Tweet

---

October, 1946

---

Since A. Reyrolle & Co., Ltd., introduced their type GA8 room-switches for use with conveyors and the like, they have concentrated on the production of a similar lightweight panel of minimum dimensions for the control of drills. The new room-drill-switch (see Fig. 1), rated at 1 kVa, 615-125 V, three-phase, 50 cycles per second, is defined as a type GA9 single-circuit drill-panel, and is suitable for separate use or for forming part of a multi-panel room-switch switchboard, comprising, say, conveyor, loader, and drill circuits.

The room-drill-switch consists of a main skid-mounted welded-steel flameproof enclosure, and is so arranged that within the main enclosure there are two entirely separate flameproof compartments. The upper compartment accommodates three 300-A air-insulated copper busbars, which terminate at each end of the panel in flameproof bushing-type terminals, and a triple-pole air-break reversing isolator capable of breaking full-load current. The isolator is fully interlocked so that it must be in the off position before the lower compartment becomes accessible. All connections from the busbar enclosure to the lower compartment are taken through flameproof bushes, which are near the front of the panel to allow easy access. The lower compartment contains a three-phase main transformer having an output of 175 kVa at 50 cycles per second, and a ratio of 625, or 600, or 550, or 500, or 440, to 125 V; a single-phase auxiliary transformer for the control circuit with primary taps as for the main transformer and a 25 V secondary; a triple-pole main fuse-board with cartridge fuses to protect the primary circuit against short circuits a triple-pole electrically operated contactor in the primary circuit, the operating coil acting as an under-voltage release ; earth-fault protective equipment arranged to protect the 125 V circuit and to open and lock out a three-pole thermal time-lag over-current relay, which also has an electromagnetic action giving instantaneous short-circuit protection, connected in the secondary circuit but arranged to open the primary contactor. The control system is arranged so that as long as both pilot and earth connections are continuous the operation of the switch on the drill closes the main contactor. The contactor can then be opened by the release of the switch on the drill, by the operation of the over-current or earth-fault equipment, by opening the isolator, or by an attempt to disconnect the plugs and sockets connecting the trailing-cable to the panel or machine.

The main cable to and from the busbars of the room-drill-switch can be accommodated in a standard detachable cable-box or in a flit-plug box, and the outgoing cable to the drill can be coupled by means of a 30 A restrained or bolted (or by a 15 A restrained) plug and socket. This means that all the cables may be jointed and compounded, if required, away from the switchgear. Units can be added to or removed from each other very quickly, since it is only necessary to insert or remove a terminal chamber between the busbar-chamber ends, and to couple or uncouple the skids.

Drawings and Photographs accompanying the article