NR/L2/SIG/11107 Issue: 4 Date: 03/03/2012 Compliance date: 03/03/2012. Ref:

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2 User information This Network Rail standard contains colour-coding according to the following Red Amber Green classification. Red requirements No deviations, could stop the railway Red requirements shall always be complied with and achieved. Red requirements shall be presented in a red box with the word shall or expressed as a direct instruction. Accountability for the efficacy of red requirements lies with the Professional Head/Standard Owner. Red requirements are monitored for compliance. Corrective actions shall be enforced if deviations are discovered through functional checks (e.g. engineering verification visits, audit or Operations Self- Assurance). Amber requirements Controlled deviations, approved risk analysis and mitigation Amber requirements shall be complied with unless deviation has been approved in advance. Amber requirements shall be presented with an amber sidebar and with the word shall or expressed as a direct instruction. Accountability for the efficacy of these requirements lies with the Professional Head/Standard Owner, or their nominated Delegated Authority. Amber requirements are monitored for compliance. Deviations may be permitted. Deviations are approved by the Standard Owner or through existing Delegated Authority arrangements. Corrective actions shall be enforced if non-approved deviations are discovered through functional checks (e.g. engineering verification visits, audit or Operations Self-Assurance). Green Guidance Guidance is based on good practice. Guidance represents supporting information to help achieve Red and Amber requirements. Guidance shall be presented with a dotted green sidebar and with the word should (usually in notes) or as a direct instruction. Guidance is not mandatory and is not monitored for compliance. Alternative solutions may be used. Alternative solutions do not need to be formally approved. Decisions made by a competent person to use alternative solutions should be backed up by appropriate evidence or documentation. Page 2 of 11

3 Issue record Issue Date Comments 1 Dec 2000 First Issue 2 August 2008 Updated to reflect Phase 2A / Engineering reorganisation responsibility change, no technical changes. 3 December 2011 Standards rewritten to new format (RAG) (CCMS document number ) 4 March 2012 Reference to record cards in clause 4 corrected (CCMS document number ) Compliance This Network Rail standard is mandatory and shall be complied with by Network Rail and its contractors if applicable from 03/03/2012. When this standard is implemented, it is permissible for all projects that have formally completed GRIP Stage 3 (Option Selection) to continue to comply with the issue of any relevant Network Rail standards current when GRIP Stage 3 was completed and not to comply with requirements contained herein, unless stipulated otherwise in the scope of this standard. Reference documentation NR/L3/SIG/10663 Signal Maintenance Specifications (NR/SMS/EL00, NR/SMS/EL21 & NR/SMS/EL31) NR/SIG/L3/31655 Inspection of Cable & Wire Insulation Disclaimer In issuing this document for its stated purpose, Network Rail makes no warranties, express or implied, that compliance with all or any documents it issues is sufficient on its own to ensure safe systems of work or operation. Users are reminded of their own duties under health and safety legislation. Supply Copies of documents are available electronically, within Network Rail s organisation. Hard copies of this document may be available to Network Rail people on request to the relevant controlled publication distributor. Other organisations may obtain copies of this document from IHS. Tel: Page 3 of 11

4 Contents 1 Purpose 5 2 Scope 5 3 Definitions 5 4 Inspection Regime Types of signalling equipment often susceptible to Silver Migration Conditions & Risks for Silver Migration Examples 7 5 Competance of those carrying out Silver Migration Inspections 10 6 Remedial Action 11 Figure 1 P Style Relays 8 Figure 2 Evidence of Silver Migration around contacts D6/D7 8 Figure 3 Evidence of Silver Migration around contacts A1 & A5 9 Figure 5 Westpac Mk 1 10 Figure 6 Westpac Mk 3 10 Page 4 of 11

5 1 Purpose Silver Migration can lead to wrong side failures. This standard specifies: a) The required inspection regime b) Remedial actions to be taken c) Competence for staff undertaking inspections The high risk conditions are also described. Ref: 2 Scope Applies to all relays, plugboards and plug couplers formed of black phenolic material. 3 Definitions Heated Relay Room Plugboard Relay Base Silver Migration Phenolic Material An equipment room which is kept at a temperature of at least 10 degrees centigrade If for a period of upto 2 years, the equipment room has been unheated and then heating introduced, it shall be treated as a heated relay room An electrical switchboard to which the relay base plugs into The rear portion of a plug-in relay which supports the coil and contact assembly internally and has exposed contact spring feet and any coding pins externally for mounting into a plugboard The movement of metallic silver over and/or through insulation A type of thermosetting plastic made from a phenolic resin 4 Inspection Regime Inspect all relays, plugboards and plug couplers at risk, in accordance with NR/SMS/EL21 (Service B) or NR/SMS/EL31 (Service B) at the site specified, annually. When carrying out inspections, attention should be given to the site wire degradation categorisation (NR/SIG/L3/31655). Record findings on NR/SMS/EL21-31/RC/02 Record Card. NOTE Lighting is very important to assist when checking for Silver Migration. It is recommended to use a good torch during inspection Page 5 of 11

6 4.1 Types of signalling equipment often susceptible to Silver Migration Silver Migration can form in the following types of signalling equipment: P style relays Phenolic relay plugboards SGE Geographical set plug couplers/sets Full size double-width relay within apparatus cases Westinghouse Signals WESTPAC Units This list is not exhaustive NOTE Black phenolic base material is suspectable to silver migration both on and within the phenolic material. Other non-phenolic base material (blue, cream, & grey) is mainly confined to surface contamination BR 829 Type Phenolic Plugboards A programme to remove these shall be in place, with priority given to single cut circuitry. Within heated relay rooms, visually inspect by randomly selecting 1% of the population. If any Silver Migration is found, replace all BR 829 type phenolic plugboards as soon as practicable and within 12 months of discovery. Within apparatus cases and unheated relay rooms, these plugboards should have been removed by April NOTE There is no need to change plugboards where tin plated connectors have been used P Style Phenolic Plugboards A programme to remove these is to be completed. Within heated relay rooms, until these are removed, 5% will be replaced annually with non-phenolic plugboards. If any Silver Migration is found, replace all P style phenolic plugboards as soon as practicable and within 12 months of discovery. Single cut circuitry is not permitted with these plugboards. Within apparatus cases and unheated relay rooms, these plugboards should have been removed by April NOTE silver migration may be hidden between the two parts of the plugboard P Style Relays A programme to re-service these is to be completed. Priority should be given to the replacement of phenolic relay contact spacers with a non-phenolic type. Phenolic relay contact spacers in relays housed within appartus cases and unheated relay rooms, should have been removed by April In heated relay rooms, these should have been removed by April NOTE The contact springs inside the relay are silver plated, hence why Silver Migration can occur. Page 6 of 11

7 4.1.4 Large Plug-In Relay Plugboards Ref: Visually inspect a random selection of 1% of the population. If any Silver Migration is found, replace all Large Plug-In Relay Plug Boards at that site and within 12 months of discovery Phenolic SGE Geographical Set Plug Couplers A programme to replace these is to be completed. Within appartus cases and unheated relay rooms, these should have been removed by April In heated relay rooms, these should have been removed by April WESTPAC and GEC Geographical Units If any Silver Migration is found, the unit shall be sent for re-service. A risk assessment shall be undertaken to determine the impact on all units at that site. NOTE Manage very carefully any obsolescence issues with re-servicing these units 4.2 Conditions & Risks for Silver Migration For Silver Migration to take place, the following simultaneous conditions are needed: Silver or silver plated components Moisture dc voltage across the insulation When these metallic silver particles form an electrical path, the following risks can occur: Bypass contacts in a circuit Introduce connections between different circuits The risk is greater for single cut circuits than double cut. Silver Migration most commonly occurs on relay plugboards and within certain relays and plug couplers. Initially it is restricted to the surface, but over time penetrates into the structure of the material. 4.3 Examples The following images show examples of equipment and Silver Migration Page 7 of 11

8 Figure 1 P Style Relays Figure 2 Evidence of Silver Migration around contacts D6/D7 Page 8 of 11

9 Figure 3 Evidence of Silver Migration around contacts A1 & A5 Relay Base Plugboard Figure 4 Plugboard and Relay base Page 9 of 11

10 Figure 5 Westpac Mk 1 Figure 6 Westpac Mk 3 5 Competance of those carrying out Silver Migration Inspections Those carrying out silver migration inspection require to be authorised to undertake this activity, competence development will include as a minimum: Received technical briefing on this standard Watched and confirmed understanding of Going for Silver video Confirmed understanding of the briefing note for Going for Silver Page 10 of 11

11 Competence assessment should also include: Ref: Awareness of the environment in which Silver Migration can be found Awareness of the method for Silver Migration inspection Awareness of the possible visual signs of Silver Migration Awareness of the equipment which may be affected by Silver Migration, including practical sessions as necessary Record Silver Migration checks on the Record Card 6 Remedial Action The S&TME is responsible for managing any programme of equipment replacement. Page 11 of 11

12 25/05/ Version 1 Standards Briefing Note Ref: Title: Silver Migration Publication Compliance Standard Owner: Professional Head (S&T) Non-Compliance rep (NRNC): Professional Head (S&T) Further information contact: Pardip Basran Tel: Purpose: Silver Migration can lead to wrong side failures. This standard specifies: a) The required inspection regime b) Remedial actions to be taken c) Competence for staff undertaking inspections The high risk conditions are also described. Scope: Applies to all relays, plugboards and plug couplers formed of black phenolic material. What s New/ What s Changed and Why: The standard has been rewritten into the new requirements let format. The requirements are written so that they are Accurate, Brief and Clear. The standard also contains the competency requirements and images to assist with the identification of Silver Migration. Reference to record cards in clause 4 has been corrected. Affected documents: Reference ISSUE 3 Impact Superseded Briefing requirements: Where Technical briefing (T) is required, the specific Post title is indicated. These posts have specific responsibilities within this standard and receive briefing as part of the Implementation Programme. For Awareness briefing (A) the Post title is not mandatory. Please see for guidance. Briefing (A-Awareness/ Post Team Function T-Technical) A Route Asset Manager (S&T) soon to be (Signals) SP&C Asset Management A S&TME IMDM Network Operations A Section Manager (Signals) S&TME Network Operations A Signal Technicians Delivery Unit Network Operations A Training Delivery Specialist [S&T] National Training Manager Human Resources A Workforce Development Specialist (S&T) Training Delivery Manager Human Resources A Senior Programme Engineering Manager Signalling & Electrification Investment Projects *NOTE: Contractors are responsible for arranging and undertaking their own Technical and Awareness Briefings in accordance with their own processes and procedure