Electrical news and engineering . c-cident proof, and well nigh fool proof as well. The action of the switch is automatic, and consists ofstrong springs attached to the contact parts and controlledby a trigger. This trigger is released by overload, failureof power or by hand. When the switch passes the neutralpoint, the spring snaps it the rest of the way. The switchis shown in the accompanying illustration. Safety to theoperator from injury due to contact with live parts. This isassured by the entirely enclosed, dust-and-dirt proof is impossible to touch the live parts by accident for
Electrical news and engineering . c-cident proof, and well nigh fool proof as well. The action of the switch is automatic, and consists ofstrong springs attached to the contact parts and controlledby a trigger. This trigger is released by overload, failureof power or by hand. When the switch passes the neutralpoint, the spring snaps it the rest of the way. The switchis shown in the accompanying illustration. Safety to theoperator from injury due to contact with live parts. This isassured by the entirely enclosed, dust-and-dirt proof is impossible to touch the live parts by accident for thisreason. Safety to the operator and equipment from restartingafter the machine has shut down. When power leaves theequipment, a low voltage protective relay releases the trig-ger and throws the switch. Upon the return of power, itis necessary for the operator to move the handle first to thereset position and then to the running position, before themotor can again be started. Any undue overload causes the overload relav to re-. lease a trigger which opens the switch the same as on tail-ure of voltage. Overload throws off the switch just thesame as no power, and the switch must again be reset be-fore the motor can again be started. This overload relayprevents burn-out of the motor. Motor burn-outs may arisefrom two causes—an overloaded machine or the opening ofone wire, due to the blowing of a fuse or other cause andsubjecting the remaining phase to a double burden. Theoverload relay may be set to open the switch at any desiredpoint, such as 105%, 110%, 150% of full load. Fuse protec-tion is not sufficient to guard motors against burn-out. Afuse that will carry, without blowing, the starting currentwhich is several times the operating current, will also carry,without blowing, sufficient overload to burn out the overload relay is provided with oil dash pots, whichafford a time element, permitting the carrying of small peakloads and the starting current without inte
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Keywords: ., bo, bookcentury1800, bookdecade1890, bookidelectricalnewsen28donm
