G are fitted on the contact plugs, so that they will not be injured if current

is broken at this point.

Some of the feeder panels are illustrated in fig. 158, and a sectional view of these feeder panels is shown in fig. 159. Each feeder is connected to the lower contact plug of the duplex fuse A. Above this is mounted the emergency circuit-breaker B. The contacts of this circuit-breaker are divided into four blades. Three of these blades are directly connected to the shaft about which they turn, whereas the fourth blade is loose on the

FIG. 159.-Section through feeder panels (Glasgow).

shaft. By this arrangement a comparatively quick break may be obtained. The first effect of pulling the operating handle is to break the circuit through the three rigidly connected blades, leaving the supply momentarily maintained through the remaining blade. The circuit is finally broken by the loose blade being knocked out by the weight on the end of the operating lever. To prevent burning of the contacts, the final spark is taken by carbon blocks.

The front panel carries the operating handle of the emergency circuitbreaker, the contact blocks for the plug connectors, and a combined recording ammeter and voltmeter for each feeder. The latter extremely useful combination was made by Messrs Kelvin and White. The advantage of having a daily record of the current and E. M.F. of each

FIG. 160.-Kelvin and White's Glasgow Exhibition L.T. switchboard.

feeder on one chart is obvious. The rotating drums of these instruments are all actuated by a pawl and ratchet movement controlled by one regulating clock situated in the centre of the switchboard gallery. These instruments, in addition to recording the current and pressure, also indicate the same at each instant on a vertical scale.

A feature of this switchgear is the magnitude of the conducting

circuits. Provision has been made for dealing with no less than forty pairs of feeders, and each of the feeder connections is designed to carry 1000 amperes, with a wide margin. All the contact blocks, etc., are of solid forged copper, and are very massive. It is stated that over 40 tons of copper were used for the main 'bus bars alone.

The switchboard gallery itself is of novel construction, being built of iron and paved with glass blocks. The glass projects above the iron in such a manner that attendants are thoroughly insulated from earth, and the use of rubber mats is therefore unnecessary. A further advantage of this construction is that the generator panels below the switchboard gallery are efficiently lighted.

Kelvin and White's
Switchboard.

The supply of the whole of the current for the Glasgow International Exhibition in 1900-1 was controlled by the switchboard illustrated in fig. 160. Panels are provided for twelve generators and eight feeders, dealing in all with 3000 amperes. The middle panel is fitted with bar and dynamo voltmeters, electro-static voltmeters, recording voltmeters, an earth current recorder, middle wire and earth ampere gauges, voltmeter switches, etc.

Balancing and pilot illuminated dial voltmeters are mounted on swivel brackets on the top of the switchboard frame. Positive and negative panels for each feeder' are mounted, one directly above the other, immediately to the right and left of the middle panel, all the positive panels being at the top. Each positive generator panel is equipped with an ammeter and main switch, and each negative panel carries a FergusonWhite return current cutout, a dynamo field regulating hand-wheel, and a pair of sockets for a Kelvin portable paralleling voltmeter. An illustration of this voltmeter is shown in fig. 161. Its use does away with a large number of small wires between the paralleling voltmeters and switches, which are often a source of trouble. All the positive feeder panels are fixed at the left end of the board, and the corresponding negative panels at the right end. Each panel is fitted with a switch and a combined recording ammeter and voltmeter similar to that described above. These recorders are all controlled by the clock erected above the top of the board. The whole of the panels are of polished white marble carried on a steel framework.

Ferranti Low-Tension Switchboard.

Messrs Ferranti have recently turned their attention to constructing switchboards for controlling low-tension systems. Fig. 162 is a section and front elevation of a portion of a switchboard they have constructed to Mr E. T. Ruthven-Murray's specification for the Willesden Corporation. The general design of this board is somewhat similar to the standard Ferranti high-tension board described in the previous chapter.

A special feature of the arrangement, suggested by Mr RuthvenMurray, is the 'bus bar change-over switch for connecting the respective generators and feeders to any one pair of the four pairs of 'bus bars provided. This arrangement is shown in fig. 162.

The positive terminal of each generator is connected to the release coil A of a maximum and reverse current cutout. This coil is carried in a case, which is provided with contacts somewhat on the lines of the standard Ferranti fuse. The operation of removing it and replacing it by another is, therefore, very simple. The connection to the positive 'bus bars D1 D2 D3 D4 is completed through the switch B, an ammeter C, and the four-way switch referred to above. The connection from the negative terminal of the dynamo is carried directly to the four-way switch E in the top compartment of the switchboard. Voltmeters F for various purposes are mounted above the switchboard. These voltmeters are carried on miniature tram rails G, one of these rails being divided into sections, and the circuits across which potential readings are required are connected to different sections of this divided rail. By merely pushing the

voltmeter along these rails to the desired section any reading required may be obtained. The generator field switches H and field ammeters J are mounted on a panelled desk in front of the switchboard. Hand-wheels K for regulating the field resistances are mounted on shafts connected to the rheostats situated below the gallery floor. Receptacles are also provided on the top of this desk panel for receiving the contacts of a portable paralleling voltmeter L. Somewhat similar panels to the

FIG. 162.-Section through Willesden L.T. switchgear. generator panels shown in fig. 162 are provided for the feeders, boosters, and balancing circuits.

A section of another Ferranti low-tension board is shown in fig. 163. This board was constructed for the Hackney Corporation to the specification of the consulting engineer, Mr Robert Hammond. A feature of this board is the back-to-back arrangement of the generator and feeder panels.

The combined main switches and automatic cutouts used in the generator circuits are of the Ferranti loose handle type. Provision is