Windy Afternoon Splice Tray With Worn Electrodes
You are fusion splicing a 24-fibre G.652D aerial loose-tube cable at a joint pole on a rural distribution route. The splicer's arc counter shows 4,150 arcs; the manufacturer specifies electrode replacement every 3,000 arcs, and there is no record of an arc calibration on this machine. Ambient temperature is 38 °C with gusting wind, and the splice tent only partly shields the set. Twelve splices are complete and the splicer's estimated losses read 0.01 to 0.03 dB. On two of them you saw a bright flash during the arc and the fibre ends appeared to pull back a little before settling. Your supervisor wants all trays closed before the shutdown window ends in 40 minutes. A spare electrode pair, a scrap-fibre arc-check routine and a bi-directional OTDR test after closure are available. The customer acceptance limit is 0.15 dB mean splice loss.
1. Diagnose the two abnormal splices and state the sequence of actions you would take before making any further splices.
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Diagnosis. The arc counter is 1,150 arcs past the 3,000-arc replacement point. Worn electrodes pit and flatten, so the arc becomes unstable and heats the two fibre ends unevenly. Gusting wind bends and cools the arc, so the set must deliver more energy for the same melt; when it cannot, the ends do not wet properly and you see a flash followed by slight pull-back as the motors feed into a soft, uneven joint.
Sequence before any more splices:
- Stop, park the set out of the wind, and leave the open fibres protected in the holder. Do not 'finish the tray and see'.
- Replace both electrodes as a matched pair and reset the arc counter.
- Run the manufacturer's arc calibration or arc-check on scrap fibre of the same type, not on customer fibre.
- Make three test splices on scrap, check cleave angle (target 0.5 degrees or better) and end-face cleanliness, inspect for bubbles, bulges or necking, and proof-load them.
- Only then cut back about 100 mm on the two suspect splices and remake them. They must be cut out, not left in place, because a splice that flashed and pulled back can still show a low estimated loss while containing a bubble or a misaligned core that will fail later under tension or temperature cycling.
2. The splicer's estimated loss reads 0.01 to 0.03 dB on all twelve splices. Why is this not acceptance evidence, and what evidence should the supervisor receive?
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Estimated loss is a value the splicer computes from the arc image and light emission during the discharge. It is useful as a trend indicator, but it is not a measurement of transmitted optical power. It is typically optimistic, it is weakly sensitive to small voids, bubbles and slight core offset, and it cannot see the effects of a contaminated end-face or a poorly stripped fibre with residual coating.
The physical evidence (flash, pull-back) contradicts the 0.02 dB estimate, and when the two disagree the physical evidence wins.
Acceptance evidence:
- Bi-directional OTDR loss at the same wavelength, usually 1550 nm, with the same pulse width and comparable averaging in both directions; splice loss is the mean of the two directions. Single-direction values are biased by backscatter-coefficient differences between the two fibres.
- Visual inspection of the splice protection sleeve, with no bubbles, bulges or dark spots.
- Proof or tensile test to the specified load, where the customer specification requires it.
- A written record of the two suspect splices that were cut out and remade, with their new bi-directional values.
3. With 40 minutes left, decide whether to close the tray now, re-work the two splices, or stop and hand over. Show the time and risk reasoning.
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Time budget. Electrode change and arc calibration: about 10 minutes. Two re-splices including cut-back and sleeve curing: about 6 minutes. OTDR verification of those two splices: about 6 minutes. Tray closure, sealing and documentation: about 8 minutes. Total roughly 30 minutes, which fits inside 40 with a small allowance. So re-work is feasible, but only if calibration passes first time.
Risk reasoning. Closing the tray with two suspect splices converts a 30-minute job today into a customer outage and a return visit later, and the tray has to be re-opened and re-sealed, which degrades the closure. Working in 38 °C heat with wind also raises the chance of a handling error, so take water and shade breaks and do not rush the cleaves.
Decision rule. Calibrate; if the arc-check passes and the first scrap splice is clean, rework and verify, then close. If calibration fails or the spare electrodes are used up without a stable arc, do not close on a failed splice: wrap and temporarily protect the cable with a bag or temporary closure, record the exact state, inform the supervisor and schedule a return. Never leave fibres open and never close a tray you know is defective.