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by Precept
ircuit breakers
3CUIT breakers perform the me protective function as a ;e in that they break the circuit len the current exceeds a gain value. Unlike a fuse, wever, the circuit breaker is t destroyed when the circuit lich it is protecting is erloaded; it can be used over d over again by pressing a ;et button.
Two basic types are available. one the current is fed through :oil similar to a relay. When current exceeds a certain lue, the "relay" operates and eases a spring catch allowing ntacts to spring open and Bak the circuit.
The second type passes the rrent through a bimetal strip lich bends when it gets hot. cessive current heats the strip til it releases a catch which ows contacts to spring apart, JS breaking the circuit.
Circuit breakers are much 3re costly than fuses and are nerally only fitted to premium hides and then only to the fety-critical circuits such as int and rear lighting. Their big vantage is that they can be 3et time and time again until fault is cleared without eding a large number of spare ;es.
The Leyland Roadtrain is fitted th 18 fuses, described in the A article (CM, August 15), and circuit breakers. These ;tures are also carried over to 3 Cruiser. The ratings and ictions of the circuit breakers the Roadtrain are set out in Table.
The photograph oyvs Ole bank of circuit eakers and above them the ses which were discussed in e last article. It will be seen at access to the circuit eakers and fuses is gained rough a door on the dash. On the inside of the door is a diagram showing the circuit which is protected by each fuse and each circuit breaker. Spare fuses are carried in the top lefthand corner of the door.
The Seddon Atkinson 401 is another vehicle fitted with circuit breakers. In the catalogue for this vehicle it is stated that "on specific circuits manually resettable circuit breakers have been added to the electrical design to combat the problem of 'current surge' with standard fuse protection."
In the past,the second type of circuit breaker has been used on American vehicles. It consists of a bimetal strip having a fixed and moving contact, the latter being at the free end of the strip.
When the current exceeds the maximum permissible value, the strip bends so that the contact moves away from the fixed contact, thus breaking the circuit. The bimetal strip then cools and the point closes completing the circuit. When used in a lighting circt the lamp will go out and then light again, repeatedly, calling attention to a faulty circuit.