. Electric railway journal . contactors inpassing from the full-field to the tapped-field positioncuts out ohm or 35 per cent of the field windings,leaving ohm or 65 per cent. table for locating POSITION of trouble FROM RESISTANCE READINGS Hesistancein 132 1330 072 ToFFM Condition of Fields First or second field or third field or fourth field shorted. No. 1 field reversed. No. 2 field reversed. No. 3 field reversed. No. 4 field reversed. The trouble in the cases referred to was fou
. Electric railway journal . contactors inpassing from the full-field to the tapped-field positioncuts out ohm or 35 per cent of the field windings,leaving ohm or 65 per cent. table for locating POSITION of trouble FROM RESISTANCE READINGS Hesistancein 132 1330 072 ToFFM Condition of Fields First or second field or third field or fourth field shorted. No. 1 field reversed. No. 2 field reversed. No. 3 field reversed. No. 4 field reversed. The trouble in the cases referred to was found tobe due to two causes. First, in some cases a short-circuit had occurred between the two sections of someof the fields and secondly, some fields had been installedupside down and end for end which made the terminalscome right for connecting but reversed the amount ofresistance and the winding in the circuit from whatwas originally intended. In both of these cases motorswould rotate properly, but as a wrong percentage of. AT LEFT, SCHEMATIC DIAGRAM FOR THE WINDINGS OFA TAPPED FIELD MOTOR; AT RIGHT, INDIVIDUAL FIELDCOIL FOR A TAPPED FIELD MOTOR the field was being cut out in the tapped-field positiontrouble occurred. The severity of this depended uponthe position of the field in the circuit. In one case a short-circuit was found between A andQ so that in the full-field position the entire fieldwindings would be short-circuited for this motor. Inother cases short-circuits were found in field coils otherthan the first one in circuit. With a short-circuit be-tween BC and OP the resistance between F and FF,was ohm instead of ohm. With a short-circuit between DE and NL the resistance between theterminals F and FF, was ohm. By comparingthese with the resistances that should have been in-dicated, the variation in the results will be understood. In the cases where the fields were installed thewrong way around the resistance as read between theterminals F and FF, wou
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