Chelmsford Amateur Radio Society Advanced Course (9) Safety

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

• Must comply with National Radiological Protection
  Board (NRPB) Investigation Levels for exposure to
  RF radiation.
• The lowest limit for electric field strength was
  50V/m in the 14-146 MHz range
• 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.nrpb.org/press/information_sheets/amate
  ur_radio.htm
• Field Strength calculations are covered in the
  EMC Section

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RF Safety Levels
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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

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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.