In every factory, mercantile establishment, mill or workshop, effective means shall be provided for immediately disconnecting the power, so that in case of need or accident any particular machine, group of machines, room or department, can be promptly and effectively shut down. Where machines are required to be started and stopped frequently, they shall, wherever practicable, be provided with tight and loose pulleys, clutch or other effective disengaging device. When provided with tight and loose pulleys, the shifting of the belt shall be accomplished by the use of a belt shifter, placed within easy reach of the operator. When a clutch or other disengaging device is used, an effective means for throwing such device into or out of engagement shall be provided, and shall be placed within easy reach of the operator. Where machines are directly connected with the prime mover (electric motor, steam, gas or gasoline engine, or other source of power), a switch, throttle, or other power controlling device shall be furnished and shall be placed within easy reach of the operator or his coworker. Where machines are arranged in groups, rooms or departments, and power is supplied by a prime mover, located within the confines of such group, rooms or department, a switch, throttle, or other controlling device shall be furnished, and shall be placed within easy reach of the operators affected, so that all shafting, transmitting machinery and machines of such group, room or department, can be simultaneously shut down. Where machines are arranged in groups, rooms or departments, and are supplied by power through the use of main or line shafts receiving power from some prime mover located without the group, room or department, the power receiving wheel or such main or line shaft shall, wherever possible, be provided with a friction clutch, or other effective power disengaging device, with suitable means for operating the clutch, or power disengaging device, and these means shall be placed within the confines of such group, room or department, and within easy reach of employees or operatives affected, so that all machines, shafting and other transmission machinery within such group, room or department, can be simultaneously shut down. In addition to such safeguard, communication, consisting of speaking tubes, electric bells, electric colored lights, or other approved and effective means, shall be provided in all cases covered by this section between each such group, room or department and the room in which the engineer or prime mover is located, so that in case of need or accident the motive power of such group, room or department can be promptly stopped or controlled.