Chapter 10 — SAFETY; TEST EQUIPMENT; TEST METHODS 



HANDGRIP 

 (INSULATOR) 



SOLDER 



GROUNDING 

 CABLE 



Figure 10-1.- 



GROUNDING 

 CLIP 



1.1(71) 

 ■Shorting bar. 



of time. On many electronic equipments, charges 

 upwards of 14,000 volts are present. Usually, 

 such large charges are discharged by mechanical 

 means when the equipment is opened. Many 

 other capacitors, however, must be discharged 

 manually by the man working on the circuit. 



To drain capacitor charges, the device you will 

 use is the shorting bar, shown in figure 10-1. 

 The shorting bar usually consists of a copper rod, 

 which has an insulated grip on one end. A heavy 

 braided cable is soldered to the rod near the grip. 

 On the free end of the cable is a battery clip. 

 When using the shorting bar, first secure power 

 to the equipment, clamp the cable clip firmly to 

 the frame or other good ground, then discharge 

 each capacitor by holding the insulated handgrip 

 and touching the terminals of the capacitors with 

 the copper rod. Always ground the capacitor at 

 least twice, because the capacitor's chai'ge may 

 not be completely drained by one application of 

 the shorting bar. 



Practically all electronic equipments have a 

 metal grounding strap connecting the equipment 

 chassis to the ship's hull. The purpose of the 

 grounding strap is to place the equipment's frame 

 and the hull at the same electrical potential, thus 

 permitting personnel to touch the equipment with- 

 out danger of receiving an electric shock. As 

 you know, a difference in potential is what causes 

 current to flow. If a component should develop 

 a short to the chassis, the short-circuited power 

 will bleed off to ground through the strap. If 

 there is a faulty or open ground strap connection, 

 however, a potential difference is established. 

 Should you then come in contact with the equipment, 

 you becoms the ground strap. In other words, 

 the current passes from the equipment through 

 you to ground, resulting in an electric shock — 

 possibly a fatal one. You must ensure, therefore, 

 that all ground connections are tight and free of 



foreign matter, such as dirt, grease, or paint, 

 that might interfere with the required metal-to- 

 metal contact at the ground connection points. 

 Fuses are another source of potential danger 

 to the careless Sonar Technician. The purpose 

 of a fuse is to protect electric circuits and com- 

 ponents. A fuse blows because more current 

 than the fuse can handle tries to pass through it. 

 The cause of the current overload may be a momen- 

 tary surge in ship's power, or it may be a short 

 circuit. Whatever the cause, two precautions must 

 be observed when replacing fuses. First, use a; 

 fuse puller, even If power is secured. (Although 

 it is desirable to secure power to the affected 

 circuit, it is not always necessary or practical 

 to do so.) If you were to use a screwdriver, 

 pliers, or your bare fingers, great harm may be 

 done if you contact adjacent Uve circuits. Second, 

 always replace a fuse with one having the same 

 rating. Substituting a higher rated fuse may cause 

 serious dam^age to the equipment. If the circuit 

 does not burn out, dangerous potentials may exist 

 that normally would not be present, thus endanger- 

 ing servicing personnel. 



Cathode ray tubes (CRT) are used in all sonar 

 equipment. They are of rugged construction, and 

 normally have a long life. They do require replace- 

 ment from time to time, however, and a few pre- 

 cautions must be observed in handling them. A 

 CRT must be handled gently to prevent breaking 

 it and to avoid displacing its internal elements. 

 Always place a CRT face down on cushioning 

 material. If the tube is broken, don't handle the 

 glass with bare hands because the tube's inner 

 surface is coated with a toxic material. Gloves 

 and special face masks are available for wear by 

 personnel handling CRTs. 



SAFETY WITH POWER TOOLS 



Hazards associated with the use of portable 

 electric power tools include electrical shock, 

 bruises, cuts, falls, particles in the eyes, explo- 

 sions, and the like. All Sonar Technicians should 

 become familiar with the safety practices con- 

 tained in NavShips Technical Mimual, chapter 

 9600, section II. Following are some of the gen- 

 eral safety precautions you should observe when 

 working with power tools. 



1. Ensure that the tools are grounded in 

 accordance with articles 60-25 through 60- 

 27 and 60-29 of the NavShips Technical 

 Manual.^ 



2. Avoid, if possible, using spliced cables. 



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