Calculating Ballast Resistance

[t o m]

How do you calculate ballast resistance?

 

[NLC1072]

How do you calculate ballast resistance?

Sorry, what is that?

 

[Ploughman]

I take it you mean the amount of resistance given by the ballast to lateral movement of a sleeper?

 

[t o m]

Ballast resistance is the total resistance between the rails due to the ballast, sleepers, point fittings etc.

It can affect track circuits. As you may know a current flows through the rails to form a track circuit but if there is low ballast resistance, due to wet weather for example, it can shunt some of the current away before it gets to the relay end and cause the relay to drop, thus showing the track as being occupied.

 

[NLC1072]

Ballast resistance is the total resistance between the rails due to the ballast, sleepers, point fittings etc.

It can affect track circuits. As you may know a current flows through the rails to form a track circuit but if there is low ballast resistance, due to wet weather for example, it can shunt some of the current away before it gets to the relay end and cause the relay to drop, thus showing the track as being occupied.

Got it!

 

[John Webb]

The ISRE (Institution of Railway Signal Engineers) 'Green Book' No. 9 deals in broad terms with track circuits. It says that the ballast resistance can vary from 1 ohm to 30ohm per 1000 feet of track depending on the type of track and particularly the weather! Voltages are kept as low as possible to minimise losses in the ballast resistance.
Unfortunately the book does not describe the usual method of measuring the ballast resistance, but it would presumeably involve precise measurement of an input voltage and the resultant current; specialist equipment would be needed to do this.

 

[The Snap]

The ISRE (Institution of Railway Signal Engineers) 'Green Book' No. 9 deals in broad terms with track circuits. It says that the ballast resistance can vary from 1 ohm to 30ohm per 1000 feet of track depending on the type of track and particularly the weather! Voltages are kept as low as possible to minimise losses in the ballast resistance.
Unfortunately the book does not describe the usual method of measuring the ballast resistance, but it would presumeably involve precise measurement of an input voltage and the resultant current; specialist equipment would be needed to do this.

We use the Megger equipment at work. See here: http://www.tklink.co.uk/products/megger.aspx
This allows us to test for continuity and stray current in the rails.

Don't ask me how they work or the principles of measurement though, as I don't know!

 

[John Webb]

We use the Megger equipment at work. See here: http://www.tklink.co.uk/products/megger.aspx
This allows us to test for continuity and stray current in the rails.

Don't ask me how they work or the principles of measurement though, as I don't know!

Is it the DLRO10 low resistance ohmmeter tester you use? (Pardon the question but I spent 30 years mostly measuring things!)