STANDARD TECHNIQUE : SD5P/2

Transcription

1 Company Directive STANDARD TECHNIQUE : SD5P/2 Design of Un-metered Connections ST:SD5P/2 7 th December of 10 -

2 1.0 INTRODUCTION This document specifies the requirements for the design of un-metered connections and includes a number of standard arrangements. 2.0 POLICY 2.1 Load Acceptance The Electricity (Unmetered Supply) Regulations 2001 specify strict criteria for determining whether or not a connection can be un-metered. These criteria are described below: a) The load must be predictable. If the value of load or its duration cannot be readily predicted the connection must be metered. Standard electricity sockets may not be installed at an un-metered connection as equipment connected to the socket cannot be determined. b) The connected load at each exit point should be rated below 500W. In some limited circumstances, where it is not practical to install metering due to high costs, technical difficulties or legal reasons, it is acceptable for load in excess of 500W to be un-metered. All loads above 500W shall be submitted to the Un-metered Connection Team who will determine if the load can be un-metered. Appendix A includes a list of equipment that can normally be un-metered. Load data associated with different types of un-metered equipment is published by Elexon and is available from the following link: \\plodcs01\national\library\bsc\bscp\umso_operational_information.pdf 2.2 Standard Arrangements There are a number of standard arrangements for providing un-metered connections. In each case a connection will only be made to a fused cut-out / distribution board housed within a secure weather proof cubicle, pillar or street lighting column. Connections will not be provided to cut-outs located within traffic bollards or to compartments placed below ground. Where a connection is required for equipment located on a motorway (or equivalent dual carriageway) e.g. lighting, signs etc. the highway authority shall provide a pillar / enclosure remote from the motorway carriageway. Access to the pillar / enclosure shall be provided from land adjacent to the motorway and not from the hard shoulder. ST:SD5P/2 7 th December of 10 -

3 The minimum service cable sizes for new installations are 16mm 2 Copper Concentric or Split Concentric and 25mm 2 hybrid. The maximum cut-out fuse size for individual items of un-metered equipment is generally 25A. Cut-out fuses for new installations shall be cartridge type (e.g. to BS1361 or BS7654). Existing installations may utilise semi-enclosed fuses (e.g. to BS 3036) Arrangement 1 This is a commonly used arrangement and is applicable where the mains system is relatively close to the un-metered connections. A separate service is provided to each street lighting column or kiosk. Each un-metered connection has its own exit point. The PME earth electrode (where PME is available) must be installed at, or beyond, the last service joint that connects to an unmetered connection. ST:SD5P/2 7 th December of 10 -

4 2.2.2 Arrangement 2 This is similar to Arrangement 1 but in this case a service cable is looped from the bottom of the first cut-out to the next un-metered connection. This is repeated for each subsequent connection. Each un-metered connection has a separate exit point. A PME earth terminal is required at the last un-metered connection (where PME is available) Arrangement 3 This is a commonly used arrangement, where WPD provide a single phase cut-out and provide one exit point within the customer s pillar or enclosure. The customer (typically a street lighting authority) installs their own cables and distributes to individual items of equipment. Where PME is available a PME electrode must be installed at either the service joint which connects to the customer s pillar, or at a position along the mains circuit that is more remote from the source substation than that service joint. In addition the customer installs an earth electrode at their most remote installation (irrespective of whether they distribute with CNE or SNE cables). As only one exit point is provided the total load of the connected equipment must satisfy the criteria specified in 2.1 (i.e. it must be predictable and, in most circumstances, rated below 500W). Page Revised 29 th January 2010 ST:SD5P/2 7 th December of 10 -

5 2.2.4 Arrangement 4 This is similar to Arrangement 3 but in this case a 3 phase connection is provided and one exit point is provided per fuse-way. This arrangement may be applicable where the customer wishes to distribute to several items of equipment with a total load in excess of 500W. Where PME is available WPD shall install a PME electrode at the pillar. In addition, the customer installs an earth electrode at the most remote installation on each of their circuits (irrespective of whether they distribute with CNE or SNE cables). The total load of the connected equipment at each exit point must satisfy the criteria specified in 2.1 (i.e. it must be predictable and, in most circumstances, rated below 500W). Customer s Equipment Substation One exit point provided at the outgoing terminals of each fuse-way - Customer owns enclosure / pillar - WPD owns cut-out PME Earth Electrode Page Revised 30 th December 2009 ST:SD5P/2 7 th December of 10 -

6 2.2.5 Arrangement 5 This is similar to Arrangement 4 but in this case a 3 phase multi-way distribution board is installed within the customer s enclosure. This allows several un-metered exit points to be provided (one per fuse-way). Where PME is available WPD shall install a PME electrode at the pillar. In addition, the customer installs an earth electrode at the most remote installation on each of their circuits (irrespective of whether they distribute with CNE or SNE cables). The total load of the connected equipment ay each exit point must satisfy the criteria specified in 2.1 (i.e. it must be predictable and, in most circumstances, rated below 500W). Customer s Equipment One exit point is provided at the outgoing terminals of each fuse-way Substation PME Earth Electrode Page Revised 30 th December 2009 ST:SD5P/2 7 th December of 10 -

7 2.3 Design Requirements Whichever arrangement is used the planner shall ensure: the voltage at each exit point is within statutory limits. equipment (cables overhead line etc.) are not overloaded. the earth fault level at each un-metered exit point is above the rating of the fuses that protect the incoming service. mains cable / overhead line shall be adequately protected by the source protection (i.e. the source fuses shall be capable of operating before the short circuit rating of the cable / overhead line is exceeded. the phase to neutral loop impedance at each exit point is less than 1.5 ohms. for Arrangement 1 and 2 the length of service (from the connection with the mains cable or overhead line to the most remote connection) shall not exceed 250m. The planner must also determine and agree earthing requirements for the exit point. Windebut can be used to check the voltage and circuit loading aspects described above and also to check that mains cables / lines are adequately protected. Windebut can also be used to provide earth fault levels and loop impedance values. Further guidance on Windebut is given ST:SD6K Earthing Earthing requirements are specified in ST:TP21D. Un-metered equipment is often installed in metal enclosures that are accessible to the public. These types of installations can create touch potential risks where PME connections are provided. Given this there are certain restrictions on the provision of PME Street Electrical Fixtures PME or SNE connections can be provided to street electrical fixtures, including, streetlights, traffic signals, advertising hoardings, bus shelters and public telephones etc. situated on or adjacent to roads, streets or footpaths. Where PME is made available to these installations a PME earth electrode must be provided at, or beyond, the service joint / connection to each unmetered installation. These requirements are shown in the previous drawings. In addition to this, earth electrodes are also required at the most remote customer installations where the customer installs their own infrastructure (see Arrangement 3, 4 and 5). Page revised 14 October 2011 ST:SD5P/2 7 th December of 10 -

8 Other Housings Accessible to the Public For other types of housing accessible to the public it is recommended that the installation has Class II insulation (as defined in the IET Wiring Regulations BS7671). Where this is the case a PME earth terminal is not is not required. Single phase installations that are not defined as Class II can be offered a PME earthing terminal as long as: Load connected at the housing is below 2kW. The customer installs and maintains an earth electrode system, bonded to the earth terminal with a resistance of 20 ohms or less. Three phase or split phase (single phase - three wire) installations that are not defined as Class II may only be offered a PME earth terminal if the load is well balanced across the phases. If PME cannot be provided then either an SNE (TN-S) earthing terminal shall be offered or, if this is not suitable, then direct earthing (TT type) will be provided. Where direct earthing is to be used WPD do not provide an earthing terminal and, if the installation is not defined as Class II, the customer must provide their own earth electrode and RCD. ST:SD5P/2 7 th December of 10 -

9 APPENDIX A TYPES OF UNMETERED EQUIPMENT The following list shows typical types of equipment which may be considered for unmetered connections, providing the load complies with the requirements in 2.1. The list is not exhaustive and is for illustration purposes only. Advertising Hoardings Alarm Systems Bus Shelters Cable Network Pillar Cathodic Protection Clocks Communication Cabinets Fire Warning System Flood Warning System Ice Detector Illuminated Bollards Illuminated Map Cabinets Information Signs Navigation Signal Pay & Display Machines Radio Transmitter Red Runner Camera Security Camera Sewage flow recorder Speed Camera Storm overflow Street Lighting Telephone Kiosk (lighting) Telephone Kiosk (phonecard) Ticket Machine TV Aerial TV Amplifier TV Camera TV Relay Traffic Counter Traffic Master Units Traffic Signs Traffic Signal/Pelican Crossing Warden call equipment ST:SD5P/2 7 th December of 10 -

10 APPENDIX B SUPERSEDED DOCUMENTS ST:SD5P/1 APPENDIX C ASSOCIATED DOCUMENTS ST:TP21D ST:SD5K ST:NC1N BS7671 HV and LV System Earthing Use of Windebut Software Procedure for Unmetered Connections and Disconnections Requirements for Electrical Installations (IET Wiring Regulations) ENA Engineering Recommendation G12/3, Requirements for the application of Protective Multiple Earthing to Low Voltage networks. POLICY IMPLEMENTATION APPENDIX D This Standard Technique shall be implemented on issue for all new and substantially modified connections. Managers shall brief relevant staff (including those involved with the design, construction, maintenance and replacement of un-metered connections) on the requirements of this document. IMPACT APPENDIX E 1) Earthing requirements have been added to clause 2.2.1, 2.2.2, 2.2.3, and The associated diagrams have been modified to illustrate these aspects. 2) Significant changes have been made to the design requirements specified in Section 2.3, including the requirement for a maximum earth fault loop impedance of 1.5 ohms and a maximum service length of 250m. 3) Earthing requirement in have been modified. 4) Design requirements are now checked using Windebut rather than the spreadsheet provided in the previous version of the document. KEYWORDS Un-metered, Un-metered Connection, Street Lamp, Street Light DOCUMENT LAST REVIEWED December 2009 APPENDIX G APPENDIX H ST:SD5P/2 7 th December of 10 -