~Ques. How does the inverse time limit type operate?~
Ans. The actuating and contact mechanism is attached directly to an air bellows and in operation tends to compress the bellows against the action of a specially constructed escape valve in the latter.
[Illustration: FIG. 2,310.--Condit type "B" ~time limit attachment~, designed to give sufficient time to allow an induction motor to start without opening the circuit breaker, and not have the circuit breaker trip on the momentary rush of current. ~Its action is inverse~; that is, _the greater the current the less time it takes to operate_ and is so arranged that four to five times full load current or a short circuit will trip the circuit breaker instantly. The time limit attachment is applied directly to the armature which trips the circuit breaker and is adapted for the so called primary trip. It consists of an air vacuum dash pot with a graphite piston, the dash pot being fastened to the stationary calibrating ring of the trip coil and the moving outside cylinder is fastened to the armature of the circuit breaker. When the current reaches a point where it overcomes the weight of the armature and lifts the same, the magnetic force tending to raise the armature is opposed by the vacuum created in the interior of the cylinder. As the magnetic force continues the vacuum is overcome due to the leakage of air past the plunger and the armature gradually moves up until it reaches the point where it trips the circuit breaker. If at any point of the armature travel, the current drop back to normal, the armature immediately resets itself by means of a ball valve in the top of the brass cylinder.]
~Ques. Why is the arrangement called _inverse_ time limit?~
Ans. Because the retardation varies inversely with the pressure on the bellows, and therefore inversely with the magnitude of the abnormal condition.
~Ques. What other device may be used to retard the operation?~
Ans. A damping magnet is sometimes used which acts on a disc or drum and which may be adjustable.
[Illustration: FIGS. 2,311 and 2,312.--General Electric alternating current ~low pressure~ series overload relays. Fig. 2,311, instantaneous time limit relay; fig. 2,312, inverse time limit relay. These relays have carbon contacts and will make or break a direct current circuit of 10 amperes at 125 volts without auxiliary circuit opening switch. They are used where several circuits are controlled by one automatic oil break switch or one shunt trip, overload and shunt trip or low voltage release carbon break circuit breaker. These relays may be used for signal purposes; they are back connected, the connections can be seen in the illustrations.]