Chelmsford Amateur Radio Society Advanced Course 9 Safety

Chelmsford Amateur Radio Society Advanced Course (9) Safety Chelmsford Amateur Radio Society Advanced Licence Course Clive Ward G 1 EUC Slide Set 17: v 1. 1, 8 -Sep-2005 (9) Safety 1

High Voltages • Anything over 30 V can be dangerous! • All exposed metal surfaces should be earthed • Unless impractical, work should never be carried out on live equipment • Valve equipment generally uses power supplies with potentials much higher than domestic mains voltage • Recommend Residual Current Devices (RCDs) on mains Chelmsford Amateur Radio Society Advanced Licence Course Clive Ward G 1 EUC Slide Set 17: v 1. 1, 8 -Sep-2005 (9) Safety 2

Portable Operation • Operating /P can introduce new hazards: – Overhead lines – Poor electrical supplies – Trailing cables – Damp ground – Excessive field strengths • So survey first, check cable routes/protection (trip hazards), use correct fusing, and use RCD’s. • No live working!!! Chelmsford Amateur Radio Society Advanced Licence Course Clive Ward G 1 EUC Slide Set 17: v 1. 1, 8 -Sep-2005 (9) Safety 3

Mobile Operation • Operating in vehicles and vessels can bring new hazards – Insecure equipment – Long flexible aerials – Accidental shorts to earth – Distracted driving – RF induction into vehicle/vessels control circuits • Secure equipment, check cable routing/protection, use correct fusing, use hands free equipment, pay attention to good radio housekeeping Chelmsford Amateur Radio Society Advanced Licence Course Clive Ward G 1 EUC Slide Set 17: v 1. 1, 8 -Sep-2005 (9) Safety 4

RF Field Strengths • Health Protection Agency superseded the NRPB in April 2005 • Must comply Investigation Levels for exposure to RF radiation. • Limits now tightened to 28 V/m in the 10 -146 MHz range and also lowered considerably for LF/MF • If the Investigation Level is exceeded the cause must be investigated and reduced to a desirable one. • Check the latest levels. They are published at: http: //www. hpa. org. uk/radiation/understand/information_sheets/amateur_radio. htm • Field Strength calculations are covered in the EMC Section Chelmsford Amateur Radio Society Advanced Licence Course Clive Ward G 1 EUC Slide Set 17: v 1. 1, 8 -Sep-2005 (9) Safety 5

RF Safety Levels HPA Investigation Levels Webpage NB: Tightest Levels are at 11 -146 MHz Chelmsford Amateur Radio Society Advanced Licence Course Clive Ward G 1 EUC Slide Set 17: v 1. 1, 8 -Sep-2005 (9) Safety 6

Lightning Protection • Thunderstorms carry heavy static charges! • The static charge can ionise the air to form a low resistance path to ground allowing a very high current to flow as a lightning strike • The resulting risk to life, domestic property and electronic equipment associated with a strike and/or build up of a static charge is very high. • Little can be done to protect against a direct strike. Good static discharge systems can prevent dangerous static build up on aerial systems. Disconnecting aerials reduces risk Chelmsford Amateur Radio Society Advanced Licence Course Clive Ward G 1 EUC Slide Set 17: v 1. 1, 8 -Sep-2005 (9) Safety 7

Protective Multiple Earthing • PME systems are where the mains earth terminal is connected to the neutral of the electricity service at the consumers premises, and are usually identified with a warning label. • All metal pipes and fittings within the premises are connected to the PME bonding point. • Under severe fault conditions (such as a neutral break) PME systems have the potential to cause fatal electric shocks and/or fires in Amateur Radio Stations. • The RF Earth in an Amateurs station should be connected to the PME bonding point to maintain safety under fault conditions in accordance with the IEE Wiring Regs. Chelmsford Amateur Radio Society Advanced Licence Course Clive Ward G 1 EUC Slide Set 17: v 1. 1, 8 -Sep-2005 (9) Safety 8

Summary • All exposed metals should be earthed. • No work on live equipment, be careful with valves. • Working /P can bring new hazards. • Mobile working can bring new hazards. • Compliance with NRPB RF exposure minimum Investigation Levels is essential. • Thunderstorms can be dangerous, take necessary precautions • PME: Amateur Radio equipment RF earths should be connected to the PME bonding point. Chelmsford Amateur Radio Society Advanced Licence Course Clive Ward G 1 EUC Slide Set 17: v 1. 1, 8 -Sep-2005 (9) Safety 9