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Chelmsford Amateur Radio Society
Advanced Course
(9) Safety
Chelmsford Amateur Radio Society
Advanced Licence Course
Clive Ward G1EUC
Slide Set 17: v1.0, 12-Aug-2004
(9) Safety
1
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
Chelmsford Amateur Radio Society
Advanced Licence Course
Clive Ward G1EUC
Slide Set 17: v1.0, 12-Aug-2004
(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 G1EUC
Slide Set 17: v1.0, 12-Aug-2004
(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 G1EUC
Slide Set 17: v1.0, 12-Aug-2004
(9) Safety
4
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/amateur_radio.htm
• Field Strength calculations are covered in the EMC Section
Chelmsford Amateur Radio Society
Advanced Licence Course
Clive Ward G1EUC
Slide Set 17: v1.0, 12-Aug-2004
(9) Safety
5
RF Safety Levels
Chelmsford Amateur Radio Society
Advanced Licence Course
Clive Ward G1EUC
Slide Set 17: v1.0, 12-Aug-2004
(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 G1EUC
Slide Set 17: v1.0, 12-Aug-2004
(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 G1EUC
Slide Set 17: v1.0, 12-Aug-2004
(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 G1EUC
Slide Set 17: v1.0, 12-Aug-2004
(9) Safety
9