC-2/AMC-3/AMc.4 . Weight: 2 ibs. 8 oz. (1.1 3Kg). MODEL BANGES VOLTAGE ACCURACY AMC-2 9-100 M2 (1Ma midscate) S0ovoc 5% of reading rom -1 SOMO 10% of reading at all other points 9-200 ofmns (109 midscae) | syne 10% of reading AMC-3 9-500 MQ (SMO midscale) to00v0C 5% ol reading trom .5 to 200M . 10% of readiog af af other points 9-200 obms (100 midscaie) 6yoC 10% of reading AMC-4 [0-100 MG (MO midscal) S00vDC | 5% of reading from -1 we SoMa 10% of reading at all other points 0-500 Ma (6Ma midscale) 1 s000vD 5% of reading from -5 to 100M0 2 10% of readiog at all other points 9-200 ohms (100 midscale) 6vDC 10% of reading Size: 4" x 3.625" x 7 . (101.6mm x 92.1mm x 177.8mm)wm OPERATING INSTRUCTIONS IMPORTANT: See Precautions for Personal and Instrument Pro- tection before proceeding. ; Note: Pointer is free-floating until crank Is rotated. 1. To use as a megohmmmeter or an ohmmeter, disconnect the device or circuit to be tested from the line. . 2, Set range switch to appropriate range MEG-OHM* for insulation resistance testing and other high resistance measurements; OHM" for continuity checks and low resistance measurements. - 3. Select a pair of test leads (one probe and one clip type o two clip type) that best fits your application. 4. Depress button over the EARTH Jack and Insert the black fead. Depress button over the LINE Jack and insert red 5. Connect test leads to device or circuit to be tested. 6. Place instrument on a firm and level surface. 7. Turn crank handle in a clockwise ditection at a speed that causes the crank to free-wheel. 8 Take reading on scale corresponding to range switch : position. . *On AMC-4, 1000V/S500MQ or S00V/H00MO GUARD TERMINAL There are two possible conducting or leakage paths in the in- sulation of all electrical apparatus one t ough the in sulating material and the other over its surface. By using the Guard Terminal the surface leakage can be separated and a direct measurement made of the insulation itself. See Fig. 2 for a typical use of the Guard Terminal. Why insulation Resistance Testing? The primary purpose of insulation is to keep electricity flow- 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 Isn't 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. 6a Core Wire LINE Insulating Materiat AMC-2 Lead-Sheatheg AMC-3 Wire or 1 AMC-4 EARTH Figure 2 Unless there is accidental damage of some Sort, insulation falture is generally gradual rather sudden. This is because failure is generally a wearing down Process due to repeated heating and Seng, the related expansion and contraction, abrasion, Vibration, moisture and chemicats, 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- fon may reach a point where it May permit a enough Current flow through the insulation to Catise 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 concemed about insulation fesistance! An Insulation Resistance Testing Program helps reveal fail. Ing insulation before itb eS a Serious problem. Such a esting Program consists of periodic insulation resistance tests on critical equipment and syst results are Fecorded on a control Card or file for each plece of ulpmnt Or each test point in @ system. Any trend that | icates a easing Insulation resistance value is an indication that the insulation fs failing and that corrective maintenance should be Scheduled. 7TN a tne oe cane geen, entimeete also affect readings, either raising or lowering mM, 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 8 aperiodic insulation resistance measurements can not be taken at the same temperature, it is important that resistance measurements be adjusted to a base temperature. From 1EEE Std 43-1961 for Rotating Machin. ery. = Ktsoc X Re where Rue = insulation resistance (la megohms) conecteg to 40C Rt= measured insulation resistance (in megohms) a Ktsoc = temperature coefficient of insulation resis- ance @S observed for temperature tc see ig. Example: An insulation has a resistance of 100 megohms at C. From Fig. 3, Ktsoc is 0.5 =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 Nluminating Companies,(AANATION MEOETANE TEMPERATURE SOLPFOEHT, tsa g Approximate Temperature Coeificient Insulation Resistance Rotating Machine Armature Windings Figure 3 e Tie 6 BEC Typical curve of Insulation resistance {in megohms) versus time Figure 4 9r? eaten ister stte batne vamen eee TIME 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. 4. The most common megohmmeter measurement Is taken at the end of a 60 second Interval as this time period generally gives a satisfact measurement of the insulation resistance: on 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. Gonerally 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 tion Index is helpful in evaluating the winding dryness and fitness for over-potential testing. For a fuller explanation of these ratios and safe values see IEEE Std 43-1961 IEEE Standard Guide for Testing Insula- tlon Resistance of Rotating Machinery and *IEEE Std 62-1958 Recommended Guide for Making Dielec- tric Measurements in the Fleld *May be ordered from: : JEEE 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 rotating machines is 1.5 for 105C (Class A) insulation systems and 2.0 for 130C (Class B) insulation systems. ; , . 10WHAT 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 J some basic guide lines that are usable. From the IEEE Std 43-1961 Standard Guide for Testing Insuta- ry: . ' tion Resistance of Rotating Machine. a Rm=Ky + 4 where Rm= recommended minimum insulation resistance in Megohms at 40C of the entire machine winding Kv= rated machine Potential, in ktlovolts if winding is not at temperature of 40C, temperature correc- tfon should be-made. See page 8. : This essentially follows an old rule of thumb which set a minimum value of 4 megohm for every thousand volts of equipment rating. For specific information about Individual products, contact - the manufacturer for s ifications 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 falling. 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 b checked,Tn eee erat aeete eetee ee meme eetelleetenen we meee WHAT TO RECORD So that your periodic. insulation resistance measurements can be compared meaningfully, you must have certain Infor- mation recorded. Each plece of equipment should have Its pwn record card on file. Typicat Information that should be Inc! : 1) Equipment description including rating and serial number. Equipment location (department, floor, etc.) Date of installation. 4) Dates of repairs and description. 5) Spectfic test points (6.9. motor frame and motor lead disconnected at motor junction box). In some cases a sketch might help another person performing the test at a tater time. 6) Equipmerit 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 18 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 plece of equi 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 gulde 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. See Precautions for Personal and instrument Protec- tlon on page 4. 12POWER TOOLS AND SMALL APPLIANCES This test would aiso apply to other similar equipment that has a line cord. For double-insulated Power tools, the megohmmeter lead shown connected to the housing woutd be connected to some metal part of the tool (e..g chuck, blade), See Fig. 5 Note: The switch of the device must be In the ON position. Megohm- meter Figure &- MOTORS ACDisconnect the motor fron the fine 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 : 13If 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. DCDisconnect 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, ralse 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. MOTOR pon . GROUND = CONNECT TO +R ARTER MOTOR HOUSING ON Position) + MAIN SWITCH - CONNECT TO MEGOHMMETER MOTOR SIDE OF SWITCH Figure 6 14la MEGOHMMETER Figure 7 CABLES Disconnect the cable from the line. Also disconnect opposite end to avold errors due to leakage from other equipment. Check each conductor to ground and/or lead shea by con- necting one megohmmeter lead to a Pigued and/or lead sheath and the o megohmmetr lead to each of the con- ductors In tum. Check insulation resistance between con- . puctors by connecting megohmmeter leads to conductors in rs. 15HERMETIC COMPRESSOR The following tabte SYSTEMS. may be used as a pulde to determine the extent to which a system may have NN Contaminated by moisture, MEGOHM- . SUGGESTED METER COMPRESSOR PREVENTIVE CONDITION MAINTENANCE 100 Megohms to Good . None necessary Infinity 50 to 100 Moisture Present Change drier Megohms 20 to 50 Severe moisture Change numerous Megohms and possible con. driers, change oii taminated oif 0 to 20 Severe Dump oi! and Megohms contamination entire refriger- ant charge evacuate tem, install tiquid and suction line driers, re-charge System with new oil and refrigerant - CIRCUIT BREAKERS AND SWITCHES Disconnect from line. nect one megohmmeter lead to the frame or ground and con- nect the megohmmeter lead to each tenninal, one after the 16RELAYS 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 tmegohmmeter between one coll lead and core. For relay, connect one megohmmeter lead to the relay con- tact and the other megohmmeter lead to th 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 slip with sufficient cushioning material in a shipping carton; make cer- packlng sir ship prepaha aia iS pee On BOX 88 yor Air c slip; ship prepa LP: @ available) or Air - pater hod insured. tor Service Division AMPROBE INSTRUMENT 630 Merrick Road {Use for UPS.) P.O. Box 329 (Use for Parcel Post) : Lynbrook, NY 11563-0329 Outside the U.S.A. the local Amprobe representative will assist you. 17| a . i | 18 enna G3 TW18Ni atyo NOLLY907 to vit94 $s, 2 FAL nin sy oy Wis NOLdIWuoeRg ANANINOR SONVigisay NOlAVINSNE ~ Qvooay iss: CT ao Baws ts uN co