Chelmsford Amateur Radio Society Advanced Course (9) Safety

1. Chelmsford Amateur Radio Society Advanced Course(9) Safety

2. High Voltages • Anything over 30V 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

3. 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!!!

4. 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

5. RF Field Strengths • Health Protection Agency superseded the NRPB in April 2005 • Must comply Investigation Levels for exposure to RF radiation.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 28V/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

6. RF Safety Levels HPA Investigation Levels Webpage NB: Tightest Levels are at 11-146MHz

7. 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

8. 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.

9. 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.