July 2012 in London Underground
Every time a train in roads 36 or 37 is powered up the alarm sounds, suggesting a positive earth has been detected - however, this is rarely the case. As a result, staff cancel the alarm and inform the Line Controller that it is the faulty alarm in the wash roads without always checking.
This is raising concerns that if the traction earth detection alarm for these roads is not fixed, staff could become complacent and cancel the alarm when there is in fact a genuine earth defect. The reporter feels that this is compromising safety and the effectiveness of the equipment.
Could Tube Lines:
Response from Tube Lines
Tube Lines thank the reporter for raising their concerns.
Converteam, who maintain the DC assets at Stratford Market depot,
carried out an investigation and suggested two possible causal
factors for the faulty alarm:
1. An earth leakage unit in the substation.
2. An extreme amount of damp on the roads.
The earth leakage units fitted in the two section control panels on roads 36 and 37 do not operate. These are set to two amps tripping and are tested regularly by Converteam. It is believed that the unit in the substation is not maintained and needs to be inspected. The Ambience Manager for the Jubilee Line has contacted the Network Power Link Planning Engineer to arrange testing of the unit, but they have not yet advised of a date when this will be undertaken.
Options are also being considered for drying the roads. This issue has been ongoing for several years and could take some time to rectify as it also involves a third party.