108 Experimental Switchboards and Experimental Resistances. 



The Selection of an Experimental Switchboard. 



Type of Current and Construction. 



In selecting an experimental switchboard, one is first of all guided by the type of current 

 and the voltage available on the spot. Moreover, the board may be stationary (for fixing to the wall), 

 portable, or arranged as a travelling distribution board. 



The most suitable and practical type of current for purposes of demonstration is naturally 

 direct current, as with this all fundamental experiments can be carried out. In view of arc lamps 

 and arc experiments, the voltage should be at least 65; in the majority of cases 110, 160 or 220 volts 

 are available. If funds allow it, it is advisable to provide a switchboard with 2 circuits; the con- 

 ditions are then particularly favourable: if the central station has a 3-wire main, it is desirable for 

 many reasons to be able to connect to all three lines. With a board of this type it is then possible 

 to carry out two experiments in parallel, or the accumulators can be charged from one circuit while 

 experimenting with the other. Often, in order to have different potentials available, one circuit is 

 connected to 110 and the other to 220 volts in the case of a 3-wire system of 2X110 volts. Also 

 it is possible to connect only one circuit up to heavy current, while the other is connected to a 

 battery of a few cells. 



If various types of current, e. g., direct and alternating current or direct and triphase current, 



are available, the switchboards can be adapted to work with one common circuit for the two types S 



of current, or, better, the two sorts of current can be distributed through two circuits with the one x 



board (one circuit for each type of current). In using a switchboard with a common circuit for the M 

 two kinds of current, either a special change-over switch is provided for changing from one current 



to the other, or plugs can be used in conjunction with plug boxes. If one of the currents is D. C., ^ 



and the other alternating or three-phase, hot wire instruments must be used for measuring, as these > 



alone indicate correctly on both types of current. L 



Switchboard with dead-beat standard measuring instruments should be given the preference ^ 

 over those with simple instruments having air damping, as the reading can be taken at once, since 

 the pointer of the standard instruments does not swing to and fro on deflecting, and the scale is 

 equally divided. 5. 



N 



We construct the Standard Experimental Switchboards with one Circuit, for direct current, 

 in 3 types: 



^ 



(1) Type A, for connecting to 110 160 volts working voltage, for taking currents of from 0.03 to 



30 amps, and voltages of 0,3 110 (or 160) volts, with rheostat of 36 ohms in 30 steps. ^ 



(2) Type B, for connecting to 220 volts working pressure, for taking currents of 0.04 to 20 amps. 



and pressures of 0.4 220 volts, with a 48 ohm rheostat in 30 steps. 



(3) Type C, for connecting up to 110 volts working pressure, for taking currents of from 0.04 to 



20 amps, and pressures of 0.4 110 volts, with a rheostat of 24 ohms in 21 steps. 



(The currents and voltages given are those applying when the resistance of the apparatus 

 connected up is 10 ohms.) 



Each of these 3 types is further supplied in two separate patterns: (1) with large dead-beat 

 standard measuring instruments and with an ammeter switch, for measuring the current strength 

 in the apparatus and the total current; (2) with measuring instniments having air damping, of 

 120 mm scale diameter, without ammeter switch. 



From these we accordingly have Types A', B', C", and A-', B-', C-'. 



The standard experimental switchboards for 2 circuits for the same kind of current and for 

 the same current strength are constructed in corresponding patterns and the individual types, cor- 

 responding exactly with the previous ones, are designated DI, E", FI and D*, E-', F-' respectively. 



We have also constructed a number of switchboards for special cases; this price list includes 

 some of those which are pretty frequently used and which are typical in their form. Of these may 

 be mentioned Types GI and HI having two circuits for different current densities. 



For low pressures all switchboards can be employed forthwith, the lower limit of the current 

 densities diminishing in the same ratio in which the pressure is reduced. If it be desired, say, to use 

 the switchboard at one time for the listed pressure and on another occasion for a considerably lower 

 accumulator voltage, it is desirable to order a switchboard fitted with instruments for 2 ranges. 



