Power & Distribution

No member of the public has ever left an event remarking on the quality of the temporary power. They notice this department exactly once, and only when it has failed: when the stage goes dark, when the screens fold to black, and when eleven thousand people simultaneously decide to find out what has happened. Everything below exists to prevent that single moment.

We therefore decline to measure the department by installed capacity, which is a procurement figure, and measure it instead by minutes of unplanned outage per season. Across 412 events in 2002 MGH Production recorded 4.2 minutes of unplanned loss of supply to a public-facing load, of which 3.1 minutes were attributable to a single incoming DNO fault at Braithwaite Park that was outside our demarcation. The internal target for 2003 is 3.50 minutes. Head of Power is Kelvin Aboah, who has held the figure below six minutes since 1997 and regards this as unremarkable.

BS 7909 and the paperwork that precedes the cable

All MGH temporary installations are designed, installed, tested and certificated to BS 7909, the code of practice for temporary electrical systems for entertainment and related purposes. In practice this means four things, none of them optional:

• A named competent person for the installation, appointed in writing, who signs the completion and inspection certificate and who alone authorises energisation.
• A defined earthing and bonding regime selected for the site: TN-S from the incomer where the DNO earth is proven, TN-S derived at the generator star point on generated sites, with earth electrode resistance recorded and never accepted above 20 Ω.
• RCD discrimination throughout, so that a fault at a catering unit trips a 30 mA final circuit device and not the 300 mA time-delayed device feeding the trading avenue above it. Discrimination is proved by test, not by inspection of the schedule.
• A written distribution schedule, issued to the client, the venue and the production office before the first cable leaves the truck, showing every source, every distribution board, every circuit, its protective device and its intended load.

Generation

The Dunstable fleet is entirely silenced diesel, load-banked at 100% for two hours before it leaves the yard and again on site before handover. Sets are synchronised in parallel where the load justifies it, which gives us the ability to drop a machine for service mid-event without interrupting supply. Life-safety and control-room loads are configured N+1 as a matter of policy, with automatic transfer in under 8 seconds and a static bypass on the UPS ahead of it.

Endurance is for the integral base tank at 75% of prime rating with no bowser top-up; noise is free-field at 7 m. Residential-specification exhaust silencing is available on request and is assumed at Braithwaite Park.

Loads that are never on a single source

Certain loads are held on UPS with a dual upstream source, and no production schedule, however tight, has ever persuaded us to derogate from the list:

• The GOLDCELL™ event control room, its radio infrastructure and its CCTV recording. See Crowd Safety & Security.
• Emergency and escape lighting, including exit signage on all temporary structures.
• Public address and voice alarm, which must survive the loss of the show system it shares a rigging position with.
• Medical centre, triage tentage and the ambulance loading point.

Fuel management

Every set stands in a bunded enclosure retaining not less than 110% of the tank volume; every compound carries a graded spill kit and a nominated first responder; and refuelling is drip-trayed and supervised without exception. Storage above 200 litres is notified to the local authority and, on watercourse-adjacent sites, to the Environment Agency before the licence application is submitted. Consumption is forecast from the distribution schedule and reconciled daily; the 2002 season closed at 3.1% variance against forecast. A B20 biodiesel trial ran on eleven sets throughout the Cheltondale County Show in August 2002, at a 1.9% penalty in specific fuel consumption and with no filter incidents. A wider trial is scheduled for 2003.

Cable, matting and the public

Distribution runs are planned to avoid public routes entirely; where a crossing is unavoidable it is made in steel-cored ramp, or buried under trackway coordinated with Temporary Structures. A trip survey is walked at dusk on build completion and repeated each morning before gates. All distribution boards, connectors and generator terminations are inspected thermographically each day of the event and logged; a connector running more than 20 °C above its neighbours is remade before it is used again. Dimmer and moving-light loads are coordinated with Lighting & Rigging at the design stage so that harmonic and neutral currents are engineered rather than discovered.

Load enquiries, single-line diagrams and provisional distribution schedules: contact MGH Production, telephone +44 (0)1582 496 200; 24-hour Event Control Desk +44 (0)1582 496 999. Download the temporary power datasheet (PDF, 412 Kb)

Page last updated 27 January 2003. Prepared by K. A, Head of Power.