16 December 2014
The big project for our working week was undertaking the modifications to the telecoms cable routing, at either end of Moelwyn Tunnel in advance of the new portal construction. However, as always, other jobs also managed to get a look-in.
Harbour Station Batteries
With the urgent need to undertake repairs to the creaking attic space of Harbour Station, early in the week, the job of very carefully removing the old telephone exchange batteries fell to our two ‘Ebola’ compliant operatives!
Moelwyn Portal Project
With our S&T train stabled at Glan-y-Pwll and the work site miles from anywhere, it was important we ensured we had all that we needed to do the job. To that end, our first action was to call a meeting in the OED building and examine the construction plans for the portals.
Each of the jobs was assessed for required equipment and materials. This left us with a shopping list that involved some scavenging from the yard and purchasing supplies from Porthmadog. We split into three groups to achieve this, prior to setting off for Blaenau around lunch time on the Wednesday.
There were a number of tasks at both ends of the tunnel, each will be addressed separately.
Here, the telecoms cable exited a conduit on the hill side of the existing concrete portal and then headed directly up to a catenary suspension point directly over the centre line of the tunnel. This was going to get in the way of the construction site and was also not acceptable from an aesthetics point of view.
A new location to support the cable, high up the rock face on the ‘Hill’ side of the cutting was agreed and here, a hole was drilled to take an M16 stainless steel threaded bar which was securely grouted into place.
A new catenary mount was fabricated and the catenary wire cut back and secured, then a rope to a winch, located on the original fixing point, was used to take the tension ready to attach to the new rock anchor. A rope, slung round the cable, gave sufficient side pull to drag the new mount into position. Once in place, all the old equipment was stripped down.
At the same time, the cable ends, which were terminated in the location cabinet (LOC287) besides the portal were disconnected and the cabinet cut from its rusty mounting post. This was a really bad place, with permanent damp, to site a cable joint.
In order that a new piece of duct could be constructed into the new portal, we inserted a 5 metre length of conduit over a free end so that a new line joint could be made to restore the circuits.
It is quite likely that this joint will ultimately have to live inside the conduit, so a top quality solution was needed. This took the form of a resin potted cable joint. Each of the wires were stripped and twisted with their opposite number and then the end solder tipped. Finally an insulated nib was placed over the joint. An independent inspection of the work ensured that all was correct before mixing the resin, which had been basking on the engine block of Moel Hebog to warm up a little!
The process went well and once the addition of a clipped catenary strain relief had been assembled, the joint was left to cure. With the cable removed from the duct inside the concrete portal, a new position, high up on the wall, near the roof, was selected and number of 6mm studs inserted to take ‘P’ clips to support the cable.
To protect the Network Rail fibre optic cable, the cable was detached from its track side clips for a distance either side of the work site and dragged over to the rail and clipped in place, providing protection from damage by means of the rail head.
A project plan had been produced in advance of this working party, but like most best laid plans, the reality of the work enforced a change of thinking and in this case, to a simpler concept. It had been intended to run the cable off to the left hand side of the portal and fix it high up on the rock face, but access was very difficult and we were not confident that there would be enough cable spare to do the job. Any spare cable was going to be scavenged from the two drops that fed the location cabinet at Moelwyn Tunnel South G.F. To this end, the cables were disconnected.
Plan ‘B’ moved the cable to a ground duct which emanated from inside the tunnel and continued for some 50 metres out to the first telegraph pole. The idea here is to dig the duct in, when the mini digger is on site.
This necessitated the addition of an end stay on the final pole to support the new loading of the cable terminating there. A fixing was made in the base of the wall around the culvert, which offered plenty of support. Again, this was a grouted M16 stud.
With the conduit in place, it was possible to see if the end would still reach the location cabinet to terminate. Fortunately it did and this permitted us to remake the circuits. One side benefit of this was that it also simplified the provision of the telephone feed which was to come up from Gelliwiog. A suitable pair of wires was selected from the number of spares and the circuit patched through and tested. TYB46, which is also the phone line to Dduallt Station is now ready for use as a site office phone feed.
The treatment of the Network Rail cable was repeated for the south end, a simple and effective solution, which can all be undone when the project is complete. Final checks at the location cabinet were undertaken to verify that the Carrier and other circuits were fully restored and functioning.
Half of one day was spent in the training room when two of our group received refresher courses for their Cherry Picker and Crane tickets to fly. Whilst this was going on, the remaining crew set about loading cables onto the train for future work re wiring the wig-wag heads on Glan-y-Pwll Crossing.
An annoying case of droopy cable in the section above Archer Dam was attended to. A catenary clamp was released that the cable worked northwards to transfer the droop to a span that did not overhang the loading gauge. An attempt was also made to straighten up a leaning pole near Power Station Summit.
On the homework front
A latching signalling relay which had been zapped by lightning during the storms and taken home for a rewind was dealt with over a number of lunch breaks. The main coil, which consisted of two windings, one of 2500 turns, the other of no less than 4,500 turns of 0.25mm wire had broken down in the strike.
It took a while to rewind, but at least the turns did not need to be manually counted back on. On reassembly, all new PTFE insulated wires linked to the large screw terminals under the base. It remains to be tested.
With no winding machine at hand, it was a case of creating a rig that could do the job relatively quickly. This took the form of an old electric drill, a magnet and a reed switch to send pulses to a counter, a selection of insulating tapes and of course, the copper wire.
Firstly, the weather varied from good to just outright stunning, perfect for our labours up in the hills. A very productive working week and we have now done our bit to enable the long awaited construction of the stone portals on Moelwyn Tunnel to proceed.