Tom Bishop, P.E. 
EASA Technical Support Specialist

Performing work at a customer site is often more challenging than service center work. The main reasons are that the personnel and material resources are limited to the person(s) sent to the site and the equipment they have brought with them. 

To put it another way, the on-site technician can't simply call another technician over from another part of the service center to assist (the service center may be a great distance away), and the service center stockroom is likewise not available. Plus there is the added pressure of having someone (or several people) looking over your shoulder. 

The following is a series of tips to help you when performing on-site ser­vices. While these will not completely overcome the challenge of working remotely, applying several of them may reduce some of the challenge in on-site service work. 

Fan/blower balancing 
Take initial vibration readings and then clean the fan or blower blades. Quite often the unbalance is caused by dirt buildup. Repeat the vibration readings after cleaning to determine if this has resolved the unbalance condi­tion. If the readings are satisfactory, service by advising the customer to periodically clean the fan or blower. That can save them the cost of having a .rm such as yours called in for the unbalance condition and may extend the life of the fan or blower by keep­ing vibration levels low. If the dirt buildup condition cannot be avoided (that is, it is chronic), consider install­ing permanent vibration sensors that can set off an alarm when vibration levels become too high. That, too, is a value-added service you can offer your customer. 

Motor soft foot 
Sometimes a beat frequency vibra­tion is detected. The sound typically is a “wah-waah,” and is especially noticeable on 2-pole motors. The beat frequency is caused by two independent sources of vibration or sound that are at almost the same frequency. Loosen the foot hold-down bolts one at a time, and check for a change in the beat frequency sound; it often goes away when the soft foot is unbolted. Insert shims to correct the soft foot condition (Figure 1), and then tighten the foot bolt. Also, be sure to retighten each foot bolt before loosen­ing the next one. A soft foot is not the only cause of a beat frequency; a 2-pole motor beat frequency can also indicate an open rotor. 

Alignment 
Whenever possible, saves time, as you don't have to mea­sure to con.rm shim thickness with a micrometer, which you may not have with you. 

Pre-removal alignment 
Before removing a motor, check the existing alignment. In some cases, nota­bly horizontal motors and pumps, even with the motor .at on the base (i.e., no shims) the motor is high relative to the driven equipment. That means that the motor feet must be milled down to re­duce height and allow proper alignment. It is better to make that determination be­fore repairs rather than after.

Otherwise, alignment will have to be accomplished by shimming the driven equipment. This is not always possible. Also, sometimes side-to-side alignment will require mak­ing the holes in the motor feet larger. By determining and correcting for this prior to re-installation, the non-preferred use of undersize bolt bodies can be avoided. 

DC motor/generator testing 
Keep a 500 volt-ampere (500 va) transformer, 120/240 to 12/24 volts, in your .eld service vehicle. It can be used as a power supply for the inter-pole test of DC machines. With a full wave diode bridge it can also be used to apply low DC voltage to re-establish residual polarity of self excited shunt .eld motors or generators, and also AC generators. 

Keeping clean 
High-density polyethylene .ber (e.g., Tyvek^®) coveralls may make you hot, since they don't “breathe” well; however, they are very effective at keeping dirt and contaminants off your work clothes. And, the coveralls are disposable after use. 

Lifting equipment 
Use chain-type hoisting devices; that is, don't use cable-type “come­alongs.” The cable tends to fray and curl with use. 

If you do a lot of work in multi-floor buildings, consider purchase of a “stair-climber” hand truck. They are relatively expensive, but much safer and easier to use than standard hand trucks when moving heavy equipment up (especially) or down stairs. Also, be certain that the stairway can support the weight of the hand truck and load. 

Note: Before attaching lifting devices to beams or other structural items, make certain the structure can support the load to be lifted. And, obtain permission from the customer and/or building owner before using their structure to support your lifting device. 

Measuring low-level AC current 
In general, an analog clamp-on ammeter reading of less than 1/3 of full scale is not considered accurate. That is unless the reading is at least 1/3 of full scale it is not reliable. A typical lower limit for an analog ammeter is 6 amps, which means that readings below 2 amps may not be accurate. 

To measure such low currents with an analog or digital ammeter, make a current transformer coil. Do this by making a circu­lar coil with 10 turns of #14 AWG (1.6 mm) magnet wire, about 2 inches (5 cm) inside diameter. Attach #14 AWG (1.6 mm) lead wire, about 6 inches (15 cm) long to the magnet wire ends. Wrap the coil with two half-wrap layers of mica tape, and two half-lap layers of untreated glass tape. Dip and bake it for rigidity, and electrical and physical protection. Attach small al­ligator clips to each end of the leads. 

To use the coil, place it in series with the circuit to be measured. Place the jaws of the clamp-on ammeter around the coil and measure the cur­rent (Figure 2). With the 10 turn coil the actual current will be 1/10 of the measured current because the coil acts as a current multiplier. For example, if the measured current is 3.8 amps, the actual current is 0.38 amps. Another alternative is to wrap the lead around the jaws of the clamp-on ammeter several times, and divide the current reading obtained by the number of wraps. 

Digital camera 
A digital camera can be used to photograph a job site before, during and after a service. The photos can be invaluable when determining the equipment needed for service, such as removal of a motor, particularly when an issue comes up that is not addressed in the notes of the initial survey. For example, does the motor to be removed have an eyebolt, or must it be lifted by other means? 

Photographing the nameplates of the motor and driven equipment also can provide data that may not normally be recorded, such as the motor design or kVA code letters. Or, the nameplate photo may resolve an error if the equipment serial, model or other iden­tifying nomenclature is erroneously recorded. In some cases, time can be saved if the customer takes photos of the job site and sends them to you via e-mail. Not only can that save time for your employees, it also eliminates the cost of fuel to travel to and from the potential job site. 

Motor bearing numbers 
Consider this scenario: A customer calls and requests to have bearings changed with the motor remaining at the installation site. You can gather the tools and equipment to dismantle the motor, change bearings, and reassemble it. However, you don't know the bear­ing sizes. The customer wants the work done in the middle of the night, and at a location hours away from your service center. How can the bearing sizes be determined before you send someone to the customer location? 

Note that this scenario is essentially the same as when the customer plans to send the motor to the service center for emergency repairs; probably over a weekend or night when bearing suppliers are not normally open. 

In many cases, especially with newer motors, there are coded bearing numbers on the nameplate (Figure 3). Sometimes these are motor manufac­turer numbers, but in most cases, the designations are “ABMA” numbers. 

That is, numbers established by the American Bearing Manufacturers As­sociation (formerly AFBMA). There is a direct way to convert these numbers into bearing numbers. The following is a simplified explana­tion of how this conversion is ac­complished. If the bearing numbers on the nameplate do not appear to be ABMA numbers, consult the motor manufacturer for bearing code identifi­cation. Also, “Section 2” of the EASA Technical Manual has listings of many motor manufacturers' common bearing sizes, based on frame size, horsepower and speed. 

Using the nameplate in Figure 3 as an example, the customer reads the bearing numbers on the nameplate and they are “45BC03JP3” for both bearings. (Caution: Some manufactur­ers may denote the bearing locations as “front” and “back.” The NEMA de.nition for the front of a motor is the opposite drive end and the back is the output shaft end.) 

The first two numerals before the letters denote the bearing bore size in mil­limeters. In our examples, these numerals are 45. For larger bearings the bore size may use 3 numbers, e.g., 120 for a 120 mm bore bearing. To determine part of the bearing number, the .rst numerals are divided by 5, yielding “09” (45 5) in the example. 

Proceeding through the bearing number designation, the two letters after the .rst numerals denote the bearing type. The “BC” in our examples is the code for a “ball Conrad,” or deep-groove ball bear­ing. Other common bearing types are “BL” and “BT,” denoting a maximum capacity ball bearing and angular contact ball bearing for thrust, respectively. 

The two numerals after the bearing type designation identify the dimension series. The “03” in our example denotes a 300 series bearing; if it had been “02,” it would have been a 200 series bearing. At this point we now know that bearings are both basically 309. 

The nomenclature after the dimen­sion series numbers in our example iden­ti.es more subtle characteristics of the bearings. The “J” in the examples means that the cage is steel. Other common des­ignations include “K” (bronze or brass cage centered by one race), “M” (bronze or brass cage centered by the balls), and “D” (phenolic). The “P” designation indicates single shield. A “PP” designa­tion would indicate double shields; that is, shields on each side of the bearing. Similarly “E” denotes single sealed and “EE” double sealed. The last digit, the “3,” identi.es the internal clearance; that is, a C/3 internal clearance fit. 

The reason we mentioned the ex­amples were simpli.ed is that the bearing designation can consist of more numbers and letters than those in our example. Not just different combinations of letters and numbers, but longer designations, such as “45BC03JP30H.” For the sake of completeness, the last 2 digits indi­cate a standard ABEC (Annular Bearing Engineers Committee of the ABMA) 1 tolerance (the “0”) and a high temperature 275° F (135° C) grease (the “H”). 

A detailed list of ABMA nomencla­ture for ball and roller bearing designa­tions can be found in “Section 9” of the EASA Technical Manual. 

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