. Electric railway journal . w of the contacts for inspection. This pioneer magnetic blow-out has proved very suc-cessful for handling currents up to 75 amp, and mostof the hand controllers now in service have this type insome modified form. Many other types and arrange-ments of controller blow-outs have since been developed,however, in an effort to provide a more efficient blow-out and to overcome some of the principal objectionsto the pioneer type, namely: The coil occupies muchspace at a point that could be utilized to advantage forconnections or contacts; the stray fields are very large,so
. Electric railway journal . w of the contacts for inspection. This pioneer magnetic blow-out has proved very suc-cessful for handling currents up to 75 amp, and mostof the hand controllers now in service have this type insome modified form. Many other types and arrange-ments of controller blow-outs have since been developed,however, in an effort to provide a more efficient blow-out and to overcome some of the principal objectionsto the pioneer type, namely: The coil occupies muchspace at a point that could be utilized to advantage forconnections or contacts; the stray fields are very large,so that a big portion of the lines of force is not avail-able for blow-out purposes; the contacts most distantfrom the coil have a smaller magnetic field and conse-quently a weaker magnetic blow-out than the contactsnearer this coil; as the arc is blown sidewise againstthe arc deflectors it does not have sufficient space toexpand properly, causing excessive burning of the arcdeflector plates. Troubles with the coils themselves. J3low Oi/r Oo/l. FIRST CONTROLLER BLOW-OUT 592 have been very few and are confined chiefly to short-circuits which result from the burning of insulation,due to the floating back of the arc from the contactsor to the expansion of the coils when hot whereby theinsulation is rubbed by the drum or some other movingpart. Troubles with the arc shield, which may be includedas a part of the controller blow-out, are the following: ^>oi.£ 7=>/e:<=£ ^ Oct Oo/l SHAFT TYPE OF CONTROLLER BLOW-OUT Burned arc deflectors and broken or split splitting of the arc deflectors is due principallyto the use of wood screws for fastening them togetherand to the pole piece. Much attention has been given toward developingan insulating material which will withstand the severearcing to which arc deflectors are subjected and alsoto permit fastening with wood screws to provide asolid support. So far, however, nothing entirely sat-isfactory has been produ
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