Program Policy Manual - VOLUME V - Mine Safety and Health ...

More documents

Recommendations

Info

MSHA PROGRAM POLICY MANUAL VOLUME V grounded side of the grounding resistor to the frame of the stationary equipment. 2. The cable supplying power to the stationary equipment is shielded or steel armored and the shielding or armor is grounded at both ends. Resistance grounded circuits extending to stationary low- or medium-voltage three-phase equipment located on the surface are not required to be equipped with ground check circuits. 75.902-2 Approved Ground Check Systems Not Employing Pilot Check Wires This Section requires MSHA approval of all wireless ground check circuits; therefore, only wireless ground check devices bearing an MSHA acceptance number will be acceptable. 75.903 Disconnecting Devices A connecting plug on the outby end of the trailing cable connected to the power center or distribution box will be accepted as a disconnecting device. Other means, such as switches with visible contacts, may also be acceptable for this purpose. Molded-case circuit breakers are not acceptable as visible disconnecting devices. Disconnecting devices shall be plainly marked for identification to reduce the chance of energizing a cable while repairs are being made on the cable. While identification could take a variety of forms, one example of compliance with §§ 75.601, 75.903, and 75.904 would be to label the loading machine #1 cable plug, receptacles, and the circuit breaker through which the loading machine #1 is receiving power as “loader #1.” Consequently, each of these would be labeled alike and easily identified. 75.904 Identification of Circuit Breakers The circuit breaker must be marked to identify the circuit or machine receiving power through the circuit breaker. For example: A circuit breaker through which “loader 1” is powered, is marked as “loader 1.” Either metal or plastic tags or markers may be used to identify circuit breakers if the tags or markers are attached securely to the circuit breaker enclosure and are large enough to be readily seen. The tag or marker should clearly identify the circuit or machine receiving power through the circuit breaker. June 2008 (Release V-40) 85
MSHA PROGRAM POLICY MANUAL VOLUME V Subpart K Trolley Wires and Trolley Feeder Wires 75.1001-1 Devices for Overcurrent Protection; Testing and Calibration Requirements; Records To provide the short-circuit protection required by this Section, trolley systems must be designed, installed, and maintained to assure, at all times, that a short circuit at any location in the trolley system will be cleared by one or more automatic circuit-interrupting devices. Automatic circuit breakers and fuses used to protect trolley circuits shall have a voltage rating that equals or exceeds the maximum no-load voltage of the trolley circuit and shall be capable of interrupting the maximum fault current that can flow through the interrupting device. Molded-case circuit breakers are sometimes installed in trolley circuits with noload voltages ranging from 275 to 350 volts d.c. Since most molded case circuit breakers are rated only 250 volts d.c., it is often necessary to connect two or more poles of the circuit breaker in series to achieve an adequate voltage rating. When two or more poles of a molded case circuit breaker are connected in series, the poles of the circuit breaker should be wired so the bottom of one pole is connected to the top of the next pole to decrease the voltage stress between adjacent poles when the circuit breaker opens under load. It is not acceptable to connect fuses in series to achieve a higher voltage rating. A "short circuit" is defined as an abnormal connection of relatively low resistance, made accidentally or intentionally, between two points of different potential in a circuit. The setting of an automatic circuit-interrupting device should not exceed 75 percent of the minimum available shortcircuit current in the protected circuit to compensate for inaccuracies in the setting and the voltage drop across arcing faults. This safety factor is consistent with accepted engineering practice; however, in determining whether a violation of this Section exists, the safety factor shall not be used. When a molded-case circuit breaker in the a.c. input leads of a rectifier bridge is used to provide short-circuit protection for a trolley circuit, the required instantaneous setting of the circuit breaker will be less than the required February 2003 (Release V-33) 86
Page 1 and 2:
MSHA PROGRAM POLICY MANUAL VOLUME V
Page 3 and 4:
Page 5 and 6:
Page 7 and 8:
Page 9 and 10:
Page 11 and 12:
Page 13 and 14:
Page 15 and 16:
Page 17 and 18:
Page 19 and 20:
Page 21 and 22:
Page 23 and 24:
Page 25 and 26:
Page 27 and 28:
Page 29 and 30:
Page 31 and 32:
Page 33 and 34:
Page 35 and 36:
Page 37 and 38:
Page 39 and 40:
Page 41 and 42:
Page 43 and 44:
Page 45 and 46:
Page 47 and 48:
Page 49 and 50: MSHA PROGRAM POLICY MANUAL VOLUME V
Page 99: MSHA PROGRAM POLICY MANUAL VOLUME V
Page 127 and 128: MSHA PROGRAM POLICY MANAUL VOLUME V
Page 151 and 152:
Page 153 and 154:
Page 155 and 156:
Page 157 and 158:
Page 159 and 160:
Page 161 and 162:
Page 163 and 164:
Page 165 and 166:
Page 167 and 168:
Page 169 and 170:
Page 171 and 172:
Page 173 and 174:
Page 175 and 176:
Page 177 and 178:
Page 179 and 180:
Page 181 and 182:
Page 183 and 184:
Page 185 and 186:
Page 187 and 188:
Page 189 and 190:
Page 191 and 192:
Page 193 and 194:
Page 195 and 196:
Page 197 and 198:
Page 199 and 200:
Page 201 and 202:
Page 203 and 204:
Page 205 and 206:
Page 207 and 208:
Page 209 and 210:
Page 211 and 212:
Page 213 and 214:
Page 215 and 216:
Page 217 and 218:
Page 219 and 220:
Page 221 and 222:
Page 223 and 224:
Page 225 and 226:
Page 227 and 228:
Page 229 and 230:
Page 231 and 232:
Page 233 and 234:
MSHA PROGRAM POLICY MANAUL VOLUME V
Page 235 and 236:
MSHA PROGRAM POLICY MANAUL VOLUME V
show all

Program Policy Manual - VOLUME V - Mine Safety and Health ...

Create successful ePaper yourself

Delete template?

Save as template?