1 Chelmsford Amateur Radio Society Advanced Licence Course Clive Ward G1EUC Slide Set 17: v1.1, 8-Sep-2005 (9) Safety Chelmsford Amateur Radio Society

1Chelmsford Amateur Radio SocietyAdvanced Licence Course

Clive Ward G1EUC Slide Set 17: v1.1, 8-Sep-2005(9) Safety

Chelmsford Amateur Radio Society Chelmsford Amateur Radio Society

Advanced CourseAdvanced Course(9) Safety(9) Safety



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



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!!!



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



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• Health Protection Agency superseded the NRPB in April 2005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



RF Safety Levels

HPA Investigation Levels Webpage

NB: Tightest Levels are at 11-146MHz



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



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.



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.

Documents

1 Chelmsford Amateur Radio Society Advanced Licence Course Clive Ward G1EUC Slide Set 17: v1.1, 8-Sep-2005 (9) Safety Chelmsford Amateur Radio Society