L&NWRy Tel Dept Dry Core Test Box?

[kermit]

Small metal plate. Think I found it at a model railway junk table sale in the 70s. Any ideas to what it refers?

Thanks!

 

[krus_aragon]

My first instinct is that it labelled some (portable?) equipment for testing telephone/telegraph lines, presumably between signal boxes. I assume dry core refers to dry-cell batteries, but core might also refer to the core of an insulated cable.

 

[kermit]

The thickness of the metal plate suggests a permanent installation rather then the thinner sort of plate you would find on a portable device.

I wondered about the "dry core" referring to an earthing rod - but tbh that's complete guesswork, with no evidence at all!

Obviously the LNWR bit dates it, but googling the "dry core test box" term produces absolutely nothing as far as I can tell - which is fairly unusual in my experience.

 

[John Webb]

Some early cables, particularly ones carrying power, were insulated by pressurising the cable core with a suitable liquid, eg like transformer cooling oil - ie a 'Wet core'. As materials improved, the liquid wasn't needed, and so we had a 'Dry core'; the label was no doubt to deter technicians from trying to fill a cable with oil that didn't need it. It would have been mounted either on the cabinet where the cable started from or ended, or possibly on a 'Joint box' at the junction of two cables.

 

[kermit]

Thanks John, that's fascinating. Were there reasons other than traction current for carrying sufficiently high power for this sort of insulation to be needed? The plate probably originated in NW England, so could have been associated with Morecambe electrification - but Tel Dept suggests not linked to electrification necessarily......