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THE ‘SHORT CIRCUIT’

Prevention is better than cure.

This means that you must always follow good track laying practice and ballasting from the outset and follow that by using good wiring practices.  

Make sure that the track bed is perfectly flat and where you come to a station of yard ensure that the entire area is flat.

So, what exactly is a `Short Circuit’ and why are they so damaging?

In a DC circuit, we have a POSITIVE supply and a NEGATIVE supply.

These should not be joined together – Rule Three says so!

A non-technical explanation of a `short circuit’ is when these two supplies ARE joined together.  

A fuse that `blows’ when this happens protects most equipment.

What actually happens is that the path created by a conductor touching Both supply lines has little of no resistance to the flow of the current

 – the `short’ circuit.

The current flowing through the conductor causes heat, lots of heat, sufficient heat to melt the conductor and that is exactly what happens to the

wire in the fuse – it melts and breaks the circuit – the ‘blown’ fuse.

In a DC system, we are talking 12V and a maximum current of about 1A.

In a DCC system, we are talking 17V AC and a current flow up to 5A.

A Circuit Breaker is like a fuse.  It breaks a circuit to prevent the current flow damaging any component in the circuit.  The big difference is that it is re-settable.

When a de-railment occurs, we are most likely to get a ‘short’ circuit.  The Circuit Breaker ‘breaks’ the circuit feeding the section BEFORE the current flow gets high enough to bring the whole system down.

The supply is wired through a switch so that in the event of a ‘short’, BOTH circuits to the Section can be broken until the cause is established and rectified.

These type of switched are known as ‘Double Pole Double Throw’ switches (DPDT)

When we have re-railed the offending rolling stock and cleared the ‘short’ we can re-set the Circuit Breaker and then switch the DPDT back on to restore power to the ‘Section’ so that we can continue operation.