Each arc light manufacturer who made arc lights for street lighting service since day one used either pintype insulators or spools mounted on top of the fixture to accept the line wire which was draped from these insulators to the pole. These were either glass or porcelain. Here's a cool arc light that has a flat jelly-jar bottom arc light enclosure with what looks like glass spools or pintypes on the bracket above the fixture. In many instances a short wood crossarm was installed facing the fixture on the adjacent wooden pole (as seen here and in some follow-up photos) whereby the two wires that fed the light would remain pretty much physically straight as the luminaire was pulled in to the pole for periodic maintenance. This was true for most suspension style arc lights (whether on a mast arm or on a span-wire) including those that were commonly lowered to ground level for regular maintaining.