Improving conductivity through fish plates

[phil-b259]

On 08/11/2020 at 13:08, ejstubbs said:

 

I would regard conductive grease as grease that happens to be somewhat conductive, rather than a good conductor that also happens to be greasy.  And that's before you get in to the question of applying grease to (or close to) a surface on which you will be relying on metal-to-metal contact for traction...

 

I use conductive lubricant on the real railway when installing impedance bond connections - however too much of it will definitely act as an insulator.

 

When you consider that a typical 3rd rail is pulling 1000s of amps, any areas of high resistance soon end up growing and causing issues.

 

The goal of such a grease is actually to fill in the minor imperfections in the metal surfaces to be bolted together, eliminating the minute air pockets which will occur and thus increasing the electrical contact area.

 

The best way of applying it actually involves wiping most of it off afterwards - if you can still see it then there is too much!

 

Now on a model railway the currents involved are far less - but the same principle applies - the grease is there to fill in scratches or other imperfections in the metal surfaces issues meaning that good electrical contact is not made in spite of the fishplate being tight. It is not there as a substitute for a tight fitting metal on metal fastening - though it may of course help prevent oxidisation if there are any air pockets within the fishplate.

[newbryford]

Whilst I use DCC and and advocate "best practice" of soldering a dropper to every piece of rail [*], there are times when that doesn't happen.

For example:

My fiddle yard is in four foot long sections and there is only a maximum of one rail joiner per one "electrically uninterrupted" section along a baseboard, so I've soldered the rail joiners.

No problem with expansion as the maximum length can only be 4'.............. The rail ends are soldered to brass screws (or copper clad) fixed to the baseboard, but still have the tiniest amount of "give" to accommodate any excess expansion.

The same soldered joiner happens if there are any short sections of rail between points up to an isolated gap - say up to a maximum of 10-12" - they will also be soldered.

 

[*] In reality for DC as well, soldering droppers to every section of rail fed by a particular section switch should also be "best practice"